Definition: Glycosides are non-reducing organic compounds that yield on hydrolysis with acids, alkalis or enzymes: 1- A sugar (or glycone, formed of one or more sugar units). 2- A non-sugar moiety (also called aglycone or genin). Glycosides are widely distributed in nature. They usually accompanied with enzymes used in either their synthesis or hydrolysis.
Solubility: Glycosides are water soluble compounds and insoluble in the organic solvents. Glycone part: water soluble, insoluble in the organic solvents. Aglycone part: water insoluble, soluble in the organic solvents. Some glycosides soluble in alcohol.
Colorless, solid, amorphous, nonvolatile (flavonoid- yellow, anthraquinone-red or orange). Give positive reaction with Molisch's and Fehling's solution test (after hydrolysis). They are water soluble compounds, insoluble in organic solvents.
Converting toxic materials to non or less toxic. Transfer water insoluble substances by using monosaccharide. Source of energy (sugar reservoir). Storing harmful products such as phenol. Regulation for certain functions(growth). Some have beautiful colours(pollenation process).
Some glycosides have antibacterial activity, so they protect the plants from bacteria and diseases. Bitter almond Amygdalin bacteria HCN hydrolysis kill Eomlsin enzyme
O-glycosides : in these glycosides the sugar part is linked with alcoholic or phenolic hydroxyl or carboxyl group. S-glycosides : in these glycosides the sugar attached to a Sulfur atom of aglycone such as in sinigrin. N-glycosides : in these glycosides the sugar linked with Nitrogen atom of (-NH 2,-NH- )amino group of aglycone like in nucleosides DNA,RNA C-glycosides : in these glycosides the sugar linked (condensed) directly to Carbon atom of aglycone like in aloin.
Anthracene glycosides are oxygenated derivatives of pharmacological importance that are used as laxatives or cathartics, anti-inflammatory, antibacterial, antifungal and also as natural dyes.
Forms of Anthracene derivatives in Plants: Aglycones:
Anthraquinone glycosides: They are pharmacologically active constituents of several laxatives and purgatives of plant origin e.g. Senna, Aloe, Cascara, Frangula, Rhubarb.
For Aglycones: Extract plant material with organic solvent. Shake with NH 4 OH OR KOH. For O-Glycosides: Boil plant material with dil. HCl for 10 min, filter and shake with organic solvent (Ether or Benzene). Separate the organic solvent. Shake with NH 4 OH OR KOH. For C-Glycosides: Boil plant material with dil. HCl/FeCl 3, filter and shake with organic solvent (Ether or Benzene). Separate the organic solvent. Shake with NH 4 OH OR KOH. Positive result indicated by Rose Red colour in the aqueous alkaline layer.
They produce phenolic aglycone when subjected to hydrolytic processes. The phenolic aglycone may be: Examples -Bearberry
3. Flavonol Glycosides Large group of glycosides which widely distributed in the plants kingdom and in all plants parts (leaves, roots, rhizomes, fruits peels) Various colors in flowers( yellow, orange, red, purple.) They are benzo-pyrone derivatives. Their chemical structure based on (C 6 C 3 C 6 ). Examples :-Silymarin,Gingko,Buck wheat etc. The general uses of Flavonoids and Flavonoid glycosides. 1.Increase elasticity of blood vessels specially Rutin and hesperidin which known as vitamin (p) 2.Anti inflammatory activity like Taxifolin
4. Isothiocyanate group of glycoside ( sulfur glycoside or thio glycoside ) 1. Group of glycosides which contains sulfur (S- glycoside) 2. They are also known as glucosinolate compounds. 2. Present in many cruciferous plants, on hydrolysis. 3. They produce isothiocynate (SCN) aglycone Such as : 1.sinigrin which founded in Black Mustard seeds 2.sinalbin which founded Brassica alba --- White Mustard seeds.
5. Cyanogenic glycosides It is widely distributed between the members of Rosaceae family. They gave HCN (Hydrocyanic acid) with hydrolysis. They derived from nitrile of mandelic acid. They are also known as cyanophore glycosides. About 110 family are reported to have cyanogenic glycosides. CHEMICAL TEST: it is based on liberation of HCN due to its sodium picrate (Yellow) changes to sodium purpurate (brick red). Examples :- a. Bitter almond seeds. b. Wild cheery Bark. c. Plums seeds. d. Peaches seeds
These drugs are used in medicine as mainly to increase the tone and contractility of the cardiac muscle. Also as diuretic due to the increased renal circulation. Thet are present in leaves of Digitalis, seeds of Strophanthus and the bulb of Squill.
Attachment of unsaturated lactone ring at C17. the lactone ring is present either as a 5- membered ring (Cardinolides) e.g. lannatosides in Digitalis or as 6- membered ring (bufadienolides) e.g. Scillarin in Squill. Deoxy sugar, e.g. digitoxose.
Several chemical tests could be used for identification of cardiac glycosides Colour reactions due to aglycone moiety: A- Reactions due to (-CH 2 -) group of the lactone ring: These are characteristic for the 5-mambered lactone ring of cardenolides: 1- Kedde's test: card. + Kedde's reagent (3,5- dinitrobenzoic acid + NaOH violet colour. 2- Baljet's test: card. +Baljet's reagent (picric acid +NaOH) orange or red.
B- Reactions due to the steroidal nucleus: Liebermann's test: card. in glacial acetic acid + H 2 SO 4 red, violet, blue to green. Reactions due to the presence of 2-deoxy sugar unit in the sugar moiety: Keller-Killiani's test: card. in glacial acetic acid containing traces of FeCl 3, conc. H 2 SO 4 on the wall of the test tube blue ring is formed in between the two layers.
This group of glycosides is characterized by the following: 1. it foams in aqueous solution forming froth. 2. It causes haemolysis of red blood cells. 3. Drugs containing saponins are usually sternutatory and irritating the mucous membrane of the eyes and the nose. 4. They are highly toxic when injected into blood stream. 5. They are used in cleaning industrial equipments and fabrics, also as a powerful emulsifier of certain resins, fats and fixed oils. Examples- saponins of Quillaia bark
Soluble in water, alcohol and mixture of them. Form persistent froth with water. Used as detergent and emulsifying agents. Aglycones are called Sapogenin. Cause haemolysis of RBCs if reach the blood. Form complex with cholesterol. Only small part absorbed when taken orally. Enhace the absorption of other drugs.
According to the nature of the aglycone saponins are classified into Steroidal and Triterpenoidal saponins.
They are C-27 with 5 methyl groups. Less distributed in nature comparing to Triterpenoidal saponins. Used mainly as precursors for the partial synthesis of sex hormones and corticosteroids. Drugs containing Steroidal saponins such as: Discoria species Diosgenin Sarsaparilla Roots Sarsapogenin
They are C-30 compounds. Much more distributed in nature. Have pentacyclic skeleton with 8 methyl groups.
Coumarin is either present in free state or glycosidal form. Coumarins are the derivative of benzo- pyrone. They are present in leguminosae, solanaceae, rubiaceae, umbelliferaceae. Furanocoumarins are formed by fusion of furan ring to coumarin at either 6 and 7 position or 7 and 8 position.
9. Aldehyde glycosides: -Vanilla 10. Steriodal glycosides-Solanum khasianum 11. Glycosides bitters or miscallenous glycosides- They helps to improve apetite and they are taken before meal. They are having bitter taste. They have the stimulant effects on gustatory nerve in the mouth and lead to increase in gastric juice secration. Examples-genetian, chirata,quassia,kalmegh etc.