Carbohydrate Chemistry

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Carbohydrate
Chemistry
Ashok Katta
Dept. Of Biochemistry,
DS Medical College, Perambalur

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Ashok KattaCarbohydrate Chemistry
Introduction
The word carbohydrates is derived from their general formula
[C(H2O)]n that makes them seem to be “hydrates of carbon.”
The terms carbohydrate and saccharide are closely related.
The most abundant carbohydrates are polysaccharides.
Most important carbohydrate in the body - Glucose.
“Saccharide” comes from the word for table sugar in several languages: sarkara in Sanskrit,
sakcharon in Greek, saccharum in Latin.

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Importance of Carbohydrates
Distributed widely in nature
Key intermediates of metabolism (sugars)
Structural components of plants (cellulose)
Central to materials of industrial products: paper, fibers
Key component of food sources: sugars, flour, vegetable
fiber

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Definition
Carbohydrates may be defined as polyhydroxy
aldehyde or polyhydroxy ketone or compound that yield
these derivatives on hydrolysis.
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
D - Glucose
CH2OH
C
CH2OH
=O
CHO H
CH OH
CH OH
D - Fructose

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Glycogen
α-Amylase
D - Glucose

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Some Additional Terms
Aldose A carbohydrate that contains an aldehyde group
Ketose
Triose
Tetrose
Aldopentose
Ketohexose
A carbohydrate that contains a ketone group
A carbohydrate having three carbons
A carbohydrate having four carbons
A five-carbon carbohydrate that contains aldehyde group
A six-carbon carbohydrate that contains a ketone group

Monosaccharide
Oligosaccharide
Polysaccharide
Classification and Nomenclature
Carbohydrates are broadly classified in to three groups….
C
A
R
B
O
H
Y
D
R
A
T
E
S

Classification and Nomenclature
Carbohydrates
Monosaccharide
Functional
group
Number of
carbon
atoms
Oligosaccharide
Di-
saccharide
Tri-
saccharide
Tetra-
saccharide
Polysaccharide
Homopoly-
saccharide
Hetropoly-
saccharide
Aldoses
e.g Glucose
Trioses
Ketoses
e.g Fructose
Tetroses
Pentoses
Hexoses
Heptoses
Maltose
Lactose
Sucrose
Raffinose Stachyose
Starch
Dextrin
Glycogen
Cellulose
Inulin
Hyaluronic
acid
Heparin
Chondroitin
sulfate
Dermatan
Sulfate
Keratan
Sulfate

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Monosaccharides
One
Sugar

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Monosccharides are sub divide into different groups.
Depending upon the functional……
Aldoses (CHO) or
Ketoses (C=O)
Depending upon the number of carbon atoms they
possess,
Trioses (3C)
Tetroses (4C)
Pentoses (5C)
Hexoses (6C) and
Heptoses (7C)

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Classification of Monosaccharides
No. of
Carbon
Type of
sugar
Aldoses Ketoses
3 TRIOSES Glyceraldehydes Dihydroxyacetone
4 TETROSES Erythrose Erythrulose
5 PENTOSES Ribose, Xylose
Ribulose,
xylulose
6 HEXOSES
Glucose,
Galactose
Fructose
7 HEPTOSES Glucoheptose Sedoheptulose

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TYPES EXAMPLE IMPORTANCE
Trioses
Glyceraldehyde,
Dihydroxyacetone
Intermediates of glycolysis,
Precursor of glycerol (for lipid synth)
Tetroses D-Erythrose
Intermediates of carbohydrate
metabolism
Pentoses D-Ribose
Structural element of nucleic acid,
RNA, co-enzymes.
Hexoses
D-Glucose Main sugar of the body.
D-Fructose
Converted to glucose & utilized by the
body.
D-Galactose
Synthesized in mammary gland to make
the lactose of milk.
D-Mannose Constituent of glycoprotein, glycolipids

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Oligosaccharides
Contains 2 to 10 monosaccharide units.
Joined together by a specific bonds called glycosidic
bond.
On hydrolysis, they gives 2 to 10 molecules of simple
sugar units.
They are subdivide based on the number of
monosaccharide units.
Disaccharides
Trisaccharide
Tetrasaccharide
Pentasaccharide

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Classification of Oligosaccharides
No
“C”
Examples Type of monosaccharide
Disaccharides 2
Maltose Glucose + Glucose
Lactose Glucose + Galactose
Sucrose Glucose + Fructose
Trisaccharides 3 Raffinose Glu + Fruc + Galactose
Tetra
saccharides
4 Stachyose
2 Galactose + Glucose +
Fructose
Penta
saccharides
5 Verbascose
3 Galactose + Glucose +
Fructose

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Polysaccharides

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Polysaccharides
Contains many (more than 10) sugar units.
They have high molecular weight and are sparingly
soluble in cold water.
They are also called as Glycans.
They may be either liner or branched in structure.
They are not sweetish and do not exhibit any of the
properties of aldehyde or ketone group.

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POLYSACCHARIDES
Homopolysaccharides
Starch
Glycogen
Dextrins
Hetropolysaccharides
Agar
Pectins
Glycosaccharide

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Structural functional relationship
of
Monosaccharide
STRUCTURE OF MONOSACCHRIDES
PHYSICAL PROPERTIES
CHEMICAL PROPERTIES
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH

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Structure of Monosaccharide
Glucose is the most important
physiological and biomedical
monosaccharide.
It can be represented in…
The straight chain structure
Ring /cyclic structure
Boat and chair form.

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The straight chain structure
C
C
H2OH
=O
H
H OH
CHO H
CH OH
CH OH
C

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Ring /cyclic structure
(Haworth projection)
C
R
=OH
+ R’HO C
R
OHH
OR’
Aldehyde Alcohol Hemiacetal
C
R
=O
R”
+ R’HO C
R
OHOR’
R’’
Ketone Alcohol Hemiketal

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Haworth projection formula of glucose
O
C
O
CH2OH
OH
OH
OH
OH
C
C
CH2OH
OHH
H OH
CHO H
CH OH
CH
O
Pyranose
α-D-Glucoyranose
(Fisher structure)
α-D-Glucoyranose
(Hworth structure)
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
D - Glucose

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Haworth projection formula of fructose
OCH2OH CH2OH
OH
OH
OH
OC C
CH2OH
C
CH2OH
H
OH
CHO H
CH OH
CH
O
CH2OH
C
CH2OH
=O
CHO H
CH OH
CH OH
D - Fructose
Furanose
α-D-Fructofuranose
(Fisher structure)
α- D-Fructofuranose
(Hworth structure)

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Chair and boat from of D- glucose
O
CH2OH
OH
OH
OH
OH

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Properties
of
Monosaccharides
Isomerism
Chemical reactions

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Isomerism
The compounds possessing same molecular formula
and different structures are referred as Isomers.
The phenomenon of existence of isomer is called
Isomerism.
Structural Isomerism
Stereoisomerism

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Structural Isomerism
same molecular formulae but differ in their
structures.
Aldose-Ketose Isomerism
Glucose and fructose isomers of each other.
They are having same molecular formula C6H12O6
But differ in their structural formula.

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Aldose-Ketose Isomerism
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
D - Glucose
CH2OH
C
CH2OH
=O
CHO H
CH OH
CH OH
D - Fructose
C6H12O6

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Stereoisomerism
same molecular formula, structures but differ in their
configuration.
Asymmetric (Chirl) carbon allow the formation of
stereoisomerism.
Types of stereoisomerism of glucose are……
D and L isomerism
Optical isomerism
Epimerism
Anomerism

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L - Glyceraldehyde
C
C
CH2OH
=OH
H OH
C
C
CH2OH
=OH
HO H
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
C
C
CH2OH
=OH
HO H
CH OH
CHO H
CHO H
D and L isomerism (enantiomer)
D - Glucose L - Glucose
D - Glyceraldehyde

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D and L isomerism (enantiomer)
D and L isomers are mirror images of each other.
These two forms are called Enantiomers.

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Optical isomerism
Optical activity is the capacity of a substance to
rotate the plane polarized light passing through it.
When light rotate to right (clockwise) direction, that
substance is said to be dextrorotatory (d) (+).
When light rotate to left (anticlockwise) direction,
that substance is said to be levorotatory (l) (-).
When equal amount of d and l isomers are present, that
mixture is said to be recemic / dl mixture.

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Epimerism
Epimers are sugars which are differ with each other
with respect to single carbon, other than anomeric
carbon.
Galactose and Mannose are the epimers of the
glucose.
They differ from the glucose with the respect of
the C-4 and C-2 respectively.

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Epimers of glucose
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
D - Glucose
C
C
CH2OH
=OH
HO H
CHO H
CH OH
CH OH
D - Mannose
C
C
CH2OH
=OH
H OH
CHO H
CHO H
CH OH
D - Galactose

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Anomerism
In solution glucose predominantly exist as closed chain
structure.
Because of cyclization of sugar, an additional
asymmetric center is created at C-1 (anomeric carbon).
This leads to formation of two isomers namely….
α- D-glucopyranose
β- D-glucopyranose

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C
C
CH2OH
OHH
H OH
CHO H
CH OH
CH
O
C
C
CH2OH
HHO
H OH
CHO H
CH OH
CH
O
α- D - Glucose
β - D - Glucose

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Mutarotation
It is defined as “the change in the specific optical
rotation representing interconversion of α and β
forms of D-glucose to an equilibrium mixture.”
Equi. mixtureα- D - Glucose β - D - Glucose
Specific rotation
[α]D = +112.2˚
Specific rotation
[α]D = +52.7˚
Specific rotation
[α]D = +18.7˚

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C
C
CH2OH
OHH
H OH
CHO H
CH OH
CH
O
C
C
CH2OH
HHO
H OH
CHO H
CH OH
CH
O
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
D - Glucoseα- D - Glucose β - D - Glucose
+112.2˚ +52.7˚ +18.7˚

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Chemical Properties of
monosaccharides
Some of the important chemical properties of
monosaccharides are…
Furfural formation
Enolization
Oxidation
Reduction
Osazone formation

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Sugar when treated with strong
mineral acids like…
Conc. Sulfuric acid (H2SO4)
Conc. Hydrochloric acid (HCL)
Conc. Nitric acid (HNO3)
They undergoes dehydration loses 3 water
molecules to form furfural derivatives.
This is the basis for following reactions…
Molisch’s test
Seliwanoff’s test

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Fig. 2.10
Hydroxy methyl
furfural
CHO
C
CH2OH
CH
CH
C
O
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
D - Glucose
Coloured complex
Condense with
phenolic componudconc acids
3 H2O

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When glucose is kept in alkaline solution for several
hours, it undergoes isomerization to form D-
fructose and D- mannose.
This results in formation of a common intermediate –
enediol.
The process of shifting of hydrogen atom from one
carbon atom to another to produce enediols is known
as tautomerization.

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Alkaline solution
Glucose
Fructose
Mannose
Glucose

C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
D - Glucose
C
C
CH2OH
=OH
HO H
CHO H
CH OH
CH OH
D - Mannose
D - Fructose
C
C
CH2OH
OHH
OH
CHO H
CH OH
CH OH
Enediol
CHOH
C
CH2OH
=O
CHO H
CH OH
CH OH
H

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Enediols are good reducing agents.
And forms basis of reducing property of sugars.
Benedict’s test and
Fehling’s test.
CuSO4
Cu++ Cu+ 2Cu(OH)
Cu2O
Sugar
Enediol
Red ppt

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When glucose oxidizes under proper conditions the
sugars may form:
Monobasic Aldonic Acid: oxidation with Hydrobromous acid.
Dibasic saccharic acids or Alderic acid: oxidation with
nitric acid (HNO3).
Monobasic Uronic acid: oxidised by specific enzymes.

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Formation of Aldonic acid
D - glucose Gluconic acid
Hydrobromous acid
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
COOH
C
CH2OH
H OH
CHO H
CH OH
CH OH
Medical Importance
Calcium gluconate (gluconic acid) used as source of calcium. These
are given I.V. fluids rise the calcium levels.

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Formation of Saccharic acid
D - glucose Glucosaccharic acid
Nitric acid
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
COOH
C
COOH
H OH
CHO H
CH OH
CH OH

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Formation of Aldonic acid
D - glucose Glucuronic acid
Enzymatic
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
Medical Importance
These are present in the heteropolysaccharides and glycoproteins.
Involved in detoxification of benzoic acid, bilirubin & certain drugs
C
C
COOH
=OH
H OH
CHO H
CH OH
CH OH

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Both aldoses and ketoses may be reduced by
enzymes to the corresponding polyhydroxy alcohols.
The sugar alcohols function mainly as intermediates
in the minor pathway of carbohydrate metabolism.
Some of these alcohols are the followiing:
Sorbitol
Mannitol
Dulcitol
Ribitol

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D-Glucose D-Sorbitol
D-Mannose D-Mannitol
D-Fructose D-Sorbitol
D-Galactose D-Dulcitol
D-Ribose D-Ribitol
Medical Importance
Mannitol: It is used as an osmotic diuretic to reduce the cerebral oedema.
Sorbitol: It is accumulates in the lenses of diabetic and produces cataracts.

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Only reducing sugars gives this test positive.
The presence of free carbonyl (aldehyde or ketone)
group in the molecule is essential for the osazone
formation.
Osazones are yellow crystalline derivatives of
reducing sugars with phenylhydrazine and have a
characteristic crystal structure which can be used
for identification and characterization of different
sugars having closely similar properties.

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Osazone formed from Glucose, Fructose and Mannose are
identical because these are identical in their lower four carbon
atoms.
Non-reducing sugars like sucrose cannot form osazone due to
the absence of a free carbonyl group.
The Osazone crystals of some sugars are:
Glucosazone – Needle shaped
Maltosazone – Sunflower petals shaped
Lactosazone – Powder puff of tennis ball shaped

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Why glucose, fructose, and mannose give same
type of osazones
D - glucose
Phenyl hydrazine
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
H2N-NH-C6H5
C
C
CH2OH
=H
H OH
CHO H
CH OH
CH OH
N-NH-C6H5
Phenyl hydrazine
H2N-NH-C6H5
C
C
CH2OH
=H
H
CHO H
CH OH
CH OH
=
N-NH-C6H5
N-NH-C6H5
glucohydrozone Osazone

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D - glucose
C
C
CH2OH
=OH
H OH
CHO H
CH OH
CH OH
C
C
CH2OH
=OH
HO H
CHO H
CH OH
CH OH
D - MannoseD - Fructose
CH2OH
C
CH2OH
=O
CHO H
CH OH
CH OH

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Needle shaped crystals
Glucosazone ,
Fructosazone
Mannosazone
Powder puff or tennis ball shaped
Lactosazone
Sunflower petals shaped
Maltosazone

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When hydroxyl group on the anomeric carbon of a
monosaccharides reacts with an OH group of another
carbohydrate or non-carbohydrate leads to glycosides
formation.
The bonds joining the monosaccharides are called
glycosidic or glycosyl bonds.
There are two types of glycoside bonds:
O-glycosidic bonds
N-glycosidic bonds

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O- and -N type of Glycoside Bonds
O-type Glycoside Bond N-Type Glycoside Bond

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Stretomycin (antibiotic) – used as drugs for the
treatment of tuberculosis.
Cardiac glycosides like digoxin and digitoxin are
increase muscle contraction and used for treatment of
the congestive heart failure.
Anthacycline glycosides like Doxirubicin used to treat
wide range of cancers.
Ouabain inhibits Na-K ATPase and block the active
transport of Na.
Physiologically important glycosides

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Some derivatives of Monosaccharides are:
Phosphoric acid ester of monosaccharides. e.g- G-1-P
Amino Sugar. e.g- glucosamine
Deoxy Sugars
Sugar acids
Sugar alcohols
Derivatives of Monosaccharide

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Disaccharides
DI Two
Sugar

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Consists of two monosaccharide units held by
glycosidic bond.
They are crystalline, water soluble, and sweet taste.
They subdivide based on presence or absence of
free reducing group into…
Reducing disaccharides with free aldehyde or keto gr
Example – Maltose and Lactose
Non reducing disaccharide without free aldehyde or
keto gr
Example - Sucrose
Disaccharide

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It contains two moles of glucose units.
They linked by α-(1-4) glycosidic linkage.
It is a one of the reducing disaccharide, which has
free functional group.
Maltose

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Maltose
O
CH2OH
OH
OH
OH
O
CH2OH
OH
OH
OH
O
α- D - glucose
α- D - glucose
α (1→4) glycosidic bond

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It is present in the milk sugar.
It contains one mole of galactose and one mole of
glucose that are linked by β-(1-4) glycosidic linkage.
It is also a reducing disaccharide.
It hydrolyzed into galactose and glucose by the
enzyme lactase in human and by β-D-galactosidase in
bacteria.
It is the source of carbohydrates in breast fed
infants.
Lactose

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Lactose
O
CH2OH
OH
OH
OH O
CH2OH
OH
OH
OHO
β - D - galactose β - D - glucose
β (1→4) glycosidic bond

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It is commonly used table sugar and contributes
some calories in the diet.
It contains one mole of glucose and one mole of
fructose that are linked by α-(1-2) glycosidic linkage.
It is a non reducing disaccharide.
It hydrolyzed into glucose and fructose by the
enzyme Sucrase is also called as Invertase.
Sucrose

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Sucrose
O
CH2OH
OH
OH
OH O
OCH2OH CH2OH
OH
OH
OH
D - glucose D - fructose
α (1→2) glycosidic bond

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It is also contains two moles of glucose.
They linked by α-(1-6) glycosidic linkage.
It is derived from the digestion of starch & glycogen.
It hydrolyzed to glucose in the intestinal tract by an
enzyme called isomaltase.
Isomaltose
Trehalose
It is also one of the disaccharide having two units of
glucose linked by α-(1-1) glycosidic linkage.
It is a non reducing disaccharide.
Yeast and fungi are the sources of trehalose.

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Polysaccharides
POLY
Many Sugar

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Is reserve carbohydrate form in plants.
e.g - potato
A homopolymer composed of D-glucose units held by α-
glycosidic bonds.
It composed of two constituents, water soluble amylose
(15-20%) and water insoluble amylopectin (80-85%).
Starch

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Chemically, amylose is a long unbranched chain of 200-
1000 of D- glucose units linked by (1-4) bonds.
Amylopectin, is a branched chain with (1-6) bonds at
the branching points and (1-4) bonds everywhere else.
Amylopectin contains few thousands of units looks like
a branched tree. (20-30 units/ branch)
Starch is hydrolyzed by the enzyme amylase to
liberate dextrin and finally maltose and glucose units.
Starch

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Partial hydrolysed products of starch by acids or
enzymes.
Starch is sequentially hydrolyzed through different
dextrins and finally to maltose and glucose.
The various intermediates are soluble starch,
amylodextrins, erythrodextrins, and achrodextrins.
All dextrins have free sugar groups and can show mild
reducing property.
Dextrins

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It is the major storage form of carbohydrate in animals,
so it referred as animal starch.
It is present in high concentration in liver, followed by
muscle, brain etc.
The structure of glycogen is similar to that of
amylopectin with more no. of branches
Glycogen

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Chief coenstituent of plant cell wall.
An unbranched polymer of glucose linked by β-(1-4)
glycosidic linkages.
Since humans lack an enzyme cellulase that can
hydrolyse β-(1-4) glycosidic linkages, cellulose cannot
be digested and absorbed.
has no food value unlike starch.
Cellulose

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Cellulose, though not digested, has great importance in
human nutrition.
It is a major constituent of fibre, the non-digestable
carbohydrate.
The functions of dietary fibre include
decreasing the absorption of glucose and cholesterol from
the intestine,
increasing the bulk of stool.
Aids intestinal mobility acts as stool softener
Prevent constipation.
It reduces incidence of ….
CVD
Colon cancer
diabetes
Importance of Cellulose

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It is a polymer of D-fructose (fructosans).
Linked together by β-(1-2) glycosidic linkage.
It occurs in bulb of onion and garlic.
It is a low mol. Wt (5000) polysaccharide easily soluble
in water.
It is not utilized by the body.
It is used for assessing kidney function through
measurement of glomerular filtration rate (GFR).
Inulin

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MUCOPOLYSACCHARIDES
Heteroglycans made up of repeating units of sugar
derivatives, namely amino sugars and uronic acid.
Commonly known as glycosaminoglycans. (GAGs)
Acetylated amino groups, besides sulfate and carboxyl
groups are generally present in their structure.
Presence of sulfate and carboxyl groups contributes to
acidity of the molecules, making them acid
mucopolysaccharides.
Some of them found in the combination with proteins
to form mucoproteins or mucoids or proteoglycans.
Mucoproteins may contain…
up to 95% carbohydrate and
5% protein.

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MUCOPOLYSACCHARIDES
Mucopolysaccharides are essential components of
tissue structure.
The extra cellular spaces of tissue (connective tissue,
cartilage, skin, blood vessels, tendons) consist of
collagen and elastin fibers embedded in a matrix or
ground substance.
The ground substance is predominantly composed of
GAGs.
The important mucopolysaccharides are…
Hyaluronic acid
Chondroitin 4-sulfate
Heparin
Dermatan sulfate and
Keratan sulfate

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GAGs Composition
Tissue
Distribution
Functions
Hyaluronic
acid
D-Glucuronic acid,
N-acetylglucosamine
Connective tissue,
synovial fluid, vitrous
humor
Lubricant, shock
absorber, promotes
wound healing
Chondroti
n sulfate
D-Glucuronic acid,
N-acetylglucosamine 4-
sulfate
Cartilage, bone, skin,
blood vessel wall
Maintain structure &
shapes of tissues
Heparin
D-glucuronate 2-
sulfate,
N-sulfoglucosamine 6-
sulfate
Blood, lung, liver,
kidney, spleen
Acts as an
anticoagulant
Dermatan
sulfate
L-Iduronic acid, N-
acetyl-galactosamine
4-sulfate
Blood vessel valves,
heart valves, skin
Maintain the shapes
of tissues
Keratan
sulfate
D-Galactose,
N-acetylglucosamine 6-
sulfate
Cartilage, cornea,
connective tissues
Keeps cornea
transparent

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Thanks For Listening
Ashok Katta, 16 July 2014

Carbohydrate Chemistry

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