Phenolic glycoside constituents from Brassica rapa flowers and their α-glucosidase inhibitory activity

Two new phenolic glycoside compounds (1, 2) and ten known analogues (3−12) have been isolated from the ethanolic extract of Brassica rapa flowers and identified as 2-O-β-d-glucopyranosyl-(1S)-(4-methoxyphenyl)ethylene glycol (1), 2-(4-O-β-d-allopyranosyl)phenyl-ethanol (2), 2-O-β-d-glucopyranosyl-(1S)-phenylethylene glycol (3), 2-O-β-d-glucopyranosyl-(1R)-phenylethylene glycol (4), (Z)-p-coumaryl-O-β-d-glucopyranoside (5), phenyl-O-β-d-glucopyranoside (6), 2-phenylethyl-O-β-d-glucopyranoside (7), salidroside (8), 2-(2-hydroxyphenyl)ethanol-O-β-d-glucopyranoside (9), 4-methoxybenzyl-O-β-d-glucopyranoside (10), 2,4,6-trimethoxyphenyl-1-O-β-d-glucopyranoside (11) and sachaliside 1 (12). The structures of 1 and 2, including absolute configurations, were determined by spectroscopic data (1H NMR, 13C NMR, HSQC, HMBC and ORD) and chemical methods. In addition, most of them exhibited inhibitory activity with IC50 values ranging from 14.43 to 50.20 μM in comparison to the positive control acarbose (IC50 = 15.76 μM) in intestinal α-glucosidase inhibitory activity tests.