Investigating the Conformation of the Bridged Monosaccharide Levoglucosan

Abstract

Levoglucosan is one of the main products of the thermal degradation of glucose and cellulose and is commonly used as a tracer for biomass burning. Herein we report a conformational analysis of levoglucosan under isolation conditions, by means of microwave spectroscopy coupled with ultrafast laser vaporization in supersonic expansions. We observed three different conformations of levoglucosan in the gas phase. They all share a common heavy atom rigid bicyclic structure. The difference between the three of them lies in the network of intramolecular hydrogen bonds that arises from the OH groups at positions 2, 3 and 4. The different combinations of H-bonds give richness to the conformational landscape of levoglucosan. The gas phase conformers obtained in this work are compared to the crystal structure of levoglucosan previously reported. Although the heavy atom frame remains unchanged, there are significant differences in the positions of the H-atoms. In addition, the levoglucosan structure can be compared to the related glucose, for which gas phase conformational studies exist in the literature. In this case, in going from glucose to levoglucosan, there is an inversion in the chair conformation of the pyranose ring. This forces the OH groups to adopt axial positions (instead of the more favorable equatorial positions in glucose) and completely changes the pattern of intramolecular H-bonds.

Regioselective Acylation of Levoglucosan Catalyzed by Candida Antarctica (CaLB) Lipase Immobilized on Epoxy Resin

“…The acyl moiety of the acyl-donor is covalently bound to the active site of the enzyme during the Comparing the obtained values, it is possible to observe that the regioselectivity of N435 is slightly influenced by the temperature and size of the alkyl chain, exhibiting a similar tendency for OH at C4 and C2 in all conditions that were explored, except for ethyl laurate ( Figure 3B, 3-Ia-50 • C), where it is possible to observe a loss of regioselectivity at higher temperatures. Different values were obtained for CaLB_epoxy and PSIM where the preference occurred for OH-C4, as can be observed for ethyl oleate ( Figure 3C, 3-Id) and ethyl laurate ( Figure 3D, 3-Ia The acyl moiety of the acyl-donor is covalently bound to the active site of the enzyme during the two transition states in the catalytic triad [24,25]. Moreover, the alcohol and the acyl binding sites are close to each other.…”

Identification, functional characterization, and crystal structure determination of bacterial levoglucosan dehydrogenase

“…It has been shown that LG predominantly adopts the inverted chair ( 1 C 4 ) ring conformations, in which the three hydroxyl groups are axial and form an intramolecular hydrogen-bonding interaction in the gas phase (38) and in crystals (39). The all-axial 1 C 4 conformation was also observed in the LG molecule bound to LGK (15).…”

Levoglucosan: a promising platform molecule?

“…129 In the chair conformation, the intramolecular interactions, due to hydrogen bonding occurring between the hydroxyl of C3 in the axial position and the oxygen in C6, also in axial, contribute to a greater stabilization of the molecule, increasing its population, but decreasing its reactivity as a nucleophile. 99,130 The same interaction, hydrogen donor-acceptor, can occur with the hydroxyls in C2 and C4, according to Fig. 12A1-A3 (Fig.…”