Probing the Lewis Acid Catalyzed Acyclic Pathway of Carbohydrate Conversion in Methanol by In Situ NMR

Future bioindustries will rely on the formation of diverse chemicals at high yield through various reaction pathways. These pathways include reactions to a series of alpha-hydroxy esters and acids that can be formed from the conversion of C3-C6 carbohydrates by Lewis acidic catalysts in alcohols and water. Definitive kinetic and mechanistic insights to support the development of carbohydrate
conversion processes are arguably less developed than for analogous biocatalytic processes. Here, we visualize acyclic pathways of carbohydrate dehydration, using the acyclic C4 carbohydrate erythrulose as a probe molecule for the conversion by homogeneous SnCl4 in methanol. In situ studies allow the detection of previously postulated intermediates, identify the branch point to competing products and provide energetic and mechanistic insight by kinetic
analysis. Reversibility of reactions, stereoselectivity and differential propensity for deuterium incorporation in competing pathways can be tracked by the formation of compounds with asymmetric mass distribution.