Synthesis and antibacterial activities of novel 12-O-methylerythromycin A derivatives

The novel erythromycin A derivatives: 9(S)-9-dihydro-12-O-methylerythromycin A (6) and 12-O-methyerythromycin A (3), have been prepared using a new synthetic approach. The critical step is the regioselective methylation of the 12-hydroxyl of the boron complex of 2',4"-O-bis(trimethylsilyl)-9(S)-9-dihydroerythromycin A (8), which has unprotected 6-, 9- and 11-hydroxyl groups. The antibacterial activities of these new derivatives were compared with those of erythromycin A (1), clarithromycin (2) and 9(S)-9-dihydroclarithromycin (5).