Oxime derivatives of the intermediary oncostatic metabolites of cyclophosphamide and ifosfamide: Synthesis and deuterium labeling for applications to metabolite quantification

Article abstract of DOI:10.1002/jps.2600840403

There is ongoing interest in the selective, quantitative analysis of the cyclophosphamide metabolites 4-hydroxycyclophosphamide (2a) and aldophosphamide (3a) because these tautomers are generally believed to play a key role in oncostatic selectivity and metabolite transport. O-(2,3,4,5,6- Pentafluorobenzyl)hydroxylamine (C₆F₅CH₂ONH₂, 1 equiv) provided for the complete conversion (by ³¹P NMR, 60% reaction within 15 min at 20 °C) of 2a/3a (17 mM in H₂O/CH₃OH) to E/Z-aldophosphamide O-(2,3,4,5,6- pentafluorobenzyl)oxime [C₆F₅CH₂ON=CHCH₂CH₂OP-(O)(NH₂)N(CH₂CH₂Cl)₂; E:Z = 54:46 (±3% average deviation)]. Under these conditions, the oxime exhibited little (6%) decomposition over 3 weeks. Parallel studies showed that 4-hydroxyifosfamide/aldoifosfamide reacted completely to give the analogous aldoifosfamide oxime [C₆F₅- CH₂ON=CHCH₂CH₂OP(O)(NHCH₂CH₂Cl)₂; E:Z = 52:48 (±1% average deviation)] with 50% reaction within 15 min at 20 °C with no product decomposition over 3 weeks. In aqueous methanol and with 2 equiv C₆F₅CH₂ONH₂, clinically useful 4-hydroperoxycyclophosphamide (10 mM; τ = 10 min, 37 °C) and its isomer 4-hydroperoxyifosfamide (10 mM; τ = 25 min, 20 °C) underwent complete conversion to the corresponding aldehyde oximes. Each oxime was synthesized with deuterium in the chloroethyl moieties for use as internal standards in GC/MS applications.