A practicable method of introducing a side chain to the C-4' position of 5-O-desosamine in the 14-membered ketolides was developed. And using this method, a series of novel modified 5-O-mycaminose ketolides were synthesized. These ketolides containing 5-O-4'-carbamate mycaminose were evaluated for their in vitro antibacterial activities against some respiratory pathogens. 15b and 18e showed comparable activity to telithromycin and clarithromycin.