Synthesis of 6-O-methyl-azithromycin and its ketolide analogue via Beckmann rearrangement of 9(E)-6-O-methyl-erythromycin oxime

The synthesis of 6-O-methyl-azithromycin and its aza-ketolide analogue have been achieved by carrying out the Beckmann rearrangement of the readily available 9(E)-6-O-methyl-erythromycin oxime 1. In contrast to the C14 ketolides like HMR 3647, the aza-ketolide turns out to be inactive, thus demonstrating that the addition of a 3 keto function and ring expension, from 14 to 15 membered ring, could be deleterious for the antibacterial activity.