Phorbasins D-F: diterpenyl-taurines from a southern Australian marine sponge, Phorbas sp.

Fractionation of an Australian marine sponge, Phorbas sp., yielded the known phorbasins B (1) and C (2) together with three novel diterpenyl-taurines, phorbasins D-F (3-5). Partial absolute structures were assigned on the basis of detailed spectroscopic analysis. Phorbasins D-F (3-5) are the first reported examples of terpenyl-taurines linked via an amine moiety, and phorbasins E and F (4 and 5) incorporate an unprecedented heterocycle. A plausible biosynthetic route is proposed for the incorporation of taurine and heterocycle formation.