Hetero polysaccharides

Hetero
Polysaccharides
Ahmed M. Metwaly
Ass. Professor,
Faculty of Pharmacy,
Al-Azhar University,
Cairo, Egypt.
PAGE 1

Course
Outline
Introduction
Homosaccharides (holosides)
Heterosaccharides (heterosides)
Polysaccharides in pharmacy
Honey
PAGE 2

▪ Types
▪ Dissimilar monosaccharides
▪ Polyuronides
▪ Mucopolysaccharides
Heteropolysacchrides

Third Skill ConclusionIntroduction Homopolysaccharides
Polysaccharides in pharmacy Honey
Types
A- Dissimilar monosaccharide building units such as
• Cellulosans
• Neutral mucilages
• Guar gum
B- Derived carbohydrates which are monosaccharaides together with their sulphate esters, uronic acids or amino
derivatives such as
• Polyuronides
• Mucopolysaccharides

Dissimilar monosaccharides
• Cellulosans:
These are a type of hemicelluloses, formed of short chain polysaccharides consisting of pentosans e.g. Xylans
or hexosans (Glucans, mannans, or galactans).
They accompany cellulose and lignin in plant cell walls.
• Neutral mucilages:
They consist of polymers of d-mannans and d-galactans (galactomannans) e.g. In foenugreek seeds and
salep tubers

Guar gum
Source: guar gum is obtained from the ground endosperms of the Indian plant
Cyamopsis tetragonolobus, family Leguminosae.
Structure:
Commercial guar gum contains about 80 % of guaran ( a galactomannan) and 5-6 %
of crude protein.
Guaran is a galactomannan
polysaccharide consists of a straight
chain of D-mannose units with a D-
galactose unit attached to every
other mannose unit i.e. regular
repeated units of a trisaccharide with
the following molecular formula:
4-O-(6-O-α-D-galactopyranosyl-β-D-
mannopyranosyl)-β-D-
mannopyranose.
The molecular weight of guaran is
around 220,000.

Uses:
PAGE 7
Guar gum is used as
▪ A binder and disintegrating agent in tablets and as
▪ A thickener in lotions and creams
▪ It lowers the serum cholesterol and glucose in human and therefore,
▪ used in certain antihypercholesterimic and antidiabetic formulations.
▪ It is also used as an appetite depressant.

Polyuronides
• Polyuronides are non-crystalline. They form sticky, slimy or gelatinous solutions in water.
• Those insoluble in water are soluble in dilute alkali.
• They contain one or more uronic acid units in their structures and may include methoxy groups.
• They give positive test for uronic acids using naphtoresorcinol reagent.
• There are three common uronic acids found in nature:
1. glucuronic,
2. galacturonic and
3. mannuronic acids.
β- D- Glucuronic acid D- galacturonic acid Β- D- mannuronic acid

Examples of polyuronides
1. The hemicelluloses,
2. Plant gums,
3. Mucilages and
4. Pectic substances.
PAGE 9

The hemicelluloses
▪ Hemicelluloses are polysaccharides often associated with cellulose with a different compositions. Hemicelluloses
contain many different sugar monomers besides glucose such as
▪ five-carbon sugars xylose and arabinose,
▪ six-carbon sugars mannose and galactose,
▪ six-carbon deoxy sugar rhamnose,
▪ Acidified sugars such as glucuronic acid and galacturonic acid.
PAGE 10
hemicelluloses
Section of a cell wall; hemicellulose in green
Function
Hemicelluloses are embedded in the cell walls of plants,
they bind with pectin to cellulose to form a network of
cross-linked fibers.

Gums
Plant gums are polysaccharides exuded from certain plants as pathological products, e.g.
gum arabic and gum tragacanth.
They are a heterogeneous group of acidic substances, which swell in water to form viscous or
sticky solutions.
Acid hydrolysis of gums gives a complex mixture of uronic acids, generally (D-glucuronic or
galacturonic) acid, together with D-galactose, L- arabinose D-mannose, xylose, L-rhamnose
and L-fucose.

Gum TragacanthGum Arabic
Astragalus gummifer Family Leguminosae.Acacia Senegal Family Leguminosae.Source
Tragacanthin (water-soluble fraction)
Bassorin (water-insoluble fraction)
It consists mainly of a mixture of the calcium,
magnesium and potassium salts of esters of some
sugars (galactose, arabinose, glucuronic acid and
rhamnose) with arabic acid
Structure
D-galactose, L-arabinose, D-xylose and L-
fucose) and uronic acids (mainly
galacturonic acid).
Arabic acid, L-rhamnose, D-galactose, L-arabinose,
glucuronic acid and aldobionic acid (a disaccharide
formed of galactose and glucuronic)
Acid
hydrolysis

Structure of Gum Arabic
PAGE 13
Arabic acid

It swells into gelatinous mass with waterwater-solubleProperties
* I2 solution → blue spots
* benzidine → no color (due to the absence of
oxidase enzymes)
* lead acetate → heavy ppt.
* Basic lead acetate → no ppt.
* I2 solution → no color
* benzidine → blue color (due to the presence of oxidase
enzymes)
* lead acetate → no ppt.
* Basic lead acetate → flocculent ppt.
Chemical
test
* Suspending agent.
* binder in pills and tablets manufacture.
* Emulsifying agent for oils and resins.
* demulcent and emollient.
* In food industry as a stabilizer, emulsifier and thickening
agent in icing, fillings, soft candy, chewing gum
* Used as a binder for watercolor painting because it
dissolves easily in water
Demulcent in various cough, diarrhea and throat
preparations.
Uses

Acidic Mucilages
PAGE 15
• Unlike gums, mucilages are normal products of metabolism formed within the cell (intracellular formation).
Properties
• Mucilages are white amorphous masses.
• They swell in water and form viscous non-adhesive solutions.
• They have variable physical and chemical properties
Classification: Mucilages can be classified into the following groups:
• The neutral mucilages (dissimilar poly saccharides)
• The acidic mucilages, which are polyuronides consisting of D-galacturonic acid with monosaccharides D-
galactose, xylose, arabinose and rhamnose, e.g. mucilages of mustard, plantago and linseed.
• The sea weed mucilages, which are either sulfated polysaccharide esters, characterized by their ability to swell
in water and form gels, e.g. agar and carrageen, or alkali-soluble polysaccharides e.g. algin (sodium alginate).

Agar
O O
CH2OH
O
CH2
O
6
1
4
3
Agarobiose
O
CH2OSO3H
Sulfonated L-galactose unit
Source: Agar is the dried colloidal concentrate of the decoction of various red algae
Structure: Agar is formed of two main components, agarose and agaropectin.
AgaropectinAgarose
- Sulfonated polysaccharide
(in which galactose and galacturonic acid units are partly
esterified with sulfuric acid).
- It gives positive test for sulfate on using barium chloride.
-Galactose polymer,
(consists of alternate residues of D-galactose and 3,6-
anhydro-L-galactose (agarobiose), linked by 1,4
linkages).
- It is free from sulfate.
Responsible for the viscosity of agar solutionsResponsible for the gel strength of agar
Uses: Preparation of bacteriological culture media, as
emulsifier, thickener for ice cream, treatment of ulcers
and chronic constipation.

Algin
Source:
It is the polysaccharide obtained by alkaline
extraction of various species of brown algae.
Structure:
Its (sodium alginate) is the (Na salt of alginic
acid)
Alginic acid composed of D-mannuronic acid
units linked through β-1,4 linkages, in addition
to a small number of L-guluronic acid (oxidation
product of glucose) units.
O O
COOH
O
COOH
O
O
COOH
1
4
4
1
n
Repeating units of mannuronic acid
O
C
H
OH
OOH
L-guluronic acid
Uses:
• It is used as a stabilizer, thickener, emulsifier, deflocculating, jelling
and slimming agent.
• It is used in dentistry, food and cosmetic industries.
• It has important pharmaceutical applications in formulation of
creams, ointments, pastes, jellies and tablets

Pectic substances
Pectic substances are colloidal polyuronides of high molecular
weight.
■ They are mostly isolated from fruits as lemon and orange pulps
and their structures are changed during ripening.
Structure
Pectins consist of three components:
1- Galacturonans: (α-1,4 D-galacturonic acid residues
esterified with methanol.
The polymer chains are interrupted by rhamnose.
2- Arabinans: (α-1, 5-linked L-arabinofuranose units).
3- Galactans: (β-1, 4-linked D-galactopyranose units).
OO
O
COOCH3
O
COOCH3
O O
O
COOH
1
4
1
Galacturonan residue
4

Types of pectic substances
Pectic acidPectinic acidPectinProtopectin
- Completely de-esterified
pectin, found in over-ripe
fruits.
- Free from methyl esters.
- Partially de-esterified
pectin.
- Contains ~ 7%
methyl ester
Produced from protopectin
during ripening of the fruits.
- Contains 10-12 % methyl
ester
Precursor of pectin, found
in the unripe fruits.
- Soluble in water.
- Precipitated by calcium
ions.
- Soluble in water.
- Forms gel with calcium
ions
- Does not form gel with
sucrose
- Soluble in water.
- Precipitated by alcohol or
metal ions, e.g. iron or lead but
not calcium.
- Acidic solution forms a gel in
presence of sucrose
- Insoluble in water.
- Transformed to pectin by
heating with water or
acid.

Effect of pectic enzyme
Protopectin
Pectin
Pectic acid
protopectinase
Soluble pectin
pectinase
Galacturonic acid
(Deesterification and hydrolysis)
Pectin Pectic or pectinic acid
pectase enzyme
(Partial or complete deesterification)
pectinase
Galacturonic acid
Uses
Pectin is topically applied as a paste in cases of burns and ulcers.
In treatment of diarrhea and dysentery.
It is used as a gel and emulsion stabilizer and in manufacture of jellies
and jams.

Mucopolysaccharides
Mucopolysaccharides are polysaccharides which on hydrolysis yields amino sugar units.
Amino sugars are derived from monosaccharaides by replacement of a hydroxyl group by an amino group.
They differ from glycosylamines.
Glycosamines:
Anomeric hydrogens are replaced by nitrogen.
Nucleoside has ribose and 2-deoxyribosebonded to a nitrogenous ring system
Amino sugar:
Amino sugars have one of non-anomeric hydroxyls replaced by nitrogen.
Examples:
β-D-glucosamine is found in chitin.
NAG & NAM is found in bacterial cell walls.

Supplies the body with
glucosamine, the necessary building
block for the cartilage and for the
maintenance of the synovial fluid in
the joints that keeps them healthy
and moving comfortably

Chitin
• Exoskeletons of crustaceans, insects and spiders, and cell walls of fungi
• Similar to cellulose, but instead of glucose N-acetyl glucosamine (C-2 are N-acetyl instead of –OH)
• β-(1-4) linked N-acetylglucosamine units
• Cellulose strands are parallel while chitins can be parallel or antiparallel

Heparin & Heparin sulphate
▪ Heparin is the powerful blood anticoagulant.
▪ It can be isolated from the mast cells of liver, heart and lung.
▪ Heparin is a highly sulfated, linear polysaccharide formed of repeated 1, 4 linked uronic (iduronic
or glucuronic) acids and glucosamine residues.
▪ Heparan sulfate is an analogue structurally related to heparin.
▪ It is found in extracellular matrix and in cell membranes while heparin is only intracellular.
▪ They have different ratios of n-acetylation to o-sulfation.
PAGE 25
Heparin

Hyaluronic acid
▪ Material used to cement the cells into a tissue
Structure:
Glucouronic acid and N-acetyl glucosamine.
Uses:
▪ Hyaluronic acid has been FDA-approved to treat
osteoarthritis of the knee via intra-articular injection
▪ Locally for Dry, scaly skin
▪ As artificial tears to treat dry eye
PAGE 26

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