Terpenoids in Marine Heterobranch Molluscs

Heterobranch molluscs are rich in natural products. As other marine organisms, these gastropods are still quite unexplored, but they provide a stunning arsenal of compounds with interesting activities. Among their natural products, terpenoids are particularly abundant and diverse, including monoterpenoids, sesquiterpenoids, diterpenoids, sesterterpenoids, triterpenoids, tetraterpenoids, and steroids. This review evaluates the different kinds of terpenoids found in heterobranchs and reports on their bioactivity. It includes more than 330 metabolites isolated from ca. 70 species of heterobranchs. The monoterpenoids reported may be linear or monocyclic, while sesquiterpenoids may include linear, monocyclic, bicyclic, or tricyclic molecules. Diterpenoids in heterobranchs may include linear, monocyclic, bicyclic, tricyclic, or tetracyclic compounds. Sesterterpenoids, instead, are linear, bicyclic, or tetracyclic. Triterpenoids, tetraterpenoids, and steroids are not as abundant as the previously mentioned types. Within heterobranch molluscs, no terpenoids have been described in this period in tylodinoideans, cephalaspideans, or pteropods, and most terpenoids have been found in nudibranchs, anaspideans, and sacoglossans, with very few compounds in pleurobranchoideans and pulmonates. Monoterpenoids are present mostly in anaspidea, and less abundant in sacoglossa. Nudibranchs are especially rich in sesquiterpenes, which are also present in anaspidea, and in less numbers in sacoglossa and pulmonata. Diterpenoids are also very abundant in nudibranchs, present also in anaspidea, and scarce in pleurobranchoidea, sacoglossa, and pulmonata. Sesterterpenoids are only found in nudibranchia, while triterpenoids, carotenoids, and steroids are only reported for nudibranchia, pleurobranchoidea, and anaspidea. Many of these compounds are obtained from their diet, while others are biotransformed, or de novo biosynthesized by the molluscs. Overall, a huge variety of structures is found, indicating that chemodiversity correlates to the amazing biodiversity of this fascinating group of molluscs.

Profiling of Heterobranchia Sea Slugs from Portuguese Coastal Waters as Producers of Anti-Cancer and Anti-Inflammatory Agents

Bioprospection of marine invertebrates has been predominantly biased by the biological richness of tropical regions, thus neglecting macro-organisms from temperate ecosystems. Species that were not the object of studies on their biochemical composition include the Heterobranchia gastropods Armina maculata, Armina tigrina and Aglaja tricolorata, inhabitants of the Portuguese Atlantic coastal waters. Here, we present for the first time the fatty acid profile of neutral lipids and homarine content of these three species. Qualitative and quantitative differences in the fatty acid content among species points to the existence of a fatty acid profile of neutral lipids, particularly of each genus. The results from cytotoxicity assays, using the acetonic extracts of the gastropods on human gastric adenocarcinoma (AGS) and human lung adenocarcinoma (A549) cell lines, revealed a pronounced cytotoxic effect of the A. tigrina extract on both cell lines (IC₅₀ values of 68.75 and 69.77 μg mL⁻¹ for AGS and A549, respectively). It is worth noting the significant reduction of NO levels in LPS-challenged RAW 264.7 macrophages exposed to A. tricolorata extract, at concentrations as low as 125 μg mL⁻¹.

The chemistry and chemical ecology of nudibranchs

Covering: up to the end of February 2017Nudibranchs have attracted the attention of natural product researchers due to the potential for discovery of bioactive metabolites, in conjunction with the interesting predator-prey chemical ecological interactions that are present. This review covers the literature published on natural products isolated from nudibranchs up to February 2017 with species arranged taxonomically. Selected examples of metabolites obtained from nudibranchs across the full range of taxa are discussed, including their origins (dietary or biosynthetic) if known and biological activity.

Defense in the aeolidoidean genus Phyllodesmium (Gastropoda)

The genus Phyllodesmium (Aeolidoidea, Gastropoda) comprises shell-less marine snails, whose defense strategies are not well investigated yet. Here we report results of the first chemical investigation of P. briareum, as well as a re-investigation of P. longicirrum and P. magnum. Briarane diterpenes were isolated from P. briareum, and their origin could be traced to its prey organism Briareum sp. (Octocorallia). Considerable enrichment of the soft coral secondary metabolites in the slug was shown. Re-investigation of P. magnum led to isolation of cembrane diterpenes, 2-phenylethylamide, and furano sesquiterpenes. Sequestration of chemicals seems to have influenced speciation and evolution of Phyllodesmium species. Structural similarity or dissimilarity of particular slug metabolites suggests a closer, or more distant relationship of the respective Phyllodesmium taxa.

2-Acetoxyverecynarmin C, a New Briarane COX Inhibitory Diterpenoid from Pennatula aculeata

A new briarane-type diterpenoid, named 2-acetoxyverecynarmin C, was isolated from the methanolic extract of an octocoral, Pennatula aculeata, that exhibited cyclooxygenase (COX) inhibitory activity. The structure of the compound was elucidated by ESI-HRMS, 1D and 2D NMR spectroscopy and comparison of the measured spectral data with those reported in the literature. The relative stereochemistry at chiral carbons was established from 2D NOESY experiments. 2-Acetoxyverecynarmin C is a tricyclic compound containing a furan ring at C-7,8 of a briarane skeleton. 2-Acetoxyverecynarmin C showed moderate inhibitory activity in in vitro COX-1 and COX-2 assays.