Structure-activity relationships of trimethoxybenzyl piperazine N-type calcium channel inhibitors.

We previously reported the small organic N-type calcium channel blocker NP078585 that while efficacious in animal models for pain, exhibited modest L-type calcium channel selectivity and substantial off-target inhibition against the hERG potassium channel. Structure-activity studies to optimize NP078585 preclinical properties resulted in compound 16, which maintained high potency for N-type calcium channel blockade, and possessed excellent selectivity over the hERG (~120-fold) and L-type (~3600-fold) channels. Compound 16 shows significant anti-hyperalgesic activity in the spinal nerve ligation model of neuropathic pain and is also efficacious in the rat formalin model of inflammatory pain.