Structures and Hypotensive Effect of Flavonoid Glycosides in Young Citrus unshiu Peelings

Abstract

As a series of our studies on physiologically active substances in citrus fruit peels, we report here the differences between flavonoid glycosides in Citrus unshiu peelings (the ripe fruit peels) and flavonoid glycosides in young Citrus unshiu peelings (the unripe fruit peels). Eleven flavonoid glycosides were isolated from young Citrus unshiu peels and their structures established by UV, MS, 1H-NMR and 13C-NMR spectroscopy and also by chemical findings. They were limocitrin 3-β-D-glucoside (1). narirutin (4), rutin (5), narcissin (6), hesperidin (7), 3-hydroxy-5, 6, 7, 8, 3', 4'-hexamethoxyflavone 3-β-D-glucoside (8), 6, 8-di-C-glucosylapigenin (11), 3, 8-di-C-glucosylapigenin (12), 3, 7, 4'-trihydroxy-5, 6, 8, 3'-tetramethoxy flavone 3-β-D-glucoside (13), 3, 7, 4'-trihydroxy-5, 6, 8, 3'-tetramethoxyflavone 3-O- {[3-hydroxy-3-methylglutaryl (1→6)] -β-D-glucoside} (14) and limocitrin 3-O- {[3-hydroxy-3-methylglutaryl (1→6)] -β-D-glucoside} (15). Five flavonoid glycosides (11) (15) were found not to be present in Citrus unshiu peelings (the ripe fruit peels), but could be isolated from young Citrus unshiu peelings (the unripe fruit peels). Thus the kinds and quantity of flavonoid glycosides in ripe fruit peels and those in unripe fruit peels differ greatly. The relationship between their structures and hypotensive activity was determined by injecting the compounds intravenously in SHR-SP. Of these compounds, (13), (14), and (15) were identified here for the first time as flavonoid glycosides.