13C N.M.R. and Single-Crystal X-Ray Structural Investigation of the Fluoroquinolone Antimicrobial Drug Norfloxacin 2DCl.D2O

Abstract

The sites of deuteronation of the molecule norfloxacin.2DCl.D2O have been investigated by 13C n.m.r. and a single-crystal structure determination. The 13C n.m.r. spectrum of norfloxacin (3 M DCl ) displays 14 lines, seven of which display 19F-13C coupling. The observation of 19F-13C coupling for the resonance at 171.0 ppm (J 3.9 Hz) allows positive assignment of this resonance to the keto carbon atom. The position of this resonance was found to be sensitive to [D+]. The crystals of norfloxacin.2DCl.D2O are monoclinic, space group P21/c, with a 8.536(2), b 14.379(3), c 14.985(4) Ǻ, β 93.40(2)°, V 1836.0(7) Ǻ3, and Z = 4. The structure was refined to R 0.039 and Rw 0.041. The n.m.r. study, combined with the structural analysis permits assignment of the sites of deuteronation for this molecule as an oxygen of the carboxylic acid, the external nitrogen of the piperazine ring and the keto oxygen atom.