The leaves of Aloe arborescens var. Miller (Asphodelaceae) contain a mucilage (aloegel), which is typical for other members of the genus Aloe. The mucilage possesses various pharmacological activities, such as antiphlogistic and antiedematic effects as well as a treatment for burns including those caused by X-rays1,2, and is used mainly in cosmetics as a humectant and against sunburn3. The most important component of the aloegel is a polysaccharide that consists of a neutral glucomannan together with smaller proportions of acidic polysaccharides4T5.
There are contradictory data on the structure of the water-soluble polysaccharides of A. arborescens. Yagi ef a1.6 found a partially acetylated mannan (mol. wt. 15 000) and reported later7 an additional mannan (mol. wt. 40 000) with an acetyl content of lo%, a (1+6)-a-glucan, and a branched arabinogalactan. Kodym ef al.* reported mannose, glucose, arabinose, and galactose to be the constituents of a neutral polysaccharide, whereas other authors isolated mainly acidic, pectin-like polysaccharidesgJO.
We now report on the isolation and structures of a neutral glucomannan and an acidic arabinogalactan from the fresh leaf material of A. arborescens.
Powdered dry leaves of A. arborescens were extracted with hot ethanol, dried, and then extracted with phosphate buffer (pH 7.0) to give the crude watersoluble polysaccharides (0.10%). This polysaccharide fraction contained protein (0.8%) and uranic acid (2%), and had i.r. bands for ester groups at 1740 and 1250 cm-*.
Hydrolysis of the polysaccharide gave mannose, glucose, arabinose, and galactose in the molar ratios 60:17:11:11 (g.1.c. of the alditol acetates), and glucuronic acid (identified by t.1.c.). The total hexose content of the crude polysaccharide fraction was 40% and it was resistant to alpha-amylase, thus proving the absence of starch.
Fractionation of the crude polysaccharide on DEAE-Sephacel gave neutral and acidic fractions. The acidic fraction (10.6%), eluted with 0.4M phosphate buffer, was composed of arabinose, galactose, rhamnose, and glucose (molar ratios