Identification of Three New Flavonoids from the Peels of Citrus unshiu

Abstract

AbstractThree new flavonoids, 5,6,7,8,3′,4′‐hexamethoxyhomoflavone (1), 5,6,7,8,4′‐pentamethoxyhomoflavone (2) and 3,6,7,8,2′,5′‐hexamethoxyflavone (3) were isolated from the peels of mature fruits of Citrus unshiu Marcow (Rutaceae), together with the three known compounds 6,7,8,4′‐tetramethoxyflavone (=6,7,8‐trimethoxy‐2‐(4‐methoxyphenyl)‐4H‐1‐benzopyran‐4‐one), 3,5,7,8,2′,5′‐hexamethoxyflavone (=2‐(2,5‐dimethoxyphenyl)‐3,5,7,8‐tetramethoxy‐4H‐1‐benzopyran‐4‐one), and scopoletin (=7‐hydroxy‐6‐methoxy‐2H‐1‐benzopyran‐2‐one) of which the former two have never been isolated from natural resources, although they have been reported as synthetic compounds. The structures of 1–3 were elucidated on the basis of spectroscopic evidence, including 1D‐ and 2D‐NMR analysis.