Glycosylations

Carbohydrates

Turning an aldose/ketose into glucosides/nonreducing sugars

Attacks aldoses/ketoses

Glycosylations

• Sugar -(R-OH/H3O)-> Sugar-C1-O-R
  • Both C1 anomers Alpha Beta Sugar Designation
• Reverse Glycoside Hydrolysis

Mechanism:

Fundamentals:

• Attacks the C1 to form stable glycosides
• Cyclic form cannot open to the free carbonyl

Glycoside Properties

• Glycosides cannot spontaneously open to their open chain forms
• Glycosides do not mutarotate and are locked in one anomeric form
• Glycosides are stable in basic conditions - even Tollens reagent
  • Acetal Chemistry - Acetals are stable under neutral and basic conditions
    • Cyclic acetals cannot open to the free carbonyl compound
• Glycosides hydrolyze in aq acid to reform sugar and R-OH
  • Glycoside Hydrolysis

Anomeric/Edward Lemieux Effect

Focus - Stability of Glycosides:

• Newtonain Configurations and Molecular Orbitals
  • When it leaves, the carbocation is stabilized by the anti electron
• Hyperconjugation?
• Dipoles?

Structure of Glycoside:

• Sugar
• Glycosidic bond
• Aglycone

Salient Examples:

Concepts:

Terminology:

• Glycoside: sugars that are full acetal
  • Nomenclature - root 'oside'
• Nonreducing sugars: unreactive to Tollens reagent
• Aglycone: non-sugar residue on the C1 anomeric carbon

Additional Information:

• Anomeric Effect Wikipedia
• Anomeric pdf