In disaccharides, if the reducing groups of monosaccharides, i.e., aldehydic or ketonic groups are bonded, these are non-reducing sugars. Which of the following disaccharide is a non-reducing sugar?

1.
2.
3.
4.

HINT: Reducing sugars are sugars where the anomeric carbon has an OH group attached that can reduce other compounds. Non-reducing sugars do not have an OH group attached to the anomeric carbon so they cannot reduce other compounds.

                      

This structure represents sucrose in which α-D glucose and β-D-fructose is attached to each other by C1- C2 glycosidic linkage.

Since reducing groups of glucose and fructose are involved in glycosidic bond formation, this is considered as a non-reducing sugar.