NMR (1H and 31P) and HPLC techniques were used to study the partitioning of phosphoramide mustard (PM) and its aziridinium ions among alkylation and P-N bond hydrolysis reactions as a function of the concentration and strength of added nucleophiles at 37 degrees C and pH 7.4. With water as the nucleophile, bisalkylation accounted for only 10-13% of the product distribution given by PM. The remainder of the products resulted from P-N bond hydrolysis reactions. With 50 mM thiosulfate or 55-110 mM glutathione (GSH), bisalkylation by a strong nucleophile increased to 55-76%. The rest of the PM was lost to either HOH alkylation or P-N bond hydrolysis reactions. Strong experimental and theoretical evidence was obtained to support the hypothesis that the P-N bond scission observed at neutral pH does not occur in the parent PM to produce nornitrogen mustard; rather it is an aziridinium ion derived from PM which undergoes P-N bond hydrolysis to give chloroethylaziridine. In every buffer studied (bis-Tris, lutidine, triethanolamine, and Tris), the decomposition of PM (with and without GSH) gave rise to 31P NMR signals which could not be attributed to products of HOH or GSH alkylation or P-N bond hydrolysis. The intensities of these unidentified signals were dependent on the concentration of buffer.

SUMMARYThe ifosfamide metabolite isophosphoramide mustard (IPM) was srthesized with isotopic enrichment at each nitrogen site. Glycine-N was converted to 2-~hloroethylamine-'~N hydrochloride ( 4 steps, 21% net yield) which was then reacted with phenyl dichlorophosphate to provide N ,N ' -bis (2-chloroethyl)phosphorodi~idic-15N2 acid phenyl ester [ 6 2 % , PhOP(0) ('5NHCH2CH2C1)2]. Catalytic hydrogenation of this phenyl ester followed by the addition of cyclohexylamine (CHA) provided IPM-15N2 as the CHA salt (63%).