Mechanistic Insights into the Conversion of Biorenewable Levoglucosanol to Dideoxysugars

Abstract

A molecular understanding of the conversion of biorenewable threo-and erythro-levoglucosanol (LGOL) to 3,4dideoxysugars in aqueous medium is provided based on firstprinciples simulations. The synthetic importance of this transformation is that these intermediates can be quantitatively hydrogenated to (S,S)/(S,R) hexane-1,2,5,6-tetrol (tetrol), whose stereochemistry depends on which dideoxy sugar intermediates are formed during LGOL conversion. The thermodynamic and kinetic feasibility of the acetal (R 2 C(OR) 2 ) hydrolysis in LGOL is investigated via computing the free energy profile. In aqueous medium, the rate-determining step of LGOL hydrolysis is the protonation of the anhydro-bridge oxygen atom of LGOL concurrent with ring opening, yielding the cyclic forms of 3,4-dideoxymannose (DDM) and 3,4-dideoxyglucose (DDG) from threo-and erythro-LGOL, respectively. The measured activation energies of LGOL hydrolysis are 20.5 and 23.6 kcal/mol for DDM and DDG formation, respectively. These values are in agreement with the computed protonation free energies of 17.1 and 18.2 kcal/mol, respectively. Based on the simulations, a Brønsted base-catalyzed isomerization from DDG or DDM to 3,4-dideoxy fructose (DDF) is preferred with lower apparent activation free energy barriers compared to the acid-catalyzed isomerization. In summary, this study provides mechanistic information about the conversion of the biomass-derived anhydro-sugar LGOL to 3,4-dideoxy sugars, which are precursors to renewable high-value chemicals.

Production of Hexane-1,2,5,6-tetrol from Biorenewable Levoglucosanol over Pt-WOx/TiO2

“…The apparent activation energy was found to be 151 ± 10 kJ/mol, as shown in Figure . This apparent activation energy value is higher than those reported in literature for hydrogenolysis of C–O bonds of cyclic ethers (84–118 kJ/mol) and also higher than the computed activation energy of Lgol hydrolysis with H 2 SO 4 catalyst (t-Lgol to DDM: 86 kJ/mol; e-Lgol to DDG: 98 kJ/mol) in water …”

“…This apparent activation energy value is higher than those reported in literature for hydrogenolysis of C−O bonds of cyclic ethers 25 (84−118 kJ/mol) and also higher than the computed activation energy of Lgol hydrolysis with H 2 SO 4 catalyst (t-Lgol to DDM: 86 kJ/mol; e-Lgol to DDG: 98 kJ/mol) in water. 41 Catalyst Performance and Stability and Activity in a Flow Reactor. Figure 6 shows the performance of the Pt-WO x /TiO 2 catalyst for the hydrogenolysis of a 30 wt % aqueous Lgol solution at 120 °C over 51 h time-on-stream (TOS).…”

Reduction of 5-Hydroxymethylfurfural and 1,2-Dicarbonyl Compounds by Saccharomyces cerevisiae in Model Systems and Beer

“…By evaluation of the 1 H, COSY, HSQC, and HMBC spectra, it was possible to assign signals to four coupling groups (Table S1). These coupling groups may represent different pyranose and furanose forms; however, a higher yield of the substance should be sought after to allow for more expressive NMR experiments. Moreover, as expected in the literature, the 13 C signal of the open-chain keto form was detected (213.7 ppm) and a neighboring CH 2 signal was identified by HMBC ( 13 C, 67.2 ppm; 1 H, 4.3 ppm).…”

Hydrodeoxygenation of potential platform chemicals derived from biomass to fuels and chemicals

“…In water as a solvent, the produced cationic intermediate quickly reacts with water to give 3,4-dideoxysugars (3,4-dideoxyglucose or 3,4-dideoxymannose, depending on the stereochemistry of the levoglucosanol substrate). 68,80 The hydrogenation of 3,4-dideoxysugars over metal catalysts gives the target product 1,2,5,6-hexanetetraol. In non-water solvents, the cationic intermediate is rearranged.…”