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

Abstract

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.

Keywords:

• Brassica rapa L.
• phenolic glycoside constituents
• α-glucosidase inhibitory activity

Acknowledgements

We are also grateful to the Analytical Detective Center, Yangzhou University, for recording MS, UV and NMR spectra.