Rifamycin antibiotics—new compounds and synthetic methods. Part 4: Study of the reaction of 3-formylrifamycin SV with secondary amines and ketones

Abstract

In the fourth part of an ongoing study dealing with the search for new rifamycin antibiotics, the reaction of 3-formylrifamycin SV (1) with secondary amines (a.o. pyrrolidine) and ketones of general structure R1–CH2–CO–R2 (R1=H or alkyl and R2=alkyl or aryl) has been investigated. A new synthetic method for the preparation of stable zwitterionic rifamycin derivatives with α,β-unsaturated pyrrolidinium substituents at C3 of the naphthol chromophore has been developed. The structures of the isolated microcrystalline rifamycins and a general mechanism have been proposed on the basis of mass spectrometry results, FTIR, 1D and 2D NMR as well as TLC methods. Rifamycins displaying an aromatic substituent within the pyrrolidinium fragment at C3 displayed a good stability against hydrolysis and proved, in preliminary tests, to be active against TB and MOTT, the activity being for some particular strains (Myc. tbc. Bovis and Myc. scrofulaceum) higher than that observed with the reference drugs (RMP, RBT).