The present invention relates to a
thrombin receptor antagonist containing a compound represented by the formula (I)wherein R1a, R1b and R2 are each a
hydrogen atom, an optionally substituted
hydrocarbon group, an optionally substituted heterocyclic group, or an optionally substituted alkoxy, R3 is a group represented by the formula —NHCOR4, —NHSO2R5, —NHCON(R6a)(R6b), —NHCOOR7 or —CONHR8 wherein R4, R5, R6a, R6b, R7 and R8 are each a
hydrogen atom, an optionally substituted
hydrocarbon group, an optionally substituted heterocyclic group and the like), ring A is monocyclic aromatic ring optionally further having
substituent(s), R1a and R1b are optionally bonded to each other to form an optionally substituted
nitrogen-containing non-aromatic heterocycle, or a salt thereof or a
prodrug thereof. The
thrombin receptor antagonist of the present invention has a
thrombin receptor (particularly PAR-1) antagonistic action and is useful for the prophylaxis or treatment of PAR-1 mediated
pathological condition or
disease.