Research

12 pages, 2915 KiB

Open AccessArticle

For a Correct Application of the CD Exciton Chirality Method: The Case of Laucysteinamide A

by Gennaro Pescitelli

Mar. Drugs 2018, 16(10), 388; https://doi.org/10.3390/md16100388 - 16 Oct 2018

Cited by 13 | Viewed by 3318

The circular dichroism (CD) exciton chirality method (ECM) is a very popular approach for assigning the absolute configuration (AC) of natural products, thanks to its immediacy and ease of application. The sign of an exciton couplet (two electronic CD bands with opposite sign [...] Read more.

The circular dichroism (CD) exciton chirality method (ECM) is a very popular approach for assigning the absolute configuration (AC) of natural products, thanks to its immediacy and ease of application. The sign of an exciton couplet (two electronic CD bands with opposite sign and similar intensity) can be directly correlated with the molecular stereochemistry, including the AC. However, a correct application of the ECM necessitates several prerequisites: knowledge of the molecular conformation; knowledge of transition moment direction; and preeminence of the exciton coupling mechanism with respect to other sources of CD signals. In recent years, by using quantum-chemical CD calculations, we have demonstrated that some previous applications of ECM were wrong or based on incorrect assumptions. In a recent publication of this journal (Mar. Drugs, 2017, 15(4), 121), the ECM was employed to assign the AC of a marine metabolite, laucysteinamide A. This is a further case of incorrect application of the method, where none of the aforementioned prerequisites is fully met. Using this example, we will discuss the criteria required for a correct application of the ECM. Full article

(This article belongs to the Special Issue Advances in Marine Natural Product Characterisation and Separation Methodologies)

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15 pages, 2885 KiB

Open AccessArticle

Isolation and Chemical Characterization of Chondroitin Sulfate from Cartilage By-Products of Blackmouth Catshark (Galeus melastomus)

by José Antonio Vázquez, Javier Fraguas, Ramón Novoa-Carvallal, Rui L. Reis, Luis T. Antelo, Ricardo I. Pérez-Martín and Jesus Valcarcel

Mar. Drugs 2018, 16(10), 344; https://doi.org/10.3390/md16100344 - 20 Sep 2018

Cited by 43 | Viewed by 4758

Abstract

Chondroitin sulfate (CS) is a glycosaminoglycan actively researched for pharmaceutical, nutraceutical and tissue engineering applications. CS extracted from marine animals displays different features from common terrestrial sources, resulting in distinct properties, such as anti-viral and anti-metastatic. Therefore, exploration of undescribed marine species holds [...] Read more.

Chondroitin sulfate (CS) is a glycosaminoglycan actively researched for pharmaceutical, nutraceutical and tissue engineering applications. CS extracted from marine animals displays different features from common terrestrial sources, resulting in distinct properties, such as anti-viral and anti-metastatic. Therefore, exploration of undescribed marine species holds potential to expand the possibilities of currently-known CS. Accordingly, we have studied for the first time the production and characterization of CS from blackmouth catshark (Galeus melastomus), a shark species commonly discarded as by-catch. The process of CS purification consists of cartilage hydrolysis with alcalase, followed by two different chemical treatments and ending with membrane purification. All steps were optimized by response surface methodology. According to this, the best conditions for cartilage proteolysis were established at 52.9 °C and pH = 7.31. Subsequent purification by either alkaline treatment or hydroalcoholic alkaline precipitation yielded CS with purities of 81.2%, 82.3% and 97.4% respectively, after 30-kDa membrane separation. The molecular weight of CS obtained ranges 53–66 kDa, depending on the conditions. Sulfation profiles were similar for all materials, with dominant CS-C (GlcA-GalNAc6S) units (55%), followed by 23–24% of CS-A (GlcA-GalNAc4S), a substantial amount (15–16%) of CS-D (GlcA2S-GalNAc6S) and less than 7% of other disulfated and unsulfated disaccharides. Full article

(This article belongs to the Special Issue Advances in Marine Natural Product Characterisation and Separation Methodologies)

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18 pages, 2913 KiB

Open AccessArticle

Supercritical Carbon Dioxide Extraction of Astaxanthin, Lutein, and Fatty Acids from Haematococcus pluvialis Microalgae

by Giuseppe Di Sanzo, Sanjeet Mehariya, Maria Martino, Vincenzo Larocca, Patrizia Casella, Simeone Chianese, Dino Musmarra, Roberto Balducchi and Antonio Molino

Mar. Drugs 2018, 16(9), 334; https://doi.org/10.3390/md16090334 - 13 Sep 2018

Cited by 110 | Viewed by 8065

Abstract

Haematococcus pluvialis microalgae in the red phase can produce significant amounts of astaxanthin, lutein, and fatty acids (FAs), which are valuable antioxidants in nutraceutics and cosmetics. Extraction of astaxanthin, lutein, and FAs from disrupted biomass of the H. pluvialis red phase using carbon [...] Read more.

Haematococcus pluvialis microalgae in the red phase can produce significant amounts of astaxanthin, lutein, and fatty acids (FAs), which are valuable antioxidants in nutraceutics and cosmetics. Extraction of astaxanthin, lutein, and FAs from disrupted biomass of the H. pluvialis red phase using carbon dioxide (CO₂) in supercritical fluid extraction (SFE) conditions was investigated using a bench-scale reactor in a semi-batch configuration. In particular, the effect of extraction time (20, 40, 60, 80, and 120 min), CO₂ flow rate (3.62 and 14.48 g/min) temperature (50, 65, and 80 °C), and pressure (100, 400, and 550 bar.) was explored. The results show the maximum recovery of astaxanthin and lutein achieved were 98.6% and 52.3%, respectively, at 50 °C and 550 bars, while the maximum recovery of FAs attained was 93.2% at 65 °C and 550 bars. Full article

(This article belongs to the Special Issue Advances in Marine Natural Product Characterisation and Separation Methodologies)

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14 pages, 2982 KiB

Open AccessArticle

Synthesis, Characterization, and Antifungal Property of Hydroxypropyltrimethyl Ammonium Chitosan Halogenated Acetates

by Yingqi Mi, Wenqiang Tan, Jingjing Zhang, Lijie Wei, Yuan Chen, Qing Li, Fang Dong and Zhanyong Guo

Mar. Drugs 2018, 16(9), 315; https://doi.org/10.3390/md16090315 - 05 Sep 2018

Cited by 30 | Viewed by 3616

Abstract

Hydroxypropyltrimethyl ammonium chitosan halogenated acetates were successfully synthesized from six different haloacetic acids and hydroxypropyltrimethyl ammonium chloride chitosan (HACC) with high substitution degree, which are hydroxypropyltrimethyl ammonium chitosan bromacetate (HACBA), hydroxypropyltrimethyl ammonium chitosan chloroacetate (HACCA), hydroxypropyltrimethyl ammonium chitosan dichloroacetate (HACDCA), hydroxypropyltrimethyl ammonium chitosan [...] Read more.

Hydroxypropyltrimethyl ammonium chitosan halogenated acetates were successfully synthesized from six different haloacetic acids and hydroxypropyltrimethyl ammonium chloride chitosan (HACC) with high substitution degree, which are hydroxypropyltrimethyl ammonium chitosan bromacetate (HACBA), hydroxypropyltrimethyl ammonium chitosan chloroacetate (HACCA), hydroxypropyltrimethyl ammonium chitosan dichloroacetate (HACDCA), hydroxypropyltrimethyl ammonium chitosan trichloroacetate (HACTCA), hydroxypropyltrimethyl ammonium chitosan difluoroacetate (HACDFA), and hydroxypropyltrimethyl ammonium chitosan trifluoroacetate (HACTFA). These chitosan derivatives were synthesized by two steps: first, the hydroxypropyltrimethyl ammonium chloride chitosan was synthesized by chitosan and 3-chloro-2-hydroxypropyltrimethyl ammonium chloride. Then, hydroxypropyltrimethyl ammonium chitosan halogenated acetates were synthesized via ion exchange. The structures of chitosan derivatives were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H Nuclear magnetic resonance spectrometer (¹H NMR), ¹³C Nuclear magnetic resonance spectrometer (¹³C NMR), and elemental analysis. Their antifungal activities against Colletotrichum lagenarium, Fusarium graminearum, Botrytis cinerea, and Phomopsis asparagi were investigated by hypha measurement in vitro. The results revealed that hydroxypropyltrimethyl ammonium chitosan halogenated acetates had better antifungal activities than chitosan and HACC. In particular, the inhibitory activity decreased in the order: HACTFA > HACDFA > HACTCA > HACDCA > HACCA > HACBA > HACC > chitosan, which was consistent with the electron-withdrawing property of different halogenated acetates. This experiment provides a potential idea for the preparation of new antifungal drugs by chitosan. Full article

(This article belongs to the Special Issue Advances in Marine Natural Product Characterisation and Separation Methodologies)

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12 pages, 1306 KiB

Open AccessArticle

Elucidation of the Relationship between CD Cotton Effects and the Absolute Configuration of Sixteen Stereoisomers of Spiroheterocyclic-Lactams

by Takeshi Yamada, Tetsuya Kajimoto, Takashi Kikuchi and Reiko Tanaka

Mar. Drugs 2018, 16(7), 223; https://doi.org/10.3390/md16070223 - 29 Jun 2018

Cited by 5 | Viewed by 3597

Abstract

As part of research to search for antitumor agents in fungi originating from marine organisms, cephalimysins E–L were isolated from a culture broth of Aspergillus fumigatus that was separated from the marine fish Mugil cephalus. One- and two-dimensional nuclear magnetic resonance spectra [...] Read more.

As part of research to search for antitumor agents in fungi originating from marine organisms, cephalimysins E–L were isolated from a culture broth of Aspergillus fumigatus that was separated from the marine fish Mugil cephalus. One- and two-dimensional nuclear magnetic resonance spectra revealed their planar structures, which are diastereomers of each other. Their absolute stereostructures were established by epimerization at C-8 with acidic methanol, nuclear Overhauser effect spectroscopy (NOESY), and circular dichroism (CD) spectroscopy. These demonstrated the detailed relationships between absolute configuration and CD Cotton effects. Additionally, in the growth inhibition assay against P388, HL-60, L1210, and KB cell lines, some of the fungal metabolites or reaction products exhibited moderate activities. Full article

(This article belongs to the Special Issue Advances in Marine Natural Product Characterisation and Separation Methodologies)

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9 pages, 1233 KiB

Open AccessArticle

Absolute Configuration Determination of Retroflexanone Using the Advanced Mosher Method and Application of HPLC-NMR

by Caleb Singleton, Robert Brkljača and Sylvia Urban

Mar. Drugs 2018, 16(6), 205; https://doi.org/10.3390/md16060205 - 12 Jun 2018

Cited by 5 | Viewed by 4593

Abstract

The absolute configuration of retroflexanone (1) and a closely related phlorogluinol (2) was established using the advanced Mosher method and by application of HPLC-NMR. HPLC-NMR permitted a small scale Mosher method analysis to be carried out on these unstable phloroglucinols. Full article

(This article belongs to the Special Issue Advances in Marine Natural Product Characterisation and Separation Methodologies)

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13 pages, 1477 KiB

Open AccessArticle

Optimum Production Conditions, Purification, Identification, and Antioxidant Activity of Violaxanthin from Microalga Eustigmatos cf. polyphem (Eustigmatophyceae)

by Feifei Wang, Luodong Huang, Baoyan Gao and Chengwu Zhang

Mar. Drugs 2018, 16(6), 190; https://doi.org/10.3390/md16060190 - 01 Jun 2018

Cited by 38 | Viewed by 5111

Abstract

Violaxanthin is a major xanthophyll pigment in the microalga Eustigmatos cf. polyphem, but the amount produced after propagation can vary depending upon culture conditions. In this study, the effects of cultivation time, nitrogen concentration, light intensity, and culture mode on violaxanthin production [...] Read more.

Violaxanthin is a major xanthophyll pigment in the microalga Eustigmatos cf. polyphem, but the amount produced after propagation can vary depending upon culture conditions. In this study, the effects of cultivation time, nitrogen concentration, light intensity, and culture mode on violaxanthin production were investigated. The results showed that this microalga vigorously grew and maintained a high level of violaxanthin in the fed-batch culture, and the highest violaxanthin productivity of 1.10 ± 0.03 mg L⁻¹ d⁻¹ was obtained under low light illumination with 18 mM of initial nitrogen supply for ten days. Additionally, violaxanthin was purified from E. cf. polyphem by silica gel chromatography and preparative high-performance liquid chromatography (PHPLC), and identified with high-resolution mass spectrometry (HRMS). The antioxidant activity of the purified violaxanthin was evaluated by three tests in vitro: reducing power assay, 2,2-diphenyl-1-picrylhydrazyl (DPPH), and 2,2-azobis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) radical assays. The strongest inhibition of purified violaxanthin occurred during the scavenging of ABTS⁺ radicals, with EC₅₀ of 15.25 μg mL⁻¹. In conclusion, this is the first report to investigate the effects of different culture conditions on violaxanthin accumulation in E. cf. polyphem and provide a novel source for the production of violaxanthin that can be used for food and pharmaceutical applications. Full article

(This article belongs to the Special Issue Advances in Marine Natural Product Characterisation and Separation Methodologies)

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9 pages, 821 KiB

Open AccessArticle

Preparative Separation and Purification of Trichothecene Mycotoxins from the Marine Fungus Fusarium sp. LS68 by High-Speed Countercurrent Chromatography in Stepwise Elution Mode

by Yong Liu, Xuezhen Zhou, C. Benjamin Naman, Yanbin Lu, Lijian Ding and Shan He

Mar. Drugs 2018, 16(2), 73; https://doi.org/10.3390/md16020073 - 24 Feb 2018

Cited by 8 | Viewed by 3706

Abstract

The contamination of foods and animal feeds with trichothecene mycotoxins is a growing concern for human and animal health. As such, large quantities of pure trichothecene mycotoxins are necessary for food safety monitoring and toxicological research. A new and effective method for the [...] Read more.

The contamination of foods and animal feeds with trichothecene mycotoxins is a growing concern for human and animal health. As such, large quantities of pure trichothecene mycotoxins are necessary for food safety monitoring and toxicological research. A new and effective method for the purification of trichothecene mycotoxins from a marine fungus, Fusarium sp. LS68, is described herein. Preparative high-speed countercurrent chromatography (HSCCC) was utilized for the scalable isolation and purification of four trichothecene mycotoxins for the first time in stepwise elution mode, with a biphasic solvent system composed of hexanes–EtOAc–CH₃OH–H₂O (6:4:5:5, v/v/v/v) and (8.5:1.5:5:5,v/v/v/v). This preparative HSCCC separation was performed on 200 mg of crude sample to yield four trichothecene mycotoxins, roridin E (1), roridin E acetate (2), verrucarin L acetate (3), and verrucarin J (4) in a single run, with each of >98% purity. These compounds were identified by MS, ¹H NMR, ¹³C NMR, and polarimetry. The results demonstrate an efficient HSCCC method for the separation of trichothecene mycotoxins, which can be utilized to produce pure commercial and research standards. Full article

(This article belongs to the Special Issue Advances in Marine Natural Product Characterisation and Separation Methodologies)

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1875 KiB

Open AccessArticle

A Dereplication and Bioguided Discovery Approach to Reveal New Compounds from a Marine-Derived Fungus Stilbella fimetaria

by Sara Kildgaard, Karolina Subko, Emma Phillips, Violaine Goidts, Mercedes De la Cruz, Caridad Díaz, Charlotte H. Gotfredsen, Birgitte Andersen, Jens C. Frisvad, Kristian F. Nielsen and Thomas O. Larsen

Mar. Drugs 2017, 15(8), 253; https://doi.org/10.3390/md15080253 - 13 Aug 2017

Cited by 24 | Viewed by 5831

Abstract

A marine-derived Stilbella fimetaria fungal strain was screened for new bioactive compounds based on two different approaches: (i) bio-guided approach using cytotoxicity and antimicrobial bioassays; and (ii) dereplication based approach using liquid chromatography with both diode array detection and high resolution mass spectrometry. [...] Read more.

A marine-derived Stilbella fimetaria fungal strain was screened for new bioactive compounds based on two different approaches: (i) bio-guided approach using cytotoxicity and antimicrobial bioassays; and (ii) dereplication based approach using liquid chromatography with both diode array detection and high resolution mass spectrometry. This led to the discovery of several bioactive compound families with different biosynthetic origins, including pimarane-type diterpenoids and hybrid polyketide-non ribosomal peptide derived compounds. Prefractionation before bioassay screening proved to be a great aid in the dereplication process, since separate fractions displaying different bioactivities allowed a quick tentative identification of known antimicrobial compounds and of potential new analogues. A new pimarane-type diterpene, myrocin F, was discovered in trace amounts and displayed cytotoxicity towards various cancer cell lines. Further media optimization led to increased production followed by the purification and bioactivity screening of several new and known pimarane-type diterpenoids. A known broad-spectrum antifungal compound, ilicicolin H, was purified along with two new analogues, hydroxyl-ilicicolin H and ilicicolin I, and their antifungal activity was evaluated. Full article

(This article belongs to the Special Issue Advances in Marine Natural Product Characterisation and Separation Methodologies)

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2817 KiB

Open AccessArticle

Isolation and Tissue Distribution of an Insulin-Like Androgenic Gland Hormone (IAG) of the Male Red Deep-Sea Crab, Chaceon quinquedens

by Amanda Lawrence, Shadaesha Green and Jum Sook Chung

Mar. Drugs 2017, 15(8), 241; https://doi.org/10.3390/md15080241 - 01 Aug 2017

Cited by 11 | Viewed by 3917

Abstract

The insulin-like androgenic gland hormone (IAG) found in decapod crustaceans is known to regulate sexual development in males. IAG is produced in the male-specific endocrine tissue, the androgenic gland (AG); however, IAG expression has been also observed in other tissues of decapod crustacean [...] Read more.

The insulin-like androgenic gland hormone (IAG) found in decapod crustaceans is known to regulate sexual development in males. IAG is produced in the male-specific endocrine tissue, the androgenic gland (AG); however, IAG expression has been also observed in other tissues of decapod crustacean species including Callinectes sapidus and Scylla paramamosain. This study aimed to isolate the full-length cDNA sequence of IAG from the AG of male red deep-sea crabs, Chaceon quinquedens (ChqIAG), and to examine its tissue distribution. To this end, we employed polymerase chain reaction cloning with degenerate primers and 5′ and 3′ rapid amplification of cDNA ends (RACE). The full-length ChqIAG cDNA sequence (1555 nt) includes a 366 nt 5′ untranslated region a 453 nt open reading frame encoding 151 amino acids, and a relatively long 3′ UTR of 733 nt. The ORF consists of a 19 aa signal peptide, 32 aa B chain, 56 aa C chain, and 44 aa A chain. The putative ChqIAG amino acid sequence is most similar to those found in other crab species, including C. sapidus and S. paramamosain, which are clustered together phylogenetically. Full article

(This article belongs to the Special Issue Advances in Marine Natural Product Characterisation and Separation Methodologies)

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