BIOTRANSFORMATION OF A DIETARY SESTERTERPENOID IN THE MEDITERRANEAN NUDIBRANCH HYPSELODORIS-ORSINI

The metabolic relationship between the marine mollusc Hypselodoris ors ini and the sponge Cacospongia mollior has been reinvestigated. The pr edator-prey association has been confirmed even though the metabolic p atterns of the two invertebrates are substantially different. Most pro bably the nudibranch converts the main sponge metabolite, the sesterte rpenoid scalaradial (1), into a less oxygenated related metabolite, de oxoscalarin (4), followed by a second chemical transformation leading to a new sesterterpenoid, 6-keto-deoxoscalarin (5) which is selectivel y compartmentalized into some dorsal glands, mantle dermal formations (MDFs), strategically distributed near the gills. 6-keto-deoxoscalarin (5) has been characterized by 1D and 2D NMR methods. Finally, the unu sual association of some Chromodorididae molluscs with sponges contain ing sesterterpenoids suggests a further analysis of their taxonomical collocation is required.