Separation and identification of three epimeric pairs of new C-glucosyl anthrones from Rumex dentatus by on-line high performance liquid chromatography-circular dichroism analysis.
Six C-glucosyl anthrones were characterized as three pairs of epimers by on-line high performance liquid chromatography-circular dichroism (HPLC-CD) analysis and isolated from the roots of Rumex dentatus by column chromatography. Their structures were elucidated by mass spectrometry, nuclear magnetic spectroscopy and HPLC-CD analysis. They are 10R-C-beta-D-glucosyl-10-hydroxyemodin-9-anthrone (rumejaposide E, 1) and 10S-C-beta-D-glucosyl-10-hydroxyemodin-9-anthrone (rumejaposide F, 2), 10R-C-beta-D-glucosylemodin-9-anthrone (rumejaposide G, 3) and 10S-C-beta-D-glucosylemodin-9-anthrone (rumejaposide H, 4), 10S-C-beta-D-glucosyl-10-hydroxychrysophanol-9-anthrone (cassialoin, 5) and 10R-C-beta-D-glucosyl-10-hydroxychrysophanol-9-anthrone (rumejaposide I, 6). Rumejaposides F-I (2-4 and 6) were new C-glucosyl anthrones. Rumejaposide E (1) and cassialoin (5) were isolated for the first time in Rumex plants. On-line HPLC-UV-CD analysis was a useful tool for structure elucidating epimeric C-glycosides anthrones 3-6 because of the poor stability of the pure isomers (3 and 4) and the minute quantity of 5 and 6 in the mixture.