Chemical and chemotaxonomical studies of ferns. LXXIII. New flavonoids with modified B-ring from the genus Pseudophegopteris(Thelypteridaceae)

Chemical studies of three representatives of the genus Pseudophegopteris (Thelypteridaceae) revealed that the genus is characterized by the occurrence of unusual flavonoids with a modified B-ring related to protogenkwanin (VII). From P. hirtirachis HOLTT., three novel compounds, protogenkwanone (I), tetrahydroprotogenkwanone (II) and tetrahydroprotogenkwanin (III), were isolated, along with protogenkwanin 4'-O-β-D-glucoside (VI). From P. subaurita CHING, two new acylated glucosides of protogenkwanin, protogenkwanin 4'-O- (2-O-acetyl) -β-D-glucoside (IV) and 4'-O- (6-O-acetyl) -β-D-glucoside (V), were obtained, together with I, II and VI. From P. bukoensis HOLTT., IV, V and VI were isolated, in addition to apigenin 7-O-α-L-rhamnoside and kaempferol. The structures of the new compounds were determined by means of spectroscopic methods and chemical transformations.