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

As a subgroup of flavoalkaloids, N -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 N -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 Camellia sinensis var. assamica . Further phytochemical study on this precious black tea led to the identification of 8 flavoalkaloids, 1 – 8, along with 11 known flavan-3-ols ( 9 – 14 ) and flavonol glycosides ( 15 – 19 ). The new compounds, (−)-6-(5″ S )- N -ethyl-2-pyrrolidinone-epiafzelechin ( 1 ), (−)-8-(5″ R )- N -ethyl-2-pyrrolidinone-epiafzelechin-3- O -gallate ( 2a ), and (−)-8-(5″ S )- N -ethyl-2-pyrrolidinone-epiafzelechin-3- O -gallate ( 2b ), were identified based on extensive spectroscopic analysis. Flavoalkaloids 2 – 6 showed inhibitory activity on α-glucosidase with IC 50 values ranging from 2.09 to 8.47 μM, compared to those of quercetin and acarbose (IC 50 = 6.87 and 228.9 μM, respectively). Moreover, compounds 2, 3, and 6 displayed an inhibitory effect on acetyl-cholinesterase with IC 50 values of 14.23, 33.79, and 34.82 μM, respectively, compared to tacrine (IC 50 = 0.223 μM).