Proton magnetic resonance studies of the decomposition of 4-hydroxycyclophosphamide, a microsomal metabolite of cyclophosphamide.

The proposed tautomeric equilibrium between the microsomal metabolite of cyclophosphamide, 4-hydroxycyclophosphamide, and the open chain aldophosphamide, and the subsequent facile β-elimination to generate acrolein and phosphoramide mustard have been confirmed by proton magnetic resonance studies. When 4-hydroxycyclophosphamide, initially maintained in CDC13 at -20°C, was allowed to equilibrate at 15°C, a singlet at 9.76 δ and a triplet at 2.88 δ appeared concomitantly which were assigned to the aldehydic proton and the protons α to the carbonyl of aldophosphamide, respectively. Further reaction led to the appearance of several NMR signals that indicated the irreversible formation of acrolein (multiplet at 9.55 δ) and phosphoramide mustard. Polymerization occurred approximately 2 hours after the initiation of the reaction. The kinetic data of the reaction sequence are discussed.