γ-Glutamyl-β-phenylethylamine, a novel α-glucosidase and α-amylase inhibitory compound from Termitomyces robustus, an edible Nigerian mushroom.

Termitomyces species are known edible mushrooms in Nigeria, believed to have exceptional culinary and nutraceutical properties. Methanol extract from fruiting bodies of Termitomyces robustus was evaluated for antidiabetic activity using in vitro α-amylase and α-glucosidase assays. The isolation and structural elucidation of metabolites from the T. robustus extract afforded five compounds including a new natural product γ-glutamyl-β-phenylethylamine 3 and four known phenyl derivatives: tryptophan 1, 4-hydroxyphenylacetic acid 2, 4-hydroxyphenylpropionic acid 4, and phenyllactic acid 5. Structures were elucidated from analyses of spectroscopic data (1 D and 2 D NMR, HRESIMS) and all isolated compounds were tested for α-amylase and α-glycosidase inhibitory activity. The in vitro assay established crude extract to possess α- amylase and α-glucosidase inhibition with IC50 of 78.05 µg/mL and 86.10 µg/mL, respectively. The isolated compounds compared favourably with the standard drug, acarbose with IC50 ranging from 6.18-15.08 µg/mL and 18.28-44.63 µg/mL for α-amylase and glucosidase, respectively.