LE 300 is a potent and selective dopamine D1-like receptor antagonist with Kis of 1.9 nM and 7.5 nM in CHO cell membranes expressing human dopamine D1 and D5 receptors, respectively. LE 300 is an antagonist of the 5-HT2A receptor with a pA2 of 8.32 in a rat tail artery assay[1][2].