The selective mesylation of 2'-O-acetyl-3-des(2,6-dideoxy-3-C-methyl-3-O-methyl-alpha-L-ribohexopyranosyloxy)-6-O-methyl-3-oxoerythromycin A (I) with methanesulfonic anhydride in pyridine gives the expected 11-O-methanesulfonyl derivative (II), which is treated with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in acetone to yield the 10,11-didehydro derivative (III). The acylation of (III) with carbonyl diimidazole (IV) by means of NaH in THF affords the 12-O-acyl derivative (V), which is finally cyclocondensed with 4-[4-(3-pyridyl)imidazol-1-yl]butylamine (VI) in hot acetonitrile. The intermediate compound 4-[4-(3-pyridyl)imidazol-1-yl]butylamine (VI) is obtained as follows: The condensation of N-(4-bromobutyl)phthalimide (VII) with 4-(3-pyridyl)imidazole (VIII) by means of NaH in DMF gives N-[4-[4-(3-pyridyl)imidazol-1-yl]butyl]phthalimide (IX), which is then treated with hydrazine in refluxing ethanol.