Absolute stereochemistry of ibhayinol from a South African sea hare.

The absolute stereochemistry of the tricyclic, sesquiterpene ibhayinol (5) extracted from the sea hare Aplysia dactylomela, collected in Algoa Bay, South Africa, was established as 1S, 3S, 4S, 6R, 7S, 10R, 11S from a single-crystal X-ray diffraction experiment. The structure of ibhayinol suggested that 8-dehydroxy-1-deacetylalgoane (7) might be a biosynthetic precursor of this compound.