*3.7. Antidiabetic Activity*

From the deep sea-derived *Paraconiothyrium brasiliense* HDN15-135 EtOAc extract, new bergamotane sesquiterpenoids, brasilterpenes A-E (**66**–**70**), featuring an uncommon 6/4/5-tricyclic ring system, were separated by SiO2/RP-18/Sephadex LH-20/HPLC and assigned by diverse NMR analyses and X-ray diffraction, ECD, and DFT-NMR (density functional theory calculations of nuclear magnetic resonance) data [45]. Their hypoglycemic potential was estimated utilizing β-cell-ablated zebrafish larvae. Compounds **66** and **68** (concentration of 10 μM) remarkably lessened the glucose level down to 449.3 and

420.4 pmol/larva respectively, compared with the β-cell-ablated group (Teton+) (glucose level of 502.8 pmol/larva) and rosiglitazone (glucose level 395.6 pmol/larva) with no toxic influence on zebrafish larvae up to 200 μM. It was found that compounds **66** and **68** notably minimized free blood glucose in vivo in hyperglycemic zebrafish by suppressing gluconeogenesis and improving insulin sensitivity, which revealed that compound **68** had promising antidiabetic potential [45]. The structure–activity study revealed that the activity may be linked to the C-14 *S-*configuration of compounds **66** and **68**, which represent the main structural difference from **67** and **69.** The existence of C-3-OH may weaken the influence in **<sup>68</sup>** versus **<sup>66</sup>**; however, the <sup>2</sup> endocyclic double bond may enhance the potential in **70** versus **69** [45]. Therefore, compound **68** may provide a scaffold for hypoglycemic drug development. Compounds **66**–**70** are also biosynthesized by the FPP pathway (Scheme 4). The cyclization of FPP via NPP (nerolidyl diphosphate) followed by a bisabol intermediate yields the bergamotane skeleton. These compounds are created by further oxidation, 9-OH-nucleophilic attack, and methylation processes. Because of the nucleophilic attack direction flexibility during the furan ring formation, compounds **66**–**69** appeared as C14-epimers in pairs [45] (Scheme 4).

**Scheme 3.** Biosynthetic pathway of purpurolides B and C (**83** and **84**) [47].

Ying et al. isolated two new derivatives, expansolides C (**73**) and D (**81**), in addition to **72** and **80** from the plant pathogen *Penicillium expansum* ACCC37275 [46]. In an αglucosidase inhibition assay; the **73**/**81** epimeric mixture (ratio 2:1) possessed a more powerful effectiveness (IC50 of 0.50 mM) compared with acarbose (IC50 1.90 mM), while the **72**/**80** epimeric mixture possessed no apparent potential. It was assumed that the acetyl group in compounds **72** and **80** impeded their binding with the α-glucosidase, resulting in loss of activity [46].

### *3.8. Plant Growth Regulation*

Kimura et al. purified the tricyclic amide sesquiterpenoid pinthunamide (**44**) from the acetone extract of *Ampulliferina* sp. at pH 2.0 utilizing SiO2 and sephadex LH20 CC processing as well as crystallization from EtOAc extract, which gave positive NH2OH-HCI-FeCl3 and KMnO4 reactions [42]. The compound was assigned by X-ray diffraction and NMR methods. Its plant growth regulation effectiveness was evaluated using a lettuce

seedling assay, where it (dose 300 mg/L) produced a 150% root growth acceleration over the control seedlings (100%) while scarcely influencing the hypocotyl elongation at the tested concentrations [42]. Its structure combined a unique configuration of six-, five-, and four-membered rings that was proposed to be biosynthesized via the mevalonate/*trans*-*cis*farnesol/bisabolene/bergamotane pathway (Scheme 5) [42].

**Scheme 4.** Biosynthetic pathway of brasilterpenes A-E (**66**–**70**) [45]. IPP: isopentenyl diphosphate; FS: farnesyl synthase; NPP: nerolidyl diphosphate; TC: terpenyl cyclase; DMAPP: dimethylallyl diphosphate; FPP: farnesyl diphosphate.

**Scheme 5.** Biosynthesis pathway of pinthunamide (**44**) [42].

Furthermore, in 1990, Kimura et al. purified another two new plant growth regulators, ampullicin (**91**) and isoampullicin (**92**) from *Ampulliferina* sp. No. 27 associated with *Pinus thunbergii* dead tree by SiO2 CC utilizing benzene:acetone as an eluent [50] (Figure 10). They were stereoisomers that had γ-lactam rings. Additionally, they (doses of 300 and 30 mg/L) were shown to promote lettuce seedling root growth by 200% over the control lettuce seedlings (100%) [50]. In 1993, the same group separated a minor metabolite, dihydroampullicin (**93**), characterized by the absence of the C8-C9 double bond. The compound promoted a 160% growth rate in lettuce seedling roots (dose of 300 mg/L) compared with the control; however, it had no influence on the hypocotyl growth, indicating that the C8-C9-double bond (C8-C9) was substantial in lettuce seedlings' root growth [51]. Bermejo et al. reported the synthesis of (**+**)*−***91** and **92** from (*R*)-(-)-carvone with a 4.5% overall yield using a stereo-selective 18-step sequence application [59]. The EtOAc extract of *Aspergillus fumigatus* Fresenius separated from leaf litter yielded expansolides A (**72**) and B (**80**). They had 2*S*/4*S*/6*S*/7*R*/9*R*/11*S* and 2*S*/4*R*/6*S*/7*R*/9*R*/11*S*, respectively, based on modified Mosher's method. The compounds noticeably prohibited etiolated wheat coleoptiles growth by 100% and 59% at 10−<sup>3</sup> M and 10−<sup>4</sup> M solution compared with LOGRAN (commercial herbicide) (%inhibition of 80 and 42%) at the same concentrations [26].

**Figure 10.** Structures of tetracyclic bergamotane sesquiterpenoids (**94**–**97**).
