Lecture: Carbohydrates. mono-, di-, polysachcrides.

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chemistry

Carbohydrates. mono-, di-, polysachcrides

1. Lecture: Carbohydrates. mono-, di-, polysachcrides.

MINISTRY OF PUBLIC HEALTH
ZAPOROZHYE STATE MEDICAL UNIVERSITY
DEPARTMENT OF ORGANIC AND BIOORGANIC CHEMISTRY
LECTURE: CARBOHYDRATES.
MONO-, DI-, POLYSACHCRIDES.

2. Plan

PLAN
1. Classification of carbohydrates.
2. Nomenclature.
3. Structural representations be Fisher and Haworth.
4. Chirality. Optical isomers.
5. Tautomerism. Mutarotation.
6. Epimerization.
7. Chemical properties:
8. Identification reactions.
9. Disaccharides: maltose, galactose, cellobiose,
sucrose.
10. Polysaccharides: starch, hyaluronic acid,
chondroitin sulfate, heparin.
2

3.

Carbohydrates
The term "carbohydrate" was proposed by
K.G. Shmidt in 1844.
Cn(H2O)m
(n=3-9)
A carbohydrate is macromolecule,
consisting of carbon, hydrogen, and
oxygen
atoms, usually with a
hydrogen : oxygen atom ratio of 2:1
(as in water) with the empirical
formula Cm(H2O)n.
Structurally they are polyhydroxy
aldehydes and ketones.
3

4.

Carbohydrates. Classification.
There are two classes of carbohydrates:
simple carbohydrates and complex carbohydrates.
Simple carbohydrates are monosacrharides (2 or more
monosachcharides linked together).
Disachcharides have 2 linked monosaccharides.
Oligosacharides have 3 to 10.
Polysaccharides have 10 or more.
Homopolisaccharides consist of the same monosaccharide
residues (starch, cellulose, etc.).
Heteropolysaccharides – of different monosaccharide
4
residues (hyaluronic acid, etc.).

5.

Monosaccharide‘s classification.
type of the carbonyl
group
ketose
CH2OH
HO
C O
H
H
OH
H
OH
CH2OH
D-fructose
aldose
H
O
C
H
OH
H
OH
H
OH
Carbon chain length
3 Carbon - Trioses are not saccharides.
4 Carbon - Tetroses are unknown in nature.
5 Carbon - Pentoses
are widely used.
6 Carbon - Hexoses
CH2OH
D-ribose
5
ketohexose
aldopentose

6.

The number of optical isomers: N=2n (number of asymmetric centers)
H
triose
H
O
C
H
H
O
C
* OH
H
CH2OH
D-glyceraldehyde
* OH
* OH
CH2OH
D-eritrose
Dexter-reference
compond
tetroses
H
O
C
* H
HO
* OH
H
CH2OH
D-treose
6

7.

Structure of monosaccharides.
Carbonyl and hydroxyl groups of monosaccharides react
to form intramolecular hemiacetal:
O
R'
OH
+
H
C
OH
R'O
R
C
H
R
7

8.

The structure of monosaccharides is
presented in three forms:
1. Fisher projection:
representation.
straight
chain
2. Haworth projection: simple ring in
perspective.
3. Conformational representation:
chair and boat configurations.
8

9.

Structure of monosaccharides.
Fisher projection
β-Hemiacetal
hydroxyl
β,D-glucopyranose
Anomeric
center
Anomeric
center
D-Glucose
α-Hemiacetal
hydroxyl
Dexter
OH
α,D-glucopyranose
9

10.

Hydroxyl group at the anomeric center is called a
hemiacetal or glycoside.
Diastereomers - stereoisomers that are not mirror
images of each one.
Anomers - diastereomers differing in configuration of
the anomeric carbon atom.
At the location of α-anomer hemiacetal hydroxyl is the
same as "end" chiral center hydroxyl.
Characterisic tautomerism is ring-chain or
cyclo-oxo tautomerism.
10

11.

Prospective Haworth formula (1929)
α-Hemiacetal hydroxyl
11

12.

Prospective Haworth formula
One can remember that the β anomer is cis by the mnemonic,
"It's always better to βe up".
12

13.

Mutarotation is the change in specific rotation that
occurs when an α or β form of a carbohydrate is
converted to an equilibrium mixture of the two.
Isomeric transformation of monosaccharides by the
action of alkalis is called epimerization.
Epimers are called diastereoisomers, that are differ
by configuration of only one of several chiral
centers (D-glucose and D-mannose, D-xylose and
D-ribose, etc.).
13

14.

Epimerization in alkaline media
Keto-endiol tautomerism
14

15.

Chemical properties
1. Intermolecular dehydration
HCl; t
pentose
- 3H2O
O
O
C
H
furfural
hexose
HCl; t
- 3H2O
HOH2C
O
C
O
H
5-hydroxymethylfurfural
Reaction to distinguish pentoses from hexoses.

16.

Chemical properties
1. Intermolecular dehydration
Reaction to distinguish pentoses from hexoses.

17.

Molish test
α-naphtol
OH
O
SO3 H
HOH2 C
O
C
O
H2SO4
HOH2 C
O
C
H
HO3 S
OH
red-violet
condensation product
17

18.

Selivanov’s test
18

19.

2. Reactions involving aldehyde group
Reaction with hydroxylamine
H
O
H
C
H
OH
R
H N_OH
2
- H2O
hexose
OH
C
H
OH
-H2O
R
oxime
C
-H2O
N
H
N
OH
R
AgOH
- AgCN
- H2O
H
O
C
(the product
with one less
carbon atom)
R
19
oxinitrile
pentose

20.

Cyanohydrin’s synthesis
H
O
C N
O
C
H
O
OH
C
C
O
C
CH OH
CH OH
CH OH
CH OH
CH OH
CH OH
CH OH
CH OH O
CH OH
CH OH
CH OH
CH OH
CH OH
CH OH
CH
CH OH
CH OH
HCN
R
aldohexose
HOH
CH OH -NH
3
R
hydroxynitrile
R
hydroxy acid
-H2O
R
lactone
[H]
CH OH
R
aldoheptose
(the product
with one
more carbon
atom)
20

21.

H
C
O
H
CH2OH
OH
HO
H
H
OH
H
[H]
HO
H
CH2OH
3. Reduction
HO
OH
D-Xylitol
O
diabetic
sweeteners
C H2OH
C
H
H
CH2OH
D- Xylose
H
OH
H
OH
H
H
OH
H
OH
CH2OH
D-Glucose
[H]
HO
OH
H
H
OH
H
OH
CH2OH
D -Sorbitol
21

22.

H
C
4. a) Oxidation
in neutral and
mild acidic
media
HO
O
H
OH
C
HBrO (Br2+H2O)
H
D -Glucose
D - Gluconic acid
O
COOH
C
b) Oxidation
with strong
oxidizers
H
HO
OH
R
R
H
O
H
OH
H
H
OH
H
OH
CH2OH
D - Glucose
HNO3 conc.
HO
OH
H
H
OH
H
OH
COOH
D - Glucaric acid
22

23.

c) Oxidation by enzymes
CH2OH
O
HO
OH
H
OCH3
COOH
O
[O]
HO
COOH
O
HO
H
C
H
OH
OH
OH
OH
OH
methyl-D-glucopyranoside
OH
OCH3
H2O; H+
-CH3OH
O
OH
HO
H
H
OH
H
OH
HO
C
O
D-Glucuronic acid
23

24.

Identification of aldehyde group with:
+ [Ag(NH3)2]OH
R C
O
H
Tollen's reagent
+ Cu2+ (комплекс)
Ag +
Oxidation products
Cu2O +
Felling's reagent
24

25.

5. Glycosides formation:
CH2OH
O
2
OH
HO
OH
OH
D-Glucopyranose
Glycoside
bonds
2C2H5OH
HСl
-2H2O
CH2OH
O OC H
2 5
CH2OH
O H
HO
OH
+
HO
OC2 H5
OH
ethyl- D-Glucopyranoside
OH
H
OH
ethyl- D-Glucopyranoside
glycone aglycone
25

26.

6. Acylation:
CH2OH
O
HO
ОН
OН
5(CH3CO)2O
СН3COONa
AcO
CH2OAc
O
ОAc + 5AcOH
OAc
OAc
OH
Ас = СН3СО-
penta -O-acetyl-D-glucopyranose
7. Alkylation:
CH2OH
O
HO
OH
OH
OH
CH2OCH3
O
CH2OCH3
O
5CH3I
H3CO
OMe
OCН3
Н2О; Н+
- СН3ОН H C
3 O
OCН3
O-methyl-2,3,4,6-tetramethylD-glucopyranoside
OH
OCН3
OCН3
2,3,4,6-tetramethylD-glucopyranose
26

27.

Disaccharides (bioses)
Depending on the method of the glycosidic bond formation
reducing
nonreducing
In reducing disaccharide glycoside bond is formed by
hemiacetal (glycoside) hydroxyl group and one alcoholic
hydroxyl group (usually at C4) of another monosaccharide.
Thus, there is one free hemiacetal hydroxyl group.
In nonreducing disaccharide there is absent free
hemiacetal hydroxyl.
27

28.

Maltose
-1',4-glycosidic bond
6'
6
CH2OH
O
5'
4'
HO
1'
OH
3'
2'
OH
4
O
CH2OH
O
5
H
OH
3
1
OH
2
OH
4-O-( -D-Glucopyranosyl)-D-Glucopyranose
28

29.

Cellobiose
-1',4-glycosidic bond
6
CH2OH
O
5'
4'
HO
1'
OH
3'
2'
OH
O
4
CH2OH
O
5
OH
3
29
6'
1
OH
2
OH
4-O-( -D-Glucopyranosyl)-D-Glucopyranose

30.

Lactose
-1',4-glycosidic bond
6'
4'
1'
OH
3'
2'
OH
O
4
CH2OH
O
5
OH
3
30
6
CH2OH
O
HO 5'
1
OH
2
OH
4-O-( -D-Galactopyranosyl)- D-Glucopyranose

31.

6'
CH2OH
5'
O
Sucrose
4'
HO
1'
OH
3'
6
HO CH2
5
2'
HO O -1',2-glycosidic bond
O
HO
4
nonreducing
sugar
3
2
1CH2OH
OH
2-О-( -D-Glucopyranosyl)- -D-Fructofuranoside
"Inversion" - a sign change of the specific rotation
after the hydrolysis of sucrose.
A mixture of equal amounts of D-glucose and
D-fructose is invert sugar.
31

32.

Sucrose. chemical properties.
Doesn’t mutorotate
No reactions by aldehyde group
Hydrolysing to glucose and fructose
Alkylation to ethers
Acylation to esters
32
No silver mirror reaction

33.

Starch. Structure
Amylopectine 80%
Insoluble Н2О
Amylose 20%
Soluble in Н2О
Starch hydrolysis
(C6H10O5)n
starch
(C6H10O5)x
C12H22O11
C6H12O6
dextrins
(x < n)
maltose
D-glucose

34.

Amylose
Spiral structure
α-1,4-glycosidic bond
...
CH2OH
O
CH2OH
O
CH2OH
O
CH2OH
O
OH
OH
OH
OH
O
O
OH
OH
...
O
O
OH
OH
34

35.

Amylose with iodine forms
clastrates of dark blue color.
35

36.

...
Amylopectin
CH2OH
O
...
CH2OH
O
4'
1
OH
branched structure
1
OH
O
O
OH
CH2OH
O
α-1,4’-glycosidic bond
CH2OH
O
4'
1
OH
OH
α-1,6’-glycosidic bond
6CH
2
4'
1
OH
O
O
OH
O
O
4'
1
OH
O
OH
CH2OH
O
OH
...
O
OH
OH
36

37.

Cellulose
β-1,4-glycosidic bond
CH2OH
O
..
.
O
O
1
OH
4
1
OH
OH
HO CH2
O
HO
CH2OH
O
CH2OH
O
OH
4
O
O
HO CH2
OH
O
O
H2C OH
O
OH
H
O
O
O
O
H
1
OH
OH
H
O
O
CH2OH
O
OH
4
..
.
OH
OH
OH
O
H2C OH
O
linear
structure
Cellulose hydrolysis
(C6H10O5)n
(C6H10O5)x
cellulose
amyloid
(x < n)
C12H22O11
cellobiose
C6H12O6
D-glucose
37