X-Ray crystallographic determination of the molecular structures of the antibiotic cyanocycline A and related compounds

Abstract

The molecular structures and absolute configurations of cyanocycline A (I) and related compounds have been determined by single crystal X-ray diffraction methods using diffractometer-measured data. Compound (I) contains the molecular structure of naphthyridinomycin with a hydroxy-group replacing a cyano-group. When the pH at which crystallization is carried out is changed, the oxazolidine ring of (I) changed reversibly from the closed to the open form in the bis(hydrogen halide) salts. Two nitrogen atoms are quaternized in the bis(hydrogen halide) salts: one forms an ion-pair with a halide anion and the other has a short intramolecular contact with the oxygen of atom the hydroxymethyl group. The remaining halide anion in these salts forms a bifurcated intermolecular hydrogen bond with two hydroxy groups.