A Chromatographic Study of the Anthraquinones of Rhamnus alaternus L. III. Extraction, Isolation and Chromatographic Characterization of the Anthraglycosides of the Stem Bark

Abstract

Several anthraglycosides were isolated from the bark of Rhamnus alaternus L. These had the following Rf values when chromatographed on Whatman no. 1 paper in the solvent system n-propanol, ethyl acetate, water (40:30:30 v/v): G1, 0.98; G2, 0.92; G3, -; G4, 0.79; G5, 0.72; G6, 0.65; G7, 0.61. However, in the TLC system chloroform, ethanol-95%, water (60:30:2 v/v) on silica gel G, G5 was found to be a mixture of G5a and G5b, the latter with the lower Rf value; while G7 separated into G7a, G7b and G7c in descending order of their Rf values. G2, highest in yield, is an emodin glucoside; G4 is an alaternin glucoside; G1 occurs in least amount. G1, G5b, and G6 are diglycosides of emodin, each yielding glucose and rhamnose. G6 hydrolyzes into G2 on TLC in the solvent system methanol, ethyl acetate, water (17:100:13 v/v) on silica gel G. G5a yields physcion, glucose and rhamnose. The total yield of G5 is close to but lower than that of G2. G7 may be a mixture of dianthrone glycosides, yielding on total hydrolysis a small amount of emodin, a larger amount of physcion and a still larger amount of alaternin. G3 is an unknown glucoside.