ELECTROCHEMICAL REDUCTION OF PRISTINAMYCIN I-A AND RELATED STREPTOGRAMINS IN AQUEOUS ACIDIC MEDIUM

The electrochemical reduction of the picolinoyl residue of pristinamyc in I-A and related streptogramins was performed at a mercury cathode, in aqueous acidic medium. The presence of a peptidic lactone residue a t the amide nitrogen atom markedly modified the expected cathodic beha viour of pyridyl carboxamides: in particular, we observed the reductio n of the pyridyl ring into tetrahydropyridine derivatives. Thanks to a series of model heterocyclic carboxamides, increasing steric hindranc e at the amide nitrogen position was shown to lead to enhanced reducti on of the heterocyclic ring.