Discovery of novel pyrazole-isatin and pyrazole-triazole-isatin hybrids as DPP-4 inhibitors

Dipeptidyl peptidase-4 (DPP-4) remains an attractive target for the development of orally active antidiabetic agents. Building on the reported pyrazole, isatin, and triazole pharmacophores, we designed, synthesized, and evaluated two series of DPP-4 inhibitors: pyrazole-isatin hybrids (Sa–Sg) obtained by SN2 O-alkylation and pyrazole-triazole-isatin hybrids (7a–7f) constructed via CuAAC “click” chemistry. All final compounds and key intermediates were fully characterized by IR, ¹H/¹³C NMR, HPLC, and MS. In vitro ELISA assays at 50, 75, and 100 nM demonstrated potent DPP-4 inhibition across both series. Within the triazole-linked set, compound 7e showed 87.95% inhibition with an IC₅₀ of 1.56 nM, while 7d and 7c also displayed low-nanomolar IC₅₀ values, comparable to the reference drugs sitagliptin and teneligliptin under identical conditions. Structure-based studies against human DPP-4 (PDB: 3VJK) using induced-fit docking and MM-GBSA rationalized the observed SAR, revealing recurrent occupation of the S1/S2/S1′/S2′ subsites and key interactions with TYR666, PHE357, ARG125, SER630, and ASN710. Molecular dynamics simulations (200 ns) of the 7c, 7d and 7e-bound complexes supported persistent binding and protein stability, with 7e exhibiting the most favorable dynamic interaction profile. QikProp-based ADMET predictions indicated generally drug-like properties, high predicted oral absorption, and good compliance with Lipinski and Jorgensen rules. Overall, the pyrazole-triazole-isatin chemotype, particularly analogues 7d and 7e, emerges as a promising lead framework for next-generation, orally available DPP-4 inhibitors, meriting further optimization for selectivity, safety, and in vivo antidiabetic efficacy.