Carbohydrates chemistry

Dr : Abdel

naser

Badawy

‐

Carbohydrates are organic molecules found in nature, 

constituting one of the four major classes of biomolecules. 

‐‐

The other three are proteins, nucleic acids and lipids.

-- Saccharides

(saccharo

is Greek for ―sugar)

•

Carbohydrates are aldehyde

or ketone

compounds with multiple

hydroxyl groups.•

The basic molecular formula

(C.H2

O)n

where n = 3 or more.•

The term ―carbohydrate comes from the observation that when you heat sugars, you get carbon and water (hence, hydrate of carbon).

Classification 

They are classified according to the number of structural units into:

1‐Monosaccharides=

They are the simplest carbohydrates that can not 

be hydrolysed

into simpler units.

2‐

Disaccharides=

produce 2 molecules of monosaccharide on 

hydrolysis.

3‐

Oligosaccharides=

produce three to ten monosaccharide units on 

hydrolysis

4‐

Polysaccharides=

: produce more than 10 monosaccharide units on 

hydrolysis

Monosaccarides-1

•

* Def :

They are the simplest carbohydrate unites which can not be hydrolyzed to a simpler form

•

* General formula:

(CH2

O)n

n≥3

:* Nomenclature

•

1-

According to active group in the sugar:–

If monosaccharide contains aldehyde

group (CHO) → it's

called aldose.–

And if contain ketone

group

(c=o) → it's called ketose.

According to the number of carbon atoms (n):‐2

If sugar contains 

3 carbons → it's called triose,  4c→ tetrose 5c→ pentose           

6c→ hexose

7c→ heptose

Three Carbon Four Carbon

By combining the two methods , we find that:-33c-Aldotriose -ketotriose4c-Aldotetrose -ketotetrose5c-Aldopentise -ketopentose6c-Aldohexose -ketohexose

Five Carbon Six Carbon

The structure of glucose can be represented in one of the  following ways:

1.The straight – chain (open ‐

chain) structural formula :

Aldohexose

can account for some of the properties of glucose, but 

can not explain some reaction  

D-glucose

2. The cyclic structure

accounts for the remainder of the chemical 

properties of glucose. This cyclic structure can be represented in two 

forms:

a. Fischer projection formula :where the aldehyde

group reacts with 

an alcohol group on the same sugar to form a hemiacetal

ring.

C

H – C – OH   

HO – C – H 

H – C – OH  

H – C 

CH2OH  

α‐D‐Glucopyranose

H    OH

O

C

H – C – OH   

HO –C – H 

H – C – OH  

H – C 

CH2OH  

β ‐D‐Glucopyranose

oH H

O

b. Haworth formula:

Where the cyclic structure is represented in pyranose

(six –

membered) and

 

furanose

(five –

membered) rings resembling pyran

and furan rings. 

Here oH

and H written above and below instead of Right and left 

so what is on  Right  → below                     left → above 

except last carbon (which close the ring) in which  

left →below                                                      Right

→above

α‐D‐Glucopyranose

An aldehyde or ketone can react with an alcohol in a 1:1 ratio to yield a hemiacetal or hemiketal, respectively, creating a new chiral center at the carbonyl carbon

Hemiacetals or Hemiketals

:c) Boat and chair forms

represents the three dimensional configuration of sugar in nature.

formshaworthFructose in open chain & 

carbon, Asymmetric Anomeric carbon):chiralcarbon atom (

•

It is that carbon atom attached to four different groups or atoms.

•

Formation of a ring results in the creation of an anomeric

carbon

at carbon 1 of an aldose

or at carbon 2 of a ketose.

Reducing sugars•

If the oxygen on the anomeric

carbon (the carbonyl group) of a sugar is not attached to any other structure, that sugar is a reducing sugar.

•

Only the state of the oxygen on the anomeric

carbon determines

if the sugar is reducing or nonreducing—the other hydroxyl groups on the molecule are not involved

Reducing sugars

•

A reducing sugar can react with chemical reagents (for example, Benedict's solution) and reduce the reactive component, with the anomeric

carbon

becoming oxidized.

Any compound having one or more asymmetric carbon atom 

shows two properties:

1.

Optical activity.

2.

Stereoisomerism 

Optical activity-1

•

Def.

It is the ability of the compound to rotate plane polarized light to the right or to the left.

•

If the compound rotates plane polarized light to the right, it is called dextrorotatory, d or (+).

•

If it rotates plane polarized light to the left, it is called levorotatory, l or (-).

•

The direction of rotation is independent of the stereochemistry

•

of the sugar, so it may be designated D(−), D(+), L(−), or L(+).

•

For example, the naturally occurring form of fructose is the D(−) isomer.

••

dextrorotatorydextrorotatory sugar (d or +): sugar (d or +): glucose, glucose, galactosegalactose

and starchand starch

••

levorotatorylevorotatory sugar (l or sugar (l or --): ): fructose fructose and invert sugarand invert sugar..

2‐

Stereoisomerism

Compound 

that 

have 

the 

same 

structural 

formula 

but 

differ 

in 

spatial 

configuration 

are 

known 

as 

stereoisomers

and 

the 

phenomenon is called stereoisomerism. 

The 

number 

of 

possible 

isomers 

of 

a 

compound 

depends 

on 

the 

number of asymmetric carbon atoms (n) and is equal to 2n. 

Glucose, with four asymmetric carbon atoms, has 16 isomers. 

•

The more important types of isomers include –

D and L isomers,

–

pyranose

and furanose

ring structures, –

alpha and beta anomers,

–

epimers

and –

aldose-ketose

isomers.

IsomersIsomersAre compounds which have the same molecular Are compounds which have the same molecular

weight, same percentage composition, and differ weight, same percentage composition, and differ in their physical and chemical properties.in their physical and chemical properties.

--

StereoisomersStereoisomers: are compounds that have the : are compounds that have the same structural formula but differ in spatial same structural formula but differ in spatial configuration (arrangement of atoms and groups configuration (arrangement of atoms and groups of atoms in space around the asymmetric of atoms in space around the asymmetric carbon(scarbon(s) i.e. different configuration).) i.e. different configuration).

1. D and L isomers ):enantiomers(

•

A special type of isomerism is found in the pairs of structures that are mirror image of each other.

•

These mirror images are called enantiomers

and the two members of the pair are designated as a D and an L-sugar.

•

A monosaccharide is designated D if the hydroxyl group on the highest numbered asymmetric carbon= prelast

carbon

is drawn to

the right as in D- glyceraldehyde

and L if the

hydroxyl group on the highest numbered asymmetric carbon is drawn to the left as in L-

glyceraldehyde.

‐

The  majority of the sugars in humans are D‐sugars. 

‐

Two exceptions are L‐fucose

(in glycoproleins) and L‐iduronic

acid 

(in glycosaminoglycans).

ring structures: furanoseand Pyranose2. 

The   monosaccharides

are  either pyran

(a six‐membered

ring) or furan (a five‐membered

ring). 

For glucose in solution, more than 99% is in the pyranose

form.

:anomers3. Alpha and beta 

The ring structure of an aldose

is a hemiacetal, since it is 

formed by combination of an aldehyde

and an alcohol group. 

Similarly, the ring structure of a ketose

is a hemiketal. The cyclic

 

structure is retained in solution, but isomerism (C6

H12

O6

) occurs 

about position 1, the carbonyl or anomeric

carbon atom, to give

 

a mixture of α‐glucopyranose

(38%) and β‐glucopyranose

(62%). 

•

The cyclic α

and β

anomers

of a sugar in solution are in equilibrium with each other, and can be spontaneously interconverted

(a process called mutarotation)

: Epimers4. 

Isomers differing as a result of variations in configuration of 

the OH and H on carbon atoms 2, 3, and 4 of glucose are known

 

as epimers.  Biologically, the most important epimers

of 

(C6

H12

O6

) glucose  are mannose and galactose, formed by 

epimerization at carbons 2 and 4, respectively. 

Epimers of glucose

D-

glucose D-

galactose Epimer at C4

D-

mannoseEpimer at C2

isomerism: ketose‐Aldose5. 

Fructose has the same molecular formula as glucose 

(C6

H12

O6

) but differs in its structural formula, since there is  keto

group in position 2, the anomeric

carbon of fructose, whereas 

there is  aldehyde

group in position 1, the anomeric

carbon of 

glucose

Are Physiologically Important:MonosaccharidesMany 

xylose, ribuloseribose, e.g:Pentoses1 

, fructose, mannosegalactoseglucose, : Hexoses‐2

) are formed as metabolic sedoheptulose(carbon sugar ‐seven‐3

intermediates in  the pentose phosphate pathway.

g carboxylic acid derivatives of glucose are important, includin‐4

formation and in glucuronide(for glucuronate‐Da. 

glycosaminoglycans) 

)glycosaminoglycans(in iduronate‐Lb. 

acid pathway)theuronic(an intermediate in gulonate‐Lc. 

Derived Sugars

Sugars:Deoxy1. 

Lack an Oxygen Atom =Deoxy

sugars are those in which a hydroxyl 

group has  been replaced by hydrogen.   Examples: 

a. deoxyribose

in DNA. 

b. L‐fucose

occurs in glycoproteins.

c. 2‐deoxyglucose is used experimentally as an inhibitor of glucose 

metabolism..

):Hexosamines2. Amino Sugars (

Are compounds in which OH at C2 is replaced by NH2 

1. D‐glucosamine, a constituent of hyaluronic

acid , 

2. D‐galactosamine(chondrosamine), a constituent of chondroitin; 

3.  Several antibiotics (eg, erythromycin) contain amino sugars 

believed to be important for their antibiotic activity

Galactosamine

3.Sugar acids

1.1.

Produced by oxidation of Produced by oxidation of carbonyl carbon to carboxylic carbonyl carbon to carboxylic group.group.

2.2.

Or by oxidation of last hydroxyl Or by oxidation of last hydroxyl carbon to carboxylic group.carbon to carboxylic group.

3.3.

Or by oxidation of both.Or by oxidation of both.

1.Aldonic1.Aldonic

CHO

C OHH

C HHO

C OHH

C OHH

CH2OH

COOH

C OHH

C HHO

C OHH

C OHH

CH2OH

bromine water, O2

D-GluconicacidD-Glucose

UronicUronic--22

CHO

C OHH

C HHO

C OHH

C OHH

CH2OH

CHO

C OHH

C HHO

C OHH

C OHH

COOH

Dil. Nitric acid

D-GlucuronicacidD-Glucose

H2O2

AldaricAldaric--33

CHO

C OHH

C HHO

C OHH

C OHH

CH2OH

COOH

C OHH

C HHO

C OHH

C OHH

COOH

Conc. Nitric acid

D-Glucaric acidD-Glucose

O2

Glycoside Formation

•

The hemiacetal

and hemiketal

forms of monosaccharides

can react with alcohols

to form acetal

and ketal

structures called glycosides. The new carbon-oxygen bond is called the glycosidic

linkage.

AcetalGlycosides=

The OH of anomeric

carbon of monosaccharides

can react with either: 

1‐

Nitrogen of amines

(The anomeric

carbon atom of sugar can be 

linked to the nitrogen atom of an amine by N‐

glycosidic

bond) e.g

OH 

of ribose linked to nitrogen  of nitrogenous base to form nucleotides. 

OH of other -2 compound :

•

A-

May be carbohydrate

( Monosaccharides

can be linked to

each other by O-

glycosidic

bonds to form disaccharides, oligosaccharides and polysaccharides).

•

(monosaccharide+ monosaccharide)=hemiacetal+hemia

cetal=acetal.•

b-

May be non carbohydrate

e.g

glycolipid, glycoprotein. •

The non carbohydrate component of a glycoside is called aglycone.

O- and N-glycosides

•

If the group on the non- carbohydrate molecule

to which the sugar is attached is an -OH group, the structure is an O-glycoside

•

All sugar-sugar glycosidic

bonds are O-

type linkages

O- and N-glycosides

•

If the group is an -NH2 , the structure is an N-

glycoside

–

purines

and pyrimidines (found in nucleic acids),

–

aromatic rings (such as those found in steroids and bilirubin),

–

proteins (found in glycoproteins

and

glycosaminoglycans),

Naming glycosidic bonds

•

Glycosidic

bonds between sugars are named according to –

numbers of the connected carbons (1-4, 1-6),

and

–

position of the anomeric

hydroxyl

group of the sugar involved in the bond.

Naming glycosidic bonds

•

this anomeric

hydroxyl group is in the α

configuration, the linkage is an α-bond.

•

If it is in the β configuration, the

linkage is a β-bond.

Naming glycosidic bonds

•

Lactose, for example, is synthesized by forming a glycosidic

bond between carbon

1 of β-galactose

and carbon 4 of glucose. –

The linkage is, therefore:

β(1 →4)

glycosidic

bond. •

Because the anomeric

end of the

glucose residue is not involved in the glycosidic

linkage it (and,

therefore, lactose) remains a reducing sugar.

Naming of  O‐

glycosidic

bond() carbohydrate and carbohydrate

‐

Glycosidic

bonds between sugars are named according to:

1‐

The numbers of the connected carbons 

2‐

The position of the anomeric

hydroxyl group of the sugar.

If the anomeric

hydroxyl group is in α

configuration the link is α‐

bond and if it’s   in β, the link is β‐

bond. Examples

In lactose β

1 of galactose

bind to C4 of glucose by  β

1 

→ 4 

galactosidic

bond.

Examples of glycosides:

1‐

Disaccharides as maltose, lactose and sucrose

2‐

Polysaccharides.

3‐

Glycolipids.

4‐Glycoproteins.(may be O‐

or N‐

glycosidic

link)

5‐Nucleotides as ATP, GTP, UTP where aglycon

is purine

or 

pyrimidine

bases      (N‐

glycosides)

The glycosides that are important in medicine 

1. cardiac glycosides all contain steroids as the aglycone.

2. Other glycosides include antibiotics such as streptomycin.

Disaccharides

‐

Disaccharide consists of two sugars joined by an O‐

glycosidic

bond.

‐

The most abundant disaccharides are sucrose, lactose and maltose.

‐

Other disaccharides include isomaltose, cellobiose

and trehalose.

‐The disaccharides can be classified into homo disaccharides and 

hetero disaccharides. 

‐A) Homo disaccharides: are formed of the same monosaccharide units 

and include maltose, isomaltose, cellobiose

and trehalose.

‐(B) Hetero disaccharides: are formed of different monosaccharide 

units and include: sucrose, lactose. 

Lactose:Lactose:It is formed of -galactose

and -glucose linked by

-1,4-glucosidic linkageContain free anomeric

carbon so reducing sugar

It may appear in urine in late pregnancy and during lactation.

OOH

H HH

OHH

OH

CH2OH

H

OH OH ..... H

H ..... OHH

OHH

OH

CH2OH

H

and Lactose-Galactose Glucose

1 4O

SucroseSucrose•

α

D-glucopyranose

and

β

D fructofuranose

by α 1-

2 glycosidic

bond

•

No free aldehyde

or keton

gp

so non

reducing sugar•

hydrolysed

to glucose

and fructose by sucrase (invertase) enzyme.

•

* Sucrose is dextrorotatory +66.5.

OH

OH

H

H

OHH

OH

CH2OH

H 1

Sucrose

-Glucose

-FructoseCH2OH

O

H

CH2OH

OH H

H OH

O

2

Maltose (malt sugar):Maltose (malt sugar):It consists of 2 It consists of 2 --glucose units linked by glucose units linked by

--1,41,4--glucosidic linkage,glucosidic linkage,Contain free anomeric

carbon so reducing sugar.

OH

OH

H

H

OHH

OH

CH 2OH

H

OH OH ..... H

H ..... OHH

OHH

OH

CH 2OH

H

O

and Maltose -Glucose Glucose

1 4

B. B. TrehaloseTrehalose::It is formed of 2 -glucose units linked by -1,1-

glucosidic linkage. Not Contain free anomeric carbon so non reducing sugar

Present in a highly toxic lipid extracted from Mycobacterium tuberculosis.

OH

OH

H

H

OHH

OH

CH 2OH

H

O

H H

OHHO H2C

H

OHH

OH H

O11

Trehalose -Glucose -Glucose

Disaccharides Components Reduction 1-

sucrose =

cane sugar = beet sugar = table sugar

α

D- glucopyranose

and β

Dfructofuranose. by α

1-

2

glycosidic

bond

No free aldehyde

or

keton

gp

so non reducing sugar

hydrolysed

to glucose and fructose by sucrase

(invertase) enzyme.* Sucrose is dextrorotatory +66.5.

2-

Lactose (milk sugar)

β

D galactose and α

D glucose.

by β

1-4 glycosidic

bond

Contain free anomeric

carbon so reducing sugar

* It may appear in urine in late pregnancy and during lactation.

Disaccharides *Components Bond Reduction

1-

Maltose 2αD-glucose α

1-4 glycosidic Contain free anomeric

carbon so reducing sugar.

4-

Trehalose 2αD-glucose α

1-1 glycosidic Not Contain free anomeric

carbon so non reducing sugar

Oligosaccharides

•

Oligosaccharides contain from 3 to 10 monosaccharide units.

•

Raffinose

An oligosaccharide found in peas and beans

Polysaccharides (glycans)

‐

Polysaccharides consist of more than 10 monosaccharide units and / 

or their derivatives

Classification According to structure:

1‐

Homo polysaccharides (Homo glycans): contain only one type of 

monosaccharide molecule.

E.g. starch, glycogen,  dextrin, cellulose, inulin

and chitin

2‐

Hetero polysaccharides: contain more than one type of 

monosaccharides. 

E.g. glycosaminoglycan, glycoprotein.

1. Starch

‐

is a homopolymer

of glucose forming an α‐

glucosidic

chain, called a 

glucosan

or glucan. 

‐It is the most abundant dietary carbohydrate in cereals, potatoes, 

legumes, and other vegetables. 

‐The two main constituents are amylose

(15–20%), which has a 

nonbranching

helical structure) and amylopectin

(80–85%), which consists of branched chains composed of 24–30 

glucose residues united by 1 → 4linkages in the chains and by 1 → 6 

linkages at the branch points.

:Dextrins2. Are intermediates in the hydrolysis of starch.

••

AmyloseAmylose::. . Straight chain compound Straight chain compound present in the form glucose units present in the form glucose units linked by linked by --1,41,4--glucosidic bond of a glucosidic bond of a helix formed of a large number of helix formed of a large number of --

glucose.glucose.

OH H

H

OHH

OH

CH 2OH

H

OH H

OHH

OH

CH 2OH

H

O

Am ylose

14

nO O

1 4

It forms the inner part of starch granules

:Glycogen3. 

‐

is the storage polysaccharide in animals.

‐

It is a more highly branched structure than amylopectin, with chains 

of 12–14 α‐D‐glucopyranose

residues in α[1 → 4]‐glucosidic linkage),

with branching by means of α(1 → 6)‐glucosidic bonds

:Inulin4.  

is a polysaccharide of FRUCTOSE

(and hence a fructosan)

found in plants.

It is readily soluble in water .

is used to determine the glomerular

filtration rate.

Cellulose 5. 

‐Is the chief constituent of the framework of plants. 

‐It is insoluble

‐consists of β‐D‐glucopyranose

units linked by β(1 → 4) bonds to form 

long, straight chains strengthened by cross‐linked hydrogen bonds. 

Cellulose cannot be digested by mammals because of the absence

of an enzyme that hydrolyzes the β

linkage. It is an important

source of “bulk”

in the diet. So prevent constipation.

‐

Starch

Cellulose

6. Chitin 

is a structural polysaccharide in the exoskeleton of crustaceans

and insects and also in mushrooms. 

It consists of N‐acetyl‐D‐glucosamine

units joined by

β

(1 →4)‐glycosidic

linkages

Glycosaminoglycans

(GAGs)

(Mucopolysaccharides)

‐

Glycosaminoglycans

are long linear (unbranched) 

heteropolysaccharide

chains generally composed of a repeating 

disaccharide unit (acidic sugar‐amino sugar)n. 

‐The 

amino 

sugar 

is 

either 

D‐glucosamine

or 

D‐galactosamine

in 

which 

the 

amino 

group 

is 

usually 

acetylated, 

and 

sometimes 

sulphated.

There are 6 types: 

1. heparin.              2. heparan

sulphate.        3. dermatan

sulphate

4. keratan

s            5. Chondroitin

s                 6. hyaluronic

acid

)mucopolysaccharides(Glycosaminoglycans

All of the glycosaminoglycans

except hyaluronic

acid and heparin are 

found covalently attached to protein, forming proteoglycan

monomers.

Their property of holding large quantities of water and occupying 

space lubricating other structures, is due to the large number of OH 

groups and negative charges on the molecules, which, by repulsion, 

keep the carbohydrate chains apart. 

Glycoproteins

‐Are proteins to which oligosaccharides are covalently attached.

‐

Oligosaccharide chains  formed mainly  of  sialic

acids  and L‐fucose.

‐

Sialic

acids are N‐

or O‐derivatives of neuraminic

acid .

‐

Neuraminic

acid is a nine‐carbon sugar derived from mannosamine

and pyruvate.

•

Glycoproteins

have many functions: •

1-

Soluble as enzymes, hormones and

antibodies. •

2-

In lysosomes

•

3-

attached to the cell membrane (The membrane bound glycoproteins) participate in:–

a-

cell surface recognition (by other cells,

hormones, viruses)–

b-

Cell surface antigenicity

(as blood gp

antigens)

Proteoglycans Glycoprotein Carbohydrate components

Glycosaminoglycans-

Repeating disaccharide unit

-

Linear (unbranched) -

long

-

Contain uronic

acids (glucuronic and iduronic

-

N-

acetyl hexosamine-

Contain hexoses

as galactose

(in

keratin sulphate)-

contain sulphate

-

No pentoses-

No deoxy

sugar

Oligosaccharides-

No repeating units

-

Branched- short-

contain sialic

acid derivatives

(NANA)-

N-

acetyl hexasamine

-

Contain hexoses

as galactose and mannose

- No sulphate-

Contain pentose

-Contain deoxy

sugar as L-fucose

2-

Tissue distribution and functionsStructural-

Cartilage

-

Bone-

Tendons

-

Cell membrane-

Cornea

Functional and structural - mucines-

Blood groups antigens

-

some hormones- enzymes-

Immunoglobulins

and

receptors

AcidNeuraminic-Acetyl–NANA=N

-

Neuraminic

Acid=sialic

acid = mannosamine + pyruvic

acid

= amino sugar acid-

NANA found in glycoproteins.

Fucose-L

galactose-L–deoxy -= 6

=Methyl pentose

Found in glycoprotein

THE END!

Thank You