Alogliptin (also known as SYR-322), is a novel, orally-available and highly selective quinazolinone-based inhibitor of dipeptidyl peptidase-4 (DPP-4), a serine aminopeptidase catalyzing the cleavage of peptides, that potently inhibits human DPP-4 in vitro with 50% inhibition concentration IC50 value of 6.9 nM and barely exhibits any inhibition towards the closely related serine proteases, including DPP-2, DPP-8, DPP-9, fibroblast activation protein/seprase, prolyl endopeptidas and tryptase (IC50 > 100,000 nM for all). Alogliptin prevents DPP-4-catalyzed degradation of GLP-1 and GIP, which regulate concentrations of blood glucose by stimulating glucose-dependent insulin secretion, and hence is being investigated in the treatment of type 2 diabetes.