PAR4 antagonist 2 (Compound 31) is a protease activated receptor 4 ( PAR4 ) antagonist, with IC 50 values of 95 nM and 367 nM for human PAR4 and mouse PAR4. PAR4 antagonist 2 is active against PAR4 activation by the native protease thrombin cleavage but not the synthetic PAR4 agonist peptide AYPGKF.