Phytochemical investigation of the whole plant of
Andrographis viscosula has led to the isolation of three new 2′-oxygenated flavonoids, (2
R)-5-hydroxy-7,2′,3′-trimethoxyflavanone (1), 7,2′,5′-trimethoxyflavone (2), 5,7,2′,3′-tetramethoxyflavone (3), and eight known flavones, 5,7,2′-trimethoxyflavone (4), 5,7,2′,4′,5′-pentamethoxyflavone (5), echioidinin (6), 5,2′,6′-trihydroxy-7-methoxyflavone (7), 5-hydroxy-7,2′-dimethoxyflavone (8), echioidin (9), echioidinin 5-
O-glucoside (10), and 5,2′,6′-trihydroxy-7-methoxyflavone 2′-
O-glucoside (11). The structures of 1—11 were elucidated by physical and spectral methods, including extensive 2D NMR studies. The presence of 2′-oxygenated flavonoids is apparently restricted to
Andrographis species in Acanthaceae. Therefore, 2′-oxygenated flavonoids are regarded as chemotaxonomic markers of
Andrographis genus in the Acanthaceae family.
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