Sugar and Fat and All of That - Natural Products Chemistry: Sources, Separations, and Structures - page 49

FIGURE 5.8 Flowers of Echinacea purpurea , used in traditional medicine for its immune
boosting properties, believed to be due in part to the presence of polysaccharides. (Courtesy
of Steven Foster.)
5.9 A NOTE ON THE SEPARATION OF SUGARS
Due to the large number of possible isomers and, in general, the lack of any chro-
mophore, it is difficult to separate and isolate the simple sugars. The separation of
polysaccharides is even more challenging. Furthermore, almost all sugars are sensi-
tive to temperature, which not only influences their physical properties but also their
chemical stability. It may be fair to say that the isolation and structure determination
of sugars continues to be a major challenge, yet to be overcome in natural prod-
ucts chemistry.
The isolation of polysaccharide mixtures from mushrooms can be represented
by the example shown below. After the first step to obtain the crude extract, further
purification is achieved by the use of gel chromatography. The use of electrochemi-
cal detectors (ECDs) in place of UV detectors enhances the detection of eluting
polysaccharides in the purification steps. Also, size exclusion gel chromatography
can be used to separate polysaccharide fractions with aqueous solvents as eluent.