Synthesis Of Platform Chemicals Furfurylamine And Furfuralcohol From Corncob Via Chemoenzymatic Approach

Furfural（FAL）is a high-value platform chemical derived from renewable biomass feedstock,whcih has been widely employed for production of plastics,resins,fuels,pharmaceutical intermediates and other additives.As the downstream products of furfural,furfuralcohol（FOL）and furfurylamine（FLA）are both important organic compounds which can be used to synthesize a variety of bioactive molecules and polymer materials.At present,the traditional synthetic routes of FOL and FLA usually require harsh reaction conditions,such as high pressure,precious metal catalysts and serious environmental pollution with high energy consumption at the same time.The biocatalysis method has gradually replace traditional chemical synthesis pathways in fine chemicals,pharmaceuticals and other industries,and became an important means for industrially synthesizing bulk chemicals and pharmaceutical intermediates or other substances,because of mild operating conditions,high catalytic efficiency,environmental friendly and high selectivity.In this study,the tandem catalysis with biocompatible solid acid catalyst SO₄^2-/SnO₂-MS and recombinant Escherichia coli whole cell biocatalyst were used to synthesize FLA and FOL from corncob via chemoenzymatic approach.The results were obtained as follows:Firstly,SO₄^2-/SnO₂-MS solid acid catalyst was prepared using sponge-superposed structure of medical stone（MS）as the carrier.Then SO₄^2-/SnO₂-MS solid acid catalyst and fresh MS were characterized by BET,SEM,FT-IR and XRD.It was found that the treated medical stone surface became loose and porous,with the increased specific surface area of 68.0 m²/g and the pore volume of 0.048 cm³/g.However,the main structure and key chemical bonds of medical stone were not destroyed.These changes increased the contact area between the catalyst and the substrate,which led to the effective conversion of corncob to FAL by catalytic dehydration.Subsequently,43.0%yield of FAL was obtained from corncob with 3.6 wt%SO₄^2-/SnO₂-MS at 170 ^oC,indicating acidified SO₄^2-/SnO₂-MS could effectively catalyze corncob into FAL.Secondly,synthesis of FOL from corncob was carried out by tandem catalysis with acidified solid acid SO₄^2-/SnO₂-MS and recombinant E.coli CR whole cells harboring reductases.In order to increase the yield of FOL,various factors affecting the biological reduction reaction were investigated.The optimal cell dosage,cosubstrate glucose loading,NADP⁺loading,metal ion additive,surfactant additive,reaction temperature and reaction pH were 0.05 g/mL,1 mol glucose/mol FAL,1μM NADP⁺/mM FAL,Sn⁴⁺（1 mM）,and SDS（0.5 mM）,35 ^oC,7.5,respectively.Under the optimal conditions,E.coli CR could tolerate 150 mM FAL,and 100 mM FAL prepared from corncob could be completely biologiaclly converted to FOL with E.coli CR.Thus,the efficient synthesis of FOL from corncob by tandem catalysis with SO₄^2-/SnO₂-MS and E.coli CR was achieved.Thirdly,tandem catalysis with SO₄^2-/SnO₂-MS and recombinant E.coliXLS158 whole cells containing transaminase was used for converting corncob to FLA was confirmed in reaction manner.Various reaction parameters were optimized.The optimal cell loading,amine donor NH₄Cl dosage,cosubstrate glucose dose,reaction temperature and reaction pH were 0.05 g/mL,4 mol NH₄Cl/mol FAL,2 mol C₆H₁₂O₆/mol FAL,35 ^oC and 7.5,respectively.It was found that the addition of 0.5 mM Mg²⁺and10 mM PEG-4000 could facilitate the bioreaction.Under the optimal conditions,the corncob-derived FAL（71.8 mM）was subjected to the reductive amination reaction by E.coli XLS158 for 72 h,and the final yield of FLA was 76.3%.The FLA yield based on the corncob preparation process was 0.070 g FLA/g corncob.This verified the feasibility of chemoenzymatic method to synthesize FLA from corncob.Finally,in order to enhance the synthesis FLA,water-organic solventbiphasic system was established to convert corncob into FLA,and various factors affecting the reduction amination reaction in the biphasic system were optimized.The optimal organic solvent was n-octane with good biocompatibility.The volumetric ratio of water to n-octane in biocatalytic reaction media was 8:2（v:v）;the molar ratio of NH₄Cl versus FAL was 4:1（mol:mol）;the molar ratio of glucose C₆H₁₂O₆ versus FAL was 2:1（mol:mol）.The reaction temperature and pH were 35 ^oC and 7.5,respectively.The SO₄^2-/SnO₂-MS solid acid catalyzed corncob in water-n-octane medium obtained a FAL yield of 48.8%,which was 5.8%higher than that in the monoaqueous phase.The obtained FAL solution（82.2 mM）was transformed into FLA with E.coli XLS158 under optimal conditions.The yield of the reaction was 78.3%after 72 h,and the FLA yield based on the corncob preparation process was 0.080 g FLA/g corncob,which was better than the aqueous phase catalytic effect.It was showed that recombinant E.coli XLS158 could efficiently convert corncob into FLA in the water-n-octane（8:2,v:v）biphasic system.In summary,solid acid catalyst SO₄^2-/SnO₂-MS was used to synthesize FAL from corncob,and then recombinant E.coli whole-cell as biocatalyst catalyzed FAL to effectively synthesize furan derivatives（FOL and FLA）.In this way,FOL and FLA were synthesized by chemoenzymatic method,and a suitable biological amination system was explored to improve the productivity of FLA,which laid a foundation for green and efficient production of furan-based chemicals from biomass as raw material in industry.