Compounds of the invention are useful in inhibiting thrombin and associated thrombotic occlusions having the following structure: or a pharmaceutically acceptable salt thereof, wherein R2 is R3 is selected from the group consisting of 1) hydrogen, 2) halogen, 3) C1–4 alkyl, 4) C3–7 cycloalkyl, 5) CF3, 6) OCF3, 7) C1–4 alkoxy, and 8) cyano; and R12 is a 5-membered heteroaryl ring having 2, 3, or 4 heteroatoms, provided that at least 1 heteroatom is N, and at most 1 of the heteroatoms is S, said ring being unsubstituted or substituted, at any one ring atom, with CH3 .