Compounds A and B, having the same summary formula C7H14O6 but different physical properties (for example melting point and specific optical rotation), belong to the group of saccharides containing six-member heterocycles. When 1% solution of sulphuric acid is added to compound A and B respectively, the same compound C containing 40.0% C and 6.71% H is obtained at boiling. After reducing compound C (for example catalytically with hydrogen or with hydride Na[BH4] ) a crystalline product D was isolated which did not reduce Fehling's reagent and showed no optical activity. Compound C was oxidised with a mild oxidising agent (e. g. with a cold sodium hypobromite solution) yielding a salt of polyhydroxy monocarboxylic acid of D-configuration.
Suggest the structure of the compounds A, B, C, and D.
