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

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(4H)-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, (1)H 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(4H)-one derivative 19 is the most active candidate with high signi. cant neurological potencies, while 5-(4-chlorophenyl)-2-(dec-8-enyl)-5,6-dihydro-1,3-oxazepin-7-(4H)-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 GABAB agonists for further investigations. (C) 2008 Elsevier Ltd. All rights reserved.