Identification of Three New Flavonoids from the Peels of Citrus unshiu

Abstract

Three 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.

Polyphenolic Composition and Hypotensive Effects of Parastrephia quadrangularis (Meyen) Cabrera in Rat

“…. All NMR spectra (1D and 2D NMR), and mass spectrometry (Table S1) were consistent with data reported for these known compounds [13,21,[30][31][32][33].…”

“…The chloroform-soluble sub-fraction of Pq was subjected to a series of open column chromatographic (CC) separations to obtain the following seven known biologically active compounds (Figure 8): 5,4′-dihydroxy-7,3′-dimethoxyflavanone (1) [18]; 5,3′,4′-trihydroxy-7methoxyflavanone (7-methoxy-eriodictyol) (2) [19]; 7-hydroxy-6-methoxy-2H-1-benzopyran-2-one, (scopoletin, 3) [20]; p-coumaroyloxytremetone (4) [13]; 5-hydroxy-7,4′,3′-trimethoxyflavanone (5); 3,5,4′-trihydroxy-7,8,3′-trimethoxyflavone (6); and 5,4′-dihydroxy-3,7,8,3′-tetramethoxyflavone (ternatin, 7) [21]. All NMR spectra (1D and 2D NMR), and mass spectrometry (Table S1) were consistent with data reported for these known compounds [13,21,[30][31][32][33]. .…”

Five New Limonoids from Peels of Satsuma Orange (Citrus reticulata)

“…The peels of its fruits, called chinpi, have been used as an aromatic stomachic, cold medicine, expectorant, and antitussive [ 1 ]. Limonoids [ 2 , 3 ], flavonoids [ 4 , 5 , 6 , 7 ], tocopherol analogues [ 8 , 9 ] have been isolated from peels of C. reticulata , phenyl glycosides from flower buds [ 10 ], and a limonoid [ 11 ], flavonoids [ 11 ], and a cyclic peptide from its fruits [ 12 ]. Moreover, some bioactivities of constituents from C. reticulata have been reported, such as the suppression of adipogenesis by a limonoid [ 3 ], the inhibitory activity on histamine release from rat peritoneal mast cells [ 4 ], hypotensive activity [ 5 ] and antioxidant activity [ 6 ] of flavonoids, the radical-scavenging activity [ 8 ] and hepatoprotective and neuroprotective activities [ 9 ] of tocopherol analogues, as well as antimicrobial activities of essential oil [ 13 ].…”

Divergent Total Syntheses of Flavonoid Natural Products Isolated from Rosa rugosa and Citrus unshiu

“…In the same year, Shin et al reported the isolation of three previously unreported flavonoids from the peels of mature fruits of Citrus unshiu Marcow (Rutaceae), one of which was named 3,6,7,8,2′,5′-hexamethoxyflavone (4). 12 These peels have been used in traditional Chinese medicine and some isolates from C. unshiu have been reported to exhibit antiproliferative effects. Given the interesting biological profiles of compounds 1-4 (and the diverse array of properties typically associated with flavonoids in general), we were interested in a more extensive assessment of their biological activities.…”

“…Benzaldehyde precursor 11 was prepared from commercially available 4-hydroxybenzaldehyde (10) by MOM protection (Scheme 2). In parallel, the acetophenone building block 13 was accessed from 3,4-dimethoxyphenol (12). Claisen-Schmidt aldol condensation Attention was next turned toward the preparation of the polymethoxyflavone 4 (Scheme 4).…”