Synthesis, Structural Characterization and in vitro DPP-4 Inhibitory Evaluation of N-(1,3-Dioxoisoindolin-2-yl)benzamide Derivatives

This study reports the synthesis, structural characterization and experimental in vitro DPP-4 inhibitory evaluation of N-(1,3-dioxoiso-indolin-2-yl)benzamide derivatives (P1-12) that had previously been investigated computationally for DPP-4 binding. The derivatives were prepared through esterification, hydrazide formation and condensation with phthalic anhydride, affording products in 65-83% yield. Structural identities were supported by IR, 1H NMR, 13C NMR, ESI mass spectrometry and elemental analysis. DPP-4 inhibitory activity was evaluated using a continuous fluorometric Gly-Pro-AMC assay. Compounds P5 (3,5-dihydroxy; IC50 0.88 ± 0.04 nM) and P10 (3,5-dinitro; IC50 0.73 ± 0.03 nM) showed the lowest IC50 values in the series compared with alogliptin (IC50 6.82 ± 0.21 nM). The experimental SAR did not follow a simple electron-donating/electron-withdrawing trend as both P5 and P10 derivatives showed high activity, whereas the unsubstituted P1 and P4 (2,4-dichloro) derivatives were less active. These results provide experimental chemical and enzyme-inhibition validation of a compound series previously examined by molecular docking.