Synthesis of novel γ-aminobutyric acid (GABA) uptake inhibitors.: 5.: Preparation and structure-activity studies of tricyclic analogues of known GABA uptake inhibitors

On the basis of the SAR of a series of known gamma -aminobutyric acid (GABA) uptake inhibitors, including 4 (SKF 89976), new tricyclic analogues have been prepared. These novel compounds are derivatives of nipecotic acid, guvacine, and homo-beta -proline, substituted at the nitrogen of these amino acids by various lipophilic moieties such as (10,11-dihydro-5H-dibenz [b,f]azepin-5-yl)alkoxyalkyl or (10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-ylidene)alkoxyalkyl. The in vitro values for inhibition of [H-3]-GABA uptake in rat synaptosomes was determined for each compound in this new series, and it was found that several of the novel compounds showed a high potency comparable with that of the reference compounds 4, 5 (tiagabine), and 6 (CI-966). Several of the novel compounds were also evaluated for their ability in vivo to inhibit clonic seizures induced by a 15 mg/kg (ip) dose of methyl 6,7-dimethoxy-4-ethyl-beta -carboline-3-carboxylate (DMCM). One compound, (R)-1-(2-(2-(10,11-dihydro-5H-dibenz[b,f]azepin-5-yl)-ethoxy)ethyl)-3-piperidinecarboxylic acid (23), was selected for further biological investigations and showed a protective index comparable to or slightly better than that of the recently launched anticonvulsant product 5 ((R)-1-(4,4-bis(3-methyl-2-thienyl)-3-butenyl)-3-piperidinecarboxylic acid).