Chemical studies of Antarctic nudibranch molluscs

Two opisthobranchs, Austrodoris kerguelenensis and Bathydoris hodgsoni, collected from Antarctica in the framework of Spanish and German expeditions, were chemically investigated in order to identify the skin secondary metabolites, probably involved in the chemical defense of these molluscs. Some new terpenoid molecules were isolated from the mantle and their structures were established by spectroscopic methods, mainly by Nuclear Magnetic Resonance techniques. The absolute configuration at C‐2’ of the glyceryl moiety of diterpenoid 1,3‐glyceryl esters from A. kerguelenensis was determined to be R by applying the modified Mosher method. Surprisingly, this configuration is the opposite of that of all marine terpenoid diacylglycerols so far reported. Other results described here were derived from synthetic studies on optically active terpenoid diacylglycerols, structurally related to the compounds isolated from A. kerguelenensis