Chemical characterization of ASTA Z 7557 (INN mafosfamide, CIS-4-sulfoethylthio-cyclophosphamide), a stable derivative of 4-hydroxy-cyclophosphamide.

The primary metabolite of cyclophosphamide (CP, 1), i.e. 4-hydroxy-CP 2, has high pharmacological activity, but it is a very unstable compound.