New rifamicyn derivatives of the following general formula IMAGE I wherein: A may be the structure IMAGE -x- is a chemical bond or nil; R is hydrogen or acetyl R1 and R2 independently represent hydrogen, (C1-4) alkyl, benzyloxy, mono- and di-(C1-3)alkylamino- (C1-4)alkyl, (C1-3)alkoxy- (C1-4)alkyl, hydroxymethyl, hydroxy-(C2-4)-alkyl, nitro or R1 and R2 taken together with two consecutive carbon atoms of the pyridine nucleus form a benzene ring optionally substituted by one or two methyl or ethyl groups; R3 is a hydrogen atom or nil; with the proviso that, when A is A1, -x- is nil and R3 is a hydrogen atom; with the further proviso that, when A is A2, -x- is a chemical bond and R3 is nil. The compounds possess antibacterial utility.
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