Contribution of Nicotine and Nornicotine toward the Production of N'-Nitrosonornicotine in Air-Cured Tobacco (Nicotiana tabacum).

N'-Nitrosonornicotine (6) is a potent and organ-specific carcinogen found in tobacco and tobacco smoke in substantial amounts. Nicotine (1) and nornicotine (2) are proposed to be the precursors of 6 in tobacco. Since 1 can be rapidly demethylated to 2 in tobacco, to distinguish between the direct formation of 6 from these potential precursors is difficult.