Structural optimization of pyrazolo[1,5-a]pyrimidine derivatives as potent and highly selective DPP-4 inhibitors.

Our previous discovery of pyrazolo [1,5-a]pyrimidin-7(4H)-one scaffold-based DPP-4 inhibitors yielded two potent compounds b2 (IC = 79 nM) and d1 (IC = 49 nM) but characterized by cytotoxicity. Herein, with scaffold hopping and fragment-based drug design strategies, highly potent and selective pyrazolo [1,5-a]pyrimidine DPP-4 inhibitors were found featured by reduced or diminished cytotoxicity. Specifically, c24 (IC = 2 nM) exhibits a 25 to 40-fold increase of inhibitory activity respect to those of b2 and d1, respectively, 2-fold from Alogliptin (IC = 4 nM), and remarkable selectivity over DPP-8 and DPP-9 (>2000 fold). Further docking studies confirmed that the pyrazolo [1,5-a]pyrimidine core interacts with the S1 pocket whereas its substituted aromatic ring interacts with the sub-S1 pocket. The interactive mode in this case resembles that of Alogliptin and Trelagliptin. Further in vivo IPGTT assays in diabetic mice demonstrated that c24 effectively reduces glucose excursion by 48% at the dose of 10 mg/kg, suggesting that c24 is worthy of further development as a potent anti-diabetes agent.