New Flavoalkaloids with Potent α-Glucosidase and Acetylcholinesterase Inhibitory Activities from Yunnan Black Tea 'Jin-Ya'.

As a subgroup of flavoalkaloids, -ethyl-2-pyrrolidinone substituted flavan-3-ols are reported to possess various biological activities that may play important roles in the beneficial healthcare functions of tea. The HPLC and LC-MS analyses showed the existence of -ethyl-2-pyrrolidinone substituted flavan-3-ols in 'Jin-Ya', which is a Yunnan black tea produced only from the buds of the tea plant var. . Further phytochemical study on this precious black tea led to the identification of 8 flavoalkaloids, -, along with 11 known flavan-3-ols (-) and flavonol glycosides (-). The new compounds, (-)-6-(5″)--ethyl-2-pyrrolidinone-epiafzelechin (), (-)-8-(5″)--ethyl-2-pyrrolidinone-epiafzelechin-3--gallate (), and (-)-8-(5″)--ethyl-2-pyrrolidinone-epiafzelechin-3--gallate (), were identified based on extensive spectroscopic analysis. Flavoalkaloids - showed inhibitory activity on α-glucosidase with IC values ranging from 2.09 to 8.47 μM, compared to those of quercetin and acarbose (IC = 6.87 and 228.9 μM, respectively). Moreover, compounds , , and displayed an inhibitory effect on acetyl-cholinesterase with IC values of 14.23, 33.79, and 34.82 μM, respectively, compared to tacrine (IC = 0.223 μM).