Catalytic cycle of carbohydrate dehydration by Lewis acids: structures and rates from synergism of conventional and DNP NMR

Abstract

Structures and rates in the catalytic cycle of carbohydrate dehydration by Lewis acidic salt are determined through the systematic use of complementary NMR approaches.

Heterogeneous Base‐Catalyzed Conversion of Glycolaldehyde to Aldotetroses: Mechanistic and Kinetic Insight

“…Lewis acids are suspected to favor ring opening [17] and cascade reactions (often including hydride shifts) [18] upon coordination to lone pairs at the aldehyde carbonyl group and nearby alcohols. Lewis acids even render carbohydrate enol species detectable by optimized NMR methods [14a,19] and elicit a more concerted sequence of aldol addition and isomerization steps to the thermodynamically preferred tetrose ERU [16] . We therefore propose that a promising strategy for the production of rare aldotetroses would focus on the use and development of thermally stable basic resins, whose active site structures may be varied to fine‐tune the relative preference towards ERY or THR formation.…”

NMR methods for the analysis of mixtures

“…D-DNP is used extensively for kinetic studies based on the injection of hyperpolarised compounds in a mixture containing other reactants and/or catalysts, or in cell cultures. [92][93][94][95][96][97][98][99][100][101] In such applications, hyperpolarisation methods make it possible to acquire 13 C NMR spectra with a time resolution of a few seconds, which would be impossible to achieve at thermal equilibrium. They also make it possible to observe intermediate species that would be invisible with conventional NMR methods.…”

Reaction prediction via atomistic simulation: from quantum mechanics to machine learning

“…This new mechanism for 5-HMF production supports the observed glucose pyrolysis phenomena and provides important insights int to the catalytic glucose conversion. A recent NMR experiment in catalytic carbohydrate dehydration does reveal 3-deoxyglucos-2-ene (3-DGE, E ) as an on-pathway intermediate ( Jensen and Meier, 2020 ).…”