A solution-phase synthesis of an α-ketothiazole library of the general form D-Phe-L-AA-Arg-α-ketothiazole is described. The five-step synthesis is accomplished using a combination of polymeric reagents and polymer-assisted solution-phase purification concepts, including reactant-sequestering resins, reagent-sequestering resins, and tagged reagents. The multistep synthesis affords desired α-ketothiazole products in excellent purities and yields. A variety of L-amino acid inputs were used to probe the S2 pocket of tissue Factor VIIa enzyme to influence both potency and selectivity. An X-ray crystal structure of compound 10k bound to the TF/VIIa complex was obtained that explains the observed selectivity. The α-ketothiazoles were found to be potent, reversible-covalent inhibitors of tissue Factor VIIa, with some analogues demonstrating selectivity over thrombin.