Deduce the structure of the disaccharide melibiose from the following data:
1. Melibiose is a reducing sugar that undergoes mutarotation and forms a phenylosazone.
2. Hydrolysis of melibiose with acid or with an a-galactosidase gives d-galactose and D-glucose.
3. Bromine water oxidation of melibiose gives melibionic acid. Hydrolysis of melibionic acid gives d-galactose and d-gluconic acid. Methylation of melibionic acid followed by hydrolysis gives 2, 3, 4, 6-tetra-O-methyl-d-galactose and 2, 3, 4, 5-tetra-O-methyl-D-gluconic acid.
4. Methylation and hydrolysis of melibiose give 2, 3, 4, 6-tetra-O-methyl- D-galactose and 2, 3, 4-tri-O-methyl-D-glucose.