Based on the structure of YO-2 [N-(trans-4-aminomethylcyclohexanecarbonyl)-l-Tyr(O-picolyl)-NH-octyl], active site-directed plasmin (Plm) inhibitors were explored. The picolyl moiety in the Tyr(O-picolyl) residue (namely, the P2 residue) was replaced with smaller or larger groups, such as hydrogen, tert-butyl, benzyl, (2-naphthyl)methyl, and (quinolin-2-yl)methyl. Those efforts produced compound 17 {N-(trans-4-aminomethylcyclohexanecarbonyl)-l-Tyr[O-(quinolin-2-yl)methyl]-NH-octyl} [IC50=0.22 and 77μM for Plm and urokinase (UK), respectively], which showed not only 2.4-fold greater Plm inhibition than YO-2, but also an improvement in selectivity (Plm/UK) by 35-fold. The docking experiments of the Plm-17 complexes disclosed that the amino group of the tranexamyl moiety interacted with the side-chain of Asp753 which formed S1 site.