Antibacterial derivs. of (3)-formyl-rifamycin SV - prepd. by reaction with hydrazines, acylhydrazines or hydroxylamines

Crystalline rifamycin SV derivs. of formula (I) are new: (R is NR1R2, NHCOR3 or OR4; R1 is H; R2 is arylpyridazinyl (opt. substd. in aryl by alkyl or halo), benzothiazolyl, phenylsulphonate, phenyl substd. by alkoxy or opt. substd. aryloxy, (substd.) arylthio, or arylsulphonyl, or piperidine in which the N may be substd. by (ar)alkyl; R3 is phenyl substd. with NO2, acylamino or aminosulphonyl; or N-contg. heteroaromatic; or phenoxyalkyl or phenoxyalkylidene opt. ring-substd. by halo, alkyl or aminosulphonyl (itself opt. mono- or di-alkyl substd.); or benzhydryl, lower alkoxy or substd. triazolomercaptomethyl; and R4 is haloalkyl). They are prepd. by reacting 3-formylrifamycin SV with NH2R. (I) are low-toxicity antibiotics effective against rifamycin-resistant strains of Mycobacteria and with a relatively show development of resistance. They are thus useful for long-term tuberculosis therapy. They also have specific oncogenic, antiviral, immunosuppressive and human antileukaemic activities. The prepn. is rapid; allows use of crystalline 3-formylrifamycin SV or its conc. solns., proceeds at room temp., and gives high purity (I).