Enediol Rearrangement

Carbohydrates - back

Base catalyzed unfavorable reactions of sugars

Attacks aldoses

Enediol Rearrangement

• ---C1OH-------------------------H-C1-OH
• H-C2-OH <--(NaOH/H2O)--> C2=O

Mechanism:

• OH nucleophile attacks the acidic alpha proton from the carbonyl
  • The remaining electrons forms an enolate intermediate (carbanion and enolate)
  • The point where it loses its stereochemistry = C2 is no longer asymmetric
• Enolate oxygen attacks a proton from water
  • Regenerates the base
  • Formation of the ENEDIOL
• OH nucleophile attacks the alcohol
• Enolate oxygen nucleophile attacks C2
  • WHILE
    • Resonance forces the enolate double bond to attack a proton from water
      • Regenerates a carbonyl in the C2
      • Regenerate the base

Base Catalyzation Fundamentals:

• Base catalysis occurs the same way attacking the acidic alpha proton (C2 proton)
• The deviation in the products occurs form the enolate oxygen
  • -1 Reform the carbonyl from attacking the carbon it is attached to
    • RESULTING IN ENOLATE PRODUCTION
  • -2 Reduced to an alcohol from attacking a proton from water
    • RESULTING IN ENEDIOL PRODUCTION
• Under strong basic conditions a combination of enediol and epimerization leads to complex mixture of sugars

Concepts:

Salient Examples:

• Glycolysis - (G-6P) into (F-6P) - Phosphoglucose Isomerase
  • Glucose 6-phosphate into Fructose 6-phosphate

Terminology:

Additional Information: