2(3H)-benzoxazolone and 2(3H)-benzothiazolone derivatives: novel, potent and selective sigma1 receptor ligands.
A series of original 2(3H)-benzoxazolone and 2(3H)-benzothiazolone derivatives were evaluated for their affinity at sigma1 and sigma2 receptor subtypes in competition binding experiments, using [3H](+)-pentazocine or [3H]1,3-di-o-tolyl-guanidine (DTG) in the presence of 100 nM (+)-N-allylnormetazocine (NANM) in guinea-pig brain membranes. Several of these derivatives showed preferential selectivity for sigma1 binding sites. Compound 1 [3-(1-piperidinoethyl)-6-propylbenzothiazolin-2-one] emerged as a potent sigma1 receptor ligand (Ki = 0.6 nM) and displayed a moderate selectivity over the sigma2 receptor subtype (Ki for sigma2/Ki for sigma1 = 29). Compounds 2 [3-(1-piperidinopropyl)-6-propanoylbenzothiazolin-2-one] and 3 [3-(1-piperidinopropyl)-6-propanoylbenzoxazolin-2-one] still showed rather high affinities for sigma1 binding sites with Ki values of 2.3 and 8.5 nM, respectively. On the contrary, they had 87- and 58-fold less affinity at sigma2 receptors, respectively. Unlike their potent affinity for sigma binding sites, these compounds had negligible affinity for mu-, delta- and kappa-opioid receptors, 5-HT2, dopamine D2, and muscarinic M2 receptors. Sigma receptor ligands may affect neuronal transmission and display, in animal models, antipsychotic, cognitive, motor, neuroprotective and anticonvulsant activity. Therefore, on the basis of these findings, these novel sigma receptor ligands were assayed, in mice, in three tests: maximal electroshock, subcutaneous pentylenetetrazol and rotarod neurotoxicity. Compound 1, administered intraperitoneally, was the most effective against maximal electroshock-induced seizures and was devoid of significant neurotoxic effects.