New cytotoxic callipeltins from the Solomon Island marine sponge Asteropus sp.

Four new callipeltin A derivatives (N–Q) have been isolated from the Solomon Island marine sponge Asteropus sp. Their structures were established by spectroscopic techniques followed by acid hydrolysis and derivatisation of the free amino acids, and subsequent LCMS analysis of the derivatives. The compounds were evaluated for their activity against cancer cell lines A2058 (melanoma), HT-29 (colorectal adenocarcinoma) and MCF-7 (breast adenocarcinoma) and non-malignant MRC-5 fibroblast cells. While the acyclic callipeltins P and Q were inactive the cyclic callipeltins N and O showed significant cytotoxicity against all exposed cell lines with IC50 values as low as 0.16 μM confirming the role of cyclic configuration in biological activity.