Characterization of the glucuronide conjugate of cotinine: a previously unidentified major metabolite of nicotine in smokers' urine.

Recent studies in our laboratories have confirmed that a major unidentified metabolite of nicotine in smokers' urine was susceptible to enzymatic degradation by beta-glucuronidase to afford (S)-(-)-cotinine. In order to establish the identity of this metabolite, the quaternary ammonium conjugate, viz., (S)-(-)-cotinine N-glucuronide, was synthesized. Reaction of methyl 2,3,4-tri-O-acetyl-1-bromo-1-deoxy-alpha-D-glucopyranuronate with (S)-(-)-cotinine at 60 degrees C for 3 days affords the fully protected conjugate as the bromide salt. Deprotection was accomplished in 1 M NaOH overnight at 25 degrees C. The deprotected inner salt was isolated by Dowex-50W cation-exchange chromatography. Electrospray mass spectra of the inner salt revealed the presence of ions with m/z 353 (M + H)+, 375 (M + Na)+, and 391 (M + K)+ as well as ions resulting from loss of water and cleavage of the glycosidic bond. Proton and carbon nuclear magnetic resonance spectra established that the position of glucuronidation was the pyridyl nitrogen. The magnitude of the coupling between H1" and H2" of the sugar ring (8.71 Hz) and nuclear Overhauser enhancements were consistent with the beta-isomer of the glucuronide conjugate. The synthetic (S)-(-)-cotinine N-glucuronide was susceptible to enzymatic hydrolysis by beta-glucuronidase to afford (S)-(-)-cotinine. Application of a cation-exchange high-performance liquid chromatographic method enabled the collection of a fraction containing (S)-(-)-cotinine N-glucuronide from a smoker's urine. The electrospray mass spectrum of this fraction contained ions consistent with the presence of (S)-(-)-cotinine N-glucuronide. The concentrated fraction was subjected to enzymatic hydrolysis by beta-glucuronidase to afford (S)-(-)-cotinine.(ABSTRACT TRUNCATED AT 250 WORDS)