New process for the synthesis of pyrido-imidazo-refamycins

A new process for the synthesis of pyrido-imidazo-rifamycins of formulawherein R is hydrogen or acetyl, R, and R2 independently represent hydrogen, (C1-4)-alkyl, benzyloxy, mono- or di-(C1-3)-alkylamino-(C1-4)-alkyl. (C1-3)-alkoxy-(C1-4)-alkyl, hydroxymethyl, hydroxy-(C2-4)-alkyl, cyano, halogen, nitro, mercapto, (C1-4)-alkylthio, phenylthio, carbamoyl, mono- or di-(C1-4)-alkyl-carbamoyl, 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.The process comprises reacting the rifamycin 0 of(Continuation next page) with a 2-aminopyridine of formulawherein R1 and R2 have the same meanings as before.