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

The sites of deuteronation of the molecule norfloxacin.2DCl.D2O have been investigated by C-13 n.m.r. and a single-crystal structure determination. The C-13 n.m.r. spectrum of norfloxacin (3 m DCl) displays 14 lines, seven of which display F-19-C-13 coupling. The observation of F-19-C-13 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 P2(1)/c, with a 8.536(2), b 14.379(3), c 14.985(4) angstrom, beta 93.40(2)-degrees, V 1836.0(7) angstrom3, and Z = 4. The structure was refined to R 0.039 and R(omega) 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.