5-(4-Chlorophenyl)-5,6-dihydro-1,3-oxazepin-7(4 H)-one derivatives as lipophilic cyclic analogues of baclofen: Design, synthesis, and neuropharmacological evaluation

Abstract

In trials to preserve the pharmacological profile and improve the bioavailability via lipophilicity increment of baclofen 1 and searching for more potent and less toxic muscle relaxants and analgesics, nine substituted cyclic analogues of 1 were designed and synthesized. The target derivatives 5-(4-chlorophenyl)-5,6-dihydro-1,3-oxazepin-7(4 H)-one ( 11– 19) were obtained through amide formation to the corresponding intermediates ( 2– 10) followed by cyclization using acetic anhydride. The structures of the target compounds ( 11– 19) were confirmed by IR, 1H NMR, MS, and elemental analyses. The neuropharmacological activities of these lipophilic cyclic analogues ( 11– 19) were assessed for their effects on motor activity, muscle relaxation, pain relief and impaired cognition, by intraperitoneal administration at a dose of 3 mg/kg with reference to those of baclofen 1. Our results showed that compounds 11– 14 are devoid of all of the tested pharmacological effects associated with 1. In all paradigms tested, undecyl, tridecyl, heptdec-8-enyl and benzyl substituted analogue derivatives ( 15, 16, 18, and 19) revealed a significant neurological activity being vividly favorable comparable with baclofen 1. 2-Benzyl-5-(4-chlorophenyl)-5,6-dihydro-1,3-oxazepin-7(4 H)-one derivative 19 is the most active candidate with high significant neurological potencies, while 5-(4-chlorophenyl)-2-(dec-8-enyl)-5,6-dihydro-1,3-oxazepin-7(4 H)-one derivative 17 displayed activity at relatively higher time interval. These results probe a new structurally distinct class incorporating 1,3-oxazepine nucleus as promising candidates as GABA B agonists for further investigations.