Tea catechins and flavonoids from the leaves of Camellia sinensis inhibit yeast alcohol dehydrogenase

Four new quercetin acylglycosides, designated camelliquercetisides A-D, quercetin 3-O-[α-l-arabinopyranosyl(1→3)][2-O″-(E)-p-coumaroyl][β-d-glucopyranosyl(1→3)-α-l-rhamnopyranosyl(1→6)]-β-d-glucoside (17), quercetin 3-O-[2-O″-(E)-p-coumaroyl][β-d-glucopyranosyl(1→3)-α-l-rhamnopyranosyl(1→6)]-β-d-glucoside (18), quercetin 3-O-[α-l-arabinopyranosyl(1→3)][2-O″-(E)-p-coumaroyl][α-l-rhamnopyranosyl(1→6)]-β-d-glucoside (19), and quercetin 3-O-[2-O″-(E)-p-coumaroyl][α-l-rhamnopyranosyl(1→6)]-β-d-glucoside (20), together with caffeine and known catechins, and flavonoids (1-16) were isolated from the leaves of Camellia sinensis. Their structures were determined by spectroscopic (1D and 2D NMR, IR, and HR-TOF-MS) and chemical methods. The catechins and flavonoidal glycosides exhibited yeast alcohol dehydrogenase (ADH) inhibitory activities in the range of IC50 8.0-70.3 μM, and radical scavenging activities in the range of IC50 1.5-43.8 μM, measured by using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical.