Two New α-Glucosidase Inhibitors from Haplophyllum tuberculatum: Inhibition Kinetics and Mechanistic Insights Through...

Diabetes is a multifactorial global health disorder marked by unusually high plasma glucose levels, which can lead to serious consequences including diabetic neuropathy, kidney damage, retinopathy, and cardiovascular disease. One effective therapy approach for reducing hyperglycemia associated with type 2 diabetes is to target α-glucosidase, enzymes that catalyze starch breakdown in the intestine. In the current study, two new (1, 2) and nine known (3-11) compounds were isolated from the rutaceous plant Haplophyllum tuberculatum and characterized by extensive nuclear magnetic resonance spectroscopic techniques and high-resolution electrospray ionization mass spectrometry. After structural elucidation, nine compounds were evaluated for their ability to inhibit α-glucosidase, a target for the treatment of type-2 diabetes. Among them, three compounds (7, 5, and 2) exhibited notable inhibition with half-maximal inhibitory concentration (IC₅₀) values of 3.42 ± 0.12, 5.79 ± 0.28, and 6.75 ± 1.18 µM, respectively, while the remaining six compounds (1, 3, 4, 6, 8, and 9) had a moderate activity with IC₅₀ values ranging from 12.14 ± 0.35 to 24.60 ± 0.57 µM, compared to the standard drug acarbose (IC₅₀ = 875.75 ± 1.24 µM). A kinetic study of compounds 5 and 7 exhibited the competitive type of inhibition with K_i values of 4.82 ± 0.0036 and 3.92 ± 0.0062 µM, respectively. Furthermore, a structure-based prediction of the compounds' binding mode suggested that these inhibitors fitted exceptionally well within the active site of the target enzyme, α-glucosidase, forming multiple hydrogen and hydrophobic interactions with its active site residues. In conclusion, compounds with potent α-glucosidase inhibitory activity are abundant in nature and can be explored and further developed for treating diabetes mellitus.