GLYCOSIDES DEFINITION:
These are organic compounds from plants and animal origin which an enzymatic or acidic hydrolysis fives one or more sugar moiety (glycone) along with non sugar moieties (aglycone). Aglycone moiety may be of different chemical entities like triterpenoidal, steroidal, thiocyanate etc.

• Chemically most of them are sugar ethers or acetates.

• They are formed by the interaction of OH group of aglycone and OH group of sugar with the loss of water molecule.
R-OH + X-OH ' R-O-X + H2o.
Sugar aglycone sugar ether (O-glycoside)

• Sugar moieties present may be single sugar moiety or more than one but more common is up to 4 mostly present sugars is β-D glucose.
e.g. for Diglycoside galactose, Triglycoside digitoxose and Tetra glycoside cardiac glycoside.

• Similar sugar moieties are attached at one position on aglycone molecule. that is in case of cardiac glycoside. Sugar moiety will attack at third position.

• Different sugar moieties are attached at different position on aglycone e.g. Flavonoids.

• It may be of same linkage or different linkage e.g. cascarosides have both O and C linkage.

• For the theoretical aspects both alpha and beta glycosides are considered but most of the plant contain beta glycoside (because of the presence of beta-glycosidase enzyme) but K-Strophanthidin from strophanthus is an exception because it contain alpha glycoside.

• The activity of glycoside is due to the aglycone moiety.

• The activity of glycoside increases with the increase in the sugar moiety because sugar helps in solubilisation of aglycone, absorption and distribution of aglycone in the body.

• Sugars are of different nature most common are glucose (hexose's) sometime pentoses as well as rhamnose and arabinose are also found.

• Cardiac glycoside contain deoxy sugars e.g. digitoxose.

• A molecule with maximum number of aglycone moiety is called primary glycoside. These are more active than secondary and tertiary glycoside. But are not stable. So we will isolate only secondary glycosides which are more stable.

• Primary glycosides on hydrolysis yields secondary (gives two sugar moiety) which on further hydrolysis gives tertiary glycosides.

• Sometimes uronic acid is also found in Glycyrrhizin even though it is classified under glycosides.

• Names of glycosides ends with osides or in, as in sennoside, cascaroside or digitoxin, glycyrrhizin, aloin,prenusside.

• In plants they are present in glucoside form but during srorage and drying if moisture is present. Then it activates enzyme and glycoside undergo hydrolysis to give aglycone and glycone. So care should be taken during these process.

• But in case of steroidal glycoside we are interested in aglycone moiety i.e, steroidal molecule.

• Glycosides are crystalline or amorphous substances which are soluble in water and dilute alcohol except resin glycosides but insoluble organic solvents.

• Aglycone moiety is soluble in organic solvent like ether benzene etc.

• Glycosides are hydrolyzed by enzymes water and mineral acids.

• They are optically active many of them are levorotary.

• They participate in growth regulation and protection of plant.

• Their chemical characteristic, properties depends on the aglycone moieties which are of different chemical entity.

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