Studies of Australian Soft Corals. XXXVIII. Structure Determination of Several Diterpenes Derived From a Cespitularia Species (Coelenterata, Octocorallia, Xeniidae)

Abstract

The structure elucidation of three new diterpenes , isolated from a soft coral Cespitularia species, is reported. Two of the metabolites (3), (7E,11E,1R*,3aS*,4S*,12aR*)-11-iso-propyl-1,4,8-trimethyl- 1,2,3,3a,4,5,6,9,10,12a-decahydrocyclopentacycloundecene-1,4-diol, and (4), (4E,7E,11E)-11-isopropyl-1,4,8-trimethyl-1,2,3,3a,6,9,10,12a-octahydrocyclopentacyclo-undecen-1-ol, are shown to possess a further cyclized cembrane skeleton, the structure of (3) being determined by a single-crystal X-ray determination while that of (4) was deduced from spectral comparison with (3). The structure of the remaining diterpene (5) (4,5-deoxyneodolabelline) was deduced from 1H and 13C n.m.r . spectroscopic studies and shown to be closely related to the recently reported clavularian metabolite neodolabelline (8). An authentic sample of neodolabelline (8) was chemically transformed into (5) by the action of a zinc-copper couple establishing the absolute structure of (5).