Pyrazole derivatives as partial agonists for the nicotinic acid receptor.

Nicotinic acid as a hypolipidemic agent appears unique due to its potential to increase HDL cholesterol levels to a greater extent than other drugs. However, it has some side effects, among which severe skin flushing is the most frequent and often limits patients' compliance. In a search for novel agonists for the recently identified and cloned G protein-coupled nicotinic acid receptor, we synthesized a series of substituted pyrazole-3-carboxylic acids that proved to have substantial affinity for this receptor. The affinities were measured by inhibition of [3H]nicotinic acid binding to rat spleen membranes. Potencies and intrinsic activities relative to nicotinic acid were determined by their effects on [35S]GTPγS binding to rat adipocyte and spleen membranes. Interestingly, most compounds were partial agonists. In particular, 2-diazabicyclo[3,3,04,8]octa-3,8-diene-3-carboxylic acid (4c) and 5-propylpyrazole-3-carboxylic acid (4f) proved active with Ki values of approximately 0.15 μM and EC50 values of ap...