Structure-activity relationship studies on 4''-O-acyltylosin derivatives: significance of their 23-O-mycinosyl and 4''-O-acyl moieties in antimicrobial activity against macrolide-resistant microbes.

Essential roles for both the 23-O-mycinosyl and 4''-O-acyl moieties of 4''-O-acyltylosin derivatives in the expression of antimicrobial activity against multiple macrolide-resistant strains of Staphylococci and mycoplasmas were demonstrated by in vitro comparison of the MICs of erythromycin, josamycin, tylosin and its 3- and 4''-O-acyl derivatives, demycinosyltylosin (DMT) and its 3- and 4''-O-acyl derivatives and 23-modified 3-O-acetyl-4''-O-isovaleryl-DMT derivatives.