Four New Flavan-3-ol Derivatives with Potent α-Glucosidase Inhibitory Activity from Black Tea Produced from Camellia taliensis

Black tea, a tea fully fermented by polyphenol oxidase, is widely recognized for its distinctive flavor and diverse health benefits largely attributed to its various phenolic components. An extensive phytochemical investigation of black tea made from the leaves of Camellia taliensis (Theaceae), a wild tea plant distributed in Yunnan province, China, led to the isolation and characterization of 15 flavan-3-ol derivatives, among which four previously unreported products (1–4), including two flavoalkaloids (1–2), one flavan-3-ol (3) and one nitrogen-containing phenol (4), were identified. When evaluated for α-glucosidase inhibitory activity, 10 of the isolates showed stronger activities than quercetin and acarbose (IC50 = 5.75 and 223.30 µM, respectively), with IC50 values ranging from 0.09 to 3.57 µM. Notably, compound 15 displayed exceptional potency with an IC50 of 0.09 μM, approximately 60-fold lower than that of quercetin. These findings highlight the potential of black tea produced from C. taliensis for the development of functional foods targeting postprandial hyperglycemia management.