Sanguinamide B analogs: identification of active macrocyclic structures

We report the synthesis of three new sanguinamide B (San B) analogs. We substituted in amino acids along the San B backbone with an N-Me, glycine, or an aromatic moiety (Phe or d-Phe) generating twelve derivatives in total. Testing in HCT-116 colon cancer cell lines resulted in establishing a structure–activity relationship. Our data show that the substitution of l- or d-Phe adjacent to the thiazole in the San B backbone locks the macrocycle into a single conformer, but only d-Phe analogs are cytotoxic. We demonstrate that the conformation of the macrocycle is extremely sensitive to stereochemistry and amino acid placement.