Carbohydrate Chemistry Notes

Reduction with NaBH4 and Optical Activity

• Reduction with NaBH4 Practice Problem 22.11(a):

  • Question: Would you expect D-glucitol to be optically active?

• Reduction of Monosaccharides: Alditols

  • Alditols are formed via the reduction of monosaccharides.

• Practice Problem 22.11 (b):

  • Question: Write Fischer projection formulas for all of the D-aldohexoses that would yield optically inactive alditols.

Reactions of Monosaccharides with Phenylhydrazine: Osazone

• Osazone Formation:

  • The product is called a phenylosazone.
  • Substitutions occur on C-1 and C-2 of the monosaccharide.

• Epimers:

  • Epimers differ in chirality at a single carbon.
  • Example: D-Glucose and D-Mannose are epimers.

• Osazone Formation:

  • Results in the loss of chirality at C2.

Kiliani-Fischer Synthesis

• Kiliani-Fischer Synthesis:

  • Carbons in the sugar chain are lengthened.
  • Epimers are produced during this synthesis.

• Practice Problem 22.13:

  • (a) What are the structures of L-(+)-threose and L-(+)-erythrose?
  • (b) What aldotriose would you use to prepare them in a Kiliani–Fischer synthesis?

Ruff Degradation

• Ruff Degradation:
  • Reduces the carbon chain by one carbon.
  • It is an oxidative decarboxylation process.

The D Family of Aldoses

• Practice Problem 22.17-A:
  • How many D-family stereoisomers exist:
    • (a) for 4 carbon aldoses,
    • (b) for 5 carbon aldoses, and
    • (c) for 6 carbon aldoses.

Fischer’s Proof of the Configuration of D-(+)-Glucose

• Fischer's Methodology:
  • Fischer determined the stereochemistry of (+)-glucose by chemical means.
  • The methodology included the use of:
    • Nitric Acid Oxidation,
    • Ruff Degradation, and
    • Kiliani-Fischer Synthesis.
  • The complete Fischer Proof can be found on pages 1027-1029.

Disaccharides

• Sucrose:

  • Is ordinary table sugar.
  • Is found in photosynthetic plants.
  • Composed of Glucose (as an α-pyranose).

• Maltose:

  • Is a hydrolysis product from starch.
  • Composed of Glucose (as an α-pyranose) linked to another Glucose (as an α-pyranose).

• Cellobiose:

  • Is a hydrolysis product from cellulose.
  • Composed of Glucose (as an α-pyranose) linked to another Glucose (as an α-pyranose).

• Lactose:

  • Is present in mammalian milk.
  • Composed of Galactose (as an α-pyranose) linked to Glucose (as an α-pyranose).

Polysaccharides

• Polysaccharides:

  • Sugar units linked by glycosidic (acetal) bonds.

• Homopolysaccharides:

  • Polymers with a single type of monosaccharide.
    • Glucans: glucose monomeric units.
    • Galactans: galactose monomeric units.

• Heteropolysaccharides:

  • Polymers containing more than one type of monosaccharide building block.

• Starch:

  • Found in plants.
  • Is an energy storage sugar.

• Glycogen:

  • Found in animals.
  • Is an energy storage sugar.
  • Has more α (1→6) branching than starch.

• Cellulose:

  • Found in plants.
  • Is a structural sugar.

Cellulose Derivatives

• Cellulose Derivatives:
  • Are commercially produced.
  • Converted from free OH groups.
  • Ether and Ester derivatives.
  • Examples:
    • Cellulose trinitrate (gun cotton, explosive).
    • Cellophane.
    • Rayon.
    • Cellulose acetate.
      • Old style motion picture film.
      • Highly flammable.

Other Biologically Important Sugars

• Ribose and 2-Deoxyribose:

  • Found in RNA and DNA respectively.

• Uronic Acids:

  • Found in sulfonated polysaccharide called heparin.

• Heparin:

  • Important in controlling blood clotting.

Sugars that Contain Nitrogen

• Glycosamine

  • Anomeric hydrogens are replaced by nitrogen.
  • Nucleoside has Ribose and 2-Deoxyribose bonded to a nitrogenous ring system.

• Amino sugars

  • Non-anomeric hydrogens replaced by nitrogen.
  • β-D-glucosamine is found in chitin.
  • NAG & NAM is found in bacterial cell walls.

Glycolipids and Glycoproteins of the Cell Surface: Cell Recognition and the Immune System

• Glycolipids (GL) and Glycoproteins (GP):
  • Found on cell surfaces.
  • Blood Types:
    • Are a function of GL and GP.
    • Refer to different GL & GP present.

• Note that Type H is the precursor to Type A and B.

Carbohydrate Antibiotics

• Streptomycin:
  • Inhibits the enzymes which synthesizes a key bacterial protein.