The microsomal metabolism of some analogues of cyclophosphamide: 4-methylcyclophosphamide and 6-methylcyclophosphamide

Abstract

4-Methylcyclophosphamide and 6-methylcyclophosphamide are, like cyclophosphamide, converted by rat liver microsomes into 4-hydroxy derivatives. 4-Hydroxy-4-methylcyclophosphamide was isolated directly, in admixture with the product [2-(2-chloroethylamino)tetrahydro-4-methyl-2 H-1,3,2-oxazaphosphorine 2-oxide] of dechloroethylation. P.m.r. data for the hydroxy derivative, which was also formed when 4-methylcyclophosphamide was treated with aqueous KMnO 4, indicated that it exists in aqueous solution as the acyclic tautomer, 2-oxopropyl- N, N- bis-(2-chloroethyl)phosphorodiamidate. 4-Hydroxy-6-methylcyclophosphamide was trapped by reaction with ethanol, and afforded two isomeric ethoxy derivatives analogous to those previously reported from cyclophosphamide. Treatment of the products of metabolism of 4-methyl- and 6-methylcyclophosphamide with 2,4-dinitro-phenylhydrazine afforded, respectively, the 2,4-dinitrophenylhydrazones of methyl vinyl ketone and of crotonaldehyde. 4-Methylcyclophosphamide cannot form metabolites analogous to 4-ketocyclophosphamide and carboxyphosphamide, the relatively non-toxic metabolites of cyclophosphamide. The significance of this fact is discussed in relation to a mechanism which could account for the relatively selective cytotoxicity of cyclophosphamide in vivo towards neoplastic tissue. Conventional electron impact mass spectrometry has played an important role in the characterization of the products described in this study. 4-Hydroxy-4-methylcyclophosphamide was additionally characterized by the relatively novel technique of field desorption mass spectrometry.