A potent DPP-4 inhibitor (IC50 = 1 nM for human recombinant DPP-4); ≥10,000-fold selectivity for DPP-4 over other a panel of 11 peptidases and proteases; inhibits 90% of plasma DPP-4 activity in rat; dose-dependently decreases plasma glucose and increases plasma levels of GLP-1 and insulin in Zucker diabetic fatty rats; reduces HbA1c levels in mice with high-fat diet- and low-dose streptozotocin-induced diabetes