Six candidate irreversible inhibitors of uridine-deoxyuridine phosphorylase (EC 2.4. 2.3) from Walker 256 rat tumor were synthesized. These compounds connect a terminal sulfonyl fluoride group to the 1-benzyl moiety of 1-benzyl-5-(3-ethoxybenzyl) uracil (9). Although none of the compounds were irreversible inhibitors, the four 3-[(fluorosulfonyl) benido] analogues (14-17) of 9 were good reversible inhibitors of the enzyme which were ...