One-Pot Photobiocatalytic Synthesis Of Biobased C4 Chemicals

Furfural obtained via xylose dehydration is one of important biobased platform chemicals.Due to the presence of highly reactive furan ring and formyl group in this chemical,it may be readily transformed to a series of value-added intermediates via typical chemical transformations such as oxidation,reduction and alkylation,which are widely used in the polymer,chemical,medicine and food industries.Presently,furfural can be converted to 5-hydroxy-2（5H）furanone（HFO）by photocatalysis.However,it remains challenging to realize the ring-opening and simultaneous isomerization of HFO to fumaric semialdehyde（FSA）under mild conditions.The catalysts such as strong acids and V₂O₅ are used in the traditional process toward fumaric acid（FA）,with Na Cl O as oxidant;large amounts of waste water are generated,leading to serious environmental issues.The biosynthesis of FA is mainly based on the Rhizopus fermentation,which suffers from low product yields and long production periods,etc.To date,the synthesis of FA,L-aspartic acid andβ-alanine from furfural has not been reported yet.Therefore,one-pot photobiocatalytic oxidation of furfural to HFO,maleic acid（MA）,FSA,FA,L-aspartic acid andβ-alanine was explored in this thesis.The main results are summarized as follows:1.The synthesis of HFO.Photocatalytic synthesis of HFO provided much higher yields in organic solvents than in deionized water,regardless of the substrates used（furfural and furoic acid）.Furoic acid is a better substrate for photocatalytic synthesis of HFO than furfural.So,a photobiocatalytic cascade system was constructed to oxidize furfural to HFO,in which furfural was oxidized to furoic acid by biocatalyst（E.coli-Ct VDH2-NOX cells,E.coli harboring vanillin aldehyde dehydrogenase 2 and NADH oxidase）and the latter was further oxidized to HFO by photocatalyst（rose bengal,RB;eosin Y,EY;methylene blue,MB）.It was found that the furfural conversion of 85%and the HFO yield of 74%were obtained in the one-pot,concurrent manner when the substrate concentration was 50 m M.Nonetheless,the furfural conversions were<40%with the substrate concentrations of>50 m M,likely due to the inactivation of the cells caused by reactive oxygen species produced by photocatalysis.So,photobiocatalytic synthesis of HFO was performed in a step-wise mode.Furfural was converted to furoic acid by E.coli-Ct VDH2-NOX cells,followed by addition of 30%organic co-solvent（acetone or methanol）and 2 mol%photocatalyst（RB or EY）to oxidize furoic acid,resulting in the production of HFO with the yields of up to 94%.2.The synthesis of other C4 chemicals.Macroporous weakly basic styrene-based anionic resin（DVB）could catalyze the ring opening and simultaneous isomerization of HFO to FSA under mild conditions.Laccase-TEMPO（2,2,6,6-tetramethylpiperidine-N-oxyl）system enabled the oxidation of HFO to MA as well as the oxidation of FSA to FA.One-pot,three-step synthesis of MA and FA could be implemented by integrating E.coli-Ct VDH2-NOX cells with photocatalyst and laccase-TEMPO system.MA and FA were obtained with the highest yields of 83%and 80%,respectively.The E.coli-Ec Asp A（L-aspartase）/E.coli-Cg Pan D（L-aspartateα-decarboxylase）cells coupled with the above cascade system were applied to synthesize L-aspartic acid andβ-alanine,with the yields of 63%and 75%,respectively.L-Aspartic acid was obtained with the isolated yield of 30%and the purity of 81%in the scale-up synthesis.In this study,ring opening and simultaneous isomerization of HFO can be implemented under mild conditions,and a novel route toward C4 chemicals such as FA and L-aspartic acid from furfural has been established.