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Review

An Overview of Secondary Metabolites from Soft Corals of the Genus Capnella over the Five Decades: Chemical Structures, Pharmacological Activities, NMR Data, and Chemical Synthesis

by
Can-Qi Liu
,
Qi-Bin Yang
,
Ling Zhang
and
Lin-Fu Liang
*
College of Chemistry and Chemical Engineering, Central South University of Forestry and Technology, Changsha 410004, China
*
Author to whom correspondence should be addressed.
Mar. Drugs 2024, 22(9), 402; https://doi.org/10.3390/md22090402
Submission received: 30 July 2024 / Revised: 29 August 2024 / Accepted: 30 August 2024 / Published: 2 September 2024
(This article belongs to the Special Issue Bioactive Compounds from Soft Corals and Their Derived Microorganisms)
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Abstract

:
There has been no specific review on the secondary metabolites from soft corals of the genus Capnella till now. In this work, all secondary metabolites from different species of the title genus were described. It covered the first work from 1974 to May 2024, spanning five decades. In the viewpoint of the general structural features, these chemical constituents were classified into four groups: sesquiterpenes, diterpenes, steroids, and lipids. Additionally, the 1H and 13C NMR data of these metabolites were provided when available in the literature. Among them, sesquiterpenes were the most abundant chemical compositions from soft corals of the genus Capnella. A variety of pharmacological activities of these compounds were evaluated, such as cytotoxic, antibacterial, antifungal, and anti-inflammatory activities. In addition, the chemical synthesis works of several representative sesquiterpenes were provided. This review aims to provide an up-to-date knowledge of the chemical structures, pharmacological activities, and chemical synthesis of the chemical constituents from soft corals of the genus Capnella.

1. Introduction

Soft corals of the subclass Octocorallia (class Anthozoa) are abundant in the ocean worldwide, where they are an important group of contributors to the chemically diverse and biologically active marine natural products [1,2,3,4]. For instance, soft corals of a vast array of genera including Sarcophyton [5,6,7], Sinularia [8,9,10,11], Lobophytum [12,13], Cladiella [14], Litophyton [15], Alcyonium [16], Dendronephthya [17], Xenia [18], Verrucella [19], Cespitularia [20], and Lemnalia [21] have been extensively studied and furnished with a wealth of secondary metabolites with various structural features including sesquiterpenes, diterpenes, dimeric terpenes, meroterpenes, steroids, ceramides, etc. Moreover, these metabolites exhibited a variety of pharmaceutical properties, such as antibacterial [22], promoting angiogenesis [23], anti-inflammatory [24], osteoclastogenesis inhibitory [25], cytotoxic [26,27,28], TNF-α inhibitory [29], anti-COVID [30], and antituberculosis [31] effects. Due to their unique complex structures, these compounds gained great attention from synthetic scientists for their total synthesis [32,33].
In our continuous work on the discovery of structurally intriguing molecules from soft corals of different genera [22,29,34,35,36,37,38], we compiled systematic reviews of soft corals [14,15,39] and sponges [40,41] recently. During the process of literature collection of the genus Litophyton, we encountered the title genus Capnella because both of them were reported to belong to the family Nephtheidae of the subclass Octocorallia [42]. It might be worth pointing out that this genus was recently revisited and revised as a genus of the new family Capnellidae by phylogenomics [43].
The soft corals of the genus Capnella strictly inhabit the Indo-Pacific region. These marine organisms offer an enormous source of potentially novel secondary metabolites, such as sesquiterpenes [44], diterpenes [45], steroids [46], and lipids [47]. These chemical constituents showed a library of pharmacological efficacies including cytotoxic [48], antibacterial [49], antifungal [50], and anti-inflammatory [51] activities. Notably, the well-known capnellane sesquiterpenes are the characteristic chemical constituents of this genus, the skeleton name of which was named after the genus name [52]. Featured by the fascinating tricyclic backbone along with the highly complex chirality, the capnellane sesquiterpenes were attractive targets for synthetic scientists for a long time [53,54,55,56], who devoted themselves to the development of different methods to efficiently synthesize them. However, there has been no specific review on the secondary metabolites from soft corals of the genus Capnella till now. In this work, all the secondary metabolites reported from different species of this genus from 1974 to May 2024 were summarized, including their pharmacological activities and 1H and 13C NMR data whenever available. Moreover, the chemical synthesis works of several representative sesquiterpenes were presented.

2. An Overview of Secondary Metabolites from Soft Corals of the Genus Capnella

This review covers the secondary metabolites from soft corals of the genus Capnella from 1974 to May 2024, based on an extensive literature search using SciFinder, Web of Science, and PubMed. As revealed by the literature survey, 69 chemical components were isolated and identified from soft corals of this genus over the five decades (Table 1). These metabolites possessed diverse structural features, which could be generally grouped as sesquiterpenes, diterpenes, steroids, and lipids (Figure 1a). Obviously, sesquiterpenes were the dominant type of chemical composition from soft corals of the genus Capnella. In-depth insights into the chemical diversities of sesquiterpenes could be further divided into eight subclasses including capnellane, precapnellane, bicyclogermacrane, germacrane, aromadendrane, cadinene, farnesane, and guaiane (Figure 1b). As shown in Figure 1b, capnellane sesquiterpenes were the most abundant metabolites in this genus.
Insights into the distributions of these secondary metabolites in different species of the genus Capnella, including Capnella imbricata, Capnella lacertiliensi, Capnella thyrsoidea, Capnella erecta, Capnella fungiformis, Capnella sp. nov., and Capnella sp. were reported as their source species (Figure 2). Among these aforementioned species, C. imbricata was the most frequently encountered species, and afforded the largest number of secondary metabolites with a total amount of 48. (Notably, some compounds were distributed in different species and they were counted separately in each species). Interestingly, diterpenes were solely found in the species C. thyrsoidea, and three species—C. lacertiliensi, C. erecta, and Capnella sp. nov.—only afforded steroids. Perhaps, these secondary metabolites could serve as chemotaxonomic markers for these species.

3. Sesquiterpenes

This was the largest cluster of secondary metabolites (Figure 1a) obtained from soft corals of the genus Capnella with an amount of 45 compounds in this work (Table 1). These compounds showed a diversity of carbon frameworks, which comprised eight categories: capnellane, precapnellane, bicyclogermacrane, germacrane, aromadendrane, cadinene, farnesane, and guaiane (Figure 3). These diverse skeletons make sesquiterpenes the most attractive type of secondary metabolites from this genus. Interestingly, the majority of sesquiterpenes were obtained from the species C. imbricata. The rest of the substances were present in the species C. fungiformis and the unclearly identified Capnella sp. (Table 1).

3.1. Capnellane Sesquiterpenes

This type of sesquiterpene was the characteristic group of secondary metabolites from soft corals of the genus Capnella (Figure 4) with the most abundance (Figure 1b). Worth mentioning was that the skeleton name capnellane was coined by scientists in their work on C. imbricata [52]. The basic skeleton of capnellane was the unique tricyclic 5/5/5 carbon framework bearing four methyls including one gem-dimethyl and one angular methyl.
In 1974, the first terpene 1 from soft corals of the genus Capnella was obtained from the Indonesian soft coral C. imbricata from Leti Island. Its structure was elucidated through the extensive analysis of spectral data along with a series of chemical conversions [52]. Importantly, the absolute configuration of 1 was successfully established by single-crystal X-ray diffraction in the subsequent study [57].
Continuing investigation on the Indonesian collection C. imbricata afforded two undescribed metabolites 2 [58] and 3 [63], in addition to 1. The complete structure of 3 was established by a single-crystal X-ray diffraction analysis, and its absolute configuration was identified as the same as that of 1 [63]. Notably, different inhabited environments caused different compositions of secondary metabolites of C. imbricata. This research team found that another sample of this species from Lakor Island had two triols 4 and 5, in addition to the diol 2 but without the tetrol 3 [58]. Meanwhile, hydrocarbon 6 was obtained from the nonpolar fraction of C. imbricata. This compound was assumed the biogenetic precursor of this class of sesquiterpene alcohols, which was confirmed by partial synthesis in the work [64].
A new terpene 7 was identified in the Papua New Guinean specimen C. imbricata. Its structure and relative configuration were determined by a single-crystal X-ray diffraction analysis. Based on the closely resembling NMR data, the relative stereochemistry at C-2 for previously described 5 was proposed as 2β [65]. This speculation was unambiguously confirmed by the diagnostic NOESY correlations and the Gaussian calculation in the recent Chung and co-workers’ research [44]. The presence of eight novel acetylated capnellenes 8–15 was described in the fresh colonies of C. imbricata, as they were the major sesquiterpenes in the living animal. According to the results of chemical transformations, the previously reported capnellene polyols, isolated from sun-dried colonies, were shown to be artifacts [66].
Chemical investigation of the South China Sea collection C. imbricata led to the discovery of two sesquiterpenes 16 [67] and 17 [68]. Their structures were established by extensive analysis of spectral data and confirmed by single-crystal X-ray diffraction experiments. It was found that the signs of the specific rotation values of 16 ([α]D −39.6) [67] and 17 ([α]D −17) [68] were respectively opposite to those of 2 ([α]D +41) [58] and 7 ([α]D +17) [65]. Consequently, these four terpenes could be regarded as two pairs of enantiomers. Preliminary bioassays showed that compound 17 had suppressive action on contracture of the removed ileums of the guinea pig and it exhibited antitumor effects on EAC at 25 μg/mL with an inhibition rate of 43% [68].
Two previously unrecorded compounds with the capnellane skeleton 18 and 19, along with one known metabolite 2, had been isolated from the Indonesian sample C. imbricata collected at Mayu Island. The cytotoxicities of all the isolates were tested against six cell lines including HL-60, K562, G402, MCF-7, HT115, and A2780. The results showed that compound 2 was cytotoxic toward all tested cell lines with IC50 values ranging from 0.7 μM to 93 μM, with the best activity being displayed against K562 leukemia. Sesquiterpene 18 was effective against the cell lines K562 and A2780 (IC50 4.6 μM and 6.6 μM, respectively). Component 19 was cytotoxic with selectivity for cell lines G402 and A2780 [48].
Interestingly, chemical constituents 2 and 18 were also found in the Formosan soft coral C. imbricata, along with seven sesquiterpenes 20–26. In this work, their anti-inflammatory activities were evaluated. Compounds 2, 20, and 21 significantly reduced the iNOS protein expression (1.2 ± 0.1%, 54.4 ± 12.0%, and 34.8 ± 10.2%, respectively). Moreover, substances 2 and 20 significantly inhibited the expression of the COX-2 protein (24.8 ± 7.5% and 62.9 ± 13.7%, respectively) [51]. Further bioassays were conducted, revealing marine-derived capnellenes 2 and 18 had anti-neuroinflammatory and anti-nociceptive properties in IFN-γ-stimulated microglial cells and in neuropathic rats, respectively [59]. Another Formosan soft coral Capnella sp. afforded the secondary metabolite 2, too. This compound together with its 10 ester derivatives were tested for cytotoxic activities against four human tumor cell lines KB, WiDr, Hela, and Daoy. Almost all esters showed superior activity against these cells compared to the parent compound 2 [61]. In recent pharmacological research, substance 2 impaired vascular development in zebrafish [60].
Study on another Formosan collection C. imbricata afforded a new secondary metabolite 27 along with two known metabolites 2 and 4. In this study, a single-crystal X-ray diffraction analysis of 4 was conducted for the first time. Compound 27 exhibited significant inhibitory effects on elastase release and superoxide generation with inhibition rate of 5.67% and 9.28%, respectively [62]. Further investigation resulted in the discovery of two new sesquiterpenes 28 and 29, as well as 4, 5, 18, 20, and 27. In the anti-inflammatory activity bioassay, components 20 and 29 showed remarkable decreases in iNOS levels (47.61% and 27.73%, respectively). Furthermore, terpenes 4, 20, and 28 exhibited significant inhibitions against COX-2 protein expressions (ranging from 7.64% to 12.57%). Notably, the chemical relationships between these sesquiterpenes and their anti-inflammatory effects was analyzed by a tool called ChemGPS-NP [44].
To the best of our knowledge, there was only one report of natural capnellane sesquiterpenes from other organisms, which did not belong to the genus Capnella. This was the investigation on the soft coral Dendronephthya rubeola, resulting in the isolation and identification of two aforementioned metabolites 2 and 8, along with four undescribed capnellane sesquiterpenes [77]. It might be worth pointing out that the illihenlactoneosides B and C from the plant Illicium henryi [78] were not capnellane-type sesquiterpenes, because their tricyclic carbon framework did not bear the key gem-dimethyl substructure. Based on these findings, all the capnellane sesquiterpenes except 2 and 8 were characteristic chemical constituents of Capnella soft corals.

3.2. Precapnellane Sesquiterpene

The sole member of this group was precapnelladiene (30) (Figure 5) from the soft coral C. imbricata. The basic precapnellane carbon framework had a fused 5- and 8-membered ring system forming an uncommon bicyclo[6.3.0]undecane carbon skeleton, carrying four methyls including one gem-dimethyl. From the biogenetic viewpoint, this type of compound might be a precursor of the co-occurring tricyclic capnellane sesquiterpenes [69].
As far as we know, there was only one additional member of precapnellane sesquiterpene called 3α,4α-epoxyprecapnell-9(12)-ene, which was afforded by the soft coral D. rubeola [77]. However, there was no further report of 30 from other biological materials. As a result, carbonhydron 30 could be regarded as the representative chemical substance of Capnella soft corals.

3.3. Bicyclogermacrane Sesquiterpenes

The bicyclogermacrane contains a bicyclo[8.1.0]undecane carbon skeleton, featured by a cyclopropane fused to a cyclodecane and the gem-dimethyl attached to the cyclopropane.
The first reported bicyclogermacrane sesquiterpenes from soft corals of the genus Capnella were capgermacrenes A (31) and B (32) (Figure 6). Interestingly, these two terpenes were a pair of isomers that differed in the configuration of double bond Δ6. However, only 31 exhibited anti-inflammatory activity, which was possibly influenced by the stereo difference [70]. Continuous study on the same species afforded another new metabolite 33, whose double bond was shifted to C-5/C-6 compared to 31 and 32. However, it did not show any obvious antibacterial activity against Escherichia coli and Staphylococcus aureus [72].
Investigation on another Bornean soft coral C. imbricata yielded four new members of bicyclogermacrane sesquiterpenes 34–37. These four chemical constituents were the respective hydroxyl or hydroperoxyl derivatives of 31 and 32. Terpenes 34 and 35 displayed bacteriostatic activity against S. aureus and MRSA, while components 36 and 37 exhibited bactericidal activity against these two bacteria [49]. Indeed, the co-existence of capgermacrenes A–G (31–37) was found in the soft coral C. imbricata. All of these metabolites except 33 exhibited different levels of cytotoxicity against S1T cells with IC50 values ranging from 0.79 μg/mL to 7.79 μg/mL [71].
Literature surveys revealed that these seven compounds have not been found in the other organisms except the aforementioned soft corals. Consequently, they served as the featured secondary metabolites of Capnella soft corals.

3.4. Germacrane Sesquiterpenes

The germacrane contains a cyclodecane bearing one isopropyl and two methyls. Formally, this could be regarded as the precursor of bicyclogermacrane.
Litseagermacrane (38) (Figure 7) was a germacrane sesquiterpene afforded by the Bornean soft coral Capnella sp. However, no obvious anti-inflammatory activity was observed in the bioassay [70]. Another study on the Bornean soft coral C. imbricata resulted in the discovery of a new germacrane sesquiterpene called capgermacrene H (39). This compound was inactive against S1T cells (IC50 > 30.0 μg/mL) [71].
Interestingly, compound 38 was also obtained from three plants Litsea verticillata [79], Dysoxylum mollissimum [80], and Syzygium cerasiforme [81]. However, there was no report of metabolite 39 from other marine organisms besides the above-mentioned soft corals. Therefore, 39 could be regarded as the characteristic chemical composition of Capnella soft corals.

3.5. Aromadendrane Sesquiterpene

The basic carbon skeleton of aromadendrane is the non-linear fused tricyclic 5/7/3 carbon framework. There are four methyls attached to the carbon skeleton, including one gem-dimethyl at the cyclopropane.
Chemical investigation of Bornean soft coral Capnella sp. led to the isolation and identification of the aromadendrane sesquiterpene 40 (Figure 8), which was inactive in the anti-inflammatory bioassay [70].
It might be worth pointing out that this sesquiterpene was widely distributed in the soft corals including Sarcophyton glaucum [82], Sarcophyton trocheliophorum [83], and Xenia umbellate [84], and plants such as Artemisia vulgaris [85], Turczaninowia fastigiate [86], Hyptis mociniana [87], Calycolpus goetheanus [88], and Calypogeia integristipula [89]. As a result, this compound had no chemotaxonomic significance.

3.6. Cadinane Sesquiterpene

The decalin is the basic carbon skeleton of cadinene, and one isopropyl and two methyls are attached to it. Structurally, one methyl and one isopropyl are in the para position.
The Bornean soft coral Capnella sp. afforded the cadinane sesquiterpene 41 (Figure 9). The antibacterial bioassay revealed the negligible inhibition against E. coli and S. aureus (MIC > 500 μg/mL) [72].
This substance was previously found in the soft coral Sarcophyton ehrenbergi [90] and the plant Scapania undulata [91]. Interestingly, the enantiomer of 41 was encountered in the investigation of soft coral Sinularia sp. [92]. These reports revealed that 41 could not be the typical component of Capnella soft corals.

3.7. Farnesane Sesquiterpenes

The farnesane is a linear carbon chain, which is formed by the head-to-tail connection of three isoprene units.
A study on the Madagascan soft coral C. fungiformis gave an inseparable mixture of Z/E-isomers 42 and 43 (Figure 10), which was determined by GC-MS and NMR spectral data [47].
It might be worth pointing out that the carboxylic acids and methyl esters of these two metabolites were reported as the isolates of soft corals Sinularia gonatodes [93], Sinularia capillosa [94], Sinularia kavarattiensis [95,96] and Sinularia tumulosa [22]. Although they were new natural products, it was difficult to evaluate whether they were characteristic secondary metabolites of Capnella soft corals.

3.8. Guaiane Sesquiterpene

The guaiane contains a bicyclo[5.3.0]decane carbon skeleton carrying one isopropyl and two methyls. Formally, this could be regarded as the precursor of aromadendrane.
A novel guaiane sesquiterpene oxyfungiformin (44) (Figure 11) was isolated from the soft coral C. fungiformis. Its structure was elucidated by detailed analysis of spectral data and quantum chemical calculations [47]. Recently, its stereochemistry was confirmed by the synthesis work, along with the determination of its absolute configuration by X-ray diffraction [97].
To the best of our knowledge, only one structurally related compound was reported from the soft coral S. kavarattiensis [96], which was a diastereoisomer of 44 at the opposite geometry of 1,5-epoxy. Consequently, 44 was a specific chemical constituent of Capnella soft corals.

4. Diterpenes

Unlike soft corals of some frequently encountered genera and species [7,11,14,15,16,39], diterpenes were extremely rare in the genus Capnella. To the best of our knowledge, only four diterpenes were found. They were xenicane diterpenes 45–48 (Figure 12), from the South African sample C. thyrsoidea [45]. Good inhibitory activity against superoxide production in rabbit neutrophils (>80%) at a concentration of 12.5 μg/mL for terpenes 45, 47, and 48, and good to moderate inhibition of superoxide production in human neutrophils (68% and 21%, respectively) at a concentration as low as 1.25 μg/mL for 45 and 47 were observed.
The xenicane featured a cyclononane ring, and usually, a tetrahydropyran ring bearing a long carbon chain fuses to the aforementioned macro ring. It might be worth pointing out that the 6β-epimer of 45, which was named 9-deacetoxy-14,15-deepoxyxeniculin, was afforded by the soft corals Xenia obscuronata [98] and Eleutherobia aurea [99], as well as the plant Boerhavia diffusa [100]. However, all of these four compounds have not been obtained from other natural sources. Therefore, they were characteristic chemical components of Capnella soft corals.

5. Steroids

An account of 20 compounds were reported from soft corals of the genus Capnella (Figure 13). These steroids could be divided into three groups: ergostane, pregnane, and gorgostane. The major difference between them is the features of the side chain. For pregnane, its side chain is usually vinyl. For gorgostane, its side chain possesses cyclopropane. The left compounds belong to the ergostane steroids.
Analysis of complex sterol mixtures of C. imbricata by the mass-analyzed ion kinetic energy spectrometry led to the identification of five sterols 49–53 [73]. Recently, the presence of steroids 50, 51, and 53 in the Madagascan soft coral C. fungiformis was reported [47].
Pregnane sterols 54–56 from Australian soft corals Capnella sp. nov. and C. erecta were illustrated. Notably, the structure of 54 was confirmed by a single-crystal X-ray diffraction [74]. It might be worth pointing out that compound 56 was also obtained from the soft coral Sinularia sp., whose structure was also corroborated by the X-ray diffraction analysis [101].
The South African soft coral C. thyrsoidea also afforded pregnane steroid 56 together with two new compounds 57 and 58. It was found that components 56 and 57 stimulated superoxide production in rabbit neutrophils [45]. Additionally, a structure-based virtual docking study suggested 56 as a potential hit with inhibitory activity against plasmodial proteases and selectivity on human cathepsins [75].
Five highly oxygenated sterols (gorgosterols 59 and 60 and ergosterols 61–63) were isolated from the Australian soft coral C. lacertiliensis. All sterols displayed the antifungal potential against Microbotryum violacea. Moreover, steroids 59 and 63 showed inhibition against Eurotium repens, whereas 61 and 63 exhibited weak tyrosine kinase p56lck inhibition [50].
Recently, the Formosan soft coral C. imbricata afforded two new sterols 64 and 65 with a cross-conjugated dienone structural unit in ring A. These two metabolites showed reduction in iNOS levels and promotion in COX-2 release [46]. Further study on this species yielded three steroids 66–68. In this study, the absolute configuration of sterol 68 was determined for the first time by single-crystal X-ray diffraction analysis. The effects of a moderate reduction in iNOS levels for secondary metabolites 66–68 were observed [76].
It is well known that steroids are one enormous cluster of secondary metabolites from soft corals [2,4]. Among the aforementioned steroids, some of the known compounds were frequently encountered in the investigations of soft corals of various species. For instance, compound 50 was found as a metabolite of soft corals such as Sinularia depressa [102], Sinularia nanolobata [103], Sinularia humilis [104], Litophyton arboreum [105], Sinularia terspilli [106], Nephthea erecta [107], Sinularia flexibilis [108], Dendronephthya sp. [109], Sinularia gibberosa [108], Litophyton viridis [110], Sarcophyton glaucum [111], etc. Accordingly, their wide distribution limited their chemotaxonomic significance. However, those new compounds have hardly been reported from other natural sources. Therefore, most of them could be considered as the specific chemical constituents of Capnella soft corals.

6. Lipid

The lipid 69 was isolated from the Madagascan soft coral C. fungiformis (Figure 14) [47].
This compound was found in various natural sources, including the soft coral Dendronephthya hemprichi [112], the terrestrial plants Euonymus latifolius [113], Trichilia gilgiana [114], and Pinus massoniana [115], and the marine seaweeds Codium tomentosum and Plocamium cartilagineum [116]. Its widespread distribution limited the possibility as a featured component of Capnella soft corals.

7. The Preliminary Summary of Structure-Activity Relationships of the Terpenes from Soft Corals of the Genus Capnella

7.1. Sesquiterpenes

7.1.1. Capnellane Sesquiterpenes

The capnellane sesquiterpenes were evaluated mainly for cytotoxic and anti-inflammatory activities as depicted in Table 1.
A comparison of 2 and 18 showed the substitution of 10-hydroxyl in 2 could broaden the cytotoxicity against different cell lines [48]. The observed assessment revealed that the presence of hydroxyl groups in C-5 and C-10 in 4 significantly inhibited COX-2 protein expression at a concentration of 10 µM, as compared with 18 [44]. Interestingly, acetylation of 8-hydroxyl and the remaining 10-hydroxyl in 20 still kept the remarkable inhibition against the expression of COX-2 [44]. It was likely that the oxidation of 8-hydroxyl in 21 and 24 led to the loss of reduction of iNOS and COX-2 expression [51]. Seemingly, the substituted 6-hydroxyl in 28 promoted the COX-2 expression, whereas 2-hydroxyl in 30 reduced the expression of COX-2 [44].

7.1.2. Bicyclogermacrane Sesquiterpenes

The seven bicyclogermacrane sesquiterpenes 31–37 were subjected to anti-inflammatory, antibacterial, and cytotoxic activities as shown in Table 1.
A comparison of 31 and 32 revealed that the Z configuration of double bond Δ6 in 32 significantly reduced the anti-inflammatory activity [70]. Additionally, the stereo difference of Δ6 in 34–37 had an impact on the antibacterial properties [49]. The shift of Δ6 to Δ5 in 33 resulted in the loss of antibacterial activity against E. coli and S. aureus [72] and cytotoxicity activity against SIT cells [71]. For the bioactive compounds 34–37, the change of hydroxyl and hydroperoxyl groups did not improve cytotoxicity [71].

7.2. Diterpenes

The result of anti-inflammatory bioassay of four xenicane diterpenes 45–48 indicated that the presence of the epoxide in 46 led to the loss of anti-inflammatory activity [45]. A comparison of 48 and 49 indicated that the substitution of a hydroxyl group at C-15 in 47 slightly improved the anti-inflammatory activity at a low concentration.

8. The Characteristic 1H and 13C NMR Data of the Secondary Metabolites from Soft Corals of the Genus Capnella

Among these secondary metabolites from soft corals of the genus Capnella, a large quantity of them were discovered from natural sources for the first time. Herein, the characteristic 1H and 13C NMR data of the new chemical constituents were provided in the following tables. However, the NMR data of known compounds such as 20, 21, 39, 41, and 42 were not given in the literature. Hopefully, the available information of NMR data will be useful for readers who are experts in the structural determination of natural products.
Based on their structural features, the reported 1H and 13C NMR data of new metabolites were present as described below.

8.1. Sesquiterpenes

8.1.1. Capnellane Sesquiterpenes

The capnellane sesquiterpenes were the most abundant sesquiterpenes from soft corals of the genus Capnella. Notably, almost all of them were found as novel compounds. It might be worth pointing out that the NMR data of some new compounds such as 7, 8, 10, 12, and 15 were not given in their corresponding works. Additionally, the full assignments of the 1H and/or 13C NMR data of a few chemical substances such as 1–3 were not completed in their very early investigations; thus, these data were presented as a paragraph instead of a table. The 1H and 13C NMR data of the left compounds were provided in Table 3, Table 4, Table 5, Table 6 and Table 7.
Compound 1: 1H NMR (CDCl3): δH 5.38 (d, J = 1.5 Hz, 2H), 4.83 (m, 1H), 4.10 (dd, J = 11.0, 6.5 Hz, 1H), 1.28 (s, 3H), 1.20 (s, 3H), 1.01 (s, 3H) [52]; 1H NMR (CDCl3): δH 5.38 (d, J = 1.5 Hz, 2H), 4.83 (m, 1H), 4.13 (dd, J = 6, 5 Hz, 1H), 1.28 (s, 3H), 1.20 (s, 3H), 1.05 (s, 3H) [58]; 13C NMR (CDCl3): see Table 2.
Compound 2: 1H NMR (CDCl3): δH 5.33 (br s, 1H), 5.31 (br s, 1H), 4.80 (m, 1H), 1.26 (s, 3H), 1.24 (s, 3H), 1.08 (s, 3H) [58]; 13C NMR (CDCl3): see Table 2.
Compound 3: 1H NMR (C5D5N/D2O 1:1): δH 5.40 (m, 2H), 5.33 (m, 1H), 4.60 (m, 1H), 3.82 (dd, 2H), 1.68 (s, 3H), 1.42 (s, 3H) [63]; 13C NMR (CD3OD): see Table 2.
Compound 4: 1H NMR (CD3OD/CD3COCD3 1:1): δH 5.20 (m, 2H), 4.80 (m, 1H), 3.86 (d, J = 5.5 Hz, 1H), 1.32 (s, 3H), 1.18 (s, 3H), 1.12 (s, 3H) [58]; 13C NMR (CDCl3): see Table 2.
Compound 5: 1H NMR (CDCl3): δH 5.37 (m, 1H), 4.70 (m, 1H), 3.70 (m, 1H), 1.45 (s, 3H), 1.28 (s, 3H), 1.16 (s, 3H) [58]; the recent full assignments of 1H and 13C NMR (CDCl3): see Table 3.
Compound 6: 1H NMR (CDCl3): δH 4.94 (br s, 1H), 4.82 (br s, 1H), 1.16 (s, 3H), 1.08 (s, 3H), 0.98 (s, 3H) [64]; 13C NMR (CDCl3): δC 158.75, 105.08, 69.12, 53.39, 52.34, 48.00, 46.07, 42.37, 41.73, 40.63, 31.83, 31.56, 30.84, 29.11, 26.07 [64].
Compound 9: 1H NMR (CDCl3): δH 5.36 (br s, 2H), 5.1 (dd, J = 12.5, 8 Hz, 1H), 4.8 (m, 1H), 1.95 (s, 3H), 1.32 (s, 3H), 1.24 (s, 3H), 0.98 (s, 3H) [66].
Compound 11: 1H NMR (CDCl3): δH 5.38 (br s, 2H), 4.8 (m, 1H), 4.6 (d, J = 6.5 Hz, 1H), 2.03 (s, 3H), 1.21 (s, 3H), 1.12 (s, 3H), 1.12 (s, 3H) [66].
Compound 13: 1H NMR (CDCl3): δH 5.18 (br s, 2H), 5.0 (dd, J = 9, 9 Hz, 1H), 4.68 (m, 1H), 3.96 (d, J = 10.5 Hz, 1H), 2.03 (s, 3H), 1.94 (s, 3H), 1.28 (s, 3H), 0.88 (s, 3H) [66].
Compound 14: 1H NMR (CDCl3): δH 5.43 (br s, 2H), 4.85 (dd, J = 6, 6 Hz, 1H), 4.8 (m, 1H), 4.66 (d, J = 5 Hz, 1H), 2.06 (s, 3H), 2.03 (s, 3H), 1.25 (s, 3H), 1.22 (s, 3H), 1.12 (s, 3H) [66].
Table 2. The 13C NMR data of compounds 1–4.
Table 2. The 13C NMR data of compounds 1–4.
No.1 [58]2 [58]3 [63]4 [58]
δC 1δC 1δC 2δC 1
138.643.344.1043.7
251.742.746.6642.4
381.441.481.0132.9
452.649.352.4253.2
545.345.645.9582.8
649.848.750.1056.1
738.136.838.4434.6
873.872.473.8472.4
9161.5160.3161.90159.9
1089.888.889.1186.0
1165.564.663.5464.0
12109.1107.5109.09108.4
1325.031.524.8030.8
1432.930.373.8431.4
1526.123.221.9624.1
1 Recorded in CDCl3. 2 Recorded in CD3OD.
Table 3. The 1H and 13C NMR data of compounds 5, 16, and 17.
Table 3. The 1H and 13C NMR data of compounds 5, 16, and 17.
No.5 [44]16 [67]17 [68]
δH 1δC 1δH 2δC 2δH 2δC 2
1 46.9 43.94 47.15
24.03 dd (5.4, 5.4)82.21.55 m43.173.57 dd (5.0, 4.0)83.37
1.46m
32.09 dd (13.8, 5.4)50.01.75 m41.982.11 m39.74
1.55 dd (13.8, 5.4) 1.57 m 2.15 m
4 47.6 49.94 50.91
51.48 m46.81.95 dd (9.0, 4.5)46.223.20 d (1.0)81.40
2.04 dd (13.8, 8.4) 1.36 dd (7.4, 6.0)
62.34 m51.12.51 m49.612.35 m57.04
72.32 m38.11.48 ddd (15.2, 9.0, 4.8)37.881.40 m35.76
1.50 m 2.35 ddd (10.0, 6.0, 2.6) 2.28 m
84.74 m73.74.80 m73.514.62 m72.00
9 162.2 162.25 162.00
10 90.5 90.13 85.12
112.17 s64.71.46 m65.692.02 s62.05
125.34 d (1.8)110.35.32 d (2.0)109.515.15 m107.21
5.39 d (1.8) 5.30 d (2.0)
131.27 s34.41.35 s32.711.03 s32.80
141.11 s24.21.09 s31.401.11 s25.33
151.27 s23.01.26 s24.081.10 s23.70
1 Recorded in CDCl3. 2 The deuterated solvent was not given.
Table 4. The 1H and 13C NMR data of compounds 18 and 19.
Table 4. The 1H and 13C NMR data of compounds 18 and 19.
No.18 [48]19 [48]
δH 1δC 1δH 1δC 1
1 42.5 43.4
21.51 m41.51.68 dd (11.2, 5.6)43.8
1.55 t (11.2)
32.09 m40.55.08 dd (10.6, 5.6)82.1
1.45 m
4 53.3 51.4
51.79 dd (13.8, 8.4)48.92.25 m45.6
1.51 dd (13.8, 4.8) 1.20 m
62.22 ddt (7.6, 3.5, 4.2)42.12.52 m49.2
72.13 dd (8.4, 4.2)40.32.35 m38.3
1.39 m 1.42 dt (14.4, 4.0)
84.74 tt (8.0, 4.2)75.64.75 m73.5
9 160.6 161.8
102.36 ddd (4.6, 2.8, 1.6)49.5 87.9
111.75 d (3.3)68.02.30 s64.9
125.05 t (2.5)105.45.30 t (2.5)109.7
4.96 t (2.4)
131.24 s32.10.82 s25.3
141.02 s30.83.55 d (9.4)74.1
3.42 d (9.4)
150.82 s26.11.31 s20.8
COCH3 171.1
COCH3 1.99 s21.0
1 Recorded in CDCl3.
Table 5. The 1H and 13C NMR data of compounds 22–24.
Table 5. The 1H and 13C NMR data of compounds 22–24.
No.22 [51]23 [51]24 [51]
δH 1δC 1δH 1δC 1δH 1δC 1
1 47.2 44.5 44.7
21.41 m36.21.46 m43.91.56 m42.3
1.58 m 1.66 m
31.42 m39.81.69 m37.51.78 m40.4
4 53.6 55.5 55.2
51.49 m48.81.60 m41.51.03 dd (12.3, 4.5)46.2
1.80 dd (12.8, 8.1) 1.88 dd (14.2, 10.1) 2.09 dd (12.3, 8.0)
62.43 m41.62.67 m49.53.02 m44.1
71.39 m39.71.59 m38.22.05 dd (18.4, 2.0)42.2
2.25 m 2.28 m 2.64 dd (18.4, 6.5)
84.51 t (5.2)75.54.78 m74.2 211.3
9 160.2 164.3 135.5
102.86 m49.1 90.6 186.7
111.89 d (3.2)65.22.02 s62.52.47 s61.9
125.00 s105.95.41 s111.84.32 dd (13.4, 1.7)56.8
5.14 s 5.43 s 4.37 dd (13.4, 1.7)
131.23 s31.63.35 m71.41.24 s30.1
141.15 s26.71.21 s30.71.21 s31.1
153.48 d (10.8)69.91.29 s23.80.87 s26.0
3.58 d (10.8)
1 Recorded in CDCl3.
Table 6. The 1H and 13C NMR data of compounds 25 and 26.
Table 6. The 1H and 13C NMR data of compounds 25 and 26.
No.25 [51]26 [51]
δH 1δC 1δH 1δC 1
1 44.3 43.9
21.45 m43.61.44 m41.7
31.54 m41.71.53 m40.9
1.64 m
4 50.2 53.6
51.26 dd (9.5, 13.8)45.31.45 m48.4
1.83 dd (9.5, 13.8) 1.77 m
62.77 m48.12.48 m42.6
71.47 m35.61.54 m36.3
2.51 m 2.25 m
85.72 m75.45.53 t (3.4)76.2
9 151.5 156.3
10 95.72.71 m49.5
112.34 s65.31.78 m67.7
125.45 d (2.2)116.44.99 s108.6
5.51 d (2.2) 5.08 s
131.09 s31.91.19 s31.6
141.11 s31.41.06 s30.2
151.12 s24.40.98 s25.5
8-COCH3 170.9 171.9
8-COCH32.07 s21.32.09 s21.4
10-COCH3 169.6
10-COCH31.95 s22.0
1 Recorded in CDCl3.
Table 7. The 1H and 13C NMR data of compounds 27–29.
Table 7. The 1H and 13C NMR data of compounds 27–29.
No.27 [62]28 [44]29 [44]
δH 1δC 1δH 1δC 1δH 1δC 1
1 49.9 42.1 44.2
21.77 dd (12.6, 6.6)38.31.47 m40.61.34 m41.0
1.41 dt (12.6, 7.2) 2.05 m
31.65 m41.91.64 m41.31.71 dd (8.0, 2.5)42.4
1.62 m 1.64 dd (8.0, 2.0)
4 49.8 49.8 47.7
51.37 dd (13.8, 8.4)46.12.04 d (13.5)55.41.83 d (13.5)52.1
1.93 dd (13.8, 9.0) 1.79 d (13.5) 1.97 d (13.5)
62.47 m49.4 88.0 72.7
72.36 dd (13.2, 8.4)37.62.26 dd (13.0, 7.5)48.32.33 dd (16.5, 8.0)43.6
1.53 dt (13.2, 6.0) 1.83 dd (13.0, 10.0) 1.91 dd (15.0, 8.0)
84.82 br s73.64.80 br s75.14.79 br s87.4
9 161.4 159.7 160.2
10 90.22.68 dd (7.0, 2.0)58.3 89.7
112.04 s65.41.62 m69.11.88 s67.0
125.40 d (1.8)110.54.99 t (2.0)107.85.38 d (2.0)112.5
5.43 d (1.8) 5.17 t (2.0) 5.42 d (2.0)
131.16 s32.71.21 s32.11.31 s33.4
141.17 s27.01.04 s30.01.03 s31.8
153.61 d (11.4)68.61.10 s26.61.38 s25.0
3.89 d (11.4)
1 Recorded in CDCl3.
Most capnellane sesquiterpenes possessed a terminal double bond Δ9(12), which was characterized by two singlet proton peaks usually at δH 5.50–5.00 and 5.00–4.50 in the 1H NMR spectrum and two carbon signals appeared at δC ca. 160 and 110 ppm in the 13C NMR spectrum. In addition, hydroxylation frequently occurred for this type of sesquiterpenes. If it was hydroxylated at C-2, the 1H NMR signal at δH 4.03 ppm indicated the 2β-orientation for the hydroxyl group; whereas δH 3.57 ppm suggested the 2α-configuration. When the hydroxyl group was substituted at C-3, the proton resonated at δH 4.10 ppm. If the hydroxyl was on the 8β face, the 1H and 13C NMR chemical shifts of the methine were δH 4.80–4.74 ppm and δC 74.2–73.6 ppm, respectively; conversely, the 1H and 13C NMR data were δH 4.62 ppm and δC 72.0 ppm, respectively. However, the chemical shifts δH 4.51 ppm and δC 75.5 ppm of sesquiterpene 22 was an exception. Perhaps it was affected by other functional groups in its chemical structure. The occurrences of hydroxylation at C-5 and C-10 resulted in the carbon resonances at δC 82.8–81.4 ppm and δC 90.6–89.1 ppm, respectively. The chemical shifts of C-10 of compounds 4, 17, and 19 were inconsistent with the aforementioned rule, which revealed the possible influences caused by other substituents in their chemical structures.

8.1.2. Precapnellane Sesquiterpene

Precapnelladiene (30) was the sole precapnellane sesquiterpene from soft corals of the genus Capnella. Only the 1H NMR data was recorded when it was discovered as a new hydrocarbon [69]. Until Paquette and co-workers completed the total synthesis of 30 [117], the 13C NMR data were reported.
Compound 30: 1H NMR (CDCl3): δH 5.34 (t, J = 8.4 Hz, 1H), 5.06 (s, 1H), 3.54 (m, 1H), 2.91 (q, J = 11.5 Hz, 1H), 2.4 (m, 2H), 1.64 (s, 3H), 1.03 (d, J = 5.2 Hz, 3H), 0.97(s, 6H) [69]; 1H NMR (CDCI3): δH 5.33 (t, J = 8.3 Hz, 1H), 5.02 (d, J =1.5 Hz, 1H), 3.51 (dt, J = 13.0, 6.0 Hz, 1H), 2.90 (dd, J = 13.0, 9.3 Hz, 1H), 2.38 (m, 2H), 1.8–1.5 (br m, 4H), 1.63 (br s, 3H), 1.42 (m, 1H), 1.25 (m, 1H), 1.04 (d, J = 6.8 Hz, 3H), 0.99 (s, 3H), 0.97 (s, 3H) [117]; 13C NMR (CDCl3): δC 145.5, 136.2, 130.3, 121.8, 42.4, 40.5, 39.6, 38.9, 38.7, 33.7, 31.5, 31.3, 29.8, 26.7, 22.0 [117].
Compared to the common structural features of capnellane sesquiterpenes, the distinct characteristics of 30 were attributable to two isolated olefinic protons (δH 5.34 and 5.06 ppm), one allylic methyl (δH 1.64 ppm) and one doublet methyl (δH 1.03 ppm).

8.1.3. Bicyclogermacrane Sesquiterpenes

All the 1H and 13C NMR data of capgermacrenes A–G (31–37) were available and supplemented in Table 8, Table 9 and Table 10.
The characteristic of these secondary metabolites was the presence of a cyclopropane ring. As demonstrated in Table 8, Table 9 and Table 10, the 1H NMR peaks at δH 1.45–0.82 and 1.39–0.68 ppm were two indicative signals of H-1 and H-10 of the cyclopropane in the chemical structures of 31–37. Interestingly, if there was no exomethylene at C-3, one signal of the cyclopropane appeared at δH 0.77 or ca. 1.38 ppm, and the other appeared at δH 1.32 or ca. 1.44 ppm. When the exomethylene existed at C-3, two signals of the cyclopropane were observed at δH 1.03–0.82 ppm and δH 1.06–0.87 ppm. However, in the 13C NMR data of C-1 (δC 33.8–25.0 ppm) and C-2 (δC 30.1–24.7 ppm), it was it difficult to recognize the presence of cyclopropane, due to the confusing wide ranges of their chemical shifts.
Another common structural feature of these secondary metabolites was the α,β-conjugated ketone moiety. The chemical shift of H-6 could be regarded as an indicator of the configuration of double bond Δ6 in the subunit α,β-conjugated ketone. No matter the presence or absence of exomethylene at C-3, the 1H NMR signal resonating at δH > 6.0 ppm supported the E-configuration of Δ6, whereas δH < 6.0 ppm suggested the Z-configuration. For compounds 34–37, the difference of 13C NMR data of C-6 and C-7 could be used to determine the configuration of Δ6. As illustrated in Table 9 and Table 10, the chemical-shift difference ΔδC≈0 ppm was observed for the E-configuration of Δ6; conversely, the chemical-shift difference ΔδC > 6 ppm.

8.1.4. Germacrane Sesquiterpene

Only compound capgermacrene H (39) was found as a new germacrane sesquiterpene. The 1H and 13C NMR data of this sesquiterpene were measured in two solvents CDCl3 and C6D6 (Table 11), respectively.
The major difference between compound 39 and the seven bicyclogermacrane sesquiterpenes 31–37 was the presence of the isopropenyl group instead of the cyclopropane. The 1H NMR signals at δH 4.79, 4.78, and 1.76 ppm recorded in CDCl3, and 13C NMR peaks at δC 145.9, 110.3, and 20.9 ppm recorded in CDCl3 were attributable to the isopropenyl group.

8.1.5. Farnesane Sesquiterpenes

The 1H and 13C NMR data of two farnesane sesquiterpenes 42 and 43 are shown in Table 12.
The chemical structures of these two compounds differed in the geometry of the double bond Δ9. As revealed in Table 12, the 1H NMR chemical shift of H-9 of the Z-geometry of Δ9 in 42 moved upfield, compared with that of 43. Meanwhile, the 13C NMR chemical shift of C-9 in 42 was upfield, too.

8.1.6. Guaiane Sesquiterpene

The 1H and 13C NMR data of guaiane sesquiterpene 44 are listed in Table 13.

8.2. Diterpenes

Four diterpenes were reported from soft corals of the genus Capnella, which were xenicanes 45–48. Their 1H and 13C NMR data are displayed in Table 14 and Table 15.
It is important to assign the cis/trans-fusion of two macro rings in the xenicane diterpenes. For compounds 47 and 48 that shared the same bicyclic nucleus, the characteristic chemical shifts of H-4a and H-11a were δH ca. 3.38 and 2.61 ppm, respectively, while the diagnostic chemical shifts of C-4a and C-11a were δC ca. 28.4 and 48.0 ppm, respectively (Table 15). However, these 1H and 13C NMR data changed with the variations of functional groups on the bicyclic nucleus. The remarkable difference in chemical shifts for diterpenes 45 and 46 is reported in Table 14.

8.3. Steroids

Among this group of secondary metabolites from soft corals of the genus Capnella, more than half were discovered as new compounds, whose 1H and 13C NMR data are provided in Table 17, Table 18, Table 19 and Table 20. Since 1H and 13C NMR data of some known compounds such as 50, 51, and 53 were recorded in the literature, their NMR data will be given in this manuscript (Table 16). It might be worth pointing out that the 13C NMR data of new compound 55 were not given in the literature. Additionally, the full assignments of the 1H and 13C NMR data of 54 as well as the 1H NMR data of 55 were not completed.
Compound 54: 1H NMR (CDCl3): δH 6.81 (d, J = 8.5 Hz, 1H), 6.69 (d, J = 8.5 Hz, 1H), 5.80 (m, 1H), 5.66 (s, 1H), 4.98 (d, J = 14 Hz, 2H), 3.86 (s, 3H), 2.93 (dd, J = 17, 5 Hz, 1H), 2.64 (m, 1H), 2.31–1.17 (m, 14H), 0.62 (s, 3H) [74]; 13C NMR (CDCl3): δC 144.04, 142.94, 139.83, 134.56, 123.46, 115.95, 114.56, 107.96, 56.13, 55.58, 54,90, 44.32, 43.84, 38.50, 37.66, 27.41, 27.41, 26.43, 24.50, 23.40, 12.88 [74].
Compound 55: 1H NMR (CDCl3): δH 7.12 (d, J = 9 Hz, 1H), 6.56 (dd, J = 9, 2 Hz, 1H), 6.51 (s, 1H), 5.8 (m, 1H), 4.93 (d, J = 14 Hz, 2H), 2.65 (m, 2H), 2.4–1.1 (m, 15H), 0.60 (s, 3H) [74].
Compound 56: 1H NMR (CDCl3): δH 7.05 (d, J = 10 Hz, 1H), 5.75 (d, J = 10 Hz, 1H), 5.65 (m, 1H), 4.9 (d, J = 14 Hz, 2H), 2.4–1.1 (m, 19H), 1.0 (s, 3H), 0.60 (s, 3H) [74]; the later full assignments of 1H and 13C NMR (CDCl3): see Table 17.
The typical 1H NMR chemical shift at δH ca. 3.51 ppm was indicative of β-OH at C-3 of steroids. Usually, there was a double bond Δ5 in the chemical structures, which was supported by the characteristic 1H NMR chemical shift at δH ca. 5.30 ppm and the 13C NMR chemical shifts at δC ca. 141 and 121 ppm. For the vinyl group, its 1H and 13C NMR signals were usually observed at δH ca. 5.75 and 5.00 ppm and δC ca. 136.0 and 116.0 ppm. The diagnostic resonances at δH ca. 0.45 and –0.14 ppm in the 1H NMR spectrum along with δC ca. 21.5 ppm in the 13C NMR spectrum was the evidence of the subunit cyclopropane in the side chain.

8.4. Lipid

Although 69 was a previously reported lipid, its 1H and 13C NMR data were given in the literature.
Compound 69: 1H NMR (CDCl3): δH 2.40 (t, J = 7.5 Hz, 2H), 2.12 (s, 3H), 1.58–1.52 (m, 2H), 1.29–1.22 (m, 26H), 0.87 (s, 3H) [47]; 13C NMR (CDCl3): δC 209.43, 43.84, 31.92, 29.85, 29.68 (×11), 29.65, 29.60, 29.47, 29.35, 23.88, 22.69, 14.12 [47].

9. Progress on the Chemical Synthesis of Sesquiterpenes from Soft Corals of the Genus Capnella

Among the secondary metabolites from soft corals of the genus Capnella, the complex polycyclic features of sesquiterpenes made them attractive targets for synthetic chemists. Since the early 1980s, dozens of chemical synthetical works have been reported, which mainly focused on the sesquiterpenes belonging to three types: capnellane, precapnellane, and guaiane.

9.1. Capnellane Sesquiterpenes

9.1.1. Δ9(12)-Capnellene (6)

This compound was the first chemically synthesized capnellane terpene as early as 1981 [118]. Since the beginning of the 1980s, a great number of chemists devoted themselves to the total synthesis of 6, developing an array of different starting materials including 2,2,5-trimethyl-5-hexenoic acid [118,119], cyclopentenyl carboxaldehyde [120], 2,2,5-trimethyl-5-hexenal [121], methylcyclopentadiene isomers and p-benzoquinone [122], trimethylcyclopentanone [123], 2-cyclopentenone [124], vinyl lactone [125], α,α-dimethyl-γ-lactone [126], 1,3-cyclopentadiene [127], 8,8-dimethylbicyclo[3.3.0]oct-1(5)-en-2-one [128], 3-butyn-l-ol [129], bicyclic lactam [130], α,α-dimethyl-7-butyrolactone [131], ester-substituted fulvene [132], (+)-Δ3-carene [133], (-)-2-methyl-4-trimethylsilyl-2-cyclopen~en-1-one [134], bicyclo[3.3.0]octane derivative [135], oxodicyclopentadiene [136], p-cresol [137,138], substituted cyclopentanone [139], 2-methoxy-4-methylphenol [140], 2,2-dimethylpent-4-enal [55], and cyclopropanated cyclopentenone [56].
Malacria et al. completed total synthesis of Δ9(12)-capnellene (6) using 2,2-dimethylpent-4-enal A0 as the starting material (Scheme 1) [55]. As outlined in Scheme 1, the first intermediate product A1 coupled with 3-iodocyclopent-2-enone to yield enynol A2, which was the precursor of A3. Catalyzed by the gold complex, A3 was transformed to triquinane A4. Undergoing a series of reactions, the capnellane A7 was gained from A4. A series of transformations conducted on A7 resulted in the key intermediate product A10. Finally, the methylenation of A10 afforded the desired 6.
Hsu et al. accomplished the total synthesis of 6 from 2-methoxy-4-methylphenol B0 (Scheme 2) [140]. As shown in Scheme 2, Diels–Alder reaction of B0 with cyclopentadiene yielded a cycloadduct B1, which was demethoxylated to afford B2. This product reacted with MeI to install the geminal dimethyl groups in B3. After the opening of the cyclopropane ring, Huang-Minlon reduction, and allylic oxidation, the linear triquinane B7 was produced. This key intermediate was subjected to hydrogenation and olefination to furnish the expected 6.
Li et al. accomplished the total synthesis of 6 from cyclopropanated cyclopentenone C0 (Scheme 3) [56]. As depicted in Scheme 3, the condensation of C1 and C2, which was the homoiodo allylsilane derivative of C0, yielded the bicyclic allylsilane C3. The expected tricyclic precursor C5 was prepared from the reduction product C4, and subjected to the methylation to furnish the triquinone derivative C6. Following the standard Barton−McCombie procedure, the reductive deoxygenation of C6 finally afforded 6.

9.1.2. Δ9(12)-Capnellene-3β,8β,10α-Triol (1)

In addition, the chemical synthesis of Δ9(12)-capnellene-3β,8β,10α-triol (1) was also investigated starting from 3-methyl-2-cyclopenten-1-one and 2-metyl-1,3-cyclopentanedione [54,141,142].
The first total synthesis of 1 starting from 3-methyl-2-cyclopenten-1-one D0 was completed by Shibasaki et al. (Scheme 4) [54]. As displayed in Scheme 4, the initial product D1 was obtained from the addition to D0, which was the precursor of the cyclized product of D2. D4 was yielded from D2 after undergoing reduction, allylic oxidation, and methylation. The sequential reduction, protection, desilylation, and oxidation afforded an important derivative D5. After a series of reactions, the key tricyclic intermediate D8 was obtained. Reduction and silylation of D8 afforded D9, which was further reduced to yield D11. The following oxidation, epoxidation, elimination, and deprotection produced the desired 1.

9.1.3. Δ9(12)-Capnellene-8β,10α-Diol (2) and Its 8-Epimer Δ9(12)-Capnellene-8α,10α-Diol (70)

The efforts on the chemical synthesis of Δ9(12)-capnellene-8β,10α-diol (2) from 3-methyl-2-cyclopenten-1-one [54], enediol [143], and 3-methylcyclopent-2-enone [144] were reported.
Shibasaki et al. also reported the first total synthesis of 2 starting from 3-methyl-2-cyclopenten-1-one D0 (Scheme 5) [54]. As displayed in Scheme 5, the aforementioned product D1 could be transformed to E1, which yielded E2 after methylation. This intermediate product was subjected to a series of reactions to afford the key tricyclic intermediate E5. Reduction of E5 gave E6, which was silylated to produce E7. Followed by reduction, epoxidation, elimination, and deprotection, 2 was successfully yielded.
3-Methylcyclopent-2-enone D0 can be used as the starting material to synthesize the 8-epimer of 2, namely Δ9(12)-capnellene-8α,10α-diol (70) (Scheme 6), which was reported by Pattenden et al. [53]. As shown in Scheme 6, alkylation of D0 followed by quenching with acetic anhydride led to the enol acetate F1, which was further converted to bicyclooctanone F2. Alkylation of F2 afforded the keto-olefin F3. The following reduction and oxidation yielded the key product F5. Cyclisation of F5 furnished tricyclic derivative F6. Treatment of F6 with THBP in the presence of catalytic SeO2 gave 70.

9.1.4. Δ9(12)-Capnellene-3β,8β,10α,14-Tetrol (3)

The chemical synthesis of Δ9(12)-capnellene-3β,8β,10α,14-tetrol (3) have also been conducted, using 2-methyl-1,3-pentanedione [141], 3-methylcyclopent-2-enone [142] and its derived ketone [145] as starting materials.
Shibasaki et al. also reported the first total synthesis of 3 starting from the above-mentioned ketone D2 (Scheme 7) [145]. As depicted in Scheme 7, G1 underwent alkylation, oxidation, and addition, affording the tricyclic derivative G3. After an array of reactions including oxidation, silylation, and reduction, G3 was converted to the key ketone G8. The following conjugate addition of a vinyl group furnished G9, which could transfer to the hydroxymethyl product G10. The subsequent silylation, oxidation, epoxidation, elimination, and desilylation yielded the expected sesquiterpene 3.

9.2. Precapnellane Sesquiterpene

9.2.1. Precapnelladiene (30)

The hydrocarbon precapnelladiene (30) was considered as a possible biosynthetic precursor to various tricyclo[6.3.0.02,6]-undecanes such as capnellane sesquiterpene 2. Due to the intriguing structural features, the total synthesis has been extensively studied, in which tricyclic bis-enone [146], 6-alkenyl-2-methylenetetrahydropyran [147], 8α-methylbicyclo[3.3.0]octan-2-one [117], cyclopentapentalenedione [148], 3-methylcyclopentenone [149], 4,4-dimethyl-2-cyclohexen-1-one [150], ethyl 2-oxocyclopentanecarboxylate [151], diisopropylsquarate [152,153], and 2-methoxycarbonyl-2-cyclopenten-1-one [154] served as the starting materials.
Paquette et al. completed the total synthesis of 30 from 8α-methylbicyclo[3.3.0]octan-2-one H0 (Scheme 8) [117]. As outlined in Scheme 8, Baeyer-Villiger oxidation of H0 provided H1, which was methylated to give H2. Cleavage oxidation of H2 produced H3, which was the precursor of H4. Treatment of H4 by Tebbe reagent followed by thermolysis afforded precapnellane derivative H6. The tosylhydrazone H7 was decomposed to give a mixture of the desired 30 and the isomer H8. Additionally, RhCl3-promoted isomerization of H8 yielded 30.
Moore et al. completed a total synthesis of 30 from diisopropylsquarate I0 (Scheme 9) [152]. As depicted in Scheme 9, I0 was subjected to addition, trifluoroacetylation, and chemoselective reduction, leading to alcohol I1. This alcohol was treated by a Grignard reagent, followed by hydrolysis and trimethylsilylation to give I2. Heating I2 yielded bicyclic derivative I3. The subsequent hydrolysis, thioacetalization, and reduction of I3 produced ketone I4. The oxy-Cope rearrangement provided the key precapnellane derivative I5. Finally, dephosphorization of I5 led to the desired 30.
Iguchi et al. synthetized 30 from 2-methoxycarbonyl-2-cyclopenten-1-one J0 (Scheme 10) [154]. As shown in Scheme 10, cycloaddition to J0 yielded the bicyclic derivative J1, which was converted to J2 by the Witting reaction. The subsequent reduction and oxidation of J2 afforded the aldehyde J5, which was transformed to J6 by the Witting reaction. Hydrolysis of J6 provided the key intermediate product I4. Conversion of I4 to the expected 30 was achieved according to the aforementioned procedure [152].

9.2.2. Epiprecapnelladiene (71)

Meanwhile, the epimer of natural product 30 called epiprecapnelladiene (71) was synthesized [155,156].
Pattenden et al. synthesized 71 from 2,4-dimethoxycyclohexa-1,4-diene K0 (Scheme 11) [156]. As displayed in Scheme 11, alkylation of K0 afforded the bisether K1, which was subjected to hydrolysis and benzoylation to give K3. Methylation of the tricyclic photoadduct K4 afforded K5. Ring cleavage of K5 yielded the key bicyclic intermediate product K6. This compound was converted to K9 after a series of reactions including aldol condensation, reduction, elimination, and hydrolysis. The Witting reaction of K9 produced K10, which transformed to 71 by isomerization.

9.3. Guaiane Sesquiterpene

Oxyfungiformin (44)

Chemical scientists were interested in the one guaiane sesquiterpene, oxyfungiformin (44), obtained from soft corals of the genus Capnella, and carried out the synthesis (Scheme 12) [97].
The selected starting material was guaiol L0, from which a mixture of γ-guaiene L1 and its diene isomers were obtained after dihydroxylation. To get the enantiomerically pure L1, the Diels–Alder addition and the decomposition of the product L2 were conducted. Lastly, double epoxidation of L1 yielded the desired oxyfungiformin (44) [97].

10. Conclusions

As presented in this work, 69 secondary metabolites were summarized from soft corals of the genus Capnella over the five decades (Table 1). Based on the general structural features, these chemical constituents can be grouped as sesquiterpenes, diterpenes, steroids, and lipids. Additionally, the 1H and 13C NMR data of these metabolites were provided when available in the literature. Interestingly, these components displayed a variety of pharmacological activities including cytotoxic, antibacterial, antifungal, anti-inflammatory, and tyrosine kinase inhibitory activities (Table 1). Due to the intriguing structural features and significant bioactivities, chemical scientists developed a vast library of strategies for the synthesis of capnellanes 1, 2, 3, and 6, precapnellane 30, and guaiane 44. Moreover, the epimers of 2 and 30 were synthesized.
As displayed on the website of the Word Register of Marine Species (WoRMS) [157], there are 29 species in the genus Capnella. However, less than one-third of the species have been chemically investigated till now (Figure 2). The limited amounts of studied species afforded a variety of secondary metabolites, which underlined the demand for a more in-depth exploration of this genus. Furthermore, it is likely that the chemotaxonomic significance of secondary metabolites needs to be highlighted, which could support the revisionary systematics of Octocorallia [43]
It might be worth pointing out that genome mining was recently applied to identify capnellane synthase CiTC-1 from C. imbricata, which could produce secondary metabolites 2 and 6 [158]. This would inspire more chemists to devote themselves to exploring more Capnella soft corals-encoded terpene cyclases.

Author Contributions

Conceptualization, L.-F.L.; formal analysis, C.-Q.L., Q.-B.Y. and L.Z.; investigation, C.-Q.L., Q.-B.Y. and L.Z.; writing—original draft preparation, C.-Q.L.; writing—review and editing, L.-F.L.; visualization, C.-Q.L., Q.-B.Y. and L.Z.; supervision, L.-F.L.; project administration, L.-F.L.; funding acquisition, L.-F.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Natural Science Foundation of Changsha (No. kq2402254) and the National Natural Science Foundation of China (No. 41876194).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The scales of different types of secondary metabolites from soft corals of the genus Capnella: (a) general groups as sesquiterpenes, diterpenes, and steroids; (b) detail classifications of sesquiterpenes.
Figure 1. The scales of different types of secondary metabolites from soft corals of the genus Capnella: (a) general groups as sesquiterpenes, diterpenes, and steroids; (b) detail classifications of sesquiterpenes.
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Figure 2. The distributions of secondary metabolites in different species of the genus Capnella.
Figure 2. The distributions of secondary metabolites in different species of the genus Capnella.
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Figure 3. Basic skeletons of sesquiterpenes reported from soft corals of the genus Capnella.
Figure 3. Basic skeletons of sesquiterpenes reported from soft corals of the genus Capnella.
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Figure 4. Chemical structures of capnellane sesquiterpenes obtained from soft corals of the genus Capnella.
Figure 4. Chemical structures of capnellane sesquiterpenes obtained from soft corals of the genus Capnella.
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Figure 5. Chemical structure of the precapnellane sesquiterpene obtained from soft corals of the genus Capnella.
Figure 5. Chemical structure of the precapnellane sesquiterpene obtained from soft corals of the genus Capnella.
Marinedrugs 22 00402 g005
Marinedrugs 22 00402 g006
Figure 6. Chemical structures of bicyclogermacrane sesquiterpenes obtained from soft corals of the genus Capnella.
Figure 6. Chemical structures of bicyclogermacrane sesquiterpenes obtained from soft corals of the genus Capnella.
Marinedrugs 22 00402 g006
Marinedrugs 22 00402 g007
Figure 7. Chemical structures of germacrane sesquiterpenes obtained from soft corals of the genus Capnella.
Figure 7. Chemical structures of germacrane sesquiterpenes obtained from soft corals of the genus Capnella.
Marinedrugs 22 00402 g007
Marinedrugs 22 00402 g008
Figure 8. Chemical structure of the aromadendrane sesquiterpene obtained from soft corals of the genus Capnella.
Figure 8. Chemical structure of the aromadendrane sesquiterpene obtained from soft corals of the genus Capnella.
Marinedrugs 22 00402 g008
Marinedrugs 22 00402 g009
Figure 9. Chemical structure of the cadinane sesquiterpene obtained from soft corals of the genus Capnella.
Figure 9. Chemical structure of the cadinane sesquiterpene obtained from soft corals of the genus Capnella.
Marinedrugs 22 00402 g009
Marinedrugs 22 00402 g010
Figure 10. Chemical structures of farnesane sesquiterpenes obtained from soft corals of the genus Capnella.
Figure 10. Chemical structures of farnesane sesquiterpenes obtained from soft corals of the genus Capnella.
Marinedrugs 22 00402 g010
Marinedrugs 22 00402 g011
Figure 11. Chemical structure of guaiane sesquiterpene obtained from soft corals of the genus Capnella.
Figure 11. Chemical structure of guaiane sesquiterpene obtained from soft corals of the genus Capnella.
Marinedrugs 22 00402 g011
Marinedrugs 22 00402 g012
Figure 12. Chemical structures of xenicane diterpenes obtained from soft corals of the genus Capnella.
Figure 12. Chemical structures of xenicane diterpenes obtained from soft corals of the genus Capnella.
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Marinedrugs 22 00402 g013
Figure 13. Chemical structures of steroids obtained from soft corals of the genus Capnella.
Figure 13. Chemical structures of steroids obtained from soft corals of the genus Capnella.
Marinedrugs 22 00402 g013
Marinedrugs 22 00402 g014
Figure 14. Chemical structure of the lipid obtained from soft corals of the genus Capnella.
Figure 14. Chemical structure of the lipid obtained from soft corals of the genus Capnella.
Marinedrugs 22 00402 g014
Marinedrugs 22 00402 sch001
Scheme 1. The route of total synthesis of 6 reported in the literature [55].
Scheme 1. The route of total synthesis of 6 reported in the literature [55].
Marinedrugs 22 00402 sch001
Marinedrugs 22 00402 sch002
Scheme 2. The route of total synthesis of 6 reported in the literature [140].
Scheme 2. The route of total synthesis of 6 reported in the literature [140].
Marinedrugs 22 00402 sch002
Marinedrugs 22 00402 sch003
Scheme 3. The route of total synthesis of 6 reported in the literature [56].
Scheme 3. The route of total synthesis of 6 reported in the literature [56].
Marinedrugs 22 00402 sch003
Marinedrugs 22 00402 sch004
Scheme 4. The route of total synthesis of 1 reported in the literature [54].
Scheme 4. The route of total synthesis of 1 reported in the literature [54].
Marinedrugs 22 00402 sch004
Marinedrugs 22 00402 sch005
Scheme 5. The route of total synthesis of 2 reported in the literature [54].
Scheme 5. The route of total synthesis of 2 reported in the literature [54].
Marinedrugs 22 00402 sch005
Marinedrugs 22 00402 sch006
Scheme 6. The route of total synthesis of 70 reported in the literature [53].
Scheme 6. The route of total synthesis of 70 reported in the literature [53].
Marinedrugs 22 00402 sch006
Marinedrugs 22 00402 sch007
Scheme 7. The route of total synthesis of 3 reported in the literature [145].
Scheme 7. The route of total synthesis of 3 reported in the literature [145].
Marinedrugs 22 00402 sch007
Marinedrugs 22 00402 sch008
Scheme 8. The route of total synthesis of 30 reported in the literature [117].
Scheme 8. The route of total synthesis of 30 reported in the literature [117].
Marinedrugs 22 00402 sch008
Marinedrugs 22 00402 sch009
Scheme 9. The route of total synthesis of 30 reported in the literature [152].
Scheme 9. The route of total synthesis of 30 reported in the literature [152].
Marinedrugs 22 00402 sch009
Marinedrugs 22 00402 sch010
Scheme 10. The route of total synthesis of 30 reported in the literature [154].
Scheme 10. The route of total synthesis of 30 reported in the literature [154].
Marinedrugs 22 00402 sch010
Marinedrugs 22 00402 sch011
Scheme 11. The route of total synthesis of 71 reported in the literature [156].
Scheme 11. The route of total synthesis of 71 reported in the literature [156].
Marinedrugs 22 00402 sch011
Marinedrugs 22 00402 sch012
Scheme 12. The route of total synthesis of 44 reported in the literature [97].
Scheme 12. The route of total synthesis of 44 reported in the literature [97].
Marinedrugs 22 00402 sch012
Table 1. Secondary metabolites from soft corals of the genus Capnella from 1974 to May 2024.
Table 1. Secondary metabolites from soft corals of the genus Capnella from 1974 to May 2024.
No.NameClassSpeciesLocalityBioassaysRef.
1Δ9(12)-capnellene-3β,8β,10α-triolcapnellane sesquiterpeneCapnella imbricataLeti Island, Indonesia – 1[52]
C. imbricataLeti Island, Indonesia – 1[57]
C. imbricataLeti Island, Indonesia – 1[58]
2Δ9(12)-capnellene-8β,10α-diolcapnellane sesquiterpeneC. imbricataLeti Island, Indonesia– 1[58]
C. imbricataLakor Island, Indonesia – 1[58]
C. imbricataMayu Island, Indonesiacytotoxic against cell lines HL-60, K562, G402, MCF-7, HT115, and A2780 (IC50 51, 0.7, 42–51, 93, 63, and 9.7 μM, respectively)[48]
C. imbricataGreen Island, Chinasignificantly reduced the levels of iNOS and COX-2 proteins (1.2 ± 0.1% and 24.8 ± 7.5%, respectively) at a concentration of 10 µM[51]
C. imbricataGreen Island, Chinaanti-neuroinflammatory and anti-nociceptive properties in IFN-γ-stimulated microglial cells and in neuropathic rats, respectively[59]
C. imbricataGreen Island, Chinaimpaired vascular development in zebrafish[60]
Capnella sp.Green Island, Chinacytotoxic against cell lines Hela and KB (IC50 3.56 and 6.06 μg/mL)[61]
C. imbricataOrchid Island, ChinaInactive against elastase release and superoxide generation by human neutrophils at a concentration of 10 μM[62]
3Δ9(12)-capnellene-3β,8β,10α,14-tetrolcapnellane sesquiterpeneC. imbricataLeti Island, Indonesia– 1[63]
4Δ9(12)-capnellene-5α,8β,10α-triolcapnellane sesquiterpeneC. imbricataLakor Island, Indonesia – 1[58]
C. imbricataOrchid Island, ChinaInactive against elastase release and superoxide generation by human neutrophils at a concentration of 10 μM[62]
C. imbricataOrchid Island, Chinasignificant inhibition against COX-2 protein expression at a concentration of 10 µM[44]
5Δ9(12)-capnellene-2β,8β,10α-triolcapnellane sesquiterpeneC. imbricataLakor Island, Indonesia – 1[58]
C. imbricataOrchid Island, Chinano obvious inhibition against COX-2 and iNOS expression at a concentration of 10 µM[44]
6Δ9(12)-capnellenecapnellane sesquiterpeneC. imbricataIndonesia– 1[64]
7Δ9(12)-capnellene-2β,5α,8β,10α-tetrolcapnellane sesquiterpeneC. imbricataLaing Island, Papua New Guinea– 1[65]
88β-acetoxy-Δ9(12)-capnellene-10α-olcapnellane sesquiterpeneC. imbricataLaing Island, Papua New Guinea– 1[66]
93β-acetoxy-Δ9(12)-capnellene-8β,10α-diolcapnellane sesquiterpeneC. imbricataLaing Island, Papua New Guinea– 1[66]
103β,8β-diacetoxy-Δ9(12)-capnellene-10α-olcapnellane sesquiterpeneC. imbricataLaing Island, Papua New Guinea– 1[66]
115α-acetoxy-Δ9(12)-capnellene-8β,10α-diolcapnellane sesquiterpeneC. imbricataLaing Island, Papua New Guinea– 1[66]
125α,8β-diacetoxy-Δ9(12)-capnellene-10α-olcapnellane sesquiterpeneC. imbricataLaing Island, Papua New Guinea– 1[66]
133β,14-diacetoxy-Δ9(12)-capnellene-8β,10α-diolcapnellane sesquiterpeneC. imbricataLaing Island, Papua New Guinea– 1[66]
142β,5α-diacetoxy-Δ9(12)-capnellene-8β,10α-diolcapnellane sesquiterpeneC. imbricataLaing Island, Papua New Guinea– 1[66]
152β,5α,8β-triacetoxy-Δ9(12)-capnellene-10α-olcapnellane sesquiterpeneC. imbricataLaing Island, Papua New Guinea– 1[66]
16Δ9(12)-capnellene-8α,10β-diolcapnellane sesquiterpeneC. imbricataXisha Islands, China– 1[67]
17Δ9(12)-capnellene-2α,5β,8α,10β-tetrolcapnellane sesquiterpeneC. imbricataXisha Islands, Chinasuppressive action on contracture of the removed ileums of the guinea pig and antitumor effects on EAC at 25 μg/mL with an inhibition rate of 43%[68]
18Δ9(12)-capnellene-8β-olcapnellane sesquiterpeneC. imbricataMayu Island, Indonesiacytotoxic against cell lines HL-60, K562 and A2780 (IC50 68, 4.6 and 6.6 μM, respectively)[48]
C. imbricataGreen Island, Chinainactive in the bioassays[51]
C. imbricataOrchid Island, Chinano obvious inhibition against COX-2 and iNOS expression at a concentration of 10 µM[44]
C. imbricataGreen Island, Chinaanti-neuroinflammatory and anti-nociceptive properties in IFN-γ-stimulated microglial cells and in neuropathic rats, respectively[59]
193β-acetoxy-Δ9(12)-capnellene-8β,10α,14β-triolcapnellane sesquiterpeneC. imbricataMayu Island, Indonesiacytotoxic against cell lines HL-60, K562, G402, MCF-7, and A2780 (IC50 713, 24, 52, 1029, and 32 μM, respectively)[48]
208α-acetoxy-Δ9(12)-capnellene-10α-olcapnellane sesquiterpeneC. imbricataGreen Island, Chinasignificantly reduced the levels of iNOS and COX-2 proteins (54.4 ± 12.0% and 62.9 ± 13.7%, respectively) at a concentration of 10 µM[51]
C. imbricataOrchid Island, Chinasignificant inhibition against iNOS and COX-2 protein expressions at a concentration of 10 µM[44]
21Δ9(12)-capnellene-10α-ol-8-onecapnellane sesquiterpeneC. imbricataGreen Island, Chinasignificantly reduced the levels of iNOS protein (34.8 ± 10.2%) at a concentration of 10 µM[51]
22Δ9(12)-capnellene-8β,15-diolcapnellane sesquiterpeneC. imbricataGreen Island, Chinainactive in the bioassays[51]
23Δ9(12)-capnellene-8β,10α,13- triolcapnellane sesquiterpeneC. imbricataGreen Island, Chinainactive in the bioassays[51]
24Δ9(10)-capnellene-12-ol-8-onecapnellane sesquiterpeneC. imbricataGreen Island, Chinainactive in the bioassays[51]
258β,10α-diacetoxy-Δ9(12)-capnellenecapnellane sesquiterpeneC. imbricataGreen Island, Chinainactive in the bioassays[51]
268β-acetoxy-Δ9(12)-capnellenecapnellane sesquiterpeneC. imbricataGreen Island, Chinainactive in the bioassays[51]
27Δ9(12)-capnellene-8β,10α,15-triolcapnellane sesquiterpeneC. imbricataOrchid Island, Chinasignificant inhibitory effects on elastase release and superoxide generation by human neutrophils with inhibition rate of 5.67% and 9.28%, respectively[62]
C. imbricataOrchid Island, Chinano obvious inhibition against COX-2 and iNOS expression at a concentration of 10 µM[44]
28Δ9(12)-capnellene-6α,8β-diolcapnellane sesquiterpeneC. imbricataOrchid Island, Chinasignificant inhibition against COX-2 protein expression (12.57%) at a concentration of 10 µM[44]
29Δ9(12)-capnellene-6α,8β,10α-triolcapnellane sesquiterpeneC. imbricataOrchid Island, Chinaremarkable decrease in iNOS level (27.73%) at a concentration of 10 µM[44]
30precapnelladieneprecapnellene sesquiterpeneC. imbricataIndonesia– 1[69]
31capgermacrene Abicyclogermacrane sesquiterpeneCapnella sp.Mantanani Island, Malaysiainhibited the accumulation of the LPS-induced pro-inflammatory IL-1β and NO production by down-regulating the expression of iNOS protein in RAW 264.7 macrophages[70]
C. imbricataMantanani Island, Malaysiacytotoxic against S1T cells (IC50 = 0.79 μg/mL)[71]
32capgermacrene Bbicyclogermacrane sesquiterpeneCapnella sp.Mantanani Island, Malaysiainactive in the bioassays[70]
C. imbricataMantanani Island, Malaysiacytotoxic against S1T cells (IC50 = 7.79 μg/mL)[71]
33capgermacrene Cbicyclogermacrane sesquiterpeneCapnella sp.Mantanani Island, Malaysianegligible inhibition against Escherichia coli and Staphylococcus aureus (MIC > 500 μg/mL)[72]
C. imbricataMantanani Island, Malaysia– 1[71]
34capgermacrene Dbicyclogermacrane sesquiterpeneC. imbricataMantanani Island, Malaysiabacteriostatic activity against S. aureus and MRSA[49]
C. imbricataMantanani Island, Malaysiacytotoxic against S1T cells (IC50 = 6.19 μg/mL)[71]
35capgermacrene Ebicyclogermacrane sesquiterpeneC. imbricataMantanani Island, Malaysiabacteriostatic activity against S. aureus and MRSA[49]
C. imbricataMantanani Island, Malaysiacytotoxic against S1T cells (IC50 = 4.75 μg/mL)[71]
36capgermacrene Fbicyclogermacrane sesquiterpeneC. imbricataMantanani Island, Malaysiabactericidal activity against S. aureus and MRSA[49]
C. imbricataMantanani Island, Malaysiacytotoxic against S1T cells (IC50 = 2.39 μg/mL)[71]
37capgermacrene Gbicyclogermacrane sesquiterpeneC. imbricataMantanani Island, Malaysiabactericidal activity against S. aureus and MRSA[49]
C. imbricataMantanani Island, Malaysiacytotoxic against S1T cells (IC50 = 3.97 μg/mL)[71]
38litseagermacranegermacrane sesquiterpeneCapnella sp.Mantanani Island, Malaysiainactive in the bioassays[70]
39capgermacrene Hgermacrane sesquiterpeneC. imbricataMantanani Island, Malaysiainactive against S1T cells (IC50 > 30.0 μg/mL)[71]
40palustrolaromadendrane sesquiterpeneCapnella sp.Mantanani Island, Malaysiainactive in the bioassays[70]
411,4-peroxy-5-muurolenecadinane sesquiterpeneCapnella sp.Mantanani Island, Malaysianegligible inhibition against E. coli and S. aureus (MIC > 500 μg/mL)[72]
42ethyl 5-[(1E,5Z)-2,6 dimthlocta-1,5,7-trienyl]furan-3-carboxylatefarnesane sesquiterpeneCapnella fungiformisMahambo, Madagascar– 1[47]
43ethyl 5-[(1E,5E)-2,6 dimthlocta-1,5,7-trienyl]furan-3-carboxylatefarnesane sesquiterpeneC. fungiformisMahambo, Madagascar– 1[47]
44oxyfungiforminguaiane sesquiterpeneC. fungiformisMahambo, Madagascar– 1[47]
45tsitsixenicin Axenicane diterpeneCapnella thyrsoideaTsitsikamma Marine Reserve, South Africagood inhibition (>80%) of superoxide production in rabbit neutrophils at a concentration of 12.5 μg/mL; good inhibition (68%) of superoxide production in human neutrophils at a concentration of 1.25 μg/mL[45]
46tsitsixenicin Bxenicane diterpeneC. thyrsoideaTsitsikamma Marine Reserve, South Africainactive in the bioassays[45]
47tsitsixenicin Cxenicane diterpeneC. thyrsoideaTsitsikamma Marine Reserve, South Africagood inhibition (>80%) of superoxide production in rabbit neutrophils at a concentration of 12.5 μg/mL[45]
48tsitsixenicin Dxenicane diterpeneC. thyrsoideaTsitsikamma Marine Reserve, South Africagood inhibition (>80%) of superoxide production in rabbit neutrophils at a concentration of 12.5 μg/mL; moderate inhibition (21%) of superoxide production in human neutrophils at a concentration of 1.25 μg/mL[45]
49cholesterolsteroidC. imbricataLesser Sunda, Indonesia– 1[73]
5024-methylenecholesterolsteroidC. imbricataLesser Sunda, Indonesia– 1[73]
C. fungiformisMahambo, Madagascar– 1[47]
5124-methylcholesterolsteroidC. imbricataLesser Sunda, Indonesia– 1[73]
C. fungiformisMahambo, Madagascar– 1[47]
52β-sitosterolsteroidC. imbricataLesser Sunda, Indonesia– 1[73]
53gorgosterolsteroidC. imbricataLesser Sunda, Indonesia– 1[73]
C. fungiformisMahambo, Madagascar– 1[47]
543-methoxy-19-norpregna-1,3,5(10),20-tetraen-4-olsteroidCapnella sp. nov.Tasmania, Australia– 1[74]
5519-norpregna-1,3,5(10),20-tetraen-3-olsteroidCapnella sp. nov.Tasmania, Australia– 1[74]
565α-pregna-1,20-dien-3-onesteroidCapnella erectaTasmania, Australia– 1[74]
C. thyrsoideaTsitsikamma Marine Reserve, South Africastimulated superoxide production in rabbit neutrophils[45]
C. thyrsoideaTsitsikamma Marine Reserve, South Africainhibitory activity against plasmodial proteases and selectivity on human cathepsins[75]
5716β-hydroxy-5α-pregna-l,20-dien-3-one 16-acetatesteroidC.thyrsoideaTsitsikamma Marine Reserve, South Africastimulated superoxide production in rabbit neutrophils[45]
583α,16β-dthydroxy-5α-pregna-1,20-diene 3,16-diacetatesteroidC.thyrsoideaTsitsikamma Marine Reserve, South Africa– 1[45]
5912β-acetoxy-7α-hydroxygorgosterolsteroidCapnella lacertiliensiGreat Barrier Reef, Australiaantifungal against Microbotryum violacea and Eurotium repens (1 mm zone at a concentration of 20 µg and 2 mm zone at a concentration of 20 µg, respectively)[50]
6012β-acetoxy-7α,19-dihydroxygorgosterolsteroidC. lacertiliensiGreat Barrier Reef, Australiaantifungal against M. violacea (2 mm zone at a concentration of 10 µg)[50]
6112β-acetoxyergost-5-ene-3β,23-diolsteroidC. lacertiliensiGreat Barrier Reef, Australiaantifungal against M. violacea (3 mm zone at a concentration of 10 µg), inhibitory against the enzyme tyrosine kinase p56lck 42% at a concentration of 200 µg/ mL[50]
6212β-acetoxyergost-5-ene-3β,11β,16-triolsteroidC. lacertiliensiGreat Barrier Reef, Australiaantifungal against M. violacea (1 mm zone at a concentration of 25 µg)[50]
6311β-acetoxyergost-5-ene-3β,12β,16-triolsteroidC. lacertiliensiGreat Barrier Reef, Australiaantifungal against M. violacea and E. repens (3 mm zone at a concentration of 10 µg and 2 mm zone at a concentration of 10 µg, respectively), inhibitory against the enzyme tyrosine kinase p56lck 47% at a concentration of 200 µg/ mL[50]
64capnesterone AsteroidC. imbricataOrchid Island, Chinainhibition against iNOS level (60%) and promotion against COX-2 release (134%)[46]
65capnesterone BsteroidC. imbricataOrchid Island, Chinainhibition against iNOS level (82%) and promotion against COX-2 release (110%)[46]
664β-hydroxy-24-methylene-5-cholesten-7-onesteroidC. imbricataOrchid Island, Chinamoderate reduction in iNOS level (64.409%) at a concentration of 10 μM[76]
673β-hydroxy-24-methylene-5-cholesten-7-onesteroidC. imbricataOrchid Island, Chinamoderate reduction in iNOS level (77.200%) at a concentration of 10 μM[76]
68gorgostan-5,25-dien-3β-olsteroidC. imbricataOrchid Island, Chinamoderate reduction in iNOS level (73.820%) at a concentration of 10 μM[76]
69octadecan-2-onelipidC. fungiformisMahambo, Madagascar– 1[47]
1 The sign ‘–’ indicated no bioassay for this compound was recorded in the work.
Table 8. The 1H and 13C NMR data of compounds 31–33.
Table 8. The 1H and 13C NMR data of compounds 31–33.
No.31 [70]32 [70]33 [72]
δH 1δC 1δH 1δC 1δH 1δC 1
11.32 dd (10.3, 8.9)26.11.45 t (8.9)27.91.44 dd (9.6, 9.6)25.0
24.87 d (10.3)125.24.61 d (8.9)122.95.01 d (9.6)126.8
3 137.1 137.6 137.3
42.34 m38.91.58 t (11.7)39.32.92 dd (17.0, 6.9)36.7
2.15 dd (11.7, 8.3) 2.46 ddd (17.2, 5.5, 2.1)
52.47 td (12.4, 8.3)25.12.25 td (12.2, 8.3)23.75.87 dddd (11.0, 6.9, 5.5, 1.8)132.7
2.31 m 2.01 dt (12.2, 8.3)
66.09 ddq (12.4, 3.4, 1.4)146.55.40 tq (8.3, 1.4)130.25.39 ddd (10.8, 7.6, 2.1)132.0
7 135.1 140.03.13 dq (7.6, 7.3)47.0
8 206.6 211.5 215.7
92.77 t (11.7)37.12.32 d (8.9)36.32.30 dd (15.0, 6.1)34.6
2.37 dd (11.7, 2.8) 2.14 dd (15.1, 9.6)
100.77 ddd (11.7, 8.9, 2.8)29.61.38 q (8.9)28.31.39 ddd (9.6, 9.6, 6.1)30.1
11 20.2 21.7 22.2
121.12 s15.91.11 s16.11.10 s15.2
131.08 s29.31.11 s29.21.09 s28.4
141.74 s13.31.88 s21.91.16 d (7.3)19.1
151.49 s16.71.55 s17.41.66 s18.5
1 Recorded in CDCl3.
Table 9. The 1H and 13C NMR data of compounds 34 and 35.
Table 9. The 1H and 13C NMR data of compounds 34 and 35.
No.34 [49]35 [49]
δH 1δC 1δH 1δC 1
10.88 dd (10.3, 8.9)33.80.82 dd (10.3, 8.9)29.9
23.99 d (10.3)70.34.17 d (10.3)83.5
3 150.6 147.4
42.39 m35.52.41 m36.0
2.30 m
52.39 m27.72.36 dt (17.2, 7.9)27.2
2.30 m 2.27 m
65.74 t (7.8)131.95.52 t (8.1)130.2
7 138.7 138.2
8 209.2 209.4
92.66 dd (14.4, 11.0)38.62.60 m39.6
2.48 dd (14.4, 1.4)
101.06 ddd (11.0, 8.9, 1.4)25.20.94 td (8.9, 3.4)24.7
11 18.4 19.2
121.13 s15.31.10 s15.5
131.15 s28.71.10 s28.5
141.83 s21.01.84 s21.2
155.23 s131.15.35 s116.4
4.93 s 5.15 s
1 Recorded in CDCl3.
Table 10. The 1H and 13C NMR data of compounds 36 and 37.
Table 10. The 1H and 13C NMR data of compounds 36 and 37.
No.36 [49]37 [49]
δH 1δC 1δH 1δC 1
11.03 dd (11.0, 8.9)31.30.87 dd (11.0, 8.9)28.2
23.70 d (11.0)73.94.08 d (11.0)86.3
3 152.5 149.5
42.66 dd (12.4, 6.9)35.32.72 ddd (12.4, 5.5)36.9
2.29 td (12.4, 6.2) 2.33 td (12.4, 5.1, 2.1)
52.50 qd (12.4, 6.2)30.22.48 qd (12.4, 5.5)30.3
2.39 m 2.39 m
66.14 ddd (12.4, 6.1, 1.4)137.36.13 ddd (12.4, 5.1, 2.1)137.1
7 137.0 137.0
8 207.3 207.1
92.78 t (12.4)38.12.79 t (13.1)38.4
2.51 dd (12.4, 2.1) 2.56 dd (13.1, 2.1)
100.68 ddd (12.2, 8.9, 2.4)28.10.73 ddd (13.1, 8.9, 2.1)28.5
11 18.6 19.6
121.15 s15.21.12 s15.6
131.13 s29.21.10 s28.9
141.66 s13.41.69 s13.3
155.27 s112.75.38 s115.7
5.00 s 5.24 s
1 Recorded in CDCl3.
Table 11. The 1H and 13C NMR data of compound 39.
Table 11. The 1H and 13C NMR data of compound 39.
No.39 [71]
δH 1δC 1δH 2δC 2
15.40 dd (11.0, 5.1)136.75.08 dd (10.3, 4.8)136.4
22.28 dt (14.6, 11.0)23.72.61 m24.1
1.98 m 1.94 m
31.75 m41.91.49 dd (14.4, 8.9)42.1
1.51 dd (14.6, 11.0) 1.16 dd (14.4, 11.0)
4 73.9 73.4
55.31 d (15.1)139.55.05 d (15.1)139.7
65.33 dd (15.1, 10.3)124.15.55 dd (15.1, 10.3)124.5
73.02 m47.42.94 m47.8
82.84 dd (12.4, 5.5)44.52.69 dd (12.4, 5.5)44.7
2.38 t (12.4) 2.51 t (12.4)
9 207.3 205.0
10 138.1 138.2
11 145.9 146.3
121.76 s20.91.69 s20.9
134.79 s110.34.89 s110.2
4.78 s 4.85 s
141.95 s20.01.65 s19.9
151.27 s29.11.12 s29.3
1 Recorded in CDCl3. 2 Recorded in C6D6.
Table 12. The 1H and 13C NMR data of compounds 42 and 43.
Table 12. The 1H and 13C NMR data of compounds 42 and 43.
No.42 [47]43 [47]
δH 1δC 1δH 1δC 1
17.88 s145.427.88 s145.42
2 120.63 120.63
36.49 s106.746.49 s106.74
4 154.61 154.61
56.05 br s 113.656.05 br s113.65
6 140.50 140.50
72.22 t (7.9)40.662.24 t (7.9)40.27
82.36 q (7.5)25.802.33 q (7.9)26.70
95.37 br t (7.3)129.755.47 br t (7.2)131.75
10 132.84 132.84
116.76 ddd (17.3, 10.8, 0.9)133.466.35 dd (17.1, 10.7)141.34
125.29 br d (17.3)113.775.09 d (17.3)110.84
5.09 dt (10.5, 1.5) 4.93 d (10.9)
13 163.38 163.38
141.96 d (1.1)18.711.97 d (1.1)18.71
151.80 q (1.1)19.741.74 s11.69
164.29 q (7.1)60.384.29 q (7.1)60.38
171.34 t (7.2)14.111.34 t (7.2)14.32
1 Recorded in CDCl3.
Table 13. The 1H and 13C NMR data of compound 44.
Table 13. The 1H and 13C NMR data of compound 44.
No.44 [47]
δH 1δC 1
1 73.69
21.69 dd (13.8, 8.4)26.75
1.79 ddd (13.8, 10.4, 8.3)
31.64 ddddq (12.2, 10.4, 8.4, 7.6, 0.5)26.72
1.12 dd (12.0, 8.3)
42.37 dq (7.6, 7.4)37.60
5 69.34
63.05 s58.08
7 68.59
81.87 dddd (15.6, 6.3, 4.0, 0.9)22.44
1.91 ddd (15.6, 10.8, 4.1)
91.77 dddd (14.6, 10.8, 4.2, 4.0)26.27
1.23 dddd (14.6, 7.5, 6.3, 4.1)
102.36 dqdd (7.5, 7.2, 4.2, 0.9)31.45
111.49 qq (7.0, 6.8)36.50
120.92 d (7.0)17.81
130.969 d (6.8)17.86
141.02 d (7.2)17.30
150.974 dd (7.4, 0.5)16.01
1 Recorded in CDCl3.
Table 14. The 1H and 13C NMR data of compounds 45 and 46.
Table 14. The 1H and 13C NMR data of compounds 45 and 46.
No.45 [45]46 [45]
δH 1δC 1δH 1δC 1
15.75 d (3.6)92.35.87 d (3.3)92.0
2////
36.52 d (1.9)142.66.51 d (1.3)142.4
4 116.1 116.2
4a2.29 m39.72.38 m37.0
52.08 m32.22.41 m31.2
1.22 m 2.23 m
62.19 m39.72.19 m39.2
2.07 m 1.19 m
7 134.4 59.8
85.73 dd (9.5, 8.0)124.32.98 dd (9.5, 8.0)62.3
92.43 m25.52.22 m25.3
2.07 m 1.43 m
102.31 m35.91.35 m31.2
2.07 m
11 149.3 146.8
11a1.96 br s50.12.43 m49.3
125.25 t (7.6)74.75.24 t (7.6)74.3
132.43 m31.42.41 m31.3
2.31 m 2.23 m
144.97 t (6.9)118.94.95 m118.6
15 135.6 134.7
161.64 br s18.11.61 s18.1
171.67 br s25.71.67 s25.7
181.67 br s17.01.31 s17.2
194,91 br s113.45.06 br s116.2
4.78 br s 4.93 br s
COCH32.07 s21.52.08 s21.4
COCH3 169.5 170.2
COCH32.01 s21.02.00 s21.0
COCH3 170.2 169.3
1 Recorded in CDCl3.
Table 15. The 1H and 13C NMR data of compounds 47 and 48.
Table 15. The 1H and 13C NMR data of compounds 47 and 48.
No.47 [45]48 [45]
δH 1δC 1δH 1δC 1
16.14 d (2.3)93.46.12 d (2.3)93.3
2////
37.25 d (2.0)151.77.26 d (2.0)151.2
4 124.3 123.5
4a3.44 m28.23.32 m28.6
51.73 m27.01.69 m26.9
1.57 m 1.55 m
62.89 m37.52.84 br t (12.2)37.8
1.46 m 1.43 m
7 83.7 83.5
85.40 d (11.9)131.25.41 d (11.8)131.4
95.59 m129.85.57 m129.7
103.17 m30.73.16 m30.8
2.63 m 2.65 m
11 145.5 145.6
11a2.63 m48.12.60 d (12.3)48.0
12 190.2 197.7
136.51 d (15.8)125.63.25 t (5.6)38.6
146.82 d (15.8)148.45.30 t (7.0)117.0
15 82.1 135.0
161.40 s24.21.74 d (1.0)25.8
171.39 s24.11.64 s18.1
181.61 s28.51.59 s28.5
195.14 d (7.0)118.15.12 d (8.3)117.9
COCH32.06 s22.32.04 s22.2
COCH3 169.2 169.3
COCH32.04 s20.92.04 s20.9
COCH3 169.2 169.1
1 Recorded in CDCl3.
Table 16. The 1H and 13C NMR data of compounds 50, 51, and 53.
Table 16. The 1H and 13C NMR data of compounds 50, 51, and 53.
No.50 [47]51 [47]53 [47]
δH 1δC 1δH 1δC 1δH 1δC 1
11.80–1.90 m37.24 37.25 37.23
1.03–1.10 m
21.80–1.90 m31.65 31.67 31.61
1.47–1.60 m
33.52 tt (11.2, 4.6)71.823.52 tt (11.2, 4.6)71.813.52 tt (11.2, 4.6)71.92
42.29 ddd (12.8, 4.9, 1.9)42.28 42.31 42.23
2.19–2.26 m
5 140.73 140.76 140.68
65.34 dt (5.0, 2.0)121.715.36 dt (5.3, 2.0)121.735.35 dt (5.0, 2.2)121.80
71.94–2.03 m31.89 31.90 31.86
1.47–1.60 m
81.40–1.47 m31.89 31.90 31.96
90.90–0.94 m50.11 50.12 50.14
10 36.49 36.50 36.51
111.47–1.60 m21.07 21.08 21.07
1.40–1.47 m
121.94–2.03 m39.76 39.76 39.85
1.10–1.19 m
13 42.35 42.31 42.76
140.99–1.01 m56.75 56.751.00 br s56.49
151.47–1.60 m24.28 24.29 24.51
1.03–1.10 m
161.80–1.90 m28.21 28.19 28.21
1.25–1.30 m
171.10–1.19 m55.97 55.98 57.90
180.67 s11.850.66 s11.850.65 s11.90
191.00 s19.391.00 s19.401.00 s19.40
201.40–1.47 m35.74 36.180.98–1.01 m35.28
210.94 d (6.4)18.700.91 d (6.8)18.880.98–1.01 m21.17
221.47–1.60 m34.67 33.710.13–0.19 m32.03
1.10–1.19 m
2332.05–2.11 m30.96 30.56 25.80
1.80–1.90 m
24 156.89 39.060.24 dqd (8.8, 7.0, 1.8)50.80
252.19–2.26 m33.79 31.45 32.14
261.011 d (6.8)21.860.77 d (6.8)17.580.85 d (6.4)21.53
271.014 d (6.8)21.990.84 d (6.8)20.520.93 d (7.5)22.18
284.64 br d (1.5)105.910.76 d (6.8)15.440.94 d (6.9)15.45
4.70 br s
29 0.45 ddd (9.1, 4.3, 2.6)21.29
–0.14 ddd (5.8, 4.4, 1.3)
30 0.89 s14.27
1 Recorded in CDCl3.
Table 17. The 1H and 13C NMR data of compounds 56–58.
Table 17. The 1H and 13C NMR data of compounds 56–58.
No.56 [45]57 [45]58 [45]
δH 1δC 1δH 1δC 1δH 1δC 1
17.13 d (10.2)158.57.12 d (10.2)158.06.18 d (10.0)142.0
25.83 d (10.0)127.45.85 d (10.2)127.55.60 ddd (10.0, 5.5, 1.2)122.5
3 200.1 200.05.15 m67.3
42.35 dd (17.7, 14.1)40.12.36 dd (17.6, 14.1)40.11.81 m31.8
2.20 dd (17.7, 3.6) 2.21 dd (17.7, 4.0) 1.53 m
51.93 m44.41.95 m44.41.58 m39.6
61.78 m27.21.45 m27.51.37 m27.6
1.55 m 1.41 m 1.37 m
71.74 m31.41.67 m31.21.68 m31.7
0.99 m 0.98 m 1.02 m
81.45 m35.81.47 m35.31.40 m35.3
90.97 m50.31.02 m50.30.99 m51.0
10 39.1 39.1 37.9
111.42 m27.61.85 m33.81.85 m33.9
1.56 m 1.58 m
121.76 m37.41.74 m37.21.71 m37.3
1.07 m 1.20 m 1.14 m
13 43.7 44.2 44.2
141.08 m55.61.38 m53.31.37 m53.4
151.76 m20.81.77 m20.41.76 m20.2
1.42 m 1.42 m 1.37 m
161.66 m24.75.11 m78.45.08 m78.5
1.18 m
171.95 m55.32.15 dd (7.7, 4.1)61.62.13 t (7.7)61.6
180.61 s13.00.69 s14.20.66 s14.2
191.00 s13.01.01 s13.10.81 s13.9
205.74 td (16.5, 10.8, 8.8)139.55.77 td (17.1, 10.5, 8.9)135.95.76 td (17.1, 10.4, 8.9)136.1
214.95 m114.75.08 m117.05.04 m116.8
COCH3 2.02 s21.22.04 s21.3
COCH3 171.1 171.1
COCH3 2.02 s21.5
COCH3 170.1
1 Recorded in CDCl3.
Table 18. The 1H and 13C NMR data of compounds 59–61.
Table 18. The 1H and 13C NMR data of compounds 59–61.
No.59 [50]60 [50]61 [50]
δH 1δC 1δH 1δC 1δH 1δC 1
11.79 m36.91.93 m33.51.41 m31.4
1.12 m
21.82 m31.21.83 m31.51.81 m31.5
1.48 m 1.35 m 1.95 m
33.55 m71.23.63 m71.13.49 m71.6
42.32 ddd (12.2, 4.9, 1.5)41.82.44 ddd (11.4, 5.6, 1.5)41.92.28 ddd (11.2, 5.6, 1.5)42.1
2.23 ddd (12.2, 11.3) 2.26 brdd (11.6, 11.4) 2.20 ddd (11.6, 11.2)
5 146.0 141.3 140.6
65.59 dd (5.3, 1.5)123.95.95 dd (5.4, 1.5)128.65.34 br s121.5
73.85 br s64.93.91 dd (3.5, 1.9) 64.71.92 m26.2
1.54 m
81.39 m36.51.89 m37.91.25 m31.0
91.41 m41.51.44 m41.61.08 m54.9
10 37.5 42.2 36.6
111.87 m27.01.90 m27.51.77 m37.2
1.40 m 1.66 m 1.07 m
124.63 dd (9.8, 4.5)80.84.61 dd (11.1, 4.6)80.84.66 dd (10.7, 4.6)81.1
13 46.1 46.4 46.2
141.56 m57.41.55 m57.41.10 m49.0
151.79 m23.61.76 m23.41.65 m23.7
1.24 m 1.24 m 1.20 m
161.94 m27.91.56 m27.91.80 m27.6
1.56 m 1.40 m
171.53 m48.31.43 m49.41.52 m55.1
180.80 s9.00.86 s9.20.80 s8.5
190.97 s18.13.90 d (11.1)63.11.00 s19.3
3.60 d (11.1)
201.15 m33.61.16 m33.61.52 m39.0
210.93 d (6.8)22.20.95 d (6.8)22.20.86 d (6.6)13.6
220.24 ddd (8.7, 5.4, 5.1)30.60.23 ddd (8.7, 5.4, 5.2)30.61.53 m41.1
0.98 m
23 25.3 25.33.81 dd (9.2, 2.5)70.8
240.23 m50.60.23 m50.71.54 m32.7
251.55 m32.21.55 m32.21.48 m35.0
260.84 d (6.8)21.50.84 d (6.8)21.50.82 d (6.6)15.2
270.93 d (6.8)22.20.93 d (6.8)22.20.85 d (6.6)20.1
280.92 d (6.8)15.40.91 d (7.2)15.40.80 d (6.6)18.0
290.45 dd (8.7, 4.5)21.50.45 dd (8.7, 4.3)21.5
–0.13 dd (5.1, 4.5) –0.13 dd (5.4, 4.5)
300.89 s13.80.90 s13.8
COCH32.01 s21.82.02 s21.82.01 s21.7
COCH3 170.7 170.8 170.5
1 Recorded in CDCl3.
Table 19. The 1H and 13C NMR data of compounds 62 and 63.
Table 19. The 1H and 13C NMR data of compounds 62 and 63.
No.62 [50]63 [50]
δH 1δC 1δH 1δC 1
11.93 m26.31.63 m26.8
21.84 m31.41.83 m31.3
33.51 m71.33.52 m71.1
42.28 m41.32.29 m41.3
5 141.5 140.6
65.23 br s120.45.27 br s121.0
72.16 m31.72.17 m31.4
1.55 m 1.46 m
81.87 m27.21.86 m27.4
91.12 m53.21.20 m52.2
10 36.9 36.2
114.26 dd (3.2, 3.2)70.45.53 dd (3.3, 3.3)73.4
124.64 dd (3.2)82.73.52 d (3.3)80.0
13 45.9 47.2
141.10 m57.21.01 m57.3
151.55 m41.11.55 m41.0
1.01 m 1.02 m
163.81 m70.73.80 ddd (9.7, 3.6, 1.3)72.4
171.54 m55.11.50 m56.7
181.01 s10.70.86 s10.2
191.26 s22.60.97 s21.9
201.45 m39.61.59 m39.7
210.87 d (6.8)13.50.98 d12.1
221.72 m23.61.71 m23.3
231.93 m36.51.84 m37.1
1.19 m 1.15 m
241.48 m35.01.48 m35.0
251.55 m32.71.55 m32.7
260.81 d (6.8)18.00.81 d (6.6)17.9
270.86 d (6.8)20.10.85 d (6.6)20.1
280.82 d (6.8)15.20.81 d (6.6)15.1
COCH32.12 s21.72.10 s21.8
COCH3 170.0 174.5
1 Recorded in CDCl3.
Table 20. The 1H and 13C NMR data of compounds 64–66.
Table 20. The 1H and 13C NMR data of compounds 64–66.
No.64 [46]65 [46]66 [76]
δH 1δC 1δH 1δC 1δH 1δC 1
17.04 d (10.2)157.07.06 d (10.2)157.01.73 m37.1
2.04 m
26.21 dd (10.2, 1.8)126.76.22 d (10.2, 1.8)126.71.58 m32.0
3 186.6 186.61.26 m38.5
2.03 m
46.16 d (1.8)125.96.17 d (1.8)186.64.36 s73.3
5 165.7 125.9 168.3
64.55 br s74.04.55 br s165.75.82 s126.3
71.30 m40.02.09 m74.0 202.0
2.07 m 2.28 m
82.05 m30.32.07 m30.42.53 m39.6
91.12 m51.31.13 m51.30.91 m53.6
10 43.5 43.5 38.0
111.74 m22.61.75 m22.61.50 m22.2
121.72 m31.61.76 m31.61.17 m39.6
2.05 m
13 47.7 47.7 42.6
141.69 m49.61.79 m49.61.35 m50.8
151.24 m23.61.25 m23.61.65 m24.1
161.85 m38.11.88 m38.11.89 m28.1
17 85.4 85.41.16 m55.9
180.81 s14.60.84 s14.60.75 s12.0
191.44 s20.41.45 s20.41.38 s19.5
201.95 t (7.2)41.21.74 m41.21.43 m35.8
211.02 d (7.2)8.71.01 d (7.2)8.70.96 d (6.6)18.7
225.32 t (7.2)74.04.18 br s74.01.16 m31.0
1.53 m
232.18 m39.22.12 m39.21.86 m34.6
2.40 dd (13.8, 7.2) 2.28 m 2.18 m
24 151.5 151.5 156.8
252.25 t (6.6)33.42.25 t (7.2)33.42.21 m33.8
261.04 d (6.6)21.71.07 d (7.2)21.71.02 d (3.0)21.9
271.05 d (6.6)21.81.05 d (7.2)21.81.03 d (3.0)22.0
284.75 s110.24.80 s110.24.66 s106.0
4.86 s 4.93 s 4.72 s
COCH32.02 s21.4
COCH3 171.4
1 Recorded in CDCl3.
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Liu, C.-Q.; Yang, Q.-B.; Zhang, L.; Liang, L.-F. An Overview of Secondary Metabolites from Soft Corals of the Genus Capnella over the Five Decades: Chemical Structures, Pharmacological Activities, NMR Data, and Chemical Synthesis. Mar. Drugs 2024, 22, 402. https://doi.org/10.3390/md22090402

AMA Style

Liu C-Q, Yang Q-B, Zhang L, Liang L-F. An Overview of Secondary Metabolites from Soft Corals of the Genus Capnella over the Five Decades: Chemical Structures, Pharmacological Activities, NMR Data, and Chemical Synthesis. Marine Drugs. 2024; 22(9):402. https://doi.org/10.3390/md22090402

Chicago/Turabian Style

Liu, Can-Qi, Qi-Bin Yang, Ling Zhang, and Lin-Fu Liang. 2024. "An Overview of Secondary Metabolites from Soft Corals of the Genus Capnella over the Five Decades: Chemical Structures, Pharmacological Activities, NMR Data, and Chemical Synthesis" Marine Drugs 22, no. 9: 402. https://doi.org/10.3390/md22090402

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