Optimization of the benzamide fragment targeting the S2′ site leads to potent dipeptidyl peptidase-IV inhibitors

•Novel benzamide fragments were designed to target the S2′ site of DPP-4.•17g showed most potent DPP-4 activity with the IC50 value of 1.6 nM for DPP-4 and excellent selectivity for DPP-8/9.•17g displayed low toxicity toward the LO2 cell line up to 100 μM.•17g robustly improved the glucose tolerance in normal mice.•17g exhibited reasonable PK profiles for oral delivery.