Synthesis of (±) [5-³H] N′-nitrosoanatabine, a tobacco-specific nitrosamine

Tobacco-specific N′-nitrosamines (TSNA) are a unique class of systemic organ-specific carcinogens. The TSNA are formed by N-nitrosation of nicotine and of the minor tobacco alkaloids after harvesting of tobacco and during smoking. The N-nitrosation of anatabine leads to N′-nitrosoanatabine (NAT; 1-nitroso-1,2,3,4-tetrahydro-2,3′-bipyridyl) which requires in-depth assays in laboratory animals other than the rat. Furthermore, delineation of its tissue distribution and metabolism is needed for structure: activity comparisons with other TSNA and for the assessment of potential human risk from this TSNA. We have, therefore, synthesized (±)[5-³ H]NAT. 5-Bromo-3-pyridine-carboxaldehyde was condensed with ethyl carbamate prior to Diels-Alder reaction with 1,4-butadiene to give the racemic anatabine ring system. Hydrolysis, followed by reduction with LiA1T₄ and nitrosation, led to (±) [5-³H]NAT (60% yield, specific activity 266 mCi/mmol, radiochemical purity of > 99%).