Excavatolides N-T, new briaran diterpenes from the Western Australian gorgonian Briareum excavatum

Abstract

A Western Australian sample of the gorgonian B. excavatum, collected at Rowley Shoals, afforded 1 known and 7 new briaran diterpenes (excavatolides N-T). Gross structures and relative stereochemistries were detd. by spectroscopic methods and by comparison of spectral data with those of previously reported briarans. Support for a proposed conformation of the 10-membered ring (stabilized by hydrogen-bonding) to explain atypical 1H NMR chem. shifts and coupling consts. in excavatolide T was obtained from energy minimization of the proposed structure by an ab initio d. functional method.