Identification of major urinary metabolites of ACNU, 3-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-1-(2-chloroethyl)-1-nitroso urea hydrochloride in rats.

Metabolites of 3-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-1-(2-chloroethyl)-1- nitrosourea hydrochloride (ACNU) in rat urine were investigated. After intravenous administration of 14C-ACNU into rats, four major radioactive metabolites and two minor ones were detected in the urine by two-dimensional thin-layer chromatographic analysis. The main metabolite was identified to be an imidazolidinone compound, 1-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-5-hydroxy-2-imidazolidinone (M-D). One of the other major metabolites was identified to be a nitrosated compound of the main metabolite i.e., 1-[(4-amino-2-methyl-5-pyrimidinyl)methyl]- 5-hydroxy-3-nitroso-2-imidazolidinone (M-C). These were new types of metabolites which have not been reported in the metabolic study of other chloroethylnitrosourea derivatives. Compared with authentic compounds, two metabolites were identified to be a denitrosated derivative of ACNU i.e., 1-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-3-(2-chloroethyl)urea (M-B), and a cyclized pyrimidopyrimidine compound which lacks the ethylene moiety of ACNU, i.e., 3,4-dihydro-7-methylpyrimido[4,5-d]pyrimidin-2-(1H)-one (M-A). The two minor metabolites were supposed to be compounds derived from M-A. Discussions were made on mechanism of formation of these metabolites in vivo.