A study on the structures of 3-methoxycarbonylrifamycins by X-ray crystallography and 1H nuclear magnetic resonance spectroscopy

Abstract

The structures of 3-methoxycarbonylrifamycins were studied by X-ray crystallography and ¹H n.m.r. spectroscopy. The results obtained by the two different methods are consistent. The comparison with the conformations of some ansamycins in the solid state shows that in this and in other active compounds the central part of the ansa-chain, directly involved in the inhibitory interaction with the bacterial enzyme DNA-dependent RNA polymerase, remains in general the same, while large conformational changes may occur at the junctions of the ansa-chain with the chromophore-rings, thus generating four kinds of conformers. Therefore the 3-methoxycarbonyl substituent does not seem to exert any influence on the conformation of the ansa-chain which can be related to the decrease of the antibacterial activity of 3-methoxycarbonylrifamycin S.