Studies of tylosin derivatives effective against macrolide-resistant strains: synthesis and structure-activity relationships.

The 4"-O-substituted tylosin derivatives were prepared by selective esterification of the 4"-OH, and relationships between the substituent groups and antimicrobial activity against macrolide-resistant strains were examined. Introduction of branched-chain aliphatic acyl groups such as 2-methoxyisovaleryl or 4-methylvaleryl group afforded derivatives with good antibacterial activity; MIC values were 12.5 microgram/ml against Staphylococcus aureus MS-8710. MIC values of tylosin, erythromycin and josamycin against this strain were 800 microgram/ml or more. Further improved activity was obtained by introduction of aromatic groups such as phenylthioacetyl, phenylsulfonylacetyl, 4-nitrophenylacetyl, 4-nitrophenylsulfonyl and phenylethanesulfonyl groups; MIC values were 6.25 microgram/ml. These derivatives had also an improved antimycoplasmal activity; MIC values were 0.08 microgram/ml against macrolide-resistant strains of Mycoplasma gallisepticum. MIC values of tylosin against these strains were from 2.5 to 10 microgram/ml. Introduction of the groups described above into the 4"-OH was confirmed to increase the uptake by a resistant strain.