Two properties of drug aloes, the bitter leaf exudate from a small number of Aloe species, are of interest to pharmacologists. Firstly, they wish to authenticate the plant origin of the material and secondly, they wish to measure the degree of purgation to be expected. The chief purgative compound in the leaf exudate, bitter aloes, is the anthrone C-glucoside, barbaloin, although O-glycosides and dianthrones, which are not present in all samples, are also active. There are various chemical methods used to detect and quantify barbaloin but these are not sufficiently accurate and reproducible because of the presence of interfering substances. To improve precision chromato-graphic separation techniques were developed to isolate the active compounds previous to chemical detection and determination. Thin-layer chromatography was convenient and economical but high performance liquid chromatography proved the most precise for a definitive analysis.
Interest in Aloe exudate compounds spread from the few drug species to the c. 400 species now described from Africa and Arabia. Many compounds have now been identified and others recognized chromatographically only and it is speculated that in view of the many folk remedies of aloes reported, some of them may have biological activities relevant to human medicine. In addition, the distribution of these compounds among the species determined by the analytical techniques described here provides clues as to aloe chemotaxonomy.
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