Ifenprodil is a selective antagonist of NMDA receptors that contain NR2B subunits (IC50 = 0.3 μM) and displays 150-fold weaker activity at those bearing NR2C or NR2D subunits.[1] Ifenprodil also acts as a potent ligand at receptors for σ1, emopamil binding proteins, and their σ-like, fungal counterpart ERG2 (Kis = 2, 5, and 1 nM).[2] This compound has been described as an α-adrenergic vasodilator, but is also reported to constrict cerebrovascular smooth muscle in vitro (EC50 = 2.4 μM).[3]

Reference:
[1]. Brauner-Osborne, H., Egebjerg, J., Nielsen, E.O., et al. Ligands for glutamate receptors: Design and therapeutic prospects J. Med. Chem. 43(14), 2609-2645 (2000).
[2]. Laggner, C., Schieferer, C., Fiechtner, B., et al. Discovery of high-affinity ligands of σ1 receptor, ERG2, and emopamil binding protein by pharmacophore modeling and virtual screening J. Med Chem. 48(15), 4754-4764 (2005).
[3]. Young, A.R., Bouloy, M., Boussard, J.F., et al. Direct vascular effects of agents used in the pharmacotherapy of cerebrovascular disease on isolated cerebral vessels Journal of Cerebral Blood Flow and Metabolism 1(1), 117-128 (1981).