The Methylation of Nornicotine to Nicotine, a Minor Biosynthetic Pathway in Nicotiana tabacum

It has been well established that nornicotine is formed in Nicotiana species by the demethylation of nicotine. However, the reverse reaction has not been unequivocally substantiated. This problem has been examined by feeding (RS)-[2'-¹⁴C]nornicotine to Nicotiana tabacum plants. Most of the administered nornicotine was recovered unchanged, but a small amount of activity was detected in the nicotine. Activity was also found in myosmine. The nicotine was degraded and found to have essentially all its radioactivity located at the C-2' position, indicative of a direct synthesis from nornicotine. It has thus been established that the methylation of nornicotine to nicotine does occur in the tobacco plant, but it is not considered to be a major pathway for the biosynthesis of nicotine.