Sitagliptin (MK-0431) phosphate monohydrate (Standard) is the analytical standard of Sitagliptin phosphate monohydrate (HY-13749B). This product is intended for research and analytical applications. Sitagliptin phosphate monohydrate is an orally active and highly selective DPP4 inhibitor with an IC50 value of 19 nM. Sitagliptin phosphate monohydrate blocks the degradation of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) by competing inhibition mechanism (K = 1 nM), thereby increasing the level of active incretin. Sitagliptin phosphate monohydrate can also directly stimulate the secretion of GLP-1 by intestinal L cells by activating the cAMP/PKA and ERK1/2 pathways, and this effect is independent of DPP-4. Sitagliptin phosphate monohydrate shows protective effects on pancreatic islet grafts in 1-type diabetes models. Sitagliptin phosphate monohydrate can be used for the study of 1-type and 2-type diabetes.