Structure determination and quantification of a new flavone glycoside with anti-acetylcholinesterase activity from the herbs of <i>Elsholtzia ciliata</i>

<p>Three acacetin triglycosides (compounds <b>1</b>, <b>2</b> and <b>3</b>) were isolated from the herbs of <i>Elsholtzia ciliata</i> (Labiatae). The structure were identified as 7-<i>O</i>-β-D-glucopyranosyl-(1 → 2)[α-L-rhamnopyranosyl-(1 → 6)]-β-D-glucopyranoside (compound <b>1</b>), 7-<i>O</i>-(6-<i>O</i>-acetyl)-β-D-glucopyranosyl-(1 → 2)[α-L-rhamnopyranosyl-(1 → 6)]-β-D-glucopyranoside (compound <b>2</b>) and 7-<i>O</i>-(6-<i>O</i>-acetyl)-β-D-glucopyranosyl-(1 → 2)[(4-<i>O</i>-acetyl)-α-L-rhamnopyranosyl-(1 → 6)]-β-D-glucopyranoside (compound <b>3</b>) of acacetin. The structures of these compounds were determined on the basis of 2D-NMR spectroscopic data. Compound <b>3</b> has not been isolated from a natural source. In addition, the three compounds were quantitatively analysed by HPLC. Acetylcholinesterase (AChE) inhibition activity was assayed to find anti-Alzheimer’s activity, since this enzyme increases the concentration of acetylcholine (ACh), a neurotransmitter, responsible for brain’s memory. Acacetin, the aglycone of the three compounds, exhibited a potent anti-cholinesterase activity (IC<sub>50</sub>, 50.33 ± 0.87), though its glycosides (<b>1</b>, <b>2</b> and <b>3</b>) were less active. HPLC analysis demonstrated that the three compounds were contained in the MeOH extract in the order of compounds <b>2</b> (12.63 mg/g extract) > <b>3</b> (3.10 mg/g) > <b>1</b> (2.92 mg/g).</p>