Aplysiols A and B, squalene-derived polyethers from the mantle of the sea hare Aplysia dactylomela

Two novel triterpenoids, aplysiols A (5) and B (6), have been isolated, together with structurally related known metabolites, from a South China Sea collection of the anaspidean mollusc Aplysia dactylomela. The structures of 5 and 6 were determined mainly by spectroscopic NMR techniques. The absolute stereochemistry of compound 5 was deduced by Mosherʹs method as well as by biogenetical consideration, whereas the absolute stereochemistry of compound 6 was established also using an integrated NMR-QM (Quantum Mechanical) approach, based on the combination of 13C NMR chemical shifts and 2,3JC–H coupling constant DFT (density functional theory) calculations.