Synthesis and antibacterial activities of 6-O-methylerythromycin A 9-O-(3-aryl-2-propenyl) oxime ketolide, 2,3-enol ether, and alkylide analogues

A facile and efficient route was presented to achieve 3-keto-clarithromycin 9-O-(3-aryl-E-2-propenyl) oxime derivatives 8, 2,3-dehydro-3-O-allyl- clarithromycin 9-O-(3-aryl-E-2-propenyl) oxime derivatives 11, and 3-O-allyl-clarithromycin 9-O-(3-aryl-E-2-propenyl) oxime derivatives 12. Among them, compound 8, particularly 8d (Ar = 6-quinolyl), exhibited improved antibacterial activities against erythromycin-susceptible Staphylococcus aureus and Streptococcus pneumoniae, and greatly enhanced activities against the resistant strains encoded by erm and mef genes, as compared to clarithromycin and azithromycin. Among the candidates, 8b (3-quinolyl), 8d (6-quinolyl) and 8e [4-(1-imidazolyl)phenyl] displayed a good antibacterial profile against both susceptible and resistant respiratory pathogens.