Chemical constituents from Parrotia persica- Structural derivatization and their potential prolyl endopeptidase inhibition activity.

The current study was aimed to evaluate the prolyl endopeptidase (PEP) inhibitory activity of glutinol (1), azadiradione (2), quercetin 3-O-β-d-glactopyranoside (3), catechin (4), quercetin (5), naringenin (6) isolated from Parrotia persica C. A. Mey. Naringenin (6) was further derivatized into 7-O-propargylnaringenin (7), 4',6',4″-O-propargylchalcone (8), and 4',4″-O-propargylchalcone (9). All compounds 1-9 were evaluated for their PEP inhibition activity. PEP is associated with several diseases, including dementia, and Alzheimer's disease (AD). Azadiradione (2) was less active with IC50 = 356.80 ± 2.9 µM, whereas quercetin (5) showed a potent activity with IC50 = 37.12 ± 2.2 µM, as compared to IC50 = 125.00 ± 1.5 µM of standard drug bacitracin. Naringenin (6) was found to be inactive, whereas its new analogues 7-9 were identified as potent inhibitors of PEP with IC50 = 35.20, 41.20, and 29.60 µM, respectively. Kinetic studies of active compounds indicated their modes of inhibition. Compounds 7-9 were found to be mixed-type inhibitors, while compound 5 was found to be non-competitive inhibitor.