Reactions of 2,2-dimethylaziridine-type alkylating agents in biological systems. I. Colorimetric estimation and stability in physiological media.

Procedures were developed for the quantitative estimation of 2,2-dimethylaziridine containing alkylating agents in blood and urine. Rapid alkalinization of the biological samples, followed by protein precipitation and extraction of the compounds at high salt concentration into acetophenone, resulted in good recoveries. The use of a nonaqueous solvent (acetophenone) and the adoption of N-phenylpiperazine as the proton-accepting reagent significantly improved the sensitivity and reproducibility of the colorimetric assay with 4-(p-nitrobenzyl)pyridine. These improvements appear to be generally applicable to the quantitative determination of aziridine-type alkylating agents. The 2,2-dimethylaziridine agents were shown to undergo extremely rapid hydrolysis under neutral or acidic conditions and were stable only in alkaline solution. The half-lives of tris(2,2-dimethyl-1-aziridinyl)phosphine oxide, bis(2,2-dimethylaziridinyl)phosphinylurethan, and ethyl bis(2,2-dimethyl-1-aziridinyl)phosphinate in whole blood, at 37°, pH 7.38, were 7, 11, and 18 min., respectively; the corresponding half-lives in plasma were approximately four times longer.