IRREVERSIBLE ENZYME INHIBITORS . 136 . 2,4- DIAMINO-5-(3,4-DICHLOROPHENYL)-6-(P-(M-FLUOROSULFONYLBENZAMIDO)PHENOXYMETHYL)PYRIMIDINE AN ACTIVE-SITE-DIRECTED IRREVERSIBLE INHIBITOR OF DIHYDROFOLIC REDUCTASE . EFFECT OF STRUCTURE ON ISOZYME SPECIFICITY

The title compound (1) was previously observed to be an active-site-directed irreversible inhibitor of dihydrofolic reductase from L1210 mouse leukemia, but not the enzyme from mouse liver, spleen, or intestine. Replacement of the CH2O bridge with (CH2)2 (2) enhanced reversible binding 15-fold, thus decreasing by this factor the concentration needed for irreversible inhibition.9 However, this structural change also led to loss of specificity since the liver dihydrofolic reductase could now be inactivated by 2. Similarly, replacement of the NHCO bridge of 1 by NHSO2 (8) resulted in a 50-fold enhancement of reversible inhibition, but specificity was again lost. Substitution on one or both of the benzene rings of the 6 side chain of 1 with Cl or Me gave only two- to fourfold enhancement of reversible binding, but specificity was maintained in some cases (7, 10, 11, 17). © 1969, American Chemical Society. All rights reserved.