Nature of the Phenol-Carbohydrate Derivatives

The more complex groups of phenols found in combination with carbohydrates in plants are summarized in formulas (1) to (13). In addition, there are also simple mono-, di-, and tri-hydric phenols existing as glycosides some of these phenols possess additional functional groups, such as methoxyl, primary hydroxyl, and aldehyde groups. Hydroxybenzoic acids and some of their aliphatic esters, and hydroxycinnamic acids, are found as glycosides, and the acids themselves may also be esterified with mono- or oligo-saccharides. 

The general nature of the phenols and of the linkages between these compounds and the carbohydrates have been discussed. The carbohydrates consist of pentoses, hexoses, 6-deoxyhexoses, hexuronic acids, disaccharides, and linear and branched trisaccharides. It is most probable that even more complicated carbohydrate structures will be revealed by future work. Harborne, for instance, has pointed out that, for just one group of phenols, the anthocyanins, only about one thousand species of plants have been examined, and in only a fifth of these have the sugar components yet been identified. 

The simplest phenolic n-glucoside is arbutin (p-hydroxyphenyl /3-d-glucopyranoside), which occurs in a number of plant species, including the pear Pyrus communis. Arbutin is usually accompanied in plant tissues by methylarbutin (p-methoxyphenyl S-D-glucopyranoside)Salix and Populus spp. contain the D-glucoside salicin, o-(hydroxymethyl)-phenyl /S-D-glucopyranoside, and certain species of poplar contain also a 

While considering glycosides of phenolic acids, it should be noted that the phenolic amino acid, -(3,4-dihydroxyphenyl)-L-alanine, which occurs free in high concentrations in Vida faba (broad bean), is also present as the 3-0-/3-D-glucopyranosyl derivative in the seed testas of this plant. It would be interesting to know whether n-tyrosine also exists combined with D-glucose. 

D-Glucosides of several hydroxyanthraquinones have been reported. For example, Schunk and Marchlewski isolated rubiadin D-glucoside from madder root. This compound was later synthesized by Jones and Robertson and shown to be 3-(/3-D-glucopyranosyloxy)-l-hydroxy-2-methyl-anthraquinone. 

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