# Trepenoids in Marine Heterobranch Molluscs
## 5 Sesterterpenoids
### Tetracyclic Sesterterpenoids  
This type of sesterterpenoids is only found in chromodorid nudibranchs. _Cadlina luteomarginata_ from Canada and its prey, the demosponge _Phorbus_ sp., both possess the sesterterpenoid ansellone A (78) (Figure 10), with unknown ecological role, but activating the cAMP signaling pathway [251]. The South African _Chromodoris hamiltoni_, a part of the compounds already mentioned above, presents the sesterterpene hamiltonin E (79) (Figure 10), together with some macrolides (lartunculins A and B) [208]. The Indian _Glossodoris atromarginata_ and its prey, the demosponge _Sopgia_ sp. present two scalaranes in their mantle dermal formation-like structures [242]. Moreover, these sea slugs were found on two other potential prey, the sponge _Hyattella cribriformis_ presenting pentacyclic scalaranes, and an unidentified sponge, possibly _Sopgia_ sp., possessing heteronemin (80) (Figure 10) and other scalaranes [242; 170; 46]. Heteronemin was further reported to display antimycobacterial activity towards _Mycobacterium tuberculosis_ H\({}_{37}\)Rv with an MIC of 6.25 ug/ml [252]. Deoxoscalarin (81) (Figure 10), previously reported in a Mediterranean sponge, was found in _G. atromarginata_ and the sponge _H. cribriformis_, supporting its dietary origin. The specimens found on _Sopgia_ instead, presented heteronemin, known from the sponge _Heteronema eercta_, as well as two scalaranes, one of them also reported from an unidentified sponge. Furthermore, _G. rufomarginata_ from China presents scalarane compounds derived from feeding on an unidentified sponge, which are biotransformed into scalaradial derivatives. In particular, scalaradial, a potent anti-inflammatory metabolite [253], and its 12-deacetyl derivative are present in the sponge, while the absence of scalaradial in the slug supports their ability to transform this toxic compound into related scalaranes [254]. Similarly, _G. pallida_ specimens from China, as well as _G. vespa_ and _G. aerni_ from Australia, contain 12-deacetoxy-12-oxoscalaradial [255], while _G. pallida_ from Guam presents different sesquiterpenes including scalaradial, deacetylscalaradial, and deoxoscalarin; these compounds are used as feeding deterrents against sympatric crabs and reef fish and are located in the mantle border of the slugs [256; 257]. Scalaradial and deacetylscalaradial are also present in the demosponge _Caacospongia_ sp., which is preyed upon by _G. pallida_. As reported above, _Glossodoris_ species probably bittransforms their dietary scalaranes into related molecules in a detoxification process. Supporting this, the injection of scalaradial in the viscera of _G. pallida_ was reported to be not toxic for the slug but resulted instead in rapid transformation of the metabolite in less than 24 h [3]. All these data support the dietary acquisition and further biotransformation of the scalarane compounds in chromodorid nudibranchs [242; 170]. On the other hand, _Glossodoris sedna_ from Costa Rica possess several scalarane sesterterpenes, 12-deacetyl-23-acetoxy-20-methyl-12-epi-scalarali, 12-deacetyl-23-acetoxy-20-methyl-12-epi-deoxoscalarin, and 12-deacetyl-20-methyl-12-epi-deoxoscalarin, the first of which moderately inhibits mammalian phospholipase A2 (IC\({}_{50}\) 18 uM) and is ichthyotoxic at 0.1 ppm against the allopatric fish _Gambusia affinis_[258]. Contrastingly, specimens of _G. dalli_ from the same place contain the scalarane sesterterpenes 20-deoxoscalarin and 12-epi-20-deoxoscalarin [258]. Additionally, in Japan, _Chromodoris inornata_ contains three cytotoxic sesterterpenes, inorolides A (82), B, and C (Figure 10), and five scalaranes [259]. Recently, _Glossodoris hikuerensis_ and _G. vespa_ from Australia have been reported to contain heteronemin in the viscera, while scalaradial, 12-deacetoxy-12-oxoscalaradial, and 12-deacetoxy-12-oxo-deoxoscalarin are present in the mantle [154].