Synthesis and cytotoxicity of desmethoxycallipeltin B: Lack of a quinone methide for the cytotoxicity of callipeltin B

The desmethoxy analogue of the cytotoxic, cyclic depsipeptide callipeltin B was synthesized to evaluate the role of its β-MeOTyr residue. The IC50 of desmethoxycallipeltin B, in which the β-MeOTyr residue was replaced by d-Tyr, against HeLa cells was found to be 128 ± 10 μM in an MTT assay, compared to 98 ± 5 μM for the natural product itself. The roughly comparable cytotoxicities suggest that the cytotoxicity of callipeltin B does not arise through the formation of a quinone methide intermediate.