© e.v. blackburn, 2008 carbohydrates saccharides - saccharum (latin) - sugar
TRANSCRIPT
© E.V. Blackburn, 2008
Carbohydrates
Saccharides - saccharum (Latin) - sugar
© E.V. Blackburn, 2008
Photosynthesis
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.
xCO2 +h
chlorophyll
(CH2O)x + xH2O xO2
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.
© E.V. Blackburn, 2008
Chlorophyll-a
N N
N N
CH3
CH2CH3
CH3
OH
C
H3C
H3CH
H
H3C H H3C H
Mg
CO2CH3
HCH2=
CH2
CH2
C=O
O
CH2
Synthesis - R.B. Woodward, 1960
© E.V. Blackburn, 2008
Carbohydrate metabolismCarbohydrates “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 metabolismN
N N
N
NH2
OH
H
OH
H
OHCH2-
H
O O
O- O-
O
O-
N
N N
N
NH2
OH
H
OH
H
OHCH2-
H
O O
O- O-
O
O-
O-P-O-P-OH + HO-P-O-adenine
ribose phosphate ion
ADP
O-P-O-P-O-P-O-
ATP
Plants and animals use the conserved energy of ATP to perform energy-requiring processes such as muscle contraction. The energy is released and the ATP hydrolyzed to ADP.
© E.V. Blackburn, 2008
D-glyceric acidCO2H
CH2OHH OH
enzymes
simple sugars starch cellulose
polymers
(C6H10O5)n
© E.V. Blackburn, 2008
D-glyceric acidCO2H
CH2OHH OH
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.
D???? The letter D designates the absolute configuration of this acid.
© E.V. Blackburn, 2008
D, L Sugars
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!
CHO
CH2OHH OH
(R)-(+)-glyceraldehyde
© E.V. Blackburn, 2008
D-Sugars
CO H
H OHHHO
H OHH OH
CH2OH
D-glucose
CO H
HO HHHO
H OHH OH
CH2OH
D-mannose
CH2OHOHHO
H OHH OH
CH2OHD-fructose
Virtually all naturally occurring monosaccharides are D sugars.
© E.V. Blackburn, 2008
EpimersExamine D-(+)-glucose and D-(+)-mannose:
CO H
H OHHHO
H OHH OH
CH2OH
D-glucose
CO H
HO HHHO
H OHH 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
CO H
H OHHHO
H OHH OH
CH2OH
CO H
H OHHHO
HO HH OH
CH2OH
D-(+)-glucose D-(+)-galactose
© E.V. Blackburn, 2008
Classification of carbohydrates
“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
“sugars” - the general name used for monosaccharides, disaccharides, oligosaccharides (low molecular weight polymers) and polysaccharides. (saccharum, Latin, sugar)
© E.V. Blackburn, 2008
(+)-Glucose
• 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!
• the most abundant monosaccharide
© E.V. Blackburn, 2008
CHOCHOHCHOHCHOHCHOHCH2OH
****
Emile Fischer, at the end of the 19th century, successfully identified glucose among the 16 possible isomers!
(+)-Glucose
CO H
H OHHHO
H OHH OH
CH2OH
1
5
The configuration at C-5 was identical to that of D-(+)-glyceraldehyde.
© E.V. Blackburn, 2008
Glucose reduces -Fehling’s solution (Cu(II) in Cu(I))
Tollens’ reagent (Ag(I) in Ag(0))
Reactivity of glucose
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?
Glucose is an aldehyde!
© E.V. Blackburn, 2008
Glucose does not form a dimethyl acetals! It forms two different monomethylated derivatives:
RCHO + 2CH3OH R-C-OCH3
H
OCH3
+ H2O
methyl- and -D-glucoside
Reactivity of glucoseAldehydes react with two equivalents of methanol to form dimethyl acetals:
CH3OH+C6H12O6 (C6H11O5)OCH3 H2O
© E.V. Blackburn, 2008
Cyclic glucose
CO H
H OHHHO
H OHH OH
CH2OH
..
D-(+)-glucose
C
CH2OH
H OHHO H
H OHH
HOH
O
a hemiacetal
O OH
O
H
OH
© E.V. Blackburn, 2008
Anomers
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.
CH2OH
H OHHO H
H OHH
H OH
O
CH2OH
H OHHO H
H OHH
HO H
O
* *
-D-Glucose -D-Glucose
© E.V. Blackburn, 2008
Haworth Projections
-D-Glucose -D-Glucose
O
OHOH
OHOH
CH2OH
1
O OH
OH
OHOH
CH2OH
1
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
-D-Glucose
H O
H
HO
H
HO
OHOHH
HOH2C
H
-D-Glucose
H O
H
HO
H
HO
HOHH
HOH2C
OH
© E.V. Blackburn, 2008
Ring Size
O O
pyran furan
-D-glucopyranose
H O
H
HO
H
HO
HOHH
HOH2C
OH
O OH
CH2OH
HOH2C
H H
HO H
OH
-D-fructofuranose
© E.V. Blackburn, 2008
Mutarotation
20o
60o
52.7o
18.7o - -D-glucose
112o - -D-glucose
© E.V. Blackburn, 2008
Mutarotation
H OH
H
HO
H
HO
HOHH
HOH2C
O
A-
HB+
H O
H
HO
H
HO
OOHH
HOH2C
H
A-
H-B+
H
64%
30%
H O
H
HO
H
HO
HOHH
HOH2C
O:H
-D-glucopyranose
:B
H:A
H O
H
HO
H
HO
O:HOHH
HOH2C
H
-D-glucopyranose
:B
H:A
© E.V. Blackburn, 2008
Reactions of Glucose With Amines
H O
H
HO
H
HO
HOHH
HOH2C
O:H
H+H O
H
HO
H
HO
HOHH
HOH2C
OH2
+
H O
H
HO
H
HOOHH
HOH2CH O
H
HO
H
HO
HOHH
HOH2C
OH2
+
H
+
© E.V. Blackburn, 2008
Reactions of Glucose With Amines
anomers of N-phenyl-D-glucosamine
H O
H
HO
H
HOOHH
HOH2C
H O
H
HO
H
HO
HOHH
HOH2C
NHG
H
+
:NH2G
+ H O
H
HO
H
HO
NHGOHH
HOH2C
H
© E.V. Blackburn, 2008
Glycosides
OHO
HOOH
HOH2C
OH
+ CH3OH HCl
cyclic acetals
OHO
HOOH
HOH2C
H
OCH3
methyl -D-glucopyranoside
OHO
HOOH
HOH2C
OCH3
Hmethyl -D-glucopyranoside
© E.V. Blackburn, 2008
Osazones
CO H
H OHHHO
H OHH OH
CH2OH
C6H5NHNH2
CH NNHC6H5
H OHHHO
H OHH OH
CH2OH
CH NNHC6H5
NNHC6H5
HHOH OHH OH
CH2OH
+
NH2
+ NH3phenylosazone of glucose
© E.V. Blackburn, 2008
C=O
(CHOH)3
CH2OH
CH2OH
fructose
CHO
(CHOH)4
CH2OHglucose andmannose
phenylhydrazine
excessCH=NNHC6H5
C=NNHC6H5
(CHOH)3
CH2OHphenylosazone of glucose, mannose andfructose
Osazones
© E.V. Blackburn, 2008
Kiliani-Fischer Synthesis
CH O
HO HH OH
OHHCH2OH
D-arabinose
+ NaCNpH 8
H2O
HO HH OH
OHHCH2OH
CH OH
N
HO HH OH
OHHCH2OH
CHO H
N
+
D-gluconitrile D-mannonitrile
1 : 1,8
HO HH OH
OHHCH2OH
CH OH
N
+ H2 + H2OPd/BaSO4
60 psi, pH 4,5HO H
H OHOHH
CH2OH
CH OH
H O
© E.V. Blackburn, 2008
Ruff Degradation
CH O
HO HH OH
OHHCH2OH
D-arabinose
Fe(OAc)3
H2O2 30%+ CO2
HO HH OH
OHHCH2OH
CH OH
H O
1. Br2/H2O
2. Ca(OH)2
HO HH OH
OHHCH2OH
CO2- Ca2+
H OH
calciumgluconate
© E.V. Blackburn, 2008
(+)-Lactose - a Disaccharide
OOH
HO
HO
R
R = CH2OH
galactose
HO OHO
OH
R
OH
glucose
HCl (1M)
D-galactose + D-glucose
-glycosidicbonding
© E.V. Blackburn, 2008
(+)-Sucrose
OHO
OO
R
R = CH2OH
HH
HO
OC
CH2OH
H
HOH
H OHHO-H2
fructose
glucose
© E.V. Blackburn, 2008
Cellulose
OHO
HO
R
R = CH2OH
HO
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 NucleosideA nucleoside is a glycosylamine in which the amino residue is a pyrimidine or a purine:
OC
H
H
OH
H
OH
N
H
H2HO
N
N
N
H2N
D-ribose
adenine
(a purine)