Structure and absolute configuration of a new rearranged chamigrane-type sesquiterpenoid from the sea hare Aplysia sp.

(6S,10S)-3,10-Dimethyl-7,11-dimethylidenespiro[5,5]undec-2-en-4-one (1), a new rearranged chamigrane-type sesquiterpenoid with two sp(2)-hybridized carbons in alpha-positions to the spiro-atom, was isolated from the alcoholic extract of the sea hare Aplysia sp. and its structure and absolute configuration were established by chemical transformations, NMR, EIMS, IR, UV and CD spectroscopy. (C) 2000 Elsevier Science Ltd. All rights reserved.