Phytochemical Studies on the Tobacco Alkaloids

Part IX. Question for Nornicotine as a Precursor of Nicotine

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dl-Ornithine-2-¹⁴C, dl-methionine-¹⁴CH₃ and partially racemized l-nornicotine-2, 5-¹⁴C, were administered to aseptically grown excised roots (N. rustica var. Brasilia). Incorporation of their radioactivity to nicotine was compared. The extent of their radioactive incorpo-ration to nicotine was high in the order of ornithine, methionine and nornicotine; incorpo-ration of radioactivity of nornicotine to nicotine was extraordinarily low. ¹⁵N-Labeled nornicotine was also fed to the same materials and ¹⁵N distribution was examined. Most of ¹⁵N still remained in the nornicotine reisolated. Marked amounts of ¹⁵N were located in the ethanol-insoluble fraction, the amino acid fraction and the substances having chro-matographic R_F value close to that of nicotine. Only small amount of ¹⁵N was incorpo-rated to the isolated nicotine.
Nornicotine is generally accepted to be a direct precursor of nicotine in tobacco plants. From these findings, however, it can be said that the biosynthesis of nicotine can occur through other routes without going through nornicotine.