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Abstract

Compounds of the formula ##STR1## wherein R.sub.1 is lower alkyl, lower alkoxycarbonyl-lower alkyl, phenyl, phenyl substituted by one or more lower alkyl or halogen, phenyl-lower alkyl optionally substituted in its side chain by lower alkyl or lower alkoxycarbonyl, thienylmethyl or thiazolyl, R.sub.2 is hydrogen or lower alkyl, or ##STR2## constitutes a 3-7-membered nitrogen-containing heterocyclic ring in which R.sub.1 and R.sub.2 are connected, R.sub.3 is hydrogen or hydroxyl, and X is oxygen or sulfur, or a non-toxic salt thereof. These compounds have stronger antibacterial activity as compared with known clinically used macrolide antibiotics such as erythromycin, oleandomycin, josamycin and leucomycin, and also have strong antibacterial activity against all macrolide antibiotic-resistant strains such as macrolide-resistant A group strains (clinical isolates or erythromycin, oleandomycin and 16-membered macrolide antibiotic resistant strains). These compounds are also stable in vivo and hence may be used for treatment of infectious diseases and also are useful for feed additives and growth stimulants.

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