Synthesis and evaluation of pyridazinylpiperazines as vanilloid receptor 1 antagonists

A structurally biased chemical library of pyridazinylpiperazine analogs was prepared in an effort to improve the pharmaceutical and pharmacological profile of the lead compound N-(4-tertiarybutylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carboxamide (BCTC). The library was evaluated for VR1 antagonist activity in capsaicin-induced (CAP) and pH 5.5-induced (pH) FLIPR assays in a human VR1-expressing HEK293 cell line. The most potent VR1 antagonists were found to have IC50 values in the range of 9–200 nM with improved pharmaceutical and pharmacological profiles versus the lead BCTC. These compounds represent possible second-generation BCTC analogs.