Presence of N-nitroso-L-thioproline and N-nitroso-L-methylthioprolines in human urine as major N-nitroso compounds.

Unknown N-nitroso compounds were found in human urine of healthy volunteers by gas chromatography-thermal energy analysis. These compounds were identified as N-nitroso-L-thioproline and cis- and trans-N-nitroso-L-methylthioprolines by gas chromatography-mass spectrometry. The precursors of these new N-nitroso compounds may be formed by the reactions of L-cysteine with formaldehyde and acetaldehyde in the human body.