Molecular networking-guided isolation of stilbene compounds from Gnetum leptostachyum Blume and their alpha-glucosidase inhibition mechanism studies

Gnetum leptostachyum (Gnetaceae), locally known as Bungug by the Kadazandusun of Borneo, is traditionally consumed both as food and for diabetes management. Despite its ethnomedicinal relevance, the plant’s bioactive constituents and pharmacological properties remain poorly understood. This study investigates the phytochemical composition and antidiabetic potential of G. leptostachyum fruits through molecular networking-guided isolation of stilbene compounds and evaluation of α-glucosidase inhibitory activity. A methanol extract was analysed using LC-MS and molecular networking, revealing 20 metabolites grouped into five molecular clusters: three stilbenoid clusters, along with distinct groups of flavonoids and terpenoids. Guided isolation yielded seven stilbenes, whose structures were unambiguously determined through extensive NMR spectroscopic analysis (¹H, ¹³C, HSQC, HMBC, and COSY). These included two monomers (resveratrol G1 and isorhapontigenin G2), one dimer (gnetin C G4), two trimers (gnetin E G5 and gnetin J G6), a trimer glucoside (gnemonoside M G3), and one tetramer (gnemonol B G7). All compounds are reported here for the first time in this species. The formation of these complex oligomers was proposed to occur via a biosynthetic pathway involving oxidative coupling and glycosylation, based on their structural relationships. In vitro α-glucosidase inhibition assays demonstrated strong activity for gnetin E (IC₅₀ = 0.316 ± 0.17 µg/mL) and gnetin J (IC₅₀ = 0.310 ± 0.14 µg/mL), both of which outperformed acarbose (IC₅₀ = 2.203 ± 0.18 mg/mL). Kinetic analysis indicated a non-competitive inhibition mechanism, further supported by molecular docking studies showing allosteric hydrogen bonding between the C-4a hydroxyl group of both compounds and ASP-408, PHE-157, and ASN-412 residues. In silico ADMET predictions suggested good intestinal absorption and low risk of metabolic interactions, although limited solubility and membrane permeability may present formulation challenges. This study provides the first detailed phytochemical and pharmacological profile of G. leptostachyum, verifying its traditional use in diabetes management and highlighting stilbenes as promising antidiabetic agents.