Fructose Ketohexose, is Cyclized by reaction between carbon 1 and 4, this form is derived from furan, furan is the form (Figure 3). Glucose but also the D-glucofuranose is not stable and is rapidly becoming D-glucopyranose. The dare is cyclizing furan form (furanose) are:

The ribose giving ribofuranose.
The 2-deoxyribose 2-giving desoxyribofuranose.
Fructose giving fructofuranose.
Generally, it is [...]