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CarbohydratesSugars or Saccharides
One of the most abundant compounds of living cells
In living cells (plants) -> carbohydrates are made by photosynthesis
- Monosaccharides : C3-C9
- Oligosaccharides : 2-10 units
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Carbohydrates
Monosaccharides (biological sugars –ose)
Most frequently found in nature: - hexoses (six-carbon sugars) -> glucose and fructose
- pentoses (five-carbon sugars) -> ribose
S, R Configuration 2 Enantiomers
Fischer ProjectionHighest Oxidation state
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Carbohydrates
Monosaccharides (biological sugars –ose)
Most frequently found in nature: - hexoses (six-carbon sugars) -> glucose and fructose
- pentoses (five-carbon sugars) -> ribose
Aldoses
Ketoses
Pyranoside Furanoside
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CarbohydratesMonosaccharides
D-Aldoses in the range of C3-C6
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CarbohydratesMonosaccharides
D-Ketoses in the range of C3-C6
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CarbohydratesMonosaccharides Stereochemistry
D-Erythrose + L-Erythrose -> Enantiomers
D-Erythrose + D-Threose -> Diastereoisomers
D-Erythrose + L-Threose -> Diastereoisomers
D-glucose + L-glucose -> Enantiomers
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CarbohydratesMonosaccharides
Enolization and Isomerization
Isomerization
Epimerization Epimerization
Base-catalysed in water:-> Epimerization + isomerization
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CarbohydratesMonosaccharides
Cyclic hemiacetals + hemiketals
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CarbohydratesMonosaccharides
Cyclic hemiacetals + hemiketals -> glucose
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CarbohydratesMonosaccharides
Cyclic hemiacetals + hemiketals -> glucose
O
CH2OH
O
CH2OH
O
CH2OH
OH
D L
O
CH2OHOH
α-Sugars have the -CH2OH group and the anomeric hydroxyl group trans.β-Sugars have the -CH2OH group and the anomeric hydroxyl group cis.
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CarbohydratesMonosaccharides
Cyclic hemiacetals + hemiketals -> glucose
Glucopyranoside more stable -> almost 100% in pyranoside form
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CarbohydratesMonosaccharides
Cyclic hemiacetals + hemiketals -> ribose
In solution mainly in pyranoside form (76%)
In nucleotides (or other combinations) mostly found in furanose form
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CarbohydratesMonosaccharides
Cyclic hemiacetals + hemiketals -> fructose
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CarbohydratesMonosaccharides
Cyclic hemiacetals + hemiketals -> fructose
In solution mainly in pyranoside form (67%)
In combinations mostly found in furanose form
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CarbohydratesMonosaccharides
The anomeric center
Carbonyl group is planar -> attack of OH from either side possible -> 2 epimeric structures (anomers)
Both anomers are in equillibrium in solution
Epimer (Anomer)
Epimer (Anomer)
Epimers:
α -> anomeric center + highest chiral center -> different configuration (R,S convention)
Hydroxyl (OH) on anomeric C Down -> α-D-sugars and β-L-sugars
β -> anomeric center + highest chiral center -> same configuration (R,S convention)
Up -> β-D-sugars and α-L-sugars
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CarbohydratesMonosaccharides
The anomeric center
Carbonyl group is planar -> attack of OH from either side possible -> 2 epimeric structures (anomers)
Both anomers are in equillibrium in solution
Epimers:
β -> anomeric center + highest chiral center -> same configuration (R,S convention)
α -> anomeric center + highest chiral center -> different configuration
R,R-> β S,R-> α
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CarbohydratesMonosaccharides
The anomeric center
Carbonyl group is planar -> attack of OH from either side possible -> 2 epimeric structures (anomers)
In solution -> all 4 forms in equillibrium !!!
Aldohexoses
Ketose
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CarbohydratesMonosaccharides
The anomeric center
Esterfication -> freezes sugar in its anomeric form (no interconvertion between α and β any more)
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CarbohydratesMonosaccharides
Alditols
Reduction of sugars -> reducing agent (NaBH4) -> reduces aldehydes + ketons
Reduction occurs at small amount of open chain form -> shift in equilibrium -> total reduction achieved
Reduction of Aldoses -> 1 product (primary alcohol) -> Alditols
Reduction of Ketoses -> 2 products (secondary alcohol) -> Alditols
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CarbohydratesMonosaccharides
Glycosides (replace suffix –ose with –oside) -> Reaction at C1 (anomeric C)
Hemiacetals + Alcohol -> Acetals (Glycoside)
Hemiketals + Alcohols -> Ketals (Glycoside)
OH on the anomeric C1
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CarbohydratesMonosaccharides
Glycosides (replace suffix –ose with –oside)
Hemiacetals + Alcohol -> Acetals (Glycoside)
Hemiketals + Alcohols -> Ketals (Glycoside)
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CarbohydratesMonosaccharides
Glycosides (replace suffix –ose with –oside) -> Reaction at C1
Hemiacetal/Hemiketal + Alcohol -> O- Glycoside -> Polysaccharides
Hemiketal/Hemiketal + Amine -> N-Glycoside
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CarbohydratesMonosaccharides
Glycosides (replace suffix –ose with –oside)
Hemiacetal/Hemiketal + Alcohol -> O- Glycoside -> Polysaccharides
Hemiketal/Hemiketal + Amine -> N-Glycoside
Template for aspirin
Nucleotides of RNA and DNA
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CarbohydratesMonosaccharides
Glycosides (replace suffix –ose with –oside)
Glucose + MeOH -> Acetal -- reaction works directly
Glucose + complex alcohol -> not that easy
Example: Production of salicin-> Template for Aspirin
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CarbohydratesMonosaccharides
Glycosides (replace suffix –ose with –oside)
Glucose + MeOH -> Acetal -- reaction works directly
Glucose + complex alcohol -> not that easy
Example: Production of salicin-> Template for Aspirin
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CarbohydratesMonosaccharides
Cyclic Acetals + Ketals -> protecting groups
2 OH groups are cis conformation -> reaction with keton
C6
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CarbohydratesMonosaccharides
Modified sugars -> in cell membranes
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CarbohydratesOligosaccharides -> a few monomers
Found in dietary products
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CarbohydratesPolysaccharides
In Plant cell wall -> cotton
In animal and plant cells
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CarbohydratesPolysaccharides
Glycogen -> mammalian sugar storage
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CarbohydratesPolysaccharides
Starch: amylose + amylopectine -> main plant food reserve
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CarbohydratesPolysaccharides - Hydrolysis
1. Chemically: - under harsh conditions: with hot acid -> monosaccharides (glucose)
- under mild conditions: with acid -> oligosaccharides (randomly)
2. Enzymatic: very specific hydrolysis
-> α-amylase -> hydrolysis α 1 -> 4 bonds in starch (mainly maltose + glucose)
-> α-1,6-glucosidase -> hydrolysis α 1 -> 6 bonds in starch
-> lactase -> hydrolysis lactose
(high activity of enzyme in infants – low activity in adults -> intolerance)
-> cellulase -> hydrolysis β 1 -> 4 bonds -> animals do not have it (need bacteria)
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CarbohydratesOxidation of sugarsUnder mild conditions -> with cupric ion (Fehling’s solution) or Br2 -> oxidation of aldehyde group -> acid (aldonic acid)
If sugars are glycosidic linked (acetal formation) -> aldehyde group not available for oxidation -> no reducing sugars
If sugar are free -> reducing sugars
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CarbohydratesOxidation of sugarsUnder strong conditions -> with HNO3 -> oxidation of aldehyde group + alcohol groups (primary alcohol) -> diacid (aldaric acid)
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CarbohydratesOxidation of sugarsDetermination of glucose level in blood or urine -> oxidation of glucose –> H2O2 involved in second reaction -> colorimetric or voltametric sensor (Biosensor)
Diabetes mellitus: Insulin deficiency
Insulin regulates blood sugar (glucose) level
If glucose level is high -> insulin level increases -> prevents break down of glycogen into glucose and conversion of fat or protein into glucose -> blood glucose level will sink again
If glucose level is low -> insulin level drops -> more glucose produced -> blood glucose level will rise
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CarbohydratesOxidation of sugarsTerminal OH group oxidized in Aldoses -> Uronic acids
Pectins: in cell walls of fruits
-> acid solutions form gels -> jam making
Also oxidized by most enzymes
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CarbohydratesOxidation of sugarsTerminal OH group oxidized in Aldoses -> Uronic acids
Pain reliefer
Even stronger pain reliefer
Morphine metabolism in human body -> make it more soluble -> excretion
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CarbohydratesOxidation of sugars
Vitamin C: most animals can synthesize Vitamin C – Humans and primates cannot NOT -> synthesized in liver from glucose
Essential for: - formation of structural proteins in skin, bones, ligaments - cofactor in synthesis reactions of amino acids and modifications - antioxidants
Deficiently (scurvy) -> muscular pain, skin lesions, fragile blood vessel, bleeding gums, tooth loss
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CarbohydratesAminosugarsReplacement of one OH group by a amino group
In nature -> done by enzymes -> 2-amino-2-deoxy sugars
Chitin: insect skeleton and shells of crustaceans
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CarbohydratesAminosugarsReplacement of one OH group by a amino group
In nature -> done by enzymes -> 2-amino-2-deoxy sugars
Bacterial cell walls -> glycycosidic bond cleaved by lysozyme
Lysozyme
β-lactam antibiotics -> inhibit peptidase linking peptide bond during biosythesis of cell wall
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CarbohydratesAminosugarsReplacement of one OH group by a amino group
In nature -> done by enzymes -> 2-amino-2-deoxy sugars
Blood groups:Determined by glycoproteins
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