Changes of major tea polyphenols and production of four new B-ring fission metabolites of catechins from post-fermented Jing-Wei Fu brick tea

• Jing-Wei Fu brick tea, a kind of brick dark tea, was chemically studied for the first time.
• Four new B ring fission catechins (BRFCs) were isolated and identified from Jing-Wei Fu brick tea.
• HPLC analysis showed that the level of major tea catechins dropped sharply in the final product.
• Possible pathways for the degradation of major tea catechins and the generation of BRFCs were provided.

HPLC analysis of samples from four major fermentation procedures of Jing-Wei Fu brick tea showed that the level of major tea catechins epigallocatechin gallate (EGCG) and epicatechin gallate (ECG) dropped increasingly to about 1/3 in the final product. Phytochemical study of the final product led to the discovery of four new B-ring fission metabolites of catechins (BRFCs) Fuzhuanin C–F (1–4) together with three known BRFCs (5–7), six known catechins (8–13), five simple phenols (14–18), seven flavones and flavone glycosides (19–25), two alkaloids (26, 27), three triterpenoids (28–30) and one steroid (31). The structures were elucidated by spectroscopic methods including 1D and 2D NMR, LC–HR-ESI-MS, IR, and CD spectra. Five compounds (16–18, 28, 29) were reported for the first time in tea. Possible pathways for the degradation of major tea catechins and the generation of BRFCs were also provided.