BackThe disaccharide lactulose consists of a D-galactopyranose subunit and a D-fructofuranose subunit joined by a β-1,4′-glycosidic linkage. After treatment of lactulose with 1. excess CH3I/Ag2O, 2. HCl/H2O, the d-galactopyranose subunit was found to have one nonmethylated OH group, whereas the D-fructofuranose subunit had two. Draw the structure of ⍺-lactulose.
Trehalose is a nonreducing disaccharide (C12H22O11) isolated from the poisonous mushroom Amanita muscaria. Treatment with an α-glucosidase converts trehalose to two molecules of glucose, but no reaction occurs when trehalose is treated with a β-glucosidase. When trehalose is methylated by dimethyl sulfate in mild base and then hydrolyzed, the only product is 2,3,4,6-tetra-O-methylglucose. Propose a complete structure and systematic name for trehalose.
How many monomers are linked together in a ?
In each of the disaccharides shown (a–c), (i) identify the reducing end of the sugar, (ii) tell what monosaccharides are used to make it, and (iii) tell what type of glycoside linkage is present.
(a)
Identify the following disaccharides as reducing sugars (RS) or non-reducing sugars (NS)
Maltose, like cellobiose, is composed of two glucose units. What is the difference between maltose and cellobiose?
In each of the disaccharides shown (a–c), (i) identify the reducing end of the sugar, (ii) tell what monosaccharides are used to make it, and (iii) tell what type of glycoside linkage is present.
(b)
Does lactose mutarotate? Is it a reducing sugar? Explain. Draw the two anomeric forms of lactose
a. Identify the sugars in amygdalin.
An unknown reducing disaccharide is found to be unaffected by invertase enzymes. Treatment with an α-galactosidase cleaves the disaccharide to give one molecule of D-fructose and one molecule of D-galactose. When the disaccharide is treated with excess iodomethane and silver oxide and then hydrolyzed in dilute acid, the products are 2,3,4,6-tetra-O-methylgalactose and 1,3,4-tri-O-methylfructose. Propose a structure for this disaccharide, and give its complete systematic name.
Identify the following disaccharides as reducing sugars (RS) or non-reducing sugars (NS)
Draw the mechanism for the formation of β-lactose from ⍺-D-galactose and β-D-glucose in dilute HCl.