Subnanomolar Affinity and Selective Antagonism at α7 Nicotinic Receptor by Combined Modifications of 2‑Triethylammonium Ethyl Ether of 4‑Stilbenol (MG624)

Modifications of the cationic head and the ethylene linker of 2-(triethylammonium)ethyl ether of 4-stilbenol (MG624) have been proved to produce selective α9*-nAChR antagonism devoid of any effect on the α7-subtype. Here, single structural changes at the styryl portion of MG624 lead to prevailing α7-nAChR antagonism without abolishing α9*-nAChR antagonism. Nevertheless, rigidification of the styryl into an aromatic bicycle, better if including a H-bond donor NH, such as 5-indolyl (31), resulted in higher and more selective α7-nAChR affinity. Hybridization of this modification with the constraint of the 2-triethylammoniumethyloxy portion into (R)-N,N-dimethyl-3-pyrrolidiniumoxy substructure, previously reported as the best modification for the α7-nAChR affinity of MG624 (2), was a winning strategy. The resulting hybrid 33 had a subnanomolar α7-nAChR affinity and was a potent and selective α7-nAChR antagonist, producing at the α7-, but not at the α9*-nAChR, a profound loss of subsequent ACh function.