Electron impact and chemical ionization mass spectrometry of cis- and trans-S-(2-hydroxycyclohexyl)-N-acetyl-(1)-cysteine methyl esters

The electron impact and chemical ionization (ammonia and methane) mass spectral behaviour of the cis- and trans-(2-hydroxycyclohexyl)-mercapturic acid methyl esters, metabolites of cyclohexeneoxide, was examined. Only with chemical ionization was it possible to differentiate between these two configurational isomers, by observing the stereoselective loss of H2O from the protonated molecular ions. Using this stereoselective process, a method was developed for the assessment of the relative amounts of stereoisomeric mercapturic acids, excreted as metabolites in the urine of rats treated with cyclohexeneoxide.