1. Reduction
• On reduction with sodium amalgam glucose is
converted into polyhydric alcohol-sorbitol
• Fructose into 2 isomeric products sorbitol and
mannitol
Sorbitol
Mannitol

2. Reaction of glucose with weak alkali
In the presence of weak alkali glucose in
converted into fructose and vice versa

3. Reaction of carbonyl group
Glucose and fructose condense with hydroxyl amine and
phenyl hydrazine to produce oximes and osazones

5. Reaction with non-reducing agents
• Pentoses on heating with HCl/H2SO4 produce
furfural-aldehyde of furan, whereas hexoses
produce hydroxy methyl furfural
• This provides the basis of tests such as
Molisch’s test, Anthrone test, Salivonoff test etc.

6. Cont’d

7. Reaction with calcium hydroxide
On reacting with calcium hydroxide, glucose produces calcium
glucosate
+ Ca (OH)2

8. Fermentation
Both glucose and fructose are attacked by
enzymes of yeast to produce ethyl alcohol and
carbon dioxide
C6H12O6 → 2C2H5OH + 2CO2

9. Reaction with acetone
2 acetone
-2 H2O

10. Methylation
On methylation glucose produces glucosides or
glycosides

11. Configuration of monosaccharides
• Due to presence of asymmetric carbon
monosaccharides rotate the plane polarized light
either toward right or left
• Those rotating towards right are dextrorotatory
(d or +) and those towards left are levorotatory
(l, -)
• (d and l) isomers are mirror image of each other
when substituents are arranged in space

12. • D and L are used in place of + and – with
reference to glyceraldehyde- the farthest
asymmetric or penultimate carbon
• Aldoses with at least three carbons and ketoses
with at least four carbons contain chiral centres

13. Cyclic Structures and Anomeric Forms
• Although Fischer projections are useful for
presenting the structures of particular
monosaccharides and their stereoisomers ,
they ignore one of the most interesting facts
of sugar structure
—the ability to form cyclic structures with
formation of an additional asymmetric
centre

14. • Alcohols react readily with aldehydes to form
hemiacetals
– A British Chemist Sir Norman Haworth showed that
the linear form of glucose and other aldohexoses
could undergo a similar intramolecular reaction to
form a cyclic hemiacetal
– The resulting six- membered, oxygen-containing ring
is similar to pyran and is designated as pyranose-
glucopyranose. The reaction is catalysed by acid or
base and is readily reversible
Pyran

16. • An analogous intramolecular reaction of a ketose
sugar such as fructose yields a cyclic hemiketal
• The five-membered ring thus formed is
reminiscent of furan and is referred to as a
furanose
• The cyclic pyranose and furanose forms are the
preferred structures for monosaccharides in
aqueous solution
• At equilibrium, the linear aldehyde or ketone
structure is only a minor component of the
mixture (generally much less than 1%)

18. • When hemiacetals and hemiketals are formed,
the carbon atom that carried the carbonyl
function becomes an asymmetric carbon atom
– Isomers of monosaccharides that differ only in their
configuration about that carbon atom are called
anomers, designated as α or β
• When the hydroxyl group at the anomeric carbon
is on the same side of a Fischer projection as the
oxygen atom at the highest numbered carbon,
the configuration at the anomeric carbon is α, as
in α-D-glucopyranose

19. • When the anomeric hydroxyl is on the
opposite side of oxygen in the Fischer
projection, the configuration is β, as in β-D-
glucopyranose

20. Muta rotation
• The addition of this asymmetric centre upon
hemiacetal and hemiketal formation alters
the optical rotation properties of
monosaccharides
Early carbohydrate chemists frequently
observed that the optical rotation of
glucose (and other sugar) solutions could
change with the time, a process called muta
rotation. This indicated that a structural
change was occurring

21. Muta rotation
• A freshly prepared D-glucose solution shows
specific rotation of +111.5o which changes to
+52.5o and becomes constant
• It was eventually found that α-D-glucose has a
specific optical rotation, +111.5°, and that β
-D-glucose has a specific optical rotation of
+19.2°. When both of these are mixed in 38:
62, specific rotation of +52.5 is obtained

22. Muta rotation
• Hence, naturally occurring glucose contains
38% α and 62% β isomer
• Therefore,
Muta rotation involves inter-conversion of
α into β forms of the monosaccharide
with intermediate formation of the linear
aldehyde or ketone

23. Derivatives of Monosaccharides
• Sugar Acids
Sugars with free anomeric carbon atoms are
reasonably good reducing agents and reduce
hydrogen peroxide, ferricyanide , certain
metals (Cu2+ and Ag+), and other oxidizing
agents. Such reactions convert the sugar to a
sugar acid

24. • Sugar Alcohols
– Prepared by the mild reduction of the
carbonyl groups of aldoses and ketoses.
Sugar alcohols are linear molecules that
cannot cyclize in the manner of aldoses
– Alditols are characteristically sweet
tasting, and are widely used as
sweetening agents
– Sorbitol build-up in the eyes of diabetics
is implicated in cataract formation

25. Deoxy Sugars
Phosphate esters

26. Amino Sugars
• D-glucosamine and D-galactosamine contain
an amino group (instead of a hydroxyl group)
at the C-2 position. They are found in many
oligo- and polysaccharides, including chitin, a
polysaccharide in the exoskeletons of insects

27. Storage Polysaccharides
• Storage polysaccharides are important
carbohydrate forms in plants and animals
• It seems likely that organisms store carbohydrates
in the form of polysaccharides rather than as
monosaccharaides to lower the osmotic pressure
of the sugar reserves
• Because, osmotic pressure depends only on
numbers of molecules
– Hence, the osmotic pressure is greatly reduced by
formation of a few polysaccharide molecules out of
thousands (or even millions) of monosaccharide units

28. Starch
• The most common storage polysaccharide in plants is
starch, which has two components:
– α-amylose
– amylopectin
• Most forms of the starch in nature contain 10-30% α-
amylose and 70-90% amylopectin
• α -Amylose is composed of linear chains of D-glucose in
α(1-4) linkages. The chains are of varying lengths,
having molecular weights from several thousand to half
a million

29. • The chain has a reducing end and a non-
reducing end
• Although poorly soluble in water, α -amylose
forms micelles in which the polysaccharide
chain adopts a helical conformation. Iodine
reacts with α-amylose to give a characteristic
blue colour, which arises from the insertion of
iodine into the middle of the hydrophobic
amylose helix

30. CH2OH 6CH OH CH2OH CH2OH CH2OH
2
O 5 O H O H O H H O H
H H H H H
H H H H H
OH H 1 4 OH H 1 OH H OH H OH H
O O O O OH
OH 2
3
H OH H OH H OH H OH H OH
amylose
Non-Reducing end
Reducing end

31. • In contrast to α-amylose, amylopectin, the other
component of typical starches, is a highly branched
chain of glucose units
• Branches occur in these chains every 12 to 30
residues
• The average branch length is between 24 and 30
residues, and molecular weights of amylopectin
molecules can range up to 100 million
• The linear linkages in amylopectin are α(1-4),
whereas the branch linkages are α(1-6)
• As is the case for α-amylose , amylopectin forms
micellar suspensions in water. Iodine reacts with
such suspensions to produce a red-violet colour

32. Starch
CH2OH 6CH OH CH2OH CH2OH CH2OH
2
O 5 O H O H O H H O H
H H H H H
H H H H H
OH H 1 4 OH H 1 OH H OH H OH H
O O O O OH
OH 2
3
H OH H OH H OH H OH H OH
amylose

33. Glycogen
• The major form of storage polysaccharide in
animals is glycogen
• Glycogen is found mainly in the liver (where it
may amount to as much as 10% of the liver mass)
and skeletal muscle (where it accounts form
1-2% of the muscle mass)
• Liver glycogen consists of granules containing
highly branched molecules, with α(1-4) linkage in
linear structure and α(1-6) linkage at branching,
which occurrs every 8-12 glucose units

34. • Like amylopectin, glycogen yields a red-violet
colour with iodine
• Glycogen can be hydrolyzed by α-amylase,
yielding glucose
• It can also be hydrolyzed by glycogen
phosphorylase, an enzyme present in liver and
muscle tissue, to release glucose-1-phosphate

36. Structural polysaccharides
• Cellulose
• Chitin
• Alginates
• Agarose
• Glycosaminoglycans

37. Cellulose
• The most abundant natural polymer found in the
world
• Found in the cell walls of nearly all plants
• One of the principal components providing physical
structural and strength
• Cotton is almost pure cellulose
• Cellulose is a linear homopolymer of D-glucose units,
just as in α-amylose.
• The structural difference, which completely alters the
properties of the polymer, is that in cellulose the glucose
units are linked by β(1-4)-glycosidic bonds, whereas in α -
amylose the linkage is α(1-4)

38. CH2OH 6CH OH CH2OH CH2OH CH2OH
2
O 5 O O H O H O OH
H H H
H H H H H
OH H 1 O 4 OH H 1 O OH H O OH H O OH H
OH H H H
H 2 H
3
H OH H OH H OH H OH H OH
cellulose
β-linkages promote intra-chain
and inter-chain H-bonds and van
der Waals interactions, that
cause cellulose chains to be
straight & rigid, and pack with a Schematic arrangement of
crystalline arrangement in thick cellulose chains in a microfibril.
bundles - microfibrils

39. Glycosaminoglycans
• Previously called mucopolysaccharides
•Linear polymers of repeating disaccharides
–The constituent monosaccharides tend to be modified,
with acidic groups, amino groups, sulfated hydroxyl
and amino groups, etc.
•Such compounds tend to be negatively
charged, because of the prevalence of acidic
groups

40. Hyaluronate (Hyaluronic acid)
•Hyaluronate is a glycosaminoglycan with a
repeating disaccharide consisting of 2 glucose
derivatives, D-glucuronic acid & N-acetyl-D-
glucosamine
•These monosaccharides are linked
through β(1→3) linkages
•Disaccharides are linked through β(1→4).

41. CH2OH
D-glucuronate 6
− H 5 O
6COO H
4 1 O
O H
H 5
H OH H
4 H 1 3 2
OH
H H NHCOCH3
3 2 O
H OH N-acetyl-D-glucosamine
hyaluronate

42. Proteoglycans
• These are also glycosaminoglycans that are covalently
linked to serine residues of specific core proteins
•The glycosaminoglycan chain is synthesized by
sequential addition of sugar residues to the core
protein

43. Heparan sulfate is initially synthesized on a membrane-
embedded core protein as a polymer of alternating N-
acetylglucosamine and glucuronate residues.
Later, in segments of the polymer, glucuronate
residues may be converted to the sulfated sugar
iduronate 2-sulfate, while N-acetylglucosamine
residues may be sulfated- N-sulfo-glucosamine-6-
sulfate
iduronate-2-sulfate N-sulfo-glucosamine-6-sulfate
H CH2OSO3−
H O H O H
−
COO H
OH H O OH H
H O
H OSO3− H NHSO3−
heparin or heparan sulfate - examples of residues

44. Heparin, a soluble glycosaminoglycan found in granules
of mast cells, has a structure similar to that of heparan
sulfates, but is more highly sulfated
When released into the blood, it inhibits clot formation
by interacting with the protein antithrombin.
Heparin has an extended helical conformation
Charge repulsion by the many negatively charged
groups may contribute to this conformation

45. Some proteoglycans of the extracellular matrix bind
non-covalently to hyaluronate via protein domains called
link modules. E.g.
• Multiple copies of the aggrecan proteoglycan
associate with hyaluronate in cartilage to form large
complexes
• Versican, another proteoglycan, binds hyaluronate in
the extracellular matrix of loose connective tissues.
CH2OH
D-glucuronate 6
− H 5 O
6COO H
4 1 O
O H
H 5
H OH H
4 H 1 3 2
OH
H H NHCOCH3
3 2 O
H OH N-acetyl-D-glucosamine
hyaluronate

46. Chitin
• A polysaccharide that is similar to cellulose, both
in its biological function and its primary,
secondary, and tertiary structure
• The structure of chitin is identical to cellulose,
except that the -OH group on each C-2 is
replaced by -NHCOCH3, so that the repeating
units are N-acetyl-D-glucosamines in β-(1-4)
linkage

47. • An other, significant difference between
cellulose and chitin is that the chains are
arranged in parallel (all the reducing ends
together at one end of a packed bundle and
all the non-reducing ends together at the
other end) or antiparallel (each sheet of
chains having the chains arranged oppositely
from the sheets above and below)

48. • Natural cellulose seems to occur only in parallel
arrangements. Chitin, however, can occur in
three forms, sometimes all in the same
organism
– alpha-Chitin is an all-parallel arrangement of the
chains
– β-chitin is an antiparallel arrangement
– d-chitin, the structure is thought to involve pairs of
parallel sheets separated by single antiparallel
sheets.