Flavoalkaloids with a Pyrrolidinone Ring from Chinese Ancient Cultivated Tea Xi-Gui

Chinese Xi-Gui tea is one ancient cultivated variety of Camellia sinensis var. assamica. At present, it is used for producing expensive and elite tea in China. Five new flavoalkaloids, (−)-6-(5′′′S)-N-ethyl-2-pyrrolidinone-epicatechin-3-O-gallate (ester-type catechins pyrrolidinone E, etc-pyrrolidinone E, 1), (−)-6-(5′′′R)-N-ethyl-2-pyrrolidinone-epicatechin-3-O-gallate (etc-pyrrolidinone F, 2) (−)-8-(5′′′S)-N-ethyl-2-pyrrolidinone-epicatechin-3-O-gallate (etc-pyrrolidinone G, 3a), (−)-8-(5′′′S)-N-ethyl-2-pyrrolidinone-catechin-3-O-gallate (etc-pyrrolidinone I, 4a), (−)-8-(5′′′R)-N-ethyl-2-pyrrolidinone-catechin-3-O-gallate (etc-pyrrolidinone J, 4b), and one new naturally occurring natural product (−)-8-(5′′′R)-N-ethyl-2-pyrrolidinone-epicatechin-3-O-gallate (etc-pyrrolidinone H, 3b) together with the known flavoalkaloids etc-pyrrolidinones A–D (5, 6, 7a, and 7b) were detected and isolated from Xi-Gui green tea. Their structures were identified by comprehensive NMR spectroscopic analyses. Absolute configurations of 1–3 were established by comparison of the CD analyses with epicatechin-3-O-gallate (ECG). Compounds 1–4 were evaluated for their protection against high glucose induced cell senescence on human umbilical vein endothelia cells (HUVECs) and showed significant protection effects (p < 0.01) at both 1.0 and 10 μM. A discussion on the possible evolution of tea plants divergent from related food plants on the basis of phytochemical view is also provided.