Discovery of N-Aryloxypropylbenzylamines as Voltage-Gated Sodium Channel NaV1.2-Subtype-Selective Inhibitors

We previously reported that a lipophilic N-(4 '-hydroxy-3 ',5 '-di-tert-butylbenzyl) derivative (1) of the voltage-gated sodium channel blocker mexiletine, was a more potent sodium channel blocker in vitro and in vivo. We demonstrate that replacing the chiral methylethylene linker between the amine and di-tert-butylphenol with an achiral 1,3-propylene linker (to give (2)) maintains potency in vitro. We synthesized 25 analogues bearing the 1,3-propylene linker and found that minor structural changes resulted in pronounced changes in state dependence of blocking human Na(V)1.2 and 1.6 channels by high-throughput patch-clamp analysis. Compared to mexiletine, compounds 1 and 2 are highly selective Na(V)1.2 inhibitors and >500 times less potent in inhibiting Na(V)1.6 channels. On the other hand, a derivative (compound 4) bearing 2,6-dimethoxy groups in place of the 2,6-dimethyl groups found in mexiletine was found to be the most potent inhibitor, but is nonselective against both channels in the tonic, frequency-dependent and inactivated states. In a kindled mouse model of refractory epilepsy, compound 2 inhibited seizures induced by 6 Hz 44 mA electrical stimulation with an IC50 value of 49.9 +/- 1.6 mg kg(-1). As established sodium channel blockers do not suppress seizures in this mouse model, this indicates that 2 could be a promising candidate for treating pharmaco-resistant epilepsy.