Biocatalytic Selective Oxidation Of5-Hydroxymethylfurfural

5-Hydroxymethylfurfural(HMF)that can be obtained via carbohydrate dehydration is an important biobased platform chemical.HMF can be selectively oxidized to 5-hydroxymethyl-2-furancarboxylic acid(HMFCA)and 2,5-furandicarboxylic acid(FDCA),which are important intermediates in the synthesis of pharmaceuticals and polymers.Currently,chemically catalytic methods are playing a mojor role in the synthesis of furan carboxylic acids.However,these methods are generally accompanied with many drawbacks such as harsh reaction conditions,unsatisfactory selectivities,and using environmentally unfriendly catalysts such as metals.Biocatalytic oxidation free of the problems described above appears to be a promising tool for the valorization of HMF.To date,biocatalyic oxidation of HMF is investigated preliminary;the biocatalysts capable of selective oxidation of HMF are limited,and their catalytic efficiencies and substrate tolerance are low.Biocatalytic efficient conversion of HMF remains challenging,because of the great inhibition and toxicity of HMF towards biocatalysts.Recently,we have isolated Comamonas testosteroni SC1588 from soil samples for selective oxidation of HMF into HMFCA.To tap the application potential of this wild-type strain,a substrate adaptation strategy was applied for improving its HMF tolerance and catalytic efficiency in this thesis.Then,this strain was combined with laccase-2,2,6,6-tetramethylpiperidine-N-oxyl(TEMPO)system for contructing a cascade biocatalytic approach to FDCA from HMF.It was found that the catalytic activities of C.testosteroni SC1588 cells as well as its substrate tolerance were significantly improved by using substrate adaptation strategy.However,no changes in the optimal pH and temperature of this strain were observed in the oxidation of HMF upon substrate adaptation.The C.testosteroni SC1588-catalyzed synthesis of HMFCA was effectively enhanced by both adding histidine of low concentrations and increasing cell concentrations.Under the optimal conditions,HMF of 200 mM could be oxidized into HMFCA within 24 h by this strain.And even at the substrate concentrations up to 200-300 mM,the desired product was obtained with 71-81% yields.In addition,the strain was able to oxidize a variety of furan aldehydes and benzaldehydes into the target carboxylic acids,with the yields up to 98%.It was firstly found that 4-tert-butylcatechol that acts as a stabilizer in HMF commercially available exerted a significantly negative effect on the catalytic activities of C.testosteroni SC1588 cells.Laccase-TEMPO system displayed a good catalytic acitivity at pH 6.0 and 30 ?.Phosphate concentrations had a great effect on the oxidation of HMF catalyzed by laccase-TEMPO system,and the synthesis of FDCA was efficiently improved by increasing its concentrations.Laccase-TEMPO system could catalyze the oxidation of 2,5-di(hydroxymethyl)furan(BHMF),HMFCA and FFCA as well as HMF.In addition,the strain displayed satisfactory activities in the oxidation of HMFCA,but the oxidation of FFCA catalyzed by this strain was very slow.TEMPO,especially at more than 20 mM,had a negative effect on the catalytic activities and stability of C.testosteroni SC1588.Based on the results obtained above,biocatalytic cascade oxidation of HMF into FDCA was performed by using the combination of laccase-TEMPO system and C.testosteroni SC1588 cells.HMF was firstly oxidized into HMFCA by C.testosteroni SC1588,and then this intermediate was converted into 5-formyl-2-furancarboxylic acid(FFCA)by laccase-TEMPO system.At last,FFCA was oxidized into FDCA by C.testosteroni SC158.The yield of FDCA up to 92% was achieved in 36 h at 100 mM HMF.In this study,the catalytic performances of C.testosteroni SC1588 were remarkably improved by a simple substrate adaptation strategy.The detrimental effect of TBC,a HMF stabilizer,on the catalytic activities of microbial cells was demonstrated.On the basis of the subsrate specificity of laccase-TEMPO system and C.testosteroni SC1588 cells,a novel and efficient biocatalytic cascade reaction for the oxidation of HMF into FDCA was contructed.The present study may not only enrich the theoretical knowledge in biocatalytic valorization of biobased platform chemicals,but also lay the technical foundation for the large-scale synthesis of value-added furan derivatives.