Isolation and identification of N1-methylnicotinic acid (trigonelline) from rat urine

A urinary metabolite of nicotinic acid, single- and double-labeled N1-methylnicotinic acid (trigonelline: Tg) were isolated as urinary excretion products of rats following portal vein injection of [carboxyl-14C]nicotinic acid (14C-NiA) and/or S-adenosyl-L-[methyl-3H]methionine (3H-SAM). The labeled compounds produced were identified as Tg by comparison of ultraviolet absorption pattern and chromatographic behavior with those of the authentic compound, and by cocrystallization with the authentic carrier. It was demonstrated that enzymatic synthesis of double-labeled Tg is accomplished by reaction between 14C-NiA and 3H-SAM, and the enzymatic product was identified using the above methods. Approximately 1.5% respectively of the radioactivity of 14C-NiA and 3H-SAM was incorporated into Tg by enzymatic reaction. Furthermore, Tg from normal rat urine was isolated by ion-exchange chromatographic procedures and was crystallized from ethyl alcohol. The isolated compound was identified as Tg by comparison of ultraviolet spectra, infrared spectra, gas-mass spectra, elemental analysis, melting point and thin layer chromatogram behavior with those of the authentic compound. From these results, it was clearly demonstrated that Tg was one of the metabolites of nicotinic acid in the rat.