The prodrug of a bifunctional sulfonate alkylating agent with myeloablative, immunosuppressive, and antineoplastic activities. Under physiological conditions, treosulfan converts nonenzymatically to L-diepoxybutane via a monoepoxide intermediate. The monoepoxide intermediate and L-diepoxybutane alkylate DNA at guanine residues and produce DNA interstrand crosslinks, resulting in DNA fragmentation and apoptosis. In escalated doses, this agent also exhibits myeloablative and immunosuppressive activities.