Structural assignment of poecillastrins B and C, macrolide lactams from the deep-water Caribbean sponge Poecillastra species.

Two new chondropsin-type macrolide lactams, poecillastrins B (1) and C (2), were isolated from aqueous extracts of the marine sponge Poecillastra sp. These trace metabolites were isolated in low yield (400-600 microg), and their structures were determined primarily by analysis of NMR data acquired using a cyrogenically cooled probe. High-quality 1D and 2D NMR data sets allowed complete assignment of the spectroscopic data and defined the new structures as 35-membered ring analogues of poecillastrin A (3). Compounds 1 and 2 showed potent cytotoxic activity against a human melanoma tumor cell line (LOX) with an IC50 value of less than 1 microg/mL.