Nicotine demethylation in Nicotiana cell suspension cultures: N′-formylnornicotine is not involved

Label from [13C,2H3-methyl]nicotine fed to Nicotiana plumbaginifolia suspension cell cultures is incorporated into cotinine but to a much lesser extent into N′-formylnornicotine. This labelling pattern directly shows that N′-formylnornicotine is not intermediate in the demethylation mechanism, but is formed by the condensation of nornicotine with formaldehyde.