Compounds of the invention are useful in inhibiting thrombin and associated thrombotic occlusions having the following structure: ##STR1## A is ##STR2## wherein Y.sup.1 and Y.sup.2 are independently hydrogen, C.sub.1-4 alkyl, C.sub.1-4 alkoxy, F.sub.u H.sub.v C(CH.sub.2).sub.0-1 O--, wherein u and v are either 1 or 2, provided that when u is 1, v is 2, and when u is 2, v is 1, C.sub.3-7 cycloalkyl, thio C.sub.1-4 alkyl, C.sub.1-4 sulfinylalkyl, C.sub.1-4 sulfonylalkyl, halogen cyano, or trifluoromethyl, and wherein b is 0 or 1.