Stachyose occurs in the roots of several species of plants. Deduce the structure of stachyose from the following data:
1. Acidic hydrolysis of 1 mol of stachyose yields 2 mol of D-galactose, 1 mol of D-glucose, and 1 mol of D-fructose.
2. Stachyose is a nonreducing sugar.
3. Treating stachyose with an a-galactosidase produces a mixture containing d-galactose, sucrose, and a nonreducing trisaccharide called raffinose.
4. Acidic hydrolysis of raffinose gives D-glucose, D-fructose, and D-galactose. Treating raffinose with an a-galactosidase yields D-galactose and sucrose. Treating raffinose with invertase (an enzyme that hydrolyzes sucrose) yields fructose and melibiose.
5. Methylation of stachyose followed by hydrolysis yields 2, 3, 4, 6-tetra-O-methyl-D-galactose, 2, 3, 4-tri-O-methyl-d-galactose, 2, 3, 4-tri-O-methyl-d-glucose, and 1, 3, 4, 6-tetra-O-methyl-d-fructose.