First Natural Analogs of the Cytotoxic Thiodepsipeptide Thiocoraline A from a Marine Verrucosispora sp.

A marine Verrucosispora sp. isolated from the sponge Chondrilla caribensis f. caribensis was found to produce thiocoraline, a potent cytotoxic compound. Five new analogs of thiocoraline were isolated and represent the first analogs of thiocoraline. 22'-Deoxythiocoraline (2), thiochondrilline C (5), and 12'-sulfoxythiocoraline (6) demonstrated significant cytotoxicity against the A549 human cancer cell line with EC(50) values of 0.13, 2.86, and 1.26 mu M, respectively. The analogs provide insight into the SAR and biosynthesis of thiocoraline. The DP4 probability method was used to analyze ab initio NMR calculations to confirm stereochemical assignments.