Phorbasins G–K: new cytotoxic diterpenes from a southern Australian marine sponge, Phorbas sp.

Abstract

Fractionation of a cytotoxic extract obtained from a southern Australian marine sponge, Phorbas sp., yielded the known diterpenes phorbasins B–F (1–5) together with five new members of the phorbasin family, phorbasins G–K (6–10). Structures were assigned to the new phorbasins based on detailed spectroscopic analysis. A preliminary structure activity relationship (SAR) evaluation based on the co-metabolites phorbasins B–K (1–10) revealed aspects of the phorbasin pharmacophore.