IRREVERSIBLE ENZYME INHIBITORS . 139 . P-(4,6-DIAMINO-1,2-DIHYDRO-2,2-DIMETHYL-S-TRIAZIN-1-YL)PHENYLPROPIONYLSULFANILYL FLUORIDE AN ACTIVE-SITE-DIRECTED IRREVERSIBLE INHIBITOR OF DIHYDROFOLIC REDUCTASE .6. FURTHER STUDIES ON EFFECTS OF SUBSTITUTION ON PROPIONAMIDE BRIDGE ON ISOZYME SPECIFICITY

Thirteen candidate irreversible inhibitors of dihydrofolic reductase that have an alkyl, aryl, or aralkyl group on the propionamide bridge of the title compound (1) have been investigated with this enzyme from Walker 256 rat tumor, rat liver, three strains of L1210 mouse leukemia, and mouse liver. Substitution of an α-methyl (6), α-phenethyl (7), or N-methyl (9) eradicated the irreversible inhibition seen with 1. Irreversible inhibition could be maintained with an α-aryl substituent such as phenyl, tolyl, anisyl, or naphthyl, but such a substitution was detrimental to the good reversible binding of 1 needed for irreversible inhibition at low concentration. The best compound emerging from the study was the β-methyl derivative (8), which showed specificity by inactivation of L1210 enzyme but not liver; however, 8 did not give complete irreversible inhibition of the L1210 enzyme due to the competition of enzyme-catalyzed hydrolysis of its SO2F group. © 1969, American Chemical Society. All rights reserved.