Phytochemical Constituents Isolated From Distichochlamys citrea M.F. Newman Rhizomes and Their Antioxidant and α-glucosidase Inhibitory Activities

Abstract

Objective/Background: Distichochlamys citrea M.F. Newman (Zingiberaceae) is an endemic plant of Vietnam and has been used as a folk medication for treatments of infection-related diseases, diabetes, and used as spice. This study aimed to characterize the antioxidant and α-glucosidase inhibitory activities of isolated compounds from D. citrea rhizomes. Methods: Compounds have been isolated from D. citrea rhizomes by different chromatographic techniques. Their chemical structures were determined based on mass spectrometry and nuclear magnetic resonance spectroscopy in comparison with those reported in the literature. The antioxidant effect was evaluated by 2,2-diphenyl-1-picrylhydrazyl-free radical neutralization whereas α-glucosidase inhibitory activity was determined by using the method of optical density measurement. Results: Seven compounds including 5-hydroxy-3,7,4'-trimethoxyflavone (1), kaempferol (2), platyphyllone (3), 5- O-caffeoylquinic acid (4), a mixture of phytosterols ( β-sitosterol (5) and stigmasterol (6)), and glycerol monostearate (7) were isolated and identified from D. citrea rhizomes. Compounds 1 and 2 simultaneously exhibited antioxidant activities (IC50 = 794.71 ± 2.68 µM, 14.08 ± 5.60 µM, respectively) and α-glucosidase inhibitory effects (IC50 = 189.40 ± 1.55 µM, and 31.86 ± 5.38 µM, respectively). Meanwhile, compound 3 and the mixture of 5 and 6 singly inhibited the enzyme α-glucosidase (IC50 = 69.41 ± 6.11 µM, 1204.82 µM, respectively), and showed weak antioxidant effects. On the contrary, compound 4 only had antioxidant activity (IC50 = 30.20 ± 1.86 µM). Compound 7 did not exhibit either antioxidant or enzymatic inhibitory effects. Conclusion: This is the first time that all of the seven compounds (1-7) and their biological activities were reported from D. citrea. Moreover, the α-glucosidase inhibitory effect of platyphyllone (3) is reported for the first time in the literature. This study revealed that flavonoids, phenolics, sterols, and monoglycerides in D. citrea rhizomes could be responsible for the antioxidant property and α-glucosidase inhibitory effect of this Vietnamese endemic medicinal plant.