Synthesis of a cytotoxic ansamycin hybrid.

The synthesis of a new ansamycin macrolactam derivative that contains an ansa chain based on ansamitocin and an aromatic core related to geldanamycin is reported. The selective introduction of the cyclic carbamoyl group at C7 and C9 relies on a biotransformation using a mutant strain of S. hygroscopicus, the geldanamycin producer. The ansamycin hybrid forms atropisomers that differ in their antiproliferative activity toward cancer cells.