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Carbohydrates Sugars or Saccharides

Carbohydrates Sugars or Saccharides. One of the most abundant compounds of living cells In living cells (plants) -> carbohydrates are made by photosynthesis Monosaccharides : C 3 -C 9 Oligosaccharides : 2-10 units. Monosaccharides (biological sugars –ose).

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Carbohydrates Sugars or Saccharides

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  1. 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

  2. Monosaccharides (biological sugars –ose) Most frequently found in nature: - hexoses (six-carbon sugars) -> glucose and fructose - pentoses (five-carbon sugars) -> ribose Carbohydrates 2 Enantiomers S, R Configuration Fischer Projection Highest Oxidation state

  3. Monosaccharides (biological sugars –ose) Most frequently found in nature: - hexoses (six-carbon sugars) -> glucose and fructose - pentoses (five-carbon sugars) -> ribose Carbohydrates Pyranoside Furanoside Aldoses Ketoses

  4. Monosaccharides D-Aldoses in the range of C3-C6 Carbohydrates

  5. Monosaccharides D-Ketoses in the range of C3-C6 Carbohydrates

  6. Monosaccharides Stereochemistry Carbohydrates D-Erythrose + L-Erythrose -> Enantiomers D-Erythrose + D-Threose -> Diastereoisomers D-Erythrose + L-Threose -> Diastereoisomers D-glucose + L-glucose -> Enantiomers

  7. Monosaccharides Enolization and Isomerization Epimerization Epimerization Carbohydrates Base-catalysed in water: -> Epimerization + isomerization Isomerization

  8. Monosaccharides Cyclic hemiacetals + hemiketals Carbohydrates

  9. Monosaccharides Cyclic hemiacetals + hemiketals -> glucose Carbohydrates

  10. Monosaccharides Cyclic hemiacetals + hemiketals -> glucose Carbohydrates a b D L α-Sugars have the -CH2OH group and the anomeric hydroxyl group trans. β-Sugars have the -CH2OH group and the anomeric hydroxyl group cis.

  11. Monosaccharides Cyclic hemiacetals + hemiketals -> glucose Carbohydrates Glucopyranoside more stable -> almost 100% in pyranoside form

  12. Monosaccharides Cyclic hemiacetals + hemiketals -> ribose Carbohydrates In solution mainly in pyranoside form (76%) In nucleotides (or other combinations) mostly found in furanose form

  13. Monosaccharides Cyclic hemiacetals + hemiketals -> fructose Carbohydrates

  14. Monosaccharides Cyclic hemiacetals + hemiketals -> fructose Carbohydrates In solution mainly in pyranoside form (67%) In combinations mostly found in furanose form

  15. Monosaccharides 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 Carbohydrates 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 Epimer (Anomer) Epimer (Anomer)

  16. Monosaccharides 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 Carbohydrates 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

  17. Monosaccharides 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 !!! Carbohydrates Aldohexoses Ketose

  18. Monosaccharides The anomeric center Esterfication -> freezes sugar in its anomeric form (no interconvertion between α and β any more) Carbohydrates

  19. Monosaccharides 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 Carbohydrates

  20. Monosaccharides Glycosides (replace suffix –ose with –oside) -> Reaction at C1 (anomeric C) Hemiacetals + Alcohol -> Acetals (Glycoside) Hemiketals + Alcohols -> Ketals (Glycoside) Carbohydrates OH on the anomeric C1

  21. Monosaccharides Glycosides (replace suffix –ose with –oside) Hemiacetals + Alcohol -> Acetals (Glycoside) Hemiketals + Alcohols -> Ketals (Glycoside) Carbohydrates

  22. Monosaccharides Glycosides (replace suffix –ose with –oside) -> Reaction at C1 Hemiacetal/Hemiketal + Alcohol -> O- Glycoside -> Polysaccharides Hemiketal/Hemiketal + Amine -> N-Glycoside Carbohydrates

  23. Monosaccharides Glycosides (replace suffix –ose with –oside) Hemiacetal/Hemiketal + Alcohol -> O- Glycoside -> Polysaccharides Hemiketal/Hemiketal + Amine -> N-Glycoside Carbohydrates Template for aspirin Nucleotides of RNA and DNA

  24. Monosaccharides Glycosides (replace suffix –ose with –oside) Glucose + MeOH -> Acetal -- reaction works directly Glucose + complex alcohol -> not that easy Carbohydrates Example: Production of salicin -> Template for Aspirin

  25. Monosaccharides Glycosides (replace suffix –ose with –oside) Glucose + MeOH -> Acetal -- reaction works directly Glucose + complex alcohol -> not that easy Carbohydrates Example: Production of salicin -> Template for Aspirin

  26. Monosaccharides Cyclic Acetals + Ketals -> protecting groups 2 OH groups are cis conformation -> reaction with keton Carbohydrates C6

  27. Monosaccharides Modified sugars -> in cell membranes Carbohydrates

  28. Oligosaccharides -> a few monomers Carbohydrates Found in dietary products

  29. Polysaccharides Carbohydrates In Plant cell wall -> cotton In animal and plant cells

  30. Polysaccharides Glycogen -> mammalian sugar storage Carbohydrates

  31. Polysaccharides Starch: amylose + amylopectine -> main plant food reserve Carbohydrates

  32. Polysaccharides - Hydrolysis • 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) Carbohydrates

  33. Oxidation of sugars Under 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 Carbohydrates

  34. Oxidation of sugars Under strong conditions -> with HNO3 -> oxidation of aldehyde group + alcohol groups (primary alcohol) -> diacid (aldaric acid) Carbohydrates

  35. Oxidation of sugars Determination 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 Carbohydrates

  36. Oxidation of sugars Also oxidized by most enzymes Terminal OH group oxidized in Aldoses -> Uronic acids Carbohydrates Pectins: in cell walls of fruits -> acid solutions form gels -> jam making

  37. Oxidation of sugars Terminal OH group oxidized in Aldoses -> Uronic acids Carbohydrates Pain reliefer Even stronger pain reliefer Morphine metabolism in human body -> make it more soluble -> excretion

  38. Oxidation 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 Carbohydrates Deficiently (scurvy) -> muscular pain, skin lesions, fragile blood vessel, bleeding gums, tooth loss

  39. Aminosugars Replacement of one OH group by a amino group In nature -> done by enzymes -> 2-amino-2-deoxy sugars Carbohydrates Chitin: insect skeleton and shells of crustaceans

  40. Aminosugars Replacement 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 Carbohydrates Lysozyme β-lactam antibiotics -> inhibit peptidase linking peptide bond during biosythesis of cell wall

  41. Aminosugars Replacement of one OH group by a amino group In nature -> done by enzymes -> 2-amino-2-deoxy sugars Carbohydrates Blood groups: Determined by glycoproteins

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