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 ##STR1##

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