Chapter 2-Basic Sugar Chemistry

Review of organic functional groups
 
 

Slides from General Organic and Biochemistry-University of Akron

The important sugars for our purposes are

the aldohexoses
 
glucose galactose mannose
and aldopentoses
 
arabinose xylose
 


 

in addition to the aldoses, other functional groups may occur

Configuration of monosaccharides

Differences are due to chiral centers

Number of stereoisomers that may exist depends on the number of chiral centers

Other stereochemical nomenclature

epimers-differ only in the configuration about C-2

Anomers differ only in configuration about C-1

C-1 becomes chiral by cyclization of the sugars


 

In three dimensions the pyranose ring can adopt several conformations with varying energies

Reactions of carbohydrates

isomerization

Mechanism of hemiacetal and acetal formation

mechanistically

Upon exposure to additional base, the products from epimerization can continue to react

formation of an isosaccharinic acid

formation of metasaccharinic acids

Reduction reactions

  • aldose to corresponding alditol
  • sodium borohydride is used analytically
  • catalytic hydrogenation is used industrially
  • Lithium aluminum hydride can also be used
  • Oxidation reactions
  • formation of acids from aldoses
  • several routes can be used to produce specific acids
  • Periodic acid oxidation

    Substitution reactions


     
     
     

    Acid hydrolysis of glycosides (catalytic addition of water) (glycosides are stable in base)

    Ethers may also form through the non-anomeric hydroxyls

    Cyclic acetals (these are still ethers)

    Other reactions

    Chain shortening reaction

    Ruff degradation