Enzyme Inhibition Assay: For enzymology studies of these compounds, recombinant guinea pig liver TGase was expressed in Escherichia coli and effectively purified (Gillet, S. M. F. G. et al J. N., Prot. Exp. & Purif. 2004, 33, 256). In addition to being easy to obtain in excellent yield and solubility, guinea pig liver TGase was chosen because it shows 80% homology with human tissue TGase (Aeschlimann, D.; Paulsson, M., Throm. Haemost. 1994, 71, 402) and may thus serve as a model for the evaluation of inhibitors of potential therapeutic utility.The IC50 values of synthetic analogues 14a-38a were determined from inhibition of the reaction of 54.4 mM of the chromogenic TGase substrate N-Cbz-Glu(γ-p-nitrophenyl ester)Gly with 0.010 U of recombinant guinea pig liver TGase as previously reported (Leblanc, A.; Gravel, C.; Labelle, J.; Keillor, J. W. Biochemistry 2001, 40, 8335) and described in detail in the Materials section below. The mode of inhibition was determined for the representative lead compound.