Purity >98%. L-748,337 is a Beta3 -adrenergic receptor antagonist that displays selectivity over Beta1 and Beta2 receptors (Ki s = 4, 390, and 204 nM, respectively). It has been shown to couple with Gi to activate MAPK signaling. L-748,337 can inhibit agonist-stimulated lipolysis in rhesus monkey adipocytes, as well as agonist-induced relaxation of smooth muscle.