Characterization of cyclophosphamide (NSC-26271) metabolites and related derivatives by field-desorption and electron-impact mass spectrometry.

Several important metabolites of cyclophosphamide (CP), such as 4-hydroxycyclophosphamide and phosphoramide mustard, some 4-alkyl(aryl)thio derivatives have been investigated by field-desorption and electron-impact mass spectrometry. The structural identification of synthetic compounds and of derivatives, isolated by thin-layer chromatography in vitro, was possible since complementary information can be obtained using the two ionization techniques. Whereas only the field-desorption mass spectra showed more abundant molecular ions, the electron-impact technique revealed a characteristic fragmentation pattern for most of the compounds studied. Examples are given which demonstrate the existence of stereoisomers of CP derivatives using thin-layer chromatography and field-desorption mass spectrometry. The results indicate that field-desorption mass spectrometry is also a particularly appropriate method for the characterization of unstable CP metabolites in vivo.