4-oxo-4-(pyridin-3-yl)butanoic acid is a monocarboxylic acid that is succinic acid in which the hydroxy group of one of the carboxy groups is replaced by a pyridin-3-yl group. A byproduct of tobacco-specific N-nitrosamines generated by cytochrome P-450 which catalyzes methylnitrosaminopyridylbutanone hydroxylation, this nicotine metabolite is commonly found in the urine of smokers. It is a member of pyridines, a monocarboxylic acid and an aromatic ketone. It is functionally related to a 4-oxo-4-(pyridin-3-yl)butanal. It is a conjugate acid of a 4-oxo-4-(pyridin-3-yl)butanoate.