Metabolic beta-hydroxylation and N-oxidation of N'-nitrosonornicotine.

3'-Hydroxy-N'-nitrosonornicotine (2), 4'-hydroxy-N'-nitrosonornicotine (3), N'-nitrosonornicotine 1-N-oxide (4) were synthesized and identified as metabolites in the F-344 rat of the tobacco-specific carcinogen N'-nitrosonornicotine (1). For the synthesis of 2, myosmine (5) was converted to 3'-bromomyosmine (6). Displacement by acetate and hydrolysis gave 3'-hydroxymyosmine (7), which was reduced and nitrosated to give 2. 4'-Hydroxymyosmine (13), the precursor to 3, was prepared by ammonolysis of 1,2-epoxy-4-(N-morpholino)-4-(3-pyridyl)-4-cyanobutane (10). N'-Nitrosonornicotine 1-N-oxide (4) was prepared by m-chloroperbenzoic acid oxidation of 1. When 1 was incubated with liver microsomes from Aroclor-pretreated F-344 rats, trace amounts of 2 and 3 were produced and 4 was a major metabolite. The urine from rats treated with N'-nitrosonornicotine-2'-14C contained only trace amounts of 2 and 3, whereas 4 accounted for 6.7-9.4% of the dose.