Anticonvulsant and Sodium Channel-Blocking Properties of Novel 10,11-Dihydro-5H-dibenz[b,f]azepine-5-carboxamide Derivatives

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Abstract
A series of esters of the major metabolite of oxcarbazepine (2), 10,11-dihydro-10-hydroxy-5H-dibenz[b,f]azepine-5-carboxamide, were synthesized and evaluated for their anticonvulsant and brain sodium channel-blocking properties. The compounds were assayed intraperitoneally and per os in rats against seizures induced by maximal electroshock (MES). Neurologic deficit was evaluated by the rotarod test. The enantiomeric acetates (R)-11 and (S)-12 were the most active of the series against MES-induced seizures with oral ED50 values at tmax of 10.9 ± 2.3 and 4.7 ± 0.9 mg/kg, respectively. After intraperitoneal administration, carbamazepine (1) behaved more potently than 2 and all other new dibenz[b,f]azepine-5-carboxamide derivatives in the MES test; compounds 2 and 12 were equally potent. In the rotarod test, low doses of 1 produced considerable motor impairment, which did not occur with 2, enantiomeric alcohols (S)-6, (R)-7, and racemic alcohol 8, or racemic acetate 10 or (R)-11. The potencies of the racemic and enantiomerically pure alcohols 8, (S)-6, and (R)-7 derived from 2 in the MES and rotarod test were found to be similar between them, and consequently they exhibit similar protective index values. All three forms of the alcohol and their corresponding acetates (pairs 8 & 10, 6 & 12, and 7 & 11) were found to differ in the MES or rotarod tests; the ED50 value for (S)-6 against MES-induced seizures was nearly 3-fold that for (S)-12. The protective index also differed markedly between all stereoisomers of the alcohol and their corresponding acetates, most pronouncedly for compound (S)-12 which attained the highest value (12.5) among all compounds tested. Blockade of voltage-sensitive sodium channels was studied by investigating [3H]batrachotoxinin A 20-α-benzoate ([3H]BTX) binding. Acetates (R)-11 and (S)-12 were more potent than the standards 1 and 2 at inhibiting the binding of [3H]BTX to sodium channels and the influx of 22Na+ into rat brain synaptosomes. It is concluded that acetates (R)-11 and (S)-12 are not simple metabolic precursors of alcohols (R)-7 and (S)-6 in rodents but that they possess anticonvulsant and sodium channel-blocking properties in their own right.