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

Abstract

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