A glucoside is a glycoside that is chemically derived from glucose. Glucosides are common in plants, but rare in animals. Glucose is produced when a glucoside is Hydrolysis by purely chemical means, or decomposed by fermentation or .
The name was originally given to plant products of this nature, in which the other part of the molecule was, in the greater number of cases, an aromatic aldehydic or natural phenol compound (exceptions are sinigrin and Jalapin or Scammonin I). It has now been extended to include synthetic , such as those obtained by acting on ethanol glucose solutions with hydrochloric acid, and also the polysaccharoses, e.g. cane sugar, which appear to be ethers also. Although glucose is the most common sugar present in glucosides, many are known which yield rhamnose or iso-dulcite; these may be termed pentosides. Much attention has been given to the non-sugar parts (aglycone) of the molecules; the constitutions of many have been determined, and the compounds synthesized; and in some cases the preparation of the synthetic glucoside effected.
The simplest glucosides are the alkyl ethers which have been obtained by reacting hydrochloric acid on alcoholic glucose solutions. A better method of preparation is to dissolve solid anhydrous glucose in methanol containing hydrochloric acid. A mixture of alpha- and beta-methylglucoside results.
The classification of glucosides is a matter of some intricacy. One method based on the chemical constitution of the non-glucose part of the molecules has been proposed that posits four groups: (1) alkyl derivatives, (2) benzene derivatives, (3) styrolene derivatives, and (4) anthracene derivatives. A group may also be constructed to include the cyanogenic glucosides, i.e. those containing prussic acid. Alternate classifications follow a botanical classification, which has several advantages; in particular, plants of allied genus contain similar compounds. This article follows the chemical classification and discusses only the more important compounds.
Ethylene derivatives
These are generally mustard oils, which are characterized by a burning taste; their principal occurrence is in
Mustard seed and
Tropaeolum seeds.
Sinigrin, or the
potassium salt of
inyronic acid not only occurs in mustard seed,
but also in
black pepper and in
horseradish root. Hydrolysis with
barium hydroxide, or decomposition by the ferment
myrosin, gives glucose, allyl mustard oil and potassium hydroxide.
Sinalbin occurs in white pepper; it decomposes to the mustard oil, glucose and
sinapin, a compound of
choline and
sinapic acid.
Jalapin or
Scammonin I occurs in
scammony; it hydrolyses to glucose and
jalapinolic acid.
Benzene derivatives
These are generally oxy and oxyaldehydic compounds.
- Benzoic acid derivatives
The benzoyl derivative
cellotropin has been used for
tuberculosis.
Populin, which occurs in the leaves and bark of
Populus tremula, is benzoyl salicin. Benzoyl-beta-D-glucoside is a compound found in the fern
Pteris ensiformis.
- Phenol derivatives
There are a number of glucosides found in
and
, as, for example, in the
chemical family.
Arbutin, which occurs in
bearberry along with
methyl arbutin, hydrolyses to
hydroquinone and
glucose. Pharmacologically it acts as a urinary
antiseptic and
diuretic;
Salicin, also termed
Saligenin and glucose occurs in the
willow. The enzymes
ptyalin and
emulsin convert it into glucose and saligenin, ortho-oxybenzylalcohol. Oxidation gives the aldehyde
helicin.
Styrene derivatives
This group contains a benzene and also an
ethylene group, being derived from
styrene.
Coniferin (C
16H
22O
8) occurs in the cambium of
conifer wood.
Emulsin converts it into glucose and coniferyl alcohol.
Oxidation of coniferin gives
glucovanillin, which yields upon treatment with emulsin glucose and
vanillin.
Syringin, which occurs in the bark of
Syringa vulgaris, is a
methoxyconiferin.
Phloridzin occurs in the root-bark of various
fruit trees; it hydrolyses to glucose and phloretin, which is the phloroglucin
ester of paraoxyhydratropic acid. It is related to the
pentosides naringin (C
27H
32O
14), which hydrolyzes to
rhamnose and
naringenin, the
phloroglucin ester of
p-Coumaric acid, and
hesperidin, which hydrolyzes to rhamnose and
hesperetin, the phloroglucin ester of
isoferulic acid (C
10H
10O
4).
-
Aesculin (C21H24O13), occurring in horse-chestnut and California buckeye,
-
Fraxin, occurring in Fraxinus excelsior, hydrolyzes to glucose and fraxetin (also known as 7,8-dihydroxy-6-methoxycoumarin)
-
Flavone or benzo-7-pyrone derivatives are numerous; in many cases they (or the non-sugar part of the molecule) are vegetable dyes.
-
Rhamnetin, a splitting product of the glucosides of Rhamnus, is monomethyl quercetin; fisetin, from Rhus cotinus, is monoxyquercetin; chrysin is phenyl-dihydroxybenzopyrone.
-
Saponarin, a glucoside found in Saponaria officinalis, is a related compound.
-
Strophanthin is the name given to two different compounds, ouabain (ouabain) obtained from Strophanthus gratus and k-strophanthin from Stroph. kombé.
Anthracene derivatives
These are generally substituted anthraquinones; many have medicinal applications, being used as purgatives, while one, ruberythric acid, yields the valuable dyestuff madder, the base of which is alizarin. Chrysophanic acid, a dioxymethylanthraquinone, occurs in rhubarb, which also contains
emodin, a trioxymethylanthraquinone; this substance occurs in combination with rhamnose in
Frangula bark.
Arguably the most important cyanogenic glucoside is amygdalin, which occurs in bitter almonds. The enzyme maltase decomposes it into glucose and mandelic nitrile glucoside; the latter is broken down by emulsin into glucose, benzaldehyde and prussic acid. Emulsin also decomposes amygdalin directly into these compounds without the intermediate formation of mandelic nitrile glucoside.
Several other glucosides of this nature have been isolated. The are a group of substances characterized by forming a lather with water; they occur in soap-bark. Mention may also be made of indican, the glucoside of the Indigo bush plant; this is hydrolysed by the Indigo bush ferment, indimulsiri, to indoxyl and indiglucin.
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