CATPB is an acetamidophenylbutanoate derivative with inverse agonist and antagonist activity against human, but not mouse or rat, FFA2 (GPR43). CATPB inhibits both constitutive and propionate (C3) -stimulated hFFA2 GTPγS incorporation (IC50 ~35 and 320 nM, respectively; [C3] = EC80, ~125 nM), as well as C3-induced hFFA2 G159E activity (IC50 ~400 nM). CATPB is shown to inhibit C3-induced intracellular ERK phosphorylation in hFFA2-expressing cells (IC50 ~3 µM against 10 mM C3).