Download Carbohydrates

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 2O
(CH 2O)x + xO 2
chlorophyll
© E.V. Blackburn, 2008
Chlorophyll-a
CH2=CH
H3C
CH3
N
H
H3C
N
Mg
N N
Synthesis - R.B. Woodward, 1960
CH2CH3
CH3
CH2 H
H
O
CH2
CO2CH3
C=O
O
CH2
H3C
H H3C
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
NH2
N
N
N
N
O
O O
H H
adenine
CH2-O-P-O-P-OH + HO-P-OOHOH
O
O
O
O
H H
phosphate
ribose
ion
ADP
NH2
N
N
N
N
O O O
H H
CH2-O-P-O-P-O-P-O OHOH
O- O- OO
H H
ATP
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
CO2H
H
OH
CH2OH
enzymes
simple sugars
starch
cellulose
polymers
(C6H10O5)n
© E.V. Blackburn, 2008
D-glyceric acid
CO2H
H
OH
CH2OH
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 2OH
(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
CH2OH
D-glucose
O
HO
HO
H
H
C
H
H
H
OH
OH
CH2OH
D-mannose
CH2OH
O
HO
H
H
OH
H
OH
CH2OH
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
CH2OH
D-glucose
O
HO
HO
H
H
C
H
H
H
OH
OH
CH2OH
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
OH
H
OH
OH
CH2OH
D-(+)-glucose
O
H
HO
HO
H
C
H
OH
H
H
OH
CH2OH
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
CH2OH
O
H
HO
H
H
1
C
Emile Fischer, at the end of the 19th
century, successfully identified
glucose among the 16 possible
isomers!
H
OH
H
OH
5
OH
CH2OH
The configuration at C-5 was
identical to that of D-(+)glyceraldehyde.
© 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(NH3)2+
O
O-
+ Ag
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 3OH
R-C-OCH 3 + H2O
OCH 3
Glucose does not form a dimethyl acetals! It forms two
different monomethylated derivatives:
C6H12O6
CH3OH
(C6H11O5)OCH3 + H2O
methyl - and -D-glucoside
© E.V. Blackburn, 2008
Cyclic glucose
O
C
H
H
HO
H
H
OH
H
OH
..
OH
CH2OH
D-(+)-glucose
H
O
O
H
H
H
HO
H
H
OH
C
OH
H
O
OH
CH2OH
a hemiacetal
O
OH
© E.V. Blackburn, 2008
Anomers
H
H
HO
H
H
* OH
OH
H
OH
O
CH2OH
-D-Glucose
HO
H
HO
H
H
*H
OH
H
OH
O
CH2OH
-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
CH2OH
O
OH
OH
CH2OH
O OH
1
OH
1
OH
OH
-D-Glucose
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
HOH2C
HO
HO
H
H O
H
OH
OH
-D-Glucose
HOH2C
HO
HO
H
H
H O
H
OH
OH
H
-D-Glucose
© E.V. Blackburn, 2008
Ring Size
O
O
pyran
furan
H
HOH2C
HO
HO
H
H O
H
OH
OH
H
-D-glucopyranose
H
OH
O
HOH2C
H
HO
OH
CH2OH
H
-D-fructofuranose
© E.V. Blackburn, 2008
Mutarotation
112o - -D-glucose
60o
20o
52.7o
18.7o - -D-glucose
© E.V. Blackburn, 2008
Mutarotation
H
H
HOH 2C
HO
HO
H O
H:A
O:H
H
:B
HOH2C
HO
HO
OH
H
H
H OH
H
AHB+
O
OH
H
H
-D-glucopyranose
64%
H
-
HOH 2C
HO
HO
H
H O
H
H
A
H
OH
O
H-B +
H
HOH2C
HO
HO
H
H O
H
H:A
H
OH
O:H
:B
-D-glucopyranose
30%
© E.V. Blackburn, 2008
Reactions of Glucose With
Amines
H
HOH 2C
HO
HO
+
H O
H
H
H
O:H
OH
H
H
HOH 2C
HO
HO
H O
H
OH
H
H
H
H
HOH 2C
HO
HO
H
H O
H
OH
H
+
OH2
HOH 2C
HO
HO
H
+
OH2
+
H O
H
OH
H
© E.V. Blackburn, 2008
Reactions of Glucose With
Amines
H
HOH 2C
HO
HO
+
H O
H
OH
H
H
:NH2G
H
H
HOH 2C
HO
HO
H
H O
H
OH
H
+
NHG
HOH 2C
HO
HO
H
H O
H
H
OH
NHG
anomers of N-phenyl-D-glucosamine
© E.V. Blackburn, 2008
Glycosides
cyclic acetals
HOH 2C
HO
HO
O
+ CH 3OH
HCl
OH
OH
HOH2C
HO
HO
O
H
OH
OCH3
methyl -D-glucopyranoside
HOH2C
HO
HO
O
OCH3
OH
H
methyl -D-glucopyranoside
© E.V. Blackburn, 2008
Osazones
O
H
HO
H
H
C
H
H
C
H
NNHC6H5
OH C H NHNH
H
OH
6 5
2
H
HO
H
OH
H
OH
OH
H
OH
CH2OH
CH2OH
C
NNHC6H5
NNHC6H5
HO
H
H
OH
H
OH
CH2OH
NH 2
phenylosazone of glucose
+
+ NH 3
© E.V. Blackburn, 2008
Osazones
CHO
excess
(CHOH)4
CH2OH phenylhydrazine
glucose and
mannose
CH2OH
C=O
(CHOH)3
CH2OH
CH=NNHC6H5
C=NNHC6H5
(CHOH)3
CH2OH
phenylosazone
of glucose,
mannose and
fructose
fructose
© E.V. Blackburn, 2008
Kiliani-Fischer Synthesis
H
C
O
HO
H
H
H
OH + NaCN
OH
CH2OH
D-arabinose
H
HO
H
H
pH 8
H 2O
C N
H
OH
HO
H
+
H
OH
H
OH
CH2OH
D-gluconitrile
:
1
H
C N
HO
H
HO
H
H
OH
H
OH
CH2OH
D-mannonitrile
1,8
O
C
C N
H
OH
OH
Pd/BaSO 4
HO
H
H + H2 + H2O
OH
OH
60 psi, pH 4,5 H
H
OH
OH
CH2OH
CH2OH
© E.V. Blackburn, 2008
Ruff Degradation
H
O
2+
CO
Ca
C
2
H
OH
H
OH 1. Br2/H2O
HO
H
HO
H
OH
H
OH 2. Ca(OH)2 H
H
OH
H
OH
CH2OH
CH2OH
calcium
gluconate
H O
C
H
Fe(OAc)3 HO
+ CO2
H
OH
H2O2 30%
H
OH
CH2OH
D-arabinose
© E.V. Blackburn, 2008
(+)-Lactose - a Disaccharide
OH
R
HO
-glycosidic
bonding
R = CH2OH
O
HO
H
galactose
O
HO
R
O
OH OH
glucose
HCl (1M)
D-galactose + D-glucose
© E.V. Blackburn, 2008
(+)-Sucrose
R = CH2OH
HO
HO
R
O
H

O
OH H
H
O
glucose
CH2OH

H O OH
HO-H2C
H
fructose
© E.V. Blackburn, 2008
Cellulose
R = CH2OH
R
HO

O
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:
H2N
N
adenine
N
HO CH2 N
O
H H
H
N
(a purine)
H
OH OH
D-ribose
© E.V. Blackburn, 2008