Effect of 7-O-glycosyl acylation of flavonoids from barley seedlings on α-glucosidase inhibition

In the present study, six 7- O -glycosyl acylation of flavonoids derived from lutonarin and saponarin were obtained from barley seedlings by medium-pressure LC, high-speed counter-current chromatography and preparative HPLC guided by UPLC-QTOF-MS/MS. Their inhibitory effects on α-glucosidase were investigated. Structure–activity relationship showed 7- O -glycosyl acylation enhanced inhibitory effect on α-glucosidase with coumaroyl > feruloyl > hydroxybenzoyl > sinapoyl. The IC₅₀ values for saponarin and its four acylated products were 802.4 ± 0.48 μg/mL, 374.6 ± 0.16 μg/mL, 461.6 ± 0.27 μg/mL, 523.8 ± 0.24 μg/mL and 585.8 ± 0.42 μg/mL, respectively. Steady-state fluorescence spectroscopy revealed 7- O -glycosyl acylation enhanced the fluorescence quenching rate of α-glucosidase. Molecular docking revealed 7- O -glycosyl acylation formed more hydrogen bonds and hydrophobic interactions with α-glucosidase. Synchronous fluorescence spectroscopy showed all compounds altered the hydrophobic microenvironment surrounding the tryptophan residues in α-glucosidase. Circular dichroism spectroscopy indicated 7- O -glycosyl acylation modified the conformation and secondary structure of α-glucosidase.