Carbohydrates

1
Carbohydrates

• Classification
• Monosaccharides
• Chiral Carbon Atoms
• Structures of Important Monosaccharides
• Cyclic Structures

2
Carbohydrates

• The most abundant organic compounds in plants
• Carbohydrate- hydrate of carbon
• Derives from formula Cn(H2O)m
• Glucose C6H12O6 C6(H2O)6
• Sucrose C12H24O12 C12(H2O)12
• Not all fit formula

3
Carbohydrates

• Major source of energy from our diet
• Composed of the elements C, H and O
• Produced by photosynthesis in plants

4
Carbohydrates

• Most carbohydrates are polyhydroxyaldehydes,
  polyhydroxyketone or a substance that yields them
  on hydrolysis

5
Types of Carbohydrates

• Monosaccharides
• Disaccharides
• Contain 2 monosacchride units
• Oligosaccharides
• Contain 3 3 dozen monosaccharide units
• Polysaccharides
• Contain 100s monosaccharide units

6
Monosaccharides

• Most common monosaccharides have 39 carbons
• Three Carbons Triose
• Four Carbons Tetrose
• Five Carbons Pentose
• Six Carbons Hexose

7
Monosaccharides

• Aldoses are monosaccharides with an aldehyde
  group and many hydroxyl (-OH) groups.
• Ketoses are monosaccharides with a ketone group
  and many hydroxyl (-OH) groups.

8
Carbohydrate Nomenclature (II)

• Monosaccharide (carbon numbers 3-7)
• Aldoses
• Contain aldehyde
• Name aldo--oses (e.g., aldohexoses)
• Ketoses
• Contain ketones
• Name keto--oses (ketohexoses)

9
Aldoses
O
HOCH2CHCH OH
C
H
O
C
HOH
same as
C
H
OH
2
glyceraldehyde
10
Ketoses
C
H
O
HOCH2CCH2OH
2OH
same as
C
O
C
H
OH
2
dihydroxyacetone
11
Learning Check

• Identify each as (aldo or keto) tetrose,
  pentose or hexose

12
Solution

• A B
• aldohexose ketopentose

13
Fischer Projection Formulas

• 2-D representation to the configuration of
  carbohydrates
• Contains a stereocenter( tetrahedral C atom that
  has 4 different groups bonded to it)

C
H
O
C
HOH
C
H
OH
2
14
Chiral Objects

• Chiral compounds have the same number of atoms
  arranged differently in space.
• A chiral carbon atom has four different groups
  attached

15
Mirror Images

• The three-dimensional structure of a chiral
  compound has a mirror image.
• Your hands are chiral. Try to superimpose your
  thumbs, palms, back of hands, and little fingers.
  Is it possible? Why or why not?

16
Learning Check C2

• Determine if there is a chiral carbon in each
  compound.
• A B

C
l
C
C
H
H
3
C
H
C
H
2
3
17
Solution C2

• A Yes, 4 different B No, the
• groups are attached 2 H
  atoms
• to the second C atom are identical

18
Examples of Stereoisomers
epimers
enantiomers
epimers
O
O
O
O
OH
HO
HO
OH
HO
HO
HO
OH
OH
OH
HO
OH
HO
OH
OH
OH
CH
OH
CH
OH
CH
CH
OH
OH
2
2
2
2
diastereomers
D-Glucose
D-mannose
D-Talose
L-Talose
19
D and L Notation

• D,L tells which of the two chiral isomers we are
  referring to.
• If the OH group on the next to the bottom carbon
  atom points to the right , the isomer is a
  D-isomer if it points left, the isomer is L.
• The D form is usually the isomer found in
  nature.

20
D notation

O
C
H
C
O
H
H
C
O
H
H
C
H
O
H
2
R
i
g
h
t



D
21
Glucose
H
C
O
C
H
O
H
C
H
H
O
O
H
H
C
H
O
H
C
C
H
O
H
2
D
-
G
l
u
c
o
s
e
22
Fructose
C
H
OH
2
C
O
C
H
H
O
O
H
H
C
H
O
H
C
C
H
O
H
2
D
-
F
r
u
c
t
o
s
e
23
Galactose
O
H
C
C
O
H
H
C
H
O
H
C
H
H
O
C
O
H
H
C
H
O
H
2

• D-galactose

24
Cyclic Structures

• Monosaccharides with 5-6 carbon atoms form cyclic
  structures
• The hydroxyl group on C-5 reacts with the
  aldehyde group or ketone group

O
o
25
ACETALS AND HEMIACETALS
aldehyde
hemiacetal
acetal
ketone
(ketal)
(hemiketal)
older term
older term
26
Cyclization of Monosaccharides
only sugars seem to make stable hemiacetals
a hemiacetal
glucose
glucopyranose
27
HAWORTH PROJECTIONS
It is convenient to view the cyclic sugars
(glucopyranoses) as a Haworth Projection, where
the ring is flattened.
Standard Position
HAWORTH PROJECTION
upper-right back
This orientation is always used for a Haworth
Projection
a-D-()-glucopyranose
28
WE WILL LEARN HOW TO CONVERT FISCHER
PROJECTIONS TO HAWORTH PROJECTIONS OF EITHER
ANOMER
GLUCOSE ENANTIOMERS
FISCHER
HAWORTH
D-()-glucose
L-(-)-glucose
29
AN OPEN CHAIN CAN CONVERT TO EITHER ANOMER
FISCHER
HAWORTH
a-ANOMER
OPEN CHAIN
b-ANOMER
You cant tell which anomer will result
(predominate) when you look at the Fischer
Projection.
That information is not contained in Fischer
Projection.
30
Sugar Anomers

• The formation of hemiketals and hemiacetals
  results in
• an asymmetric carbon atom.
• Isomers that differ only in their configuration
  about the
• new asymmetric carbon are called anomers, the
  carbonyl
• carbon is called anomeric carbon.
• a-anomer has the hydroxyl group on the same side
  of
• The oxygen at the highest numbered asymmetric
  carbon
• ß-anomer has the hydroxyl group on the opposite
  side of
• The oxygen at the highest numbered asymmetric
  carbon

31
HAWORTH PROJECTIONS
HERE ARE SOME CONVENTIONS YOU MUST LEARN
1) The ring is always oriented with the oxygen
in the upper right-hand back corner.
D
2) The -CH2OH group is placed UP for
a D-sugar and DOWN for an L-sugar.
L
3) a-Sugars have the -CH2OH group and the
anomeric hydroxyl group trans.
a
4) b-Sugars have the -CH2OH group and the
anomeric hydroxyl group cis.
b
32
SOME HAWORTH PROJECTIONS
D-SUGARS
b-D
ANOMERS
a-D
BOTH OF THESE ARE D-GLUCOSE
33
SOME HAWORTH PROJECTIONS
L-SUGARS
a-L
ANOMERS
b-L
BOTH OF THESE ARE L-GLUCOSE
34
CONVERTING TO HAWORTH PROJECTIONS
D-()-glucose
-CH2OH up D
D O W N
U P
1
6
BOTH ANOMERS OF A D-SUGAR (D-glucose)
2
5
3
1
4
4
2
3
5
6
HAWORTH PROJECTIONS
FISCHER PROJECTION
35
HAWORTH PROJECTIONS OF L-SUGARS
L-()-glucose
D O W N
U P
BOTH ANOMERS OF A L-SUGAR (L-glucose)
on left L
HAWORTH PROJECTIONS
FISCHER PROJECTION
36
CONVERTING FISCHER TO HAWORTH PROJECTIONS
CAUTION !
Students often get the erroneous impression that
all the Haworth rules are reversed for L-sugars
- this is not the case!
The only difference when converting D- and L-
sugars is
These rules are the same for both D- and
L- sugars
LEFT UP RIGHT DOWN
b cis a trans
D-sugars -CH2OH UP
L-sugars -CH2OH DOWN
37
Learning Check C3

• Write the cyclic form of ?-D-galactose

O
H
C
C
O
H
H
C
H
O
H
C
H
H
O
C
O
H
H
C
H
O
H
2
38
Solution C3
C
H
O
H
2
o
O
H
O
H
O
H
O
H
?-D-galactose
39
FRUCTOSE
standard position
cis b
up D
1
..

anomeric carbon
2
6
3
2
5
..
4
3
4
1
..
5
6
b-D-(-)-Fructofuranose
D-(-)-Fructose
40
ANOMERS
anomeric carbon
(hemiacetal)
for clarity hydroxyl groups on the chain are
not shown
anomers differ in configuration at the anomeric
carbon
41
FURANOSE AND PYRANOSE RINGS
6
a pyranose ring
two anomers are possible in each case
5
a furanose ring
for clarity no hydroxyl groups are shown on the
chains or rings
42
CONVERTING TO ACTUAL CONFORMATIONS
b-D-()-glucopyranose
-CH2OH up D
HAWORTH
CONFORMATION
a-D-()-glucopyranose
43
Monosaccharide Structures
Conformation of monosaccharide
Conformation of glucose
44
Mutarotation

• Mutarotation A small amount of open chain is
  in equilibrium with the cyclic forms.
• The most stable form of glucose is ß-D-glucose .
• ?-D-glucose D-glucose (open)
  ß-D-glucose
• (36) (trace) (64)

45
Mutarotation of Glucose
hemiacetals
66
34
open chain
lt 0.001
46
Physical Properties

• Monosaccharides are colorless crystalline solids,
  very soluble in water, but only slightly soluble
  in ethanol

D-fructose 174
honey 97
D-glucose 74
molasses 74
corn syrup 74
D-galactose 0.22
sucrose (table sugar) 100
lactose (milk sugar) 0.16
47
Glycosides (Acetals)

• Glycoside bond the bond from the anomeric carbon
  of the glycoside to an -OR group
• Glycosides are named by listing the name of the
  alkyl or aryl group attached to oxygen followed
  by the name of the carbohydrate with the ending
  -e replaced by -ide
• methyl a-D-glucopyranoside
• methyl b-D-ribofuranoside

48
Formation of Glycosides
49
Formation of Glycosides (acetals)

• Glycoside a carbohydrate in which the -OH of
  the anomeric carbon is replaced by -OR
• Methyl b-D-glucopyranoside
• (Methyl b-D-glucoside)

O
H
O
H
H
H
H
Chair conformation
Haworth projection
50
Reduction to Alditols

• The carbonyl group of a monosaccharide can be
  reduced to an hydroxyl group by a variety of
  reducing agents, including NaBH4 and H2 /M

CHO
OH
H
OH
H
Ni
H
HO
H
HO

OH
H
OH
H
OH
H
OH
H
D-Glucose
51
Sugar Derivatives

• Sugar alcohols are formed by mild reduction (with
  NaBH4 or similar) of carbonyl groups of sugars
• Add -itol to the name of the parent sugar
• Amino sugars contain an amino group in place of a
  hydroxyl group. They are found in many
  polysaccharides (for example, chitin).

52
Examples of Sugar Derivatives
CH
OH
1
2
2
OH
Sugar Alcohols
HO
3
4
OH
OH
5
6
CH
OH
2
D-Mannitol
D-Glucitol
(sweeten sugarless gum)
(sorbitol, build
up in eyes of diabetics)
6
6
CH
OH
CH
OH
2
2
O
O
C
5
C
5
OH
OH
Amino Sugars, Muramic Acid
O
OH
C
C
C
C
4
4
1
1
C
C
H
C
C
H
OH
OH
3
3
2
2
NH
NH
2
2
C
H
C
COOH
3
H
b
-D-Glucosamine
Muramic Acid
53
Oxidation to Aldonic Acids

• Oxidation of -CHO of an aldose to -CO2H can be
  carried out using Tollens, Benedicts, or
  Fehlings solutions

O
O


Tollens' solution
O
O


54
Oxidation to Aldonic Acids

• 2-Ketoses are also oxidized by these reagents
  because, under the conditions of the oxidation,
  2-ketoses equilibrate with isomeric aldoses

A 2-ketose
55
Testing for Glucose

• A rapid test for determination of glucose levels
  in biological fluids

CHO
56
Oxidation to Uronic Acids

• Enzyme catalyzed oxidation of the primary alcohol
  at carbon 6 of a hexose yields a uronic acid
• Found in connective tissue
• Used by liver

57
Carbohydrates

• Disaccharides
• Polysaccharides

58
Disaccharides

• Simplest oligosaccharides
• Contain two monosaccharides linked by a
  glycosidic bond
• The free anomeric carbon is called reducing end
• The linkage carbon on the first sugar is always
  C-1. So disaccharides can be named as
  sugar-(a,b)-1, -sugar, where a or b depends on
  the anomeric structure of the first sugar. For
  example, Maltose is glucose- a -1,4-glucose.

59
Important Disaccharides

• Maltose Glucose Glucose
• Lactose Glucose Galactose
• Sucrose Glucose Fructose

60
Structures of Disaccharides

• Note the linkage and reducing ends

6
6
CH
OH
CH
OH
2
2
O
O
5
5
OH
OH
O
HOH
4
4
1
1
OH
3
3
2
2
OH
OH
b
Cellobiose (glucose-
-1,4-glucose)
6
6
CH
OH
2
1
5
O
5
CH
OH
2
O
5
4
OH
OH
2
4
1
1
CH
OH
O
2
O
3
3
4
OH
6
3
2
OH
OH
a
Maltose (glucose-
-1,4-glucose)
a
Sucrose (glucose-
-1,2-fructose)
no reducing end
61
Sucrose
C
H
O
H
2
o
O
H
a-1,2- glycosidic bond
O
H
O
H
O
C
H
O
H
2
O
O
H
C
H
O
H
2
O
H
62
Lactose
C
H
O
H
2

• ? -1,4-glycosidic bond
• a-D-Lactose

O
C
H
O
H
2
O
H
O
O
H
O
O
H
O
H
O
H
O
H
?
63
Maltose
?

• ? -1,4-glycosidic bond
• ?- D-Maltose

C
H
O
H
C
H
O
H
2
2
O
O
O
H
O
H
O
H
O
O
H
O
H
O
H
64
Learning Check

• Identify the monosaccharides in each of the
  following
• A. lactose
• (1) glucose (2) fructose (3) galactose
• B. maltose
• (1) glucose (2) fructose (3) galactose
• C. sucrose
• (1) glucose (2) fructose (3) galactose

65
Solution

• A. lactose
• (1) glucose and (3) galactose
• B. maltose
• (1) glucose and (1) glucose
• C. sucrose
• (1) glucose and (2) fructose

66
Polysaccharides

• Starch
• Amylose
• Amylopectin
• Glycogen
• Cellulose

67
Polysaccharides

• Also called glycans
• Starch and glycogen are storage molecules
• Chitin and cellulose are structural molecules
• Cell surface polysaccharides are recognition
  molecules.

68
Polysaccharides

• Glucose is the monosaccharides of the following
  polysaccharides with different linkages and
  branches
• a(1,4), starch (more branch)
• a(1,4), glycogen (less branch)
• a(1,6), dextran (chromatography resins)
• b(1,4), cellulose (cell walls of all plants)
• b(1,4), Chitin similar to cellulose, but C2-OH is
  replaced by NHCOCH3 (found in exoskeletons of
  crustaceans, insects, spiders)

69
Polysaccharides

• Polymers of D-Glucose

C
H
O
H
2
O
O
H
O
H
O
H
O
H
70
Amylose

• Polymer with a-1,4 bonds
• a-1,4 bonds

C
H
O
H
C
H
O
H
2
C
H
O
H
2
C
H
O
H
2
2
O
O
O
O
O
H
O
H
O
H
O
H
O
O
O
O
O
O
H
O
H
O
H
O
H
71
Amylopectin

• Polymer with a-1,4 and a-1,6 bonds branches
• a-1,6 bond
• a-1,4 bonds

O
72
Cellulose

• Polymer with ß-1,4 bonds
• ß-1,4 bonds

C
H
O
H
2
O
O
O
H
C
H
O
H
2
O
O
O
H
O
H
C
H
O
H
2
O
O
O
H
O
H
O
O
H
73
Learning Check

• Identify the polysaccharide in each as
• starch 2) glycogen 3) cellulose
• A. B. C.

74
Solution

• 3) cellulose 1) starch 2)
  glycogen

75
Acidic Polysaccharides

• Hyaluronic Acid
• Contain carboxyl group and/ or sulfuric ester
  groups
• Structure and function of connective tissue
• 300-10,000 repeating units depending on organ
• Heparin
• Sulfonated polysaccharides
• Anticoagulant

76
Carbohydrates

• Carbohydrates are the most abundant organic
  molecules in nature
• Photosynthesis energy stored in carbohydrates
• Carbohydrates are the metabolic precursors of all
  other biomolecules
• Important component of cell structures
• Important function in cell-cell recognition
• Carbohydrate chemistry
• Contains at least one asymmetric carbon center
• Favorable cyclic structures
• Able to form polymers

77
Carbohydrate Nomenclature (I)

• Carbohydrate Classes
• Monosaccharides (CH2O)n
• Simple sugars, can not be broken down further
• Oligosaccharides
• Few simple sugars (2-6).
• Polysaccharides
• Polymers of monosaccharides

78
Carbohydrate Nomenclature (II)

• Monosaccharide (carbon numbers 3-7)
• Aldoses
• Contain aldehyde
• Name aldo--oses (e.g., aldohexoses)
• Memorize all aldoses in Figure ?
• Ketoses
• Contain ketones
• Name keto--oses (ketohexoses)

79
Sterochemistry of Monosaccharides (I)

• D,L steroisomers refers to the configuration of
  the highest assymmetric carbon (farthest from the
  carbonyl carbon)
• Hydroxyl group is drawn to the right -? D
• Hydroxyl group is drawn to the left -? L
• Note that D, L assignment does not specify the
  sign of rotation of plane-polarized light.
• D()-glucose is dextrorotatory D-glucose
  D(-)-fructose is levorotatory D-fructose
• D is the preferred configuration in nature

80
Sterochemistry of Monosaccharides (II)

• Each asymmetric carbon can have 2 configurations,
  thus for a sugar of n carbons, there are 2(n-2)
  possible steroisomers. Know the following
  definitions
• Diastereomers
• Isomers that have opposite configuration at one
  or more carbons but are not mirror images of each
  other
• Enantiomers
• Isomers that are mirror images
• Epimers
• Isomers that differ in only one carbon
  configuration

81
Acetals, Ketals and Glycosides

• Hemiacetals and hemiketals can react with
  alcohols in the presence of acid to form acetals
  and ketals.
• Pyranose and furanose forms
• of monosaccharides react with
• alcohols to form glycosides.

82
D and L Notation

• D,L tells which of the two chiral isomers we are
  referring to.
• If the OH group on the next to the bottom carbon
  atom points to the right , the isomer is a
  D-isomer if it points left, the isomer is L.
• The D form is usually the isomer found in nature.

83
Cyclic Hemiacetals
Haworth Projection
Fisher Projection
a-D-glucopyranose
b-D-glucopyranose
84
Cyclic Hemiacetals
Haworth Projection
Fisher Projection
a-D-glucopyranose
b-D-glucopyranose
85
Cyclic Hemiketals
Haworth Projection
Fisher Projection
a-D-fructofuranose
D-Fructose
b-D-fructofuranose
86
Cyclic Structures of Aldohexoses

• Alcohols react readily with aldehydes to form
  hemiacetals
• Linear form of aldohexoses could undergo a
  similar intra-molecular reaction to form a cyclic
  hemiacetals
• See next slide

87
Haworth Structure for D-Isomers

• The cyclic structure of a D-isomer has the final
  CH2OH group located above the ring.

88
Glycosides

• Glycoside bond the bond from the anomeric
  carbon of the glycoside to an -OR group
• Glycosides are named by listing the name of the
  alkyl or aryl group attached to oxygen followed
  by the name of the carbohydrate with the ending
  -e replaced by -ide
• methyl ?-D-glucopyranoside
• methyl ?-D-ribofuranoside

89
Formation of Glycosides

• Glycoside a carbohydrate in which the -OH of
  the anomeric carbon is replaced by OR
• Methyl ?-D-glucopyranoside (methyl ?-D-glucoside)

90
Oxidation to Aldonic Acids

• Oxidation of an aldose with a buffered solution
  of Br2 in water converts the aldehyde group to a
  carboxyl group

91
Haworth Structure for D-Glucose

• Write OH groups on the right (C2, C4) up
• Write OH groups on the left (C3) down
• The new OH on C1 has two possibilites down for
  ? anomer, up for ? anomer

92
Haworth Structure for D-Glucose
?
?
?-D-Glucose ?-D-Glucose
93
Formation of 2,2-Dimethoxypropane
THIS IS A NON-CYCLIC ACETAL
remove H2O
94
CYCLIC ACETALS
Cyclic acetals can be formed if a bifunctional
alcohol is used.
1,2-ethanediol
H
/benzene
H2O
acetophenone