Li_2020_J.Agric.Food.Chem_68_7955

As the 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 buds of tea plant, Camellia sinensis var. assamica. Further phytochemical study on this precious black tea led to the identification of eight 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 alpha-glucosidase with IC50 values ranging from 2.09 to 8.47 muM, comparing to those of quercetin and acarbose (IC50 = 6.87 and 228.9 muM, resp.). Moreover, compounds 2, 3 and 6 displayed inhibitory effect on acetyl-cholinesterase with IC50 values of 14.23, 33.79 and 34.82 muM, respectively, comparing to tacrine (IC50 = 0.223 muM).