β-Elimination as major side reaction in periodate-oxidation of cellulosic model mono- and disaccharides

To structurally characterize periodate-oxidized cellulosic substrates, methyl 4- O -methyl β- d -glucopyranoside and methyl 4’- O -methyl-cellobioside were subjected to periodate treatment at pH 4.8–5.0. Oxidation of the monosaccharide using two molar equivalents of oxidant produced 3-methoxy-2,5-dihydro-2-furanol as main product. To confirm its structure and mode of formation, 6- O -bisdeuteromethyl 4- O -methyl-β- d -glucopyranoside and methyl 4- O -trisdeuteromethyl-β- d -glucopyranoside were synthesized and oxidized to generate 3-methoxy-5-deutero-2-hydro-2-furanol in the former case and 3-trisdeuteromethoxy-2,5-dihydro-2-furanol in the latter case. Oxidation using one molar equivalent of periodate led to preferential formation of hemialdal products and ( E )-4-hydroxy-2-methoxy-2-butenal. The latter product was also formed upon end-wise oxidation of methyl 4’- O -methyl-cellobioside, wherein the reducing unit was released as non-oxidized methyl β- d -glucopyranoside. This data indicate that periodate oxidation of cellulosic model substrates might be accompanied by peeling reactions and formation of β-elimination products even under slightly acidic conditions. Graphical abstract