Nuapapuin A and sigmosceptrellins D and E: New norterpene cyclic peroxidesfrom a southern Australian marine sponge, Sigmosceptrella sp.

A Sigmosceptrella sp. from the Great Australian Eight, Australia, has yield ed the new norditerpene cyclic peroxide, nuapapuin A (2a), and the norseste rterpene cyclic peroxide sigmosceptrellin D (3a), characterized as the corr esponding methyl esters 2b and 3b. The crude methylated sponge extract also yielded the new norsesterterpene cyclic peroxide sigmosceptrellin E methyl ester (4). Relative stereochemistry about C2, C3, and C6 was assigned by e stablished empirical rules and absolute stereochemistry by the advanced Mos her procedure. A plausible biosynthetic pathway has been proposed that rati onalizes key transformations in the biosynthesis of all known norterpene cy clic peroxides and related norterpene ketones, dienes and sigmosceptrins.