Relative inhibitory activity for EPAC2-mediated Rap1b-bGDP exchange. Dose-dependent inhibition of EPAC2 GEF activity by compound 1 (black), 10 (blue), 24 (red), 27 (green), 33 (brown), in the presence of 20 μM cAMP. Relative GEF activity were presented as normalized reaction rate constant (means ± SD, n =3) described in the method.