2-C-Carboxy-D-glucitol 1,6-bisphosphate (CGBP) and 2-C-carboxy-D-mannitol 1,6-bisphosphate (CMBP) have been synthesized, isolated, and the structures of these compounds and the derived lactones elucidated by NMR spectroscopy and periodate oxidation. Both carboxyhexitol bisphosphates, which are