Mutasynthesis of C17- and C21-Substituted Ansamitocins for Use as ADC Payloads.

Strain engineering and process improvement were used to improve the titer of mutasynthetically generated ansamitocins generated by feeding 3-amino-5-hydroxybenzoic acid (AHBA) analogs to cultures of inactivated in AHBA biosynthesis. Ansamitocin analogs with fluorine and bromine substituents at C17 and C21 were then generated by feeding hydroxylated AHBA analogs. Fully processed C17 and C21 fluoro and bromo ansamitocins had cytotoxic activity similar to that of Ansamitocin P3. The C21 fluoro derivative was converted to a cytotoxic payload and an antibody drug conjugate (ADC).