In an effort to find new antibiotics, a novel series of 14-membered macrolides with imidazo [4, 5-b] pyridinyl sulfur contained alkyl side chains has been synthesized based on commercially available clarithromycin. Chemical transformation of hydroxy group at position C-3 afforded range of ketolides and acylides. Compared to telithromycin, compound 15a demonstrated improved in vitro activity against erythromycin-susceptible and-resistant ...