THE PARTITIONING OF PHOSPHORAMIDE MUSTARD AND ITS AZIRIDINIUM IONS AMONG ALKYLATION AND P-N BOND HYDROLYSIS REACTIONS

NMR (H-1 and P-31) and HPLC techniques were used to study the partitio ning of phosphoramide mustard (PM) and its aziridinium ions among alky lation and P-N bond hydrolysis reactions as a function of the concentr ation and strength of added nucleophiles at 37 degrees C and pH 7.4. W ith 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 o r 55-110 mM glutathione (GSH), bisalkylation by a strong nucleophile i ncreased to 55-76%. The rest of the PM was lost to either HOH alkylati on or P-N bond hydrolysis reactions. Strong experimental and theoretic al evidence was obtained to support the hypothesis that the P-N bond s cission observed at neutral pH does not occur in the parent PM to prod uce nornitrogen mustard; rather it is an aziridinium ion derived from PM which undergoes P-N bond hydrolysis to give chloroethylaziridine. I n every buffer studied (bis-Tris, lutidine, triethanolamine, and Tris) , the decomposition of PM (with and without GSH) gave rise to P-31 NMR signals which could not be attributed to products of HOH or GSH alkyl ation or P-M bond hydrolysis. The intensities of these unidentified si gnals were dependent on the concentration of buffer.