Several new "dual antagonists" were synthesized in which the 2,2-dimethyl (or ring C unsubstituted) aziridine phosphinyl function is linked to N-hydroxyurethane rather than the urethane moiety. Three of the new compounds showed very high activities against leukemia L1210 in mice.

Model 240 spectrophotometer equipped with an automatic samplechanging accessory. Reactions were initiated by adding a given amount of I-NE from a stock solution to a 2.5 X 10-4M solution of PLP in the appropriate buffer and decreases in absorption at 388 nm were recorded continuously until no further change was observed. Pseudo-first-order rate constants were calculated on a Hewlett-Packard 2100A digital computer, using a program designed to calculate a least-squares evaluation of a plot of I n (Ainf -A,/Ainf -A T ) vs. time. The correlation coefficients were usually greater than 0.999.Purification and Assay of COMT. COMT was purified from rat liver (male, Sprague Dawley, 180-200 g) and assayed according to the methods previously described.14'15 Kinetic data processing was also achieved as previously d e s~r i b e d . '~~'~ Acknowledgment.