Natural occurrence of both enantiomers of cadina-3,5-diene and delta-amorphene

The labile sesquiterpene hydrocarbon (-)-(1R,7S,10R)-cadina-3,5-diene was isolated from manuka oil (Leptospermum scoparium) by preparative gas chromatography, while its enantiomer is present in a chemotype of the liverwort Conocephalum conicum collected in southern Germany. The structure and absolute configuration was derived by NMR investigations, enantioselective gas chromatography and by conversion into a series of products of known stereochemistry by acid catalysed rearrangement, e.g. (-)-(7S,10R)-trans-calamenene, (-)-(7S,10R)-cadina-1(6),4-diene, (-)-(1R,7S,10R)-bicyclosesquiphellandrene and (-)(1R,10R)-zonarene. In addition, (+)-delta-amorphene was identified as a constituent of L. scoparium, while (-)-delta-amorphene is present in vetiver oil. Both enantiomers of this sesquiterpene, which has not been described as a natural product so far, were prepared by rearrangement of an enantiomeric mixture of germacrene D isolated from Solidago canadensis. Copyright (C) 1997 Elsevier Science Ltd.