The chemical defense of nudibranch molluscs: Structure, biosynthetic origin and defensive properties of terpenoids from the dorid nudibranch dendrodoris grandiflora

Nudibranch molluscs, apparently defenseless against potential predators, possess secondary metabolites localized on the body wall which help them to escape from predation. These metabolites are largely of dietary origin; in one case the biosynthetic ability of a nudibranch to elaborate its own chemical defense has been shown. From the mantle extracts of Dendrodoris grandiflora polygodial ( 1) and 6β-acethoxyolepupuane ( 4), a new sesquiterpene triacetate, was isolated. These two drimane sesquiterpenoids, both endowed with antifeedant properties, are biosynthesized de novo by the nudibranch. Extracts from the digestive glands of the same nudibranch yielded the previously known sesquiterpene esters 3, microcionin-1, -2, -3, -4 ( 7– 10), fasciculatin ( 11), furospongin-1 acetate ( 12), a new C-21 furanoterpene 14 and a mixture of new prenylated chromanols 17. All these compounds, with the exception of 3, appear to be of dietary origin. The structures of the new compounds were determined by spectral and chemical means.