N-Methylation of Nicotine and Cotinine in Vkm*

In studies on the metabolism of randomly labeled ( -)-nicotine-C4 in the anesthetized dog, it has been observed (2, 3) that the major part of the administered radioactivity, approximately 80 to 90$&, appears in the urine. Approximately one-tenth of this radioactivity is present as nicotine. From various experiments in which unlabeled (-)-nicotine and one of its metabolites, (-)-cotinine, have been employed (4-7), it can be deduced that another fraction, approximately one-third, is composed of derivatives of nicotine in which the pyrrolidine ring has undergone fragmentation or oxidative changes. Since N-demethylation of (-)-nicotine leads to carbon dioxide (8), and loss of 2 of the 4 carbon atoms of the pyrrolidine ring leads to 3-pyridylacetic acid (2), many of the urinary metabolites lack unique features and possess only those that are common to the metabolism of 1 and 2 carbon compounds. Indeed, radioactive urea is one of the products of the metabolism of nicotine-methyl-Cl4 in the rat (8). Our attention, therefore, has been directed to metabolites in which the pyridine ring remains intact. During the separation of urinary metabolites arising from randomly labeled ( -)-nicotine-Cl4 administered to the dog, it was observed (2) that the major portion (essentially 95%) of the radioactivity of the urine was retained on Dowex 50 (H+). An exhaustive elution with 4 M ammonia served to remove 65% of the activity from t,he column. Further quantities of radioactivity were removed (1) by elution with strong hydrochloric acid. The material so obtained had properties consistent with those of a strong base. Quaternary ammonium compounds derived from methylation of the pyridine ring of nicotine and its metabolites were at once suggested. The present report describes the isolation and identification of the methonium compounds formed by the biological methylation of the pyridine rings of (-)-nicotine and ( -)-cotinine in oivo.