L-Cysteine based N-type calcium channel blockers: structure–activity relationships of the C-terminal lipophilic moiety, and oral analgesic efficacy in rat pain models

This study was performed to determine the structure–activity relationships (SAR) of -cysteine based N-type calcium channel blockers. Basic nitrogen was introduced into the C-terminal lipophilic moiety of -cysteine with a view toward improvement of its physicochemical properties. -Cysteine derivative 9 was found to be a potent and selective N-type calcium channel blocker with IC50 of 0.33 μM in calcium influx assay using IMR-32 cells and was 15-fold selective for N-type calcium channels over L-type channels. Compound 9 showed improved oral analgesic efficacy in the rat formalin induced pain model and the rat chronic constriction injury (CCI) model, which is one of the most reliable models of chronic neuropathic pain, without any significant effect on blood pressure or neurological behavior.