O-Methylhydroxylamine as a new trapping reagent for quantitative studies of 4-hydroxycyclophosphamide and aldophosphamide.

31P- and 1H-NMR spectroscopy were used to demonstrate that the primary metabolites of the anticancer drug cyclophosphamide (4-hydroxycyclophosphamide and its acyclic tautomer, aldophosphamide) are quantitatively converted by O-methylhydroxylamine, at pH 7.4 and 37 degrees, into the E and Z isomers of aldophosphamide O-methyl oxime. These trapping products are readily extracted from aqueous media with either chloroform or ethyl acetate, are stable at pH 6-8 toward oxime hydrolysis and elimination of phosphoramide mustard (a secondary metabolite of cyclophosphamide), and showed no evidence for transoximination with either ketone or aldehyde acceptors. All of these features support the use of aldophosphamide O-methyl oxime in quantitative studies related to cyclophosphamide metabolism.