Carbohydrates
Saccharides - saccharum (Latin) sugar
© E.V. Blackburn, 2008
Photosynthesis
Carbohydrates are synthesized by green plants via the process
of photosynthesis. This involves the chemical combination of
carbon dioxide and water which results from the absorption of
visible light.
The detailed mechanism of the transformation is not fully
understood. There are many enzyme-catalyzed reactions
which take place, the first of which involves absorption of light
by the extended  system of chlorophyll.
h
xCO
2
+
xH 2 O
(CH
2 O) x
+ xO
2
chlorophyll
© E.V. Blackburn, 2008
Chlorophyll-a
CH 2 = C H
H 3C
N
H
CH 3
Mg
N
N
CH 2
CH 2 CH 3
N
H 3C
CH 2
Synthesis - R.B. Woodward, 1960
CH 3
H
H
O
CO 2 CH 3
C=O
O
CH 2
H 3C
H
H 3C
H
© E.V. Blackburn, 2008
Carbohydrate metabolism
Carbohydrates “store” solar energy which is released
when they are metabolized to give CO2 and water:
Cx(H2O)y + xO2  xCO2 + yH2O + energy
Much of the energy released is conserved in a new
chemical form through reactions that are coupled to the
synthesis of adenosine triphosphate from adenosine
diphosphate.
© E.V. Blackburn, 2008
Carbohydrate metabolism
NH 2
N
N
N
adenine
N
O
O
H H
CH 2 - O-P-O-P-OH
OH OH
O
H
H
O
-
O
O
+ HO-P-O
-
O
ADP
NH 2
N
N
-
phosphate
ion
ribose
N
-
N
O
O
O
H H
CH 2 -O-P-O-P-O-P-O
OH OH
O
H
H
O
ATP
-
O
-
O
Plants and animals
use the conserved
energy of ATP to
perform energyrequiring processes
such as muscle
contraction. The
energy is released
and the ATP
hydrolyzed to ADP.
-
© E.V. Blackburn, 2008
D-glyceric acid
CO 2 H
H
OH
CH 2 OH
enzymes
simple sugars
starch
cellulose
polymers
(C 6 H 10 O 5 ) n
© E.V. Blackburn, 2008
D-glyceric acid
CO 2 H
H
OH
CH 2 OH
D???? The letter D designates the absolute
configuration of this acid.
This pre-dates Cahn-Prelog-Ingold by many years!
This system was suggested by Rosanoff in 1906 and
works as follows:
the configuration is D, if the hydroxyl group of the
stereogenic centre is to the right in the Fischer
projection formula. If it is to the left, the letter L is
used.
© E.V. Blackburn, 2008
D, L Sugars
CHO
H
OH
CH 2 OH
(R)-(+)-glyceraldehyde
The configuration of (+)-glyceraldehyde was arbitrarily
assigned as (D)!
Monosaccharides have the D configuration if the OH group
attached to their highest numbered stereogenic centre is to
the right in the Fischer projection formula; L is used if it is to
the left.
In 1951, Bijvoet determined the absolute configuration of L(+)-tartaric acid and hence that of D-(+)-glyceraldehyde. The
D assignment was correct!
© E.V. Blackburn, 2008
D-Sugars
O
H
HO
H
H
C
H
OH
H
OH
OH
CH 2 OH
D-glucose
O
HO
HO
H
H
C
H
H
H
OH
OH
CH 2 OH
D-mannose
CH 2 OH
O
HO
H
H
OH
H
OH
CH 2 OH
D-fructose
Virtually all naturally occurring monosaccharides are D
sugars.
© E.V. Blackburn, 2008
Epimers
Examine D-(+)-glucose and D-(+)-mannose:
O
H
HO
H
H
C
H
OH
H
OH
OH
CH 2 OH
D-glucose
O
HO
HO
H
H
C
H
H
H
OH
OH
CH 2 OH
D-mannose
They only differ in the configuration about one stereogenic
centre, C-2.
Two diastereoisomers which only differ in the configuration
about one stereogenic carbon are called epimers.
© E.V. Blackburn, 2008
Epimers
O
H
HO
H
H
C
H
O
OH
H
H
OH
OH
CH 2 OH
D-(+)-glucose
HO
HO
H
C
H
OH
H
H
OH
CH 2 OH
D-(+)-galactose
© E.V. Blackburn, 2008
Classification of carbohydrates
“sugars” - the general name used for monosaccharides,
disaccharides, oligosaccharides (low molecular weight
polymers) and polysaccharides. (saccharum, Latin, sugar)
“monosaccharides” - sugars that cannot be hydrolyzed
into smaller molecules (monomer units)
“aldoses” - sugars with an aldehyde carbonyl group
“ketoses” - sugars with a ketone carbonyl group
© E.V. Blackburn, 2008
(+)-Glucose
• the most abundant monosaccharide
• present in the free state in fruits, plants, honey,
blood and urine of animals
• an aldohexose
• C6H12O6
• there are 4 stereogenic centres and therefore 24
(16) optical isomers are possible! All are known!
© E.V. Blackburn, 2008
(+)-Glucose
CHO
* CHOH
* CHOH
* CHOH
* CHOH
CH 2 OH
O
1
C
H
H
OH
HO
H
H
OH
H
5
Emile Fischer, at the end of the 19th
century, successfully identified
glucose among the 16 possible
isomers!
OH
The configuration at C-5 was
identical to that of D-(+)glyceraldehyde.
CH 2 OH
© E.V. Blackburn, 2008
Reactivity of glucose
Glucose reduces -Fehling’s solution (Cu(II) in Cu(I))
Tollens’ reagent (Ag(I) in Ag(0))
Glucose is an aldehyde!
O
H
Ag(NH
3)2
+
O
+ Ag
O
-
When it reacts with amines, it does not always form
imines (C=N-R). Glucose is not an aldehyde?
© E.V. Blackburn, 2008
Reactivity of glucose
Aldehydes react with two equivalents of methanol to form
dimethyl acetals:
H
RCHO
+ 2CH 3 OH
R-C-OCH
OCH
3
+ H 2O
3
Glucose does not form a dimethyl acetals! It forms two
different monomethylated derivatives:
C 6 H 12 O 6
CH 3 OH
(C 6 H 11 O 5 )OCH
3
+ H 2O
methyl - and -D-glucoside
© E.V. Blackburn, 2008
Cyclic glucose
O
H
HO
H
H
C
H
H
H
HO
H
H
OH
H
OH
..
OH
CH 2 OH
O
O
CH 2 OH
D-(+)-glucose
H
O
OH
C
OH
H
OH
a hemiacetal
H
O
OH
© E.V. Blackburn, 2008
Anomers
H
* OH
HO
H
OH
H
HO
H
H
OH
O
HO
H
*H
OH
H
O
OH
H
H
CH 2 OH
CH 2 OH
-D-Glucose
-D-Glucose
There are two different D-(+)-glucose molecules!
Stereoisomers which only differ in the configuration about
the hemiacetal carbon are called anomers.
The OH at C-1 is to the right of the chain in the  anomer
and to the left in the  anomer.
© E.V. Blackburn, 2008
Haworth Projections
CH 2 OH
O
OH
OH
1
OH
OH
-D-Glucose
CH 2 OH
O
OH
OH
1
OH
OH
-D-Glucose
The CH2OH is drawn above the ring for D sugars and
below the ring for L sugars. In D sugars, the OH at C1 is
drawn below the ring for the  anomer and above the ring
for the  anomer.
© E.V. Blackburn, 2008
Conformations of
monosaccharides
H
H
HOH 2 C
HO
HO
HOH 2 C
H O
H
H
-D-Glucose
H
HO
HO
H
OH
OH
H O
H
OH
OH
H
-D-Glucose
© E.V. Blackburn, 2008
Ring Size
O
O
pyran
furan
H
HOH 2 C
HO
HO
H O
H
OH
OH
H
-D-glucopyranose
OH
O
HOH 2 C
H
H
OH
CH 2 OH
H
HO
H
-D-fructofuranose
© E.V. Blackburn, 2008
Mutarotation
112
60
20
o
52.7
o
- -D-glucose
o
o
18.7
o
- -D-glucose
© E.V. Blackburn, 2008
Mutarotation
H
H
HOH 2 C
HO
HO
H O
H:A
:B
O:H
H
HOH 2 C
HO
HO
H OH
HB
+
OH
H
H
-
O
H
OH
H
A
H
-D-glucopyranose
64%
H
HOH 2 C
HO
HO
H
H O
H
H
A
H
-
HOH 2 C
HO
HO
H
OH
O
H O
H
H
OH
H
H-B
+
H:A
O:H
:B
-D-glucopyranose
30%
© E.V. Blackburn, 2008
Reactions of Glucose With
Amines
H
H
HOH 2 C
HO
HO
H O
H
H
O:H
OH
H
H
+
HOH 2 C
HO
HO
H O
+
OH 2
H
OH
H
H
H
H
HOH 2 C
HO
HO
H
H O
H
+
OH 2
HOH 2 C
HO
HO
OH
H
+
H O
H
OH
H
H
© E.V. Blackburn, 2008
Reactions of Glucose With
Amines
H
HOH 2 C
HO
HO
+
H O
H
OH
:NH 2 G
H
H
H
H
HOH 2 C
HO
HO
H
H O
H
+
NHG
OH
H
HOH 2 C
HO
HO
H
H O
H
H
OH
NHG
anomers of N-phenyl-D-glucosamine
© E.V. Blackburn, 2008
Glycosides
cyclic acetals
HOH
2C
O
+ CH
HO
HO
3 OH
HCl
OH
OH
HOH 2 C
HOH 2 C
O
HO
HO
H
OH
OCH
methyl -D-glucopyranoside
O
HO
HO
OCH
OH
3
3
H
methyl -D-glucopyranoside
© E.V. Blackburn, 2008
Osazones
O
H
HO
H
H
C
H
OH
H
OH
OH
CH 2 OH
H
C 6 H 5 NHNH
C
H
2
H
6H 5
C
OH
HO
H
H
H
NNHC
HO
H
OH
CH 2 OH
phenylosazone of glucose
NNHC
6H 5
OH
OH
CH 2 OH
NH
+
6H 5
H
H
OH
NNHC
2
+ NH
3
© E.V. Blackburn, 2008
Osazones
CHO
CH=NNHC
(CHOH)
4
excess
CH 2 OH phenylhydrazine
glucose and
mannose
CH 2 OH
C=O
(CHOH)
C=NNHC
(CHOH)
6H 5
6H 5
3
CH 2 OH
phenylosazone
of glucose,
mannose and
fructose
3
CH 2 OH
fructose
© E.V. Blackburn, 2008
Kiliani-Fischer Synthesis
H
HO
H
H
C
C N
C N
H
OH
O
H
+ NaCN
OH
OH
pH 8
HO
H
H
OH
H 2O
H
OH
+
H
H
D-gluconitrile
:
H
H +H
OH
OH
CH 2 OH
Pd/BaSO
2
+ H 2O
4
60 psi, pH 4,5
OH
OH
D-mannonitrile
1
C N
H
OH
H
H
CH 2 OH
CH 2 OH
CH 2 OH
D-arabinose
HO
H
H
HO
HO
H
HO
H
H
1,8
C
O
OH
H
OH
OH
CH 2 OH
© E.V. Blackburn, 2008
Ruff Degradation
H
H
HO
H
H
C
O
-
H
OH 1. Br 2 /H 2 O
HO
H
H
OH 2. Ca(OH) 2
H
OH
CH 2 OH
CO 2 Ca
OH
H
OH
OH
CH 2 OH
2+
calcium
gluconate
H
Fe(OAc)
3
H 2 O 2 30%
HO
C
O
H
H
OH
H
OH
+ CO
2
CH 2 OH
D-arabinose
© E.V. Blackburn, 2008
(+)-Lactose - a Disaccharide
OH
R
HO
-glycosidic
bonding
R = CH
O
HO
galactose
H
O
HO
2 OH
R
O
OH OH
glucose
HCl (1M)
D-galactose + D-glucose
© E.V. Blackburn, 2008
(+)-Sucrose
R = CH
HO
HO
R
2 OH
O
H

O
OH H
H
O
glucose
CH 2 OH

H O OH
HO-H 2C
H
fructose
© E.V. Blackburn, 2008
Cellulose
R = CH
2 OH
R
O
HO
HO

O
H
n
D-glucopyranose
Cellulose contains about 3,000 monomer units. It is
essentially linear. Cotton fiber is almost pure cellulose.
Wood and straw is made up of about 50% of this
polysaccharide.
© E.V. Blackburn, 2008
Starch
Starch is a polyglucose containing more than 1,000
units connected by  acetal bonds. It is easily
hydrolyzed by acid to give glucose.
© E.V. Blackburn, 2008
Adenosine - a Nucleoside
A nucleoside is a glycosylamine in which the amino residue
is a pyrimidine or a purine:
H 2N
N
N
HO C H 2 N
O
H
H
H
N
adenine
(a purine)
H
OH OH
D-ribose
© E.V. Blackburn, 2008