Maltose is a disaccharide obtained from the hydrolysis of starch. Maltose can be hydrolyzed to two equivalents of glucose and can be oxidized to an acid, maltobionic acid, with bromine water. Treatment of maltose with dimethyl sulfate and sodium hydroxide, followed by hydrolysis of the product in aqueous acid, yields one equivalent each of 2,3,4,6-tetra-O-methyl-D-glucose and 2,3,6-tri-O- methyl-D-glucose. Hydrolysis of maltose is catalyzed by a-amylase, an enzyme known to affect only a-glycosidic linkages. Give two structures of maltose consistent with these data, and explain your answers. 

Treatment of maltobionic acid with dimethyl sulfate and sodium hydroxide followed by hydrolysis of the product in aqueous acid gives 2,3,4,6-tetra-O-methyl-D- glucose and 2,3,5,6-tetra-O-methyl-D-gluconic acid.