Carboxymethyl- and Carboxyl-Catechins from Ripe Pu-er Tea

Abstract

Ripe Pu-er tea, a special microbial postfermented tea originated from Yunnan Province, China, since ancient times, is made from green Pu-er tea prepared from the leaves of <i>Camellia sinensis</i> var. <i>assamica</i> (Theaceae). Chemical investigation on thearubigin (<i>n</i>-BuOH-soluble) fraction of the commercial ripe Pu-er tea, led to the identification of four new flavan-3-ol derivatives, 8-carboxymethyl-(+)-catechin (<b>1</b>), 8-carboxymethyl-(+)-catechin methyl ester (<b>2</b>), 6-carboxymethyl-(+)-catechin (<b>3</b>), and 6-carboxyl-(−)-gallocatechin (<b>4</b>), together with 18 known compounds, including other three flavan-3-ol derivatives (<b>5</b>–<b>7</b>), 10 flavonoid glycosides (<b>8</b>–<b>17</b>), two hydrolyzable tannins (<b>18</b> and <b>19</b>), two quinic acid derivatives (<b>20</b>–<b>21</b>), and a purine alkaloid (<b>22</b>). Flavonoid glycosides <b>8</b>–<b>11</b> are reported from tea plants for the first time. The thearubigin fraction of ripe Pu-er tea was qualitatively analyzed by HPLC, and gallic acid was found to be the major component. Compounds <b>4</b>, <b>6</b>–<b>17</b>, <b>21</b> and <b>22</b> were tested for their acute activities on insulin sensitivity in differentiated 3T3-L1 adipocytes, but none of them showed significant bioactivity at a concentration of 10 μM