New black tea polyphenol having -ethyl-2-pyrrolidinone moiety derived from tea amino acid theanine: isolation, characterization and partial synthesis

Ethylpyrrolidinonyl theasinensin A, a novel polyphenol having a N-ethyl-2-pyrrolidinone moiety, was isolated from commercial black tea, and the structure was determined on the basis of spectroscopic analysis and chemical synthesis, which was achieved by condensation of theasinensin A with N-ethyl-5-hydroxy-2-pyrrolidinone. The N-ethyl-5-hydroxy-2-pyrrolidinone is spontaneously produced from theanine Strecker aldehyde by intramolecular cyclization; therefore, the presence of ethylpyrrolidinonyl theasinensin A in black tea suggested that theanine, the most abundant amino acid in tea leaf, was degraded to a Strecker aldehyde and conjugated with polyphenol A-rings during black tea production.