Extractives of Australian timbers. VI. Ebelin lactone

Abstract

Ebelin lactone, formed by hydrolysis of a saponin, is a carbotricyclic triterpene with a novel carbon skeleton. Chemical evidence leading to the structure (I) for ebelin lactone is now presented in detail. Ebelin lactone, C30H46O3, possesses a secondary, equatorial hydroxyl group shown to be the 3β-hydroxyl group located in a typical triterpene ring A (III). Spectroscopic and chemical results show that the remaining two oxygen atoms are present in a γ-lactone ring (XIII). The side- chain has been subjected to oxidative degradations; an examination of the volatile fragments, and the isolation and characterization of the non-volatile C22 octanor compounds indicate that the side-chain has one of four possible structures (XVII). Structure (XVIII) is preferred on biogenetic grounds. The side-chain is attached equatorially; the conjugated triene system is allotted the trans arrangement of the double bonds on spectroscopic evidence. The biogenesis of ebelin lactone is discussed.