Metabolism of nicotine in Nicotiana glauca

A mixture of (?)-nicotine-2′-³H] and (±)-nicotine-2′-¹⁴C] was administered to Nicotiana glauca plants for 3 days, resulting in the formation of radioactive nornicotine (49·5% incorporation) and myosmine (2·05% incorporation). Negligible activity was detected in anabasine, cotinine, or 3-acetylpyridine, the last two compounds being added as carriers to the harvested plants. The radioactive nornicotine consisted of 48% (?)-nornicotine-2′-¹⁴C,³H] and 52% (+)-nornicotine-2′-¹⁴C]. Thus if (+)-nornicotine is formed from (?)-nicotine the transformation must involve loss of the hydrogen from C-2′. Myosmine is presumably formed from nicotine via nornicotine. However by feeding myosmine-2′-¹⁴C] to N. glauca it was shown that the dehydrogenation is not reversible, no activity being detected in nornicotine. Nicotinic acid (0·14% incorporation) was a metabolite of myosmine-2′-¹⁴C]. Essentially all the activity of the nicotinic acid was located on its carboxyl group, indicating that myosmine was a direct precursor.