1. CHAPTER 22 CARBOHYDRATES
INTRODUCTION
21.1A CLASSIFICATION OF CARBOHYDRATES
Carbodydrares: polyhydroxy aldehydes and ketones or substances
that hydrolyze to yield polyhydroxy aldehydes and
ketones.
Monosaccharides: simple carbohydrates cannot be hydrolyzed into
smaller simpler carbohydrates.

2. Disaccharides: on a molecular basis, carbohydrates that undergo
hydrolysis to produce only two molecules of
monosaccharide.
Trisaccharides: those carbohydrates that yield three molecules of
monosaccharide.
Polysaccharide: carbohydrates that yield a large number of molecules
of monosaccharide (﹥10).
Disaccharides Trisaccharides and Polysaccharide are easily
Hydrolysis to monosaccharide .

3. Carbohydrares are the most abundant organic constitutes of plants.
We encounter carbohydrates at almost every turn of our daily life.
21.1B PHOTOSYNTHESIS AND CARBOHYDRATE
METABOLESM
Carbohydrates are synthesized in green plants by photosynthesis:

4. Carbohydrates can be released energy when animals or plants
metabolize them to carbon dioxide and water.
Much of the energy is conserved in ATP. Plants and animals can use
the energy of ATP to carry out all of their energy-requiring process.
When the energy in ATP is used, a coupled reaction takes place in
which ATP is hydrolyzed:

5. MONOSACCHARIDES
22.2A CLASSIFICATION OF MONOSACCHARIDES
Monosaccharides are classified according to:
The number of carbon atoms present in the molecular.
whether they contain an aldehyde or keto group.

6. These two classification are frequently combined. For example:

7. 22.2B D AND L DESIGNATIONS OF MONOSACCHARIDES
Glyceraldehyde exists two enantiomeric forms which have the
absolute configurations:
(+)-Glyceraldehyde should be designated (R)-(+)- Glyceraldehyde
and (-)-Glyceraldehyde should be designated (S)-(-)- Glyceraldehyde
(section 5.5)

8. Other system designated (+)-Glyceraldehyde as D-(+)- Glyceraldehyde
and (-)-Glyceraldehyde as L-(-)-Glyceraldehyde.
D and L designations are not necessarily related to the optical
rotations of the sugars to which they are applied.

9. Fisher projection formula: horizontal lines project out towards the
22.2C ATRUCTURAL FORMULAS FOR MONOSACCHARIDES
Fisher projection formula: horizontal lines project out towards the
reader and vertical lines project behind the plane of the page.

10. Open –chair structure (1, 2, or 3) exists equilibrium with two
cyclic forms 4 and 5 or 6 and 7.

11. The cyclic forms of D-(+)-Glucose are hemiacetals formed by an
intramolecular reaction of the –OH group at C-5 with the aldehyde
group.

12. Notes:

13. (1) These two cyclic forms are diastereomers that differ only in the configuration of C-1.
(2) In carbohydrate chemistry diastereomers of this type are called
anomers, and the hemiacetal carbon atom is called the anomeric
Carbon atom
( 3) In the orientation shown the αanomer has the –OH down and
the βanomer has the –OH up.
(4) The actual conformations of the rings are the chair forms. In the
β anomer of D-glucose, all of the large substituents, -OH, or
–CH2OH , are equatorial. In the α anomer, the only bulky axial
substituent is the -OH at C-1

14. 22.3 MUTAROTATION
The optical rotations of αand βforms are found to be significantly
different,but when an aqueous solution of either form is allowed
to stand, its rotation changed.
Mutarotation: the change in rotation towards an equilibrium value.

15. Ordinary D-(+)-glucose has the α configuration at the anomeric
carbon atom and that higher melting form has the βconfiguration.
The percentage of the α andβanomers present at equilibrium.

16. GLYCOSIDE FORMATION
When a small amount of gaseous hydrogen chloride is passed into
a solution of D-(+)-glucose in methanol, the reaction as follows:

17. The mechanism for the formation of the methyl glucosides:

18. In acidic solutions, however, glycosides undergo hydrolysis to
produce a sugar and alcohol:

19. 22.5 REACTIONS OF MONOSACCHARIDES
Dissolving monosaccharides in aqueous base causes them to undergo
a series of keto-enol tauomerizations that lead to isomerizastions.

20. 22.5A FORMATION OF ETHERS
A methyl glucoside can be converted to the derivative by treating
it with excess dimethyl sulfate in aqueous sodium hydroxide.

21. The methoxy groups at C-2,C-3,C-4 and C-6 atoms are stable in dilute
aqueous acid, but C-1is different from the others because it is Part of
an acetal linkage.
Under dilute aqueous acid the methoxy group at C-1 will hydrolyze:

22. The oxygen at C-5 dose not bear a methyl group brcause it was
originally a part of the cyclic hemiacetal linkage of D-glucose
25.5B CONVERSION TO ESTERS
Under excess acetic anhydride and a weak base monosaccharide
converts all of the hydroxyl groups to ester groups
If the reaction is carried out at a low temperature, the reaction
occurs stereospecifically:the αanomer gives the α-acetate and
the βanomer gives the β-acetate.

23. 22.5C CONVERSION TO CYCLIC ACETALS AND KETALS
Aldehydes and ketones react with open-chain 1,2-diols to produce
cyclic acetals and ketals.
If the 1,2-diol is attached to a ring, as in a monosaccharide,
formation of the cyclic acetal or ketal occurs only when the
vicinal hydroxyl froups are cis to each other.

24. This reaction can be used to protect certain hydroxyl groups of a
sugar while reactions are carried out on other parts of the molecule.
OXIDATION REACTIONS OF MONOSACCHARIDES
The most important oxidizing agents are:
Benedict’s or Tollens’ reagent
bromine water
nitric acid
periodic acid.

25. Each of these reagents produces a different and usually specific
effect.
22.6A BENEDICT’S OR TOLLENS’REAGENTS:
REDUCING SUGARS
Benedict’s and Tollens’ reagent give positive tests with aldoses
and ketoses.

26. Sugars that give positive tests with Tollens’or Benedict’s solutions
are known as reducing sugars, and all carbohydrates that contain
a hemiacetal group or a hemoketal group give positive tests.
Carbohydrates that contain only acetal or ketal group do not give
positive tests with Tollens’or Benedict’s solution.
But neither of these reagents is useful as a preparative reagent in
carbohydrate oxidations.
Oxidations with both reagents take place in alkaline solution,
and in alkaline solutions sugars undergo a complex series of
reactions that lead to isomerization.

27. 22.6B BROMINE WATER: THE SYNTHESIS
OF ALDONIC ACIDS
Bromine water is a general reagent that selectively oxidizes
-CHO group to a –COOH group.
Bromine water specifically oxidizes the βanomer, and the initial
product that forms is a δ–aldonolactone.

28. This compound may then hydrolyze to an aldonic acid, and the
aldonic acid may undergo a subsequent ring closure to form a
γ –aldonolactone.

29. 22.6C NITRIC ACID OXIDATION：ALDARIC ACIDS
Dilute nitric acid oxidizes both the –CHO group and the terminal
-CH2OH group of an aldose to –COOH groups.
It is not known whether a lactone is an intermediate in the
oxidation of an aldose to an aldaric acid; however, aldaric
acids from γandδ-lactones readily

30. The aldaric acid obtained from D-glucose is called D-glucaric acid

31. 22.6D PERIODATE OXIDATIONS: OXIDATIVE CLEAVAGE
OF POLYHYDROXY COMPOUNDS
Compounds that have hydroxyl groups on adjacent atoms undergo
oxidative cleavage when they are treated with aqueous periodic
acid. Carbon-carbon bonds breaks and carbonyl compounds
produced.

32. This reaction usually takes place in quantitative yield. By measuring
the number of molar equivalents valuable that are consumed in the
reaction, information can often be gained.
1. Three –CHOH groups : gives one molar equivalent of formiv acid
and two equivalents of formaldehyde.

33. 2. Oxidative cleavage also takes place when an –OH group is
adjacent to the carbonyl group of an aldehyde or ketone(but
no that of an acid or an ester).

34. 3. Periodic acid dose not cleave compounds in which the hydroxyl
groups are separated by an intervening –CH2 group, nor those
in which a hydroxyl group is adiacent to an ether or acetal function.
REDUCTION OF MONOSACCHARIDES:ALDITOLS

35. Aldoses( and ketoses) can be reduced with sodium borohydride to
compounds called alditols.

36. 22.8 REACTIONS OF MONOSACCHARIDES WITH
PHENYLHYDRAZINE: OSAZONES
The aldehyde group of an aldose react with such carbonyl reagents
as hydroxylamine and phenylhydrazine.
Osazone formation results in a loss of the stereocenter at C-2 but
dose not affect other stereocenters.

37. 22.9 SYNTHESIS AND DEGRADATION OF
MONOSACCHARIDES
22.9A KILIANI-FISCHER SYNTHESIS

38. Kiliani-fischer synthesis: the method of lengthening the carbon chain
of the an aldose.

40. We can be sure that the aldotetroses that we obtain from kiliani-fischer
synthesis are both D sugar because the starting compound is
D-glyceraldehyde and its stereocenter is unaffected.
22.9B THE RUFF DEGRADATION
The Ruff degradation can be used to shorten the chain by a similar
unit.
The Ruff degradation involves:
Oxidation of the aldose to an aldonic acid.
Oxidative decarboxylation of the aldonic acid to the next lower
aldose.

41. THE D FAMILY OF ALDOSES
We can place all of the aldose into families or “family trees” based
on their relation to D- or L-glyceraldehyde
Most, but not all, of the naturally occurring aldose belong to the D
family with D-(-)-glucose being by far the most common.
FISCHER’S PROOF OF THE CONFIGURATION OF
D-(+)-GLUCOSE

43. Fischer’s assignment was based on the following reasoning.
Nitric acid oxidation of (+)-glucose gives an optically active
aldaric acid.
(2) Degradation of (+)-glucose gives (-)-arabinose, and nitric acid
oxidation of (-)-arabinose gives an optically active aldaric acid.
(3) A Kiliani-Fischer synthesis beginning with (-)-arabinose gives
(+)-glucose and (+)-mannose; nitric acid oxidation of
(+)-mannose gives an optically active aldaric acid.
(4) Fischer had already developed a method for effectively
interchanging the two end groups(CHO and CH2OH) of an
aldose chain.

45. DISACCHARIDES
22.12A SUCROSE
Sucrose: the most widely occurring disaccharide of ordinary table
sugar.
Structure:

46. The structure of sucrose is based on the following evidence:
Sucrose has the molecular formula C12H22O11
Acid-catalyzed hydrolysis of 1 mol of sucrose yields 1 mol
of D-glucose and 1 mol of D-frutose.
Sucrose is a nonreducing sugar. Neither the glucose not the
fructose portion of sucrose has a hemiacetal or hemiketal
group, thus the two hexoses must have a glycoside linkage
that involves C-1of glucose and C-2 of fructose.
The hydrolysis of sucrose indicates an α configuration at the
glucoside portion and an enzyme known to hydrolyze a
β-fructofuranosides.
Methylation of sucrose gives an octamethyl derivative that,
on hydrolysis, gives 2,3,4,6-tetra-O-methyl-D-glucose and
1,3,4,6-tetra-O-methyl-D-fructose.

47. 22.12B MATOSE
Structure: or
Notes:

48. When 1 mol of maltose is subjected to acid-catalyzed hydrolysis,
it yield 2 mol of D-(+)-glucose.
Maltose is a reducing sugar.
Maltose exists in two anomeric forms: α-(+)-maltose,
, and β-(+)-maltose,
Maltose reacts with bromine water to form a monocarboxylic
acid, maltose acid.
Methylation of maltose acid followed by hydrolysis gives
2,3,4,6-tetra-O-methyl-D-glucose and 2,3,5,6-tetra-O-methyl-D-
gluconic acid.
Methylation of maltose itself, followed by hydrolysis, gives
2,3,4,6-tetra-O-methyl-D-glucose and 2,3,4,6-tri-O-methyl-
D-glucose.

50. 22.12C CELLOBIOSE
Structure:

51. or
Notes:
Cellobiose is a reducing sugar.
Cellobiose also undergoes mutarotation and forms a
phenylosazone.
Cellobiose is hydrolyzed by β-glucosidases. This is indicate
that the glycosidic linkage in cellobiose is β.
22.12D LACTOSE
Lactose is a reducing sugar that hydrolyzes to yield D-glucose
and D-galactose; the glycosidic linkage is β.

52. Structure: or
POLYSACCHARIDES

53. Homopolysaccharides: polysaccharides that are polymers of a single
monosaccharide.
Heteropolysaccharides: those made up of more than one type of
monosaccharide.
Glucan: a homopolysaccharide consisting of glucose monomeric
units.
Galactan: a homopolysaccharide consisting of galactose units
Three important polysaccharides, all of which are glucans,
glycogen, starch and cellulose.

54. 22.13A STARCH
Heating starch with water produce amylose (10-20%)and
amylopectin(80-90%).
Structure of amylose:
In amylopectin the chains are branched. Branching takes place
between C-6 and C-1at intervals of glucose units.

55. Partical structure of amylopectin:
The molecular weight is about 1-6 milion, include hundreds of
interconnecting chains of glucose units.

56. 22.13B GLYCOGEN
In glycogen the chain are much more highly branched and the
molecular weights as high as 100 million.
The size and structure of glycogen suits its function:
Its size makes it too large to across cell membranes.
The structure of glycogen solves the enormous of osmotic
pressure within the cell.
(3) The high branch structure of glycogen simplify the cell’s
logistical problems.
Glucose (from glycogen) is highly water soluble and as an ideal
Source of “ready energy”.

57. 22.13C CELLULOSE
A portion of cellulose structure:
Special property:
The outside –OH groups are ideally situated to “zip” the chains
make together by forming hydrogen bonds.

58. Zipping many cellulose chains together in this way gives a highly
insoluble.
22.13D CELLULOSE DERIVATIVES
Most of the cellulose derivatives include two or three free hydroxyl
groups of each glucose unit which have been converted to an eater
or an ether.
Rayon is made by treating cellulose with carbon disulfide in base
solution.

59. The solution of cellulose xanthate is then passed through a small
Orifice or slit into an acidic solution.
OTHER BIOLOGICALLY IMPORTANT SUGARS
Uronic acids: monosaccharide derivatives in which the –CH2OH
group at C-6 has been specifically oxidized to a carboxyl group.
For example:

60. Deoxy sugars: monosaccharides in which an –OH group has been
replaced by –H.
SUGARS THAT CONTAIN NITROGEN
22.15A GLYCOSYLAMINES

61. Glycosylamine: sugars in which an amino group replaces the
anomeric –OH. For example:
Nucleoside: glycosylamines in which the amino component is a
pyrimidine or a purine and in which the sugar
component is either D-ribose or 2-deoxy-D-ribose.
22.15B AMINO SUGARS

62. Amino sugar: a sugar in which an amino group replaces a
nonanomeric –OH group.
D-glucosamine can be obtained by hydrolysis of chitin. The repeating
units in chitin is N-acetylglucosamine and the glycosidic linkages are
β, 1:4. The structure of chitin is smaller than that of cellulose.
D-glucosamine can also be isolated from heparin.

63. 22.16 GLYCOLIIPIDS AND GLYCOPROTEINS OF THE
CELL SURFACE
Glycolipids: the carbohydrates joined through gltcosidic linkages
to lipids.
Glycoproteins: the carbohydrates joined through gltcosidic linkages
to proteins.
Glycolipids and glycoproteins on the cells are known to be the
agents by which cells interact with other cells and with invading
bacteria and viruses.
The A,B and O blood types are determined, respectively, by the
A, B and H determinants on the blood cell surface.

64. The A,B and H antigens differ only in the monodacchride units at
their nonreducing ends.
Type A antigens carry anti-B antibodies in their serum; type B
antigens carry anti-A antibodies in their serum; type AB cells
have both A and B antigens but have neither anti-A nor anti-B
antigens; type O cells have neither A nor B antigens but have
both anti-A and anti-B antigens.
CARBOHYDRATE ANTIBIOTICS
Streptomycin: isolation of the carbohydrate antibiotic.

65. Streptomycin is made up of the following three subunits:
Other members of this family are antibiotics called kanamycins,
neomycins, and gentamicins. All are based on an amino cyclitol
linked to one or more amino augars. The glycosidic linkage is
nearly always α.