Efficient reduction of 5-hydroxymethylfurfural to 2, 5-bis (hydroxymethyl) furan by a fungal whole-cell biocatalyst

Chemoselective Lipase-Catalyzed Synthesis of Amido Derivatives from 5-Hydroxymethylfurfurylamine

The acylations of furfurylamine and 5-hydroxymethylfurfurylamine (HMFA) have been studied finding immobilized Candida antarctica lipase B (CALB) as an ideal biocatalyst. CALB was used immobilized on two different supports (Novozyme 435 and EziG-CALB), with the polymer-coated controlled porosity glass carrier material from EnginZyme being an excellent carrier to yield an active and stable enzymatic preparation for the acylation of the primary amine group. The amount of the acyl donor in the reaction was a key factor to achieve the mono- and chemoselective N-protection of HMFA with large excess of ethyl acetate leading to the formation of the N,O-diacetylated product. Thus, a series of 16 nonactivated esters were used to selectively modify the amine group of HMFA, obtaining 9 hydroxy amides under mild reaction conditions and with quantitative yields through chromatography-free transformations. The influence of substrate concentration was studied, resulting in complete conversions in all cases after 22 h (100-1000 mM). Excellent results were observed at 100 and 200 mM of HMFA, while higher concentrations led to longer reaction times and, to some extent, the formation of the diacetylated product (up to 7% after 22 h at 1 M). After this optimization, a metric analysis was performed to confirm the high sustainability of the presented process (E-factor of 1.1 excluding solvents) upon intensification of the biotransformation to 1 g at 200 mM HMFA concentration. The possibility of obtaining orthogonally protected HMFA-derived amido esters has been achieved through a clean and sequential one-pot process using EziG-CALB, which involved the use of ethyl methoxy acetate as the nonactivated ester for N-acylation and the activated vinyl acetate for O-protection.

Non-conventional yeast strains: Unexploited resources for effective commercialization of second generation bioethanol

The conventional yeast (Saccharomyces cerevisiae) is the most studied yeast and has been used in many important industrial productions, especially in bioethanol production from first generation feedstock (sugar and starchy biomass). However, for reduced cost and to avoid competition with food, second generation bioethanol, which is produced from lignocellulosic feedstock, is now being investigated. Production of second generation bioethanol involves pre-treatment and hydrolysis of lignocellulosic biomass to sugar monomers containing, amongst others, d-glucose and D-xylose. Intrinsically, S. cerevisiae strains lack the ability to ferment pentose sugars and genetic engineering of S. cerevisiae to inculcate the ability to ferment pentose sugars is ongoing to develop recombinant strains with the required stability and robustness for commercial second generation bioethanol production. Furthermore, pre-treatment of these lignocellulosic wastes leads to the release of inhibitory compounds which adversely affect the growth and fermentation by S. cerevisae. S. cerevisiae also lacks the ability to grow at high temperatures which favour Simultaneous Saccharification and Fermentation of substrates to bioethanol. There is, therefore, a need for robust yeast species which can co-ferment hexose and pentose sugars and can tolerate high temperatures and the inhibitory substances produced during pre-treatment and hydrolysis of lignocellulosic materials. Non-conventional yeast strains are potential solutions to these problems due to their abilities to ferment both hexose and pentose sugars, and tolerate high temperature and stress conditions encountered during ethanol production from lignocellulosic hydrolysate. This review highlights the limitations of the conventional yeast species and the potentials of non-conventional yeast strains in commercialization of second generation bioethanol.

Rendered-Protein Hydrolysates as a Low-Cost Nitrogen Source for the Fungal Biotransformation of 5-Hydroxymethylfurfural

5-hydroxymethylfurfural (HMF) is a platform chemical that can be converted into a wide range of high-value derivatives. Industrially, HMF-based derivatives are synthesized via chemical catalysis. However, biocatalytic transformation has emerged as an attractive alternative. Significant advances have been made in the last years using isolated enzymes and whole-cell biocatalysts in HMF biotransformation. Nonetheless, one of the major bottlenecks is the cost of the process, mainly due to the microorganism growth substrate. In this work, biotransformation studies to transform HMF into 2,5-di(hydroxymethyl)furan (DHMF) were carried out with the fungus Fusarium striatum using low-cost protein hydrolysates. The protein hydrolysates were obtained from fines, an unexploited material produced during the rendering process of meat industry waste residues. Given the high content in the protein of fines, of around 46%, protein hydrolysis was optimized using two commercially available proteases, Alcalase 2.4 L and Neutrase 0.8 L. The maximum degree of hydrolysis (DH) achieved with Alcalase 2.4 L was 21.4% under optimal conditions of 5% E/S ratio, pH 8, 55 °C, and 24 h. On the other hand, Neutrase 0.8 L exhibited lower efficiency, and therefore, lower protein recovery. After optimization of the Neutrase 0.8 L process using the response surface methodology (RSM), the maximum DH achieved was 7.2% with the variables set at 15% E/S ratio, initial pH 8, 40 °C, and 10.5 h. Using these hydrolysates as a nitrogen source allowed higher sporulation of the fungus and, therefore, the use of a lower volume of inoculum (three-fold), obtaining a DHMF yield > 90%, 50% higher than the yield obtained when using commercial peptones. The presented process allows the transformation of animal co- and by-products into low-cost nitrogen sources, which greatly impacts the industrial feasibility of HMF biotransformation.

Production of Hydroxymethylfurfural Derivatives From Furfural Derivatives via Hydroxymethylation

Hydroxymethylfurfural (HMF) derivatives such as 2,5-bis(hydroxymethyl)furan (BHMF) and furandicarboxylic acid (FDCA) are promising alternative of fossil-based diols and dicarboxylic acids for synthesis of polyesters such as polyethylene terephthalate (PET). However, high cost for preparing HMF from biomass discourages the commercialization of HMF-derived polyesters. Since producing furfural (FUR) from five-carbon sugars (e.g., xylose) via dehydration is an inexpensive and commercialized process, we herein reported a method to synthesize BHMF derivatives (5-(ethoxymethyl)furan-2-methanol (EMFM), 2,5-bis(hydroxymethyl)furan monoacetate (BHMFM) and 2,5-bis(hydroxymethyl)furan diacetate (BHMFD) from furfural derivatives, i.e., (2-(ethoxymethyl)furan (EMF) and furfuryl acetate (FA)). To avoid strong acid-induced side reactions (e.g., furan ring opening, condensation and carbonization), two reaction systems, i.e., a low-concentration HCl aqueous solution combined with formaldehyde and anhydrous acetic acid combined with paraformaldehyde, were found to be suitable for such a hydroxymethylation reaction and could lead to decent product yields. In order to improve the carbon utilization, condensed furanic byproducts were further converted into hydrocarbon fuels via a reported two-step hydrodeoxygenation (HDO) process. This study not only validates the possibility of synthesizing functional HMF derivatives (EMFM, BHMFM, and BHMFD) from commercially-available FUR derivatives (EMF and FA), but also provide a new way to transform condensed furanics to value-added hydrocarbon fuels.

Whole Cell Biocatalysis of 5-Hydroxymethylfurfural for Sustainable Biorefineries

The implementation of cost-effective and sustainable biorefineries to substitute the petroleum-based economy is dependent on coupling the production of bioenergy with high-value chemicals. For this purpose, the US Department of Energy identified a group of key target compounds to be produced from renewable biomass. Among them, 5-hydroxymethylfurfural (HMF) can be obtained by dehydration of the hexoses present in biomass and is an extremely versatile molecule that can be further converted into a wide range of higher value compounds. HMF derivatives include 2,5-bis(hydroxymethyl)furan (BHMF), 5-hydroxymethyl-furan-2-carboxylic acid (HMFCA), 2,5-diformylfuran (DFF), 5-formyl-2-furancarboxylic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA), all presenting valuable applications, in polymers, bioplastics and pharmaceuticals. Biocatalysis conversion of HMF into its derivatives emerges as a green alternative, taking into account the high selectivity of enzymes and the mild reaction conditions used. Considering these factors, this work reviews the use of microorganisms as whole-cell biocatalysts for the production of HMF derivatives. In the last years, a large number of whole-cell biocatalysts have been discovered and developed for HMF conversion into BHMF, FDCA and HMFCA, however there are no reports on microbial production of DFF and FFCA. While the production of BHMF and HMFCA mainly relies on wild type microorganisms, FDCA production, which requires multiple bioconversion steps from HMF, is strongly dependent on genetic engineering strategies. Together, the information gathered supports the possibility for the development of cell factories to produce high-value compounds, envisioning economical viable biorefineries.

Establishment of Kluyveromyces marxianus as a Microbial Cell Factory for Lignocellulosic Processes: Production of High Value Furan Derivatives

The establishment of lignocellulosic biorefineries is dependent on microorganisms being able to cope with the stressful conditions resulting from the release of inhibitory compounds during biomass processing. The yeast Kluyveromyces marxianus has been explored as an alternative microbial factory due to its thermotolerance and ability to natively metabolize xylose. The lignocellulose-derived inhibitors furfural and 5-hydroxymethylfurfural (HMF) are considered promising building-block platforms that can be converted into a wide variety of high-value derivatives. Here, several K. marxianus strains, isolated from cocoa fermentation, were evaluated for xylose consumption and tolerance towards acetic acid, furfural, and HMF. The potential of this yeast to reduce furfural and HMF at high inhibitory loads was disclosed and characterized. Our results associated HMF reduction with NADPH while furfural-reducing activity was higher with NADH. In addition, furans' inhibitory effect was higher when combined with xylose consumption. The furan derivatives produced by K. marxianus in different conditions were identified. Furthermore, one selected isolate was efficiently used as a whole-cell biocatalyst to convert furfural and HMF into their derivatives, furfuryl alcohol and 2,5-bis(hydroxymethyl)furan (BHMF), with high yields and productivities. These results validate K. marxianus as a promising microbial platform in lignocellulosic biorefineries.

Improved Bio-Synthesis of 2,5-bis(hydroxymethyl)furan by Burkholderia contaminans NJPI-15 With Co-substrate

Upgrading of biomass derived 5-hydroxymethylfurfural (HMF) has attracted considerable interest recently. A new highly HMF-tolerant strain of Burkholderia contaminans NJPI-15 was isolated in this study, and the biocatalytic reduction of HMF into 2,5-bis(hydroxymethyl)furan (BHMF) using whole cells was reported. Co-substrate was applied to improve the BHMF yield and selectivity of this strain as well as HMF-tolerant level. The catalytic capacity of the cells can be substantially improved by Mn²⁺ ion. The strain exhibited good catalytic performance at a pH range of 6.0–9.0 and a temperature range of 25°C–35°C. In addition, 100 mM HMF could be reduced to BHMF by the B. contaminans NJPI-15 resting cells in presence of 70 mM glutamine and 30 mM sucrose, with a yield of 95%. In the fed-batch strategy, 656 mM BHMF was obtained within 48 h, giving a yield of 93.7%. The reported utilization of HMF to produce BHMF is a promising industrially sound biocatalytic process.