How Does Glucose Cyclize

Glucose and other 5C and 6C sugars can cyclize through intramolecular nucleophilic attack of one of the OH’s on the carbonyl C of the aldehyde or ketone. Such intramolecular reactions occur if stable 5 or 6 member rings can form.

How does sugar cyclization occur?

Under normal biological conditions monsaccharides cyclize with only small amounts of the straight chain present in solution. When an aldose cyclizes, the hydroxyl group on the second to last carbon undergoes an intramolecular reaction with the carbonyl group of the aldehyde.

What can fructose Cyclize to?

Fructose, the most common ketohexose, can cyclize to form either a furanose or pyranose ring depending on whether the C-2 keto group reacts with the hydroxyl group on C-6 or C-5 (Fig.