Cpd. (I) and their 16, 17, 18, 19, 28, 29-hexahydro and 27-demethoxy-27-hydroxy derivs. (where R1, and R2 are H, alkyl, alkenyl, alkynyl, aryl, aralkyl, heterocyclyl or cycloalkyl, provided that when one of R1 and R2 is H, or 1-4C alkyl the other may be unsubstd. alkyl or hydroxyalkyl having at least 5C or substd. alkyl other than dimethylaminoethyl or alkenyl, alkynyl, aryl, aralkyl, heterocyclyl or cycloalkyl wherein aryl is not phenyl or p-carboxyphenyl and aralkyl is not benzyl, and R3 is H or Ac) are prepd. from 3-formylrifamycin and H2NNR1R2.