Design, Synthesis, and Antidiabetic Activity of 4-Phenoxynicotinamide and 4-Phenoxypyrimidine-5-carboxamide Derivatives as Potent and Orally Efficacious TGR5 Agonists

4-Phenoxynicotinamide and 4-phenoxypyrimidine-5-carboxamide derivatives as potent and orally efficacious TGR5 agonists are reported. Several 4-phenoxynicotinamide derivatives were found to activate human and mouse TGR5 (hTGR5 and mTGR5) with EC50 values in the low nanomolar range. Compound 23g, with an EC50 value of 0.72 nM on hTGR5 and an EC50 value of 6.2 nM on mTGR5, was selected for further in vivo efficacy studies. This compound exhibited a significant dose-dependent glucagon-like peptide-1 (GLP-1) secretion effect. A single oral dose of 23g (50 mg/kg) significantly reduced blood glucose levels in db/db mice and caused a 49% reduction in the area under the blood glucose curve (AUC)(0-120) (min) following an oral glucose tolerance test (OGTT) in imprinting control region (ICR) mice. However, 23g stimulated gallbladder filling, which might result in side effects to the gallbladder.