Natural guanidine alkaloids in tea (Camellia sinensis): Identification, quantification and α-glucosidase inhibitory activity of cis- and trans-cinnamoylagmatines

Tea ( Camellia sinensis ) is rich in purine alkaloids, particularly caffeine, yet other alkaloids have garnered less attention. In this study, a pair of stereoisomers cis - and trans -cinnamoylagmatines, alkaloids with a guanidine skeleton, have been identified in tea. Their structures were characterized using ultra-high-performance liquid chromatography/Q-Exactive orbitrap mass spectrometry and were confirmed by comparison with authentic reference standards obtained through organic synthesis. The total contents of cis- and trans- cinnamoylagmatines in various made teas with different fermentation degree and fresh leaves of different tea plant varieties were quantified to be from 1.76 ± 0.024 to 111.74 ± 11.30 mg kg −1 . In the α-glucosidase activity assay, trans -cinnamoylagmatine demonstrated superior inhibitory efficiency (IC 50 : 0.288 ± 0.011 mg mL −1 ) compared to the widely used diabetes medication acarbose. This study sheds light on the presence of natural guanidine alkaloids in tea and their potential role in reducing the risk of diabetes.