New 1,5-benzodiazepine compounds: activity at native GABAA receptors

Various new 1,5-benzodiazepine compounds were synthesized and tested for their biological activity in terms of effects on GABAA receptors of rat cerebellar granules in culture. Their effects were compared to those of a 1,4-benzodiazepine agonist, flunitrazepam and the already known 1,5-benzodiazepine antiepileptic clobazam. The effects were evaluated for the two different GABAA receptor populations present in these neurons, one mediating phasic inhibition and the other one mediating tonic inhibition. Many such compounds display a profile of inverse agonist to both GABAA receptor populations. One of them presents a profile of full agonist at the component mediating phasic inhibition. Interestingly, substitution of just one oxygen atom in that compound with sulphur in a specific position of a morpholine ring resulted in a remarkable change of activity from full agonist to a probable inverse agonist. This indicates such a position as a proton accepting one for the ligand within the benzodiazepine binding pocket of the relevant GABAA receptors. In addition, that position appears to be critical for the pharmacological activity.