Terpenoids in Marine Heterobranch Molluscs

Abstract

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.

Antibacterial scalarane fromDoriprismatica stellatanudibranchs (Gastropoda, Nudibranchia), egg ribbons, and their dietary spongeSpongiacf.agaricina(Demospongiae, Dictyoceratida)

“…The new 12-deacetoxy-4-demethyl-11,24-diacetoxy-3,4-methylenedeoxoscalarin shared high similarities with 12,24-diacetoxydeoxoscalarin, a farnesoid X-activated receptor antagonist, isolated by Nam et al from a Korean sponge of the genus Spongia [ 53 ]. However, differing from the previously reported scalaranes [ 25 , 29 , 33 , 42 , 56 , 61 – 62 ], the new metabolite is functionalized at C-11 instead of C-12 and has a cyclopropane ring bridging C-3, C-22 and C-4 of ring A.…”

“…[53]. However, differing from the previously reported scalaranes [25,29,33,42,56,61,62], the new metabolite is functionalized at C-11 instead of C-12 and has a cyclopropane ring bridging C-3, C-22 and C-4 of ring A.…”

“…In general, scalarane sesterterpenes are bioactive metabolites, mainly isolated from marine sources, such as Dictyoceratida sponges and the nudibranchs that feed on them [ 7 , 25 , 29 , 33 , 56 ]. So far, only six scalaranes containing cyclopropane rings, constructed of C-4, C-19 and C-20, have been identified [ 61 – 62 ].…”

“…These colorful, shell-less sea slugs are specialized to live and feed on noxious demosponges (Demospongiae, Porifera). They evolved the ability to sequester, accumulate, and store spongian metabolites to their own advantage [2,5,9,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Besides, specific metabolites can be passed on from the sea slugs to their similarly conspicuous and physically defenceless eggs.…”

Transcriptomics provides a robust framework for the relationships of the major clades of cladobranch sea slugs (Mollusca, Gastropoda, Heterobranchia), but fails to resolve the position of the enigmatic genusEmbletonia

“…They mainly prey on a high variety of marine sessile organisms, from algae to sponges, cnidarians, bryozoans and tunicates, and very often take up the chemical compounds of the food for their own defence. These "stolen" compounds have become of high interest for pharmacists in finding new drug leads for medical applications [8][9][10]. However, they are also of high interest in understanding the evolution of photosymbiosis and the role of "stolen" chloroplasts or even whole algal cells incorporated in the slugs' body, which help the slugs survive starving periods or otherwise increase fitness [11][12][13][14].…”