SIGMOSCEPTRINS A-C - NEW NORDITERPENES FROM A SOUTHERN AUSTRALIAN MARINE SPONGE, SIGMOSCEPTRELLA SP

A Sigmosceptrella sp. of sponge collected during trawling operations i n the Great Australian Eight, Australia, has yielded a series of new n orterpenes. These include a new bisnorditerpene, sigmosceptrin-A (5); two new norditerpenes, sigmosceptrin-B (14) and sigmosceptrin-C (15), isolated as their methyl esters (6) and (7) respectively; and an ethyl ated artefact, sigmosceptrin-B ethyl ester (8). Complete stereostructu res were assigned to the sigmosceptrins by spectroscopic analysis, che mical degradation, derivatization, and by a single-crystal X-ray struc tural analysis. A biosynthetic pathway is proposed that requires a com mon biosynthetic precursor to both the sigmosceptrins and norterpene c yclic peroxides.