A new chemical class of potent DPP-4 inhibitors structurally derived from the xanthine scaffold for the treatment of type 2 diabetes has been discovered and evaluated. Systematic structural variations have led to 1 (BI 1356), a highly potent, selective, long-acting, and orally active DPP-4 inhibitor that shows considerable blood glucose lowering in different animal species. 1 is currently undergoing clinical phase IIb trials and holds the potential for once-daily treatment of type 2 diabetics.