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 R_w 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.