Phenolic glycoside constituents from <i>Brassica rapa</i> flowers and their <i>α</i>-glucosidase inhibitory activity

<p>Two new phenolic glycoside compounds (<b>1</b>, <b>2</b>) and ten known analogues (<b>3</b>−<b>12</b>) have been isolated from the ethanolic extract of <i>Brassica rapa</i> flowers and identified as 2-<i>O</i>-<i>β</i>-d-glucopyranosyl-(1<i>S</i>)-(4-methoxyphenyl)ethylene glycol (<b>1</b>), 2-(4-<i>O</i>-<i>β</i>-d-allopyranosyl)phenyl-ethanol (<b>2</b>), 2-<i>O</i>-<i>β</i>-d-glucopyranosyl-(1<i>S</i>)-phenylethylene glycol (<b>3</b>), 2-<i>O</i>-<i>β</i>-d-glucopyranosyl-(1<i>R</i>)-phenylethylene glycol (<b>4</b>), (<i>Z</i>)-<i>p</i>-coumaryl-<i>O</i>-<i>β</i>-d-glucopyranoside (<b>5</b>), phenyl-<i>O</i>-<i>β</i>-d-glucopyranoside (<b>6</b>), 2-phenylethyl-<i>O</i>-<i>β</i>-d-glucopyranoside (<b>7</b>), salidroside (<b>8</b>), 2-(2-hydroxyphenyl)ethanol-<i>O</i>-<i>β</i>-d-glucopyranoside (<b>9</b>), 4-methoxybenzyl-<i>O</i>-<i>β</i>-d-glucopyranoside (<b>10</b>), 2,4,6-trimethoxyphenyl-1-<i>O</i>-<i>β</i>-d-glucopyranoside (<b>11</b>) and sachaliside 1 (<b>12</b>). The structures of <b>1</b> and <b>2</b>, 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 <i>α</i>-glucosidase inhibitory activity tests.