Novel Cinnamoylated Flavoalkaloids Identified in Tea with Acetylcholinesterase Inhibition Effect

3-O-cinnamoylepicatechin (1) was synthesized along with four flavoalkaloids, (-)-6-(5′′′S)-N-ethyl-2-pyrrolidinone-3-O-cinnamoylepicatechin (2), (-)-6-(5′′′R)-N-ethyl-2-pyrrolidinone--3-O-cinnamoylepicatechin (3), (-)-8-(5′′′S)-N-ethyl-2-pyrrolidinone-3-O-cinnamoylepicatechin (4), and (-)-8-(5′′′R)-N-ethyl-2-pyrrolidinone-3-O-cinnamoylepicatechin (5) via esterification of epicatechin followed by phenolic Mannich reaction of 1 with theanine in the presence of heat. The new compounds 1-5 were detected in leaves of three tea cultivars, Fuding-Dabai, Huangjingui, and Zimudan with the help of ultra performance liquid chromatography hyphenated with photodiode array detector and electrospray ionization high resolution mass spectrometry (UPLC-PDA-ESI-HRMS), suggesting that they are naturally occurring in tea leaves. The structures of the novel natural products were characterized by one and two dimensional nuclear magnetic resonance (1D and 2D NMR) and mass spectroscopy. Compounds 1-5 were then evaluated for their...