Bio-guided isolation of alpha-glucosidase inhibitory compounds from Vietnamese Garcinia schomburgkiana fruits: in vitro and in silico studies

Abstract

Garcinia schomburgkiana is an edible tree widely distributed in the southern region of Vietnam. Little is known about the alpha-glucosidase inhibition of the Vietnamese Garcinia schomburgkiana. The aim of the current study was to explore the anti-diabetic potential of G. schomburgkiana fruits. All the fractions of G. schomburgkiana were evaluated for alpha-glucosidase inhibition, followed by bioassay-guided isolation. A new compound, epi-guttiferone Q (1), together with ten known compounds, guttiferones I–K (2–3), hypersampsone I (4), sampsonione D (5), sampsonione H (6), β-mangostin (7), α-mangostin (8), 9-hydroxycalabaxanthone (9), and fuscaxanthone (10), were isolated and structurally elucidated. The structure of the new metabolite 1 was confirmed through 1D and 2D NMR spectroscopy, and MS analysis. To the best of our knowledge, the metabolites (except 3) have not been isolated from this plant previously. All isolated compounds were evaluated for their alpha-glucosidase inhibition. Compounds 1–6 showed potent activity with IC₅₀ values ranging from 16.2 to 130.6 μM. Compound 2 was further selected for a kinetic study. The result indicated that it was a competitive type. Additionally, in silico docking was employed to predict the binding mechanism of 1–2 and 4–6 in the active site of alpha-glucosidase, suggesting their potential as promising anti-diabetic compounds. Molecular dynamic simulation was also applied to 1 to better understand its inhibitory mechanism.