The document discusses various reactions and properties of monosaccharides such as glucose and fructose. It explains that glucose can be converted to sorbitol or mannitol through reduction, and that glucose and fructose can isomerize to each other in weak alkali. It also describes how monosaccharides can cyclize through hemiacetal and hemiketal formation to form pyranoses and furanoses with alpha and beta anomers. Storage polysaccharides like starch, glycogen, and structural polysaccharides such as cellulose, chitin, and glycosaminoglycans are formed from linked monosaccharide units.

1. Reduction
• On reduction with sodium amalgam, glucose is
converted to 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 is
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 Molisch’s test,
Anthrone test, Seliwanoff’s 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
Methylation of glucose produce glucosides

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 for + and – with reference to
glyceraldehyde- the farthest asymetric or
penaltimate 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 a particular
monosaccharide and its stereoisomers,
but
–Such structures ignore one of the most
interesting fact 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 catalyzed by acid or
base and is readily reversible

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

21. Muta rotation
Early carbohydrate Chemists frequently
observed that the optical rotation of
glucose solution changes with the passage
of time; a process called muta rotation. This
indicated the occurrence of structural
change.

22. 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 36:
64, specific rotation of +52.5 is obtained

23. Muta rotation
• Hence, naturally occurring glucose solution
contains 36% α and 64% β isomer
• Muta rotation involves inter-conversion of α
form into β form of the monosaccharide with
intermediate linear aldehyde or ketone

24. 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

25. • Sugar Alcohols: Alditols
–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
– Characteristically sweet tasting, and are
widely used as sweetening agents
–Sorbitol build-up in the eyes of diabetics
is implicated in cataract formation

26. Deoxy Sugars
Phosphate esters

27. 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

28. 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
monosaccharides 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

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

30. H O
OH
H
OHH
OH
CH2OH
H
O H
H
OHH
OH
CH2OH
H
O
HH H O
O
H
OHH
OH
CH2OH
H
H H O
H
OHH
OH
CH2OH
H
OH
HH O
O
H
OHH
OH
CH2OH
H
O
H
1
6
5
4
3
1
2
amylose
Reducing endNon-Reducing end
• The chain has a reducing end and a non-
reducing end

31. • 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

32. • 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 after every 12 to 30
residues
• The average branch length is between 24 and 30
residues, and molecular weight 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

33. Starch
H O
OH
H
OHH
OH
CH2OH
H
O H
H
OHH
OH
CH2OH
H
O
HH H O
O
H
OHH
OH
CH2OH
H
H H O
H
OHH
OH
CH2OH
H
OH
HH O
O
H
OHH
OH
CH2OH
H
O
H
1
6
5
4
3
1
2
amylose

34. Glycogen
• The major form of storage polysaccharide in
animals is glycogen
• It is mainly found in the liver (10% of the liver
mass) and skeletal muscle (1-2% of the muscle
mass)
• It highly branched molecules of glucose, α (1-4)
linkage in linear structure and α (1-6) linkage at
branching
• The branching occurs after every 8-12 glucose
units

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

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

38. Cellulose
• The most abundant natural polymer found in the
world
• Found in the cell wall of nearly all the plants
• This is one of the principal components providing
physical structure and strength
• Cotton is the example of almost pure cellulose
• Cellulose is a linear homopolymer of D-glucose
units, just as in α-amylose
• But with 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)

39. cellulose
H O
OH
H
OHH
OH
CH2OH
H
O
H
OHH
OH
CH2OH
H
O
H H O
O H
OHH
OH
CH2OH
H
H O
H
OHH
OH
CH2OH
H
H
OHH O
O H
OHH
OH
CH2OH
H
O
H H H H
1
6
5
4
3
1
2
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 crystalline
arrangement in thick bundles -
microfibrils Schematic of arrangement of
cellulose chains in a microfibril.

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

41. 1-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).

42. H O
H
H
OHH
OH
COO−
H
H O
OH H
H
NHCOCH3H
CH2OH
H
OO
D-glucuronate
O
1
23
4
5
6
1
23
4
5
6
N-acetyl-D-glucosamine
hyaluronate

43. 2-Proteoglycans
• These are glycosaminoglycans that are covalently
linked to serine residue of a specific core protein
• The glycosaminoglycan chain is synthesized by
sequential addition of sugar residues to the core protein

44. H O
H
OSO3
−
H
OH
H
COO−
O H
H
NHSO3
−
H
OH
CH2OSO3
−
H
H
H
O
O
heparin or heparan sulfate - examples of residues
iduronate-2-sulfate N-sulfo-glucosamine-6-sulfate
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 e.g N-sulfo-glucosamine-6-sulfate

45. 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 anti-thrombin.
Heparin has an extended helical
conformation
heparin: (IDS-SGN)5
PDB 1RID
Charge repulsion by the many negatively charged groups
may contribute to this conformation

46. Some proteoglycans of the extracellular matrix bind
non-covalently to hyaluronate via protein domains called
link modules. E.g.
• Aggrecan proteoglycan associates with hyaluronate in
cartilage to form large complexes
• Versican, proteoglycan, binds hyaluronate in the
extracellular matrix of loose connective tissues.

48. 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

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

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

51. d-chitin