Method for the preparation of 2,5-furandicarboxylic acid

Abstract

A method for the preparation of 2,5-furandicarboxylic acid by oxidizing 5-formyl-2-furancarboxylic acid, which is present in an aqueous solution, to 2,5-furan dicarboxylic acid by treating with a NAD(P)+-dependent oxidoreductase in vitro, wherein the NAD(P)H generated during the oxidation is enzymatically reoxidized to NAD(P)+by the means of a dehydrogenase, after which the enzymes are removed.

Description

METHOD FOR THE PREPARATION OF 2,5-FURANDICARBOXYLIC ACID The invention relates to a method for the preparation of 2,5-furandicarboxylic acid (FDCA) from 5- formyl-2-furancarboxylic acid (FFA). Background of the Invention In 2018, approximately 90% of the plastics produced worldwide (400 Mt) were based on fossil raw materials, with the remaining shares accounted for by recycled (9%), bio-based (1%), and CO2-based plastics (<1%) (Carus et al., 2020). At the same time, global demand for plastics is also growing. In 2019, annual CO2 emissions across the entire life cycle of plastics amounted to 0.86 Gt, which corresponds to the CO₂ emissions of 189 coal-fired power plants operating at full capacity (500 MW). An increase to 2.8 Gt (equivalent to 615 coal-fired power plants) is projected for 2050 (Hamilton et al., 2019). One of the plastics based on fossil raw materials is polyethylene terephthalate (PET), which is primarily used in beverage packaging. It is a condensation polymer produced from terephthalic acid (1,4- benzenedicarboxylic acid) and ethylene glycol (ethane-1,2-diol) through the elimination of water. Terephthalic acid is produced on an industrial scale by oxidizing p-xylene (1,4-dimethylbenzene) with atmospheric oxygen at approximately 200 °C in the presence of cobalt acetate, manganese acetate, and HBr in acetic acid in the so-called AMOCO process (Tomás et al., 2013). Ethylene glycol is produced by the hydrolysis of ethylene oxide (at 200 °C), which in turn is obtained by the oxidation of ethene (derived from fossil raw materials) (Berger, 2016). Due to the fossil-based sources of the starting materials (<semantics>p<annotation encoding="application / x-tex">p< / annotation>< / semantics>-xylene and ethene), PET generally cannot be described as sustainable. To achieve the 1.5-degree target of the Paris Climate Agreement and thus limit the negative consequences of climate change, sustainable alternatives to petrochemical-based plastics must be found. For ethylene glycol, for example, there are methods based on renewable resources. For instance, ethylene can also be produced by the dehydration of bioethanol obtained by fermentation from glucose or starch (e.g., Fan et al., 2013). Fermentative conversions of xylose and / or glucose to ethylene glycol using metabolically engineered microorganisms (Escherichia coli or Saccharomyces cerevisiae) are also known (Salusjärvi et al., 2019). The second building block of PET, the aromatic compound terephthalic acid, is difficult to produce from sustainable raw materials and must therefore be replaced. An excellent substitute for terephthalic acid is 2,5-furandicarboxylic acid (FDCA), which is primarily obtained from the catalytic upgrading of biomass. By polymerization of FDCA with ethylene glycol PEF (polyethylene furanoate) is formed, which has a heteroaromatic furan ring in its structure instead of a benzene ring. Like PET, PEF is a thermoplastic, but compared to PET, it is characterized by significantly higher biodegradability and better thermal (higher glass transition temperature, lower melting temperature) and mechanical properties (higher stiffness). The most important property of PEF, however, is its reduced permeability to gases such as O₂ and CO₂. This is particularly important for beverages, as it can extend their shelf life (preventing degassing of carbonated beverages; preventing oxidation processes caused by diffused oxygen) (de Jong et al., 2022). An overview of various chemical synthesis methods can be found in the article by Cong et al. (2021). By far the most important starting material for FDCA is 5-(hydroxymethyl)furfural (HMF), which can be obtained, for example, from cellulose (and thus from renewable raw materials). Through enzymatic or chemical hydrolysis D-glucose is formed from cellulose, which is subsequently isomerized (enzymatically or chemically) to D-fructose. Through dehydration (removal of a total of three H2O molecules), D- fructose is converted to HMF. Common systems for the dehydration of fructose include, on the one hand, mineral acids such as H₂SO₄ or HCl and, on the other hand, (Brønsted or Lewis) acidic solid catalysts (Cong et al., 2021; US 9617234 B1). HMF possesses both an alcohol and an aldehyde functionality, which has to be oxidized to carboxylic acid groups to obtain FDCA. The three oxidation steps required therefor can be carried out in various ways: chemically using heterogeneous or homogeneous catalysts, electrochemically, and biocatalytically (enzymatically or using whole cells). The direct precursor of FDCA is FFA (5-formyl-2-furan carboxylic acid), which can be produced, for example, by acid-catalyzed dehydration of the sugar acid derivatives 2-keto-D-gluconate (2KGA) or 5- keto-D-gluconate (5KGA). 2KGA can be dehydrated to FFA by treatment with HBr in an acetic acid / water mixture in a flow reactor at 80 °C. In a final step, FFA can be oxidized to FDCA either with oxygen as the oxidizing agent and metals (e.g., Pt-Ru / C) or metal salts (Co and Mn salts) as catalysts, or with hydrogen peroxide (US 10087161 B2). The acid-catalyzed dehydration of 5KGA to FFA is also described in EP 3265450 B1. For the final oxidation, the reaction is carried out in acetic acid in the presence of catalytic amounts of Co acetate, Mn acetate, as well as NaBr under an excess pressure of oxygen at 180 °C (analogous to the AMOCO process). In general, the aforementioned chemical production processes for FDCA starting from FFA as an intermediate are characterized by unfavorable reaction conditions (high temperatures and pressures), the formation of byproducts, and the use of expensive and, in some cases, toxic (Co salts) catalysts, and therefore cannot be described as sustainable. Biocatalytic processes offer an alternative, as they proceed highly selectively under mild reaction conditions and use biodegradable catalysts such as cells or enzymes (Cong et al., 2021). FFA can be produced by the enzymatic oxidation of HMF (primarily using <semantics>O2<annotation encoding="application / x-tex">O_2< / annotation>< / semantics> as the oxidizing agent). One group of enzymes used to produce FFA from HMF are the aryl alcohol oxidases (AAO, EC 1.1.3.7). Carro et al. (2015) used an AAO from the mushroom Pleurotus eryngii to oxidize 3 mM HMF to FFA (98 mol%) and small amounts of FDCA in 4 h. The AAO-catalyzed oxidation of the aldehyde groups proceeds via the corresponding geminal diols (aldehyde hydrates), whereby the aldehyde groups in FFA exhibit a lower degree of hydration (FFA: 8%) compared to the precursor 2,5-diformylfuran (DFF: 53%, FFA: 8%), which explains the preferential formation of FFA over FDCA. H2O2, which is produced as a byproduct of the AAO-catalyzed oxidations, chemically oxidizes FFA to FDCA (Carro et al., 2015). In a later study by Serrano et al. (2019) on the AAO of P. eryngii, it was demonstrated that HMF can also be completely oxidized to FDCA when a catalase is used to remove <semantics>H2O2<annotation encoding="application / x-tex">H_2O_2< / annotation>< / semantics>, since the final oxidation step from FFA to FDCA is inhibited by <semantics>H2O2<annotation encoding="application / x-tex">H_2O_2< / annotation>< / semantics>. In this way, an AAO mutant was able to oxidize 1.5 mM HMF to 1.6 mM FDCA in 6 days. Other AAOs include one from Mycobacterium sp. MS1601 (completely oxidizes 4 g / L (31.7 mM) HMF to FFA in 120 h) (Sayed et al., 2022) and from the fungus Moesziomyces antarcticus (oxidizes 2 mM HMF in 24 h to 99.6 mol% FFA and 0.4 mol% FDCA; oxidizes 40% of the FFA (2 mM) to FDCA in 144 h) (Lappe et al., 2021). Qin et al. (2015) tested various laccases on 30 mM HMF using 20 mol% TEMPO ((2,2,6,6- tetramethylpiperidin-1-yl)oxyl) as a mediator. Using the laccase from the fungus Panus conchatus, 82% of the starting material was oxidized to FFA within 96 hours (with 4% 2,5-diformylfuran (DFF) and 10% FDCA as byproducts). Zhang et al. (2019) immobilized a laccase (CotA-TJ102) from Bacillus subtilis TJ-102 on magnetic nanoparticles, with which 83.3% of the starting material HMF could be oxidized to FFA (after 10 recycling cycles) with a selectivity of >96%. Jia et al. (2019) used an enzyme system consisting of GOase, an alcohol dehydrogenase from Synechocystis sp. (SADH), as well as HRP, to oxidize 97% of the HMF substrate (100 mM) to FFA in 48 hours. In addition to activating GOase <semantics>M3−5<annotation encoding="application / x-tex">M_{3-5}< / annotation>< / semantics>, HRP also serves to regenerate NAD(P)+, which is required as a cofactor for SADH. US 10344307 B2 discloses further enzyme(system)s for the oxidation of HMF to FFA: 1) NAD(P)- dependent ketoreductase & NAD(P)H oxidase for cofactor regeneration, 2) NAD(P)-dependent aldehyde dehydrogenase & NAD(P)H oxidase, and 3) xanthine oxidoreductase (such as the periplasmic aldehyde oxidoreductase (PaoABC) from E. coli; oxidizes HMF to 5-hydroxymethyl-2-furancarboxylic acid (HMFA) and DFF to FFA), galactose oxidase variant <semantics>M3−5<annotation encoding="application / x-tex">M_{3-5}< / annotation>< / semantics> (GOase <semantics>M3−5<annotation encoding="application / x-tex">M_{3-5}< / annotation>< / semantics>; oxidizes HMF to DFF and HMFA to FFA) & horseradish peroxidase (HRP; for activation of GOase <semantics>M3−5<annotation encoding="application / x-tex">M_{3-5}< / annotation>< / semantics>). For example, 50 mM DFF can be oxidized completely to FFA in 2 h at pH 6 using PaoABC, whereas at pH 7 and 8, the oxidation proceeds entirely to FDCA. The enzyme system listed under 3) is also described in detail in journal articles (McKenna et al., 2015; McKenna et al., 2017). In addition to PaoABC and AAO, other enzymes are known to catalyze the final oxidation step from FFA to FDCA. Cajnko et al. (2020) tested a series of commercially available enzymes (alcohol oxidase (AO) from Pichia pastoris; galactose oxidase from Dactylium dendroides; catalase from Aspergillus niger; laccase from Trametes versicolor; a fungal lignin peroxidase (LPO), and HRP) on 10 mM FFA and were able to observe the formation of significant amounts of FDCA (11.6% for AO, 1.1% for laccase, and 3.2% for LPO) after 72 h only for AO, the laccase, as well as the LPO. 5-Hydroxymethyl-2-furan carboxylic acid (HMFA) was identified as a byproduct (up to 18.2% for AO). Another enzyme for the oxidation of FFA to FDCA is the nonspecific peroxygenase (UPO, EC 1.11.2.1; requires H2O2 as an oxidizing agent) from Agrocybe aegerita, which can be used in combination with AAO to completely oxidize HMF to FDCA. Thus, 90% of the FFA (3 mM) can be oxidized to FDCA in 120 h (Carro et al., 2015). In addition to the oxidation of FFA to FDCA, the oxidation of HMF to FFA via DFF is also catalyzed by UPO (Lappe et al., 2021). Jia et al. (2017) used an enzyme system consisting of horse liver alcohol dehydrogenase (HLADH) and human hemoglobin (oxidized by H2O2 NADH to NAD+) to oxidize 96% of the substrate (10 mM FFA) to FDCA in 60 hours. US 8183020 B2 describes the enzymatic oxidation of FFA to FDCA using a commercially available chloroperoxidase from Caldariomyces fumago (EC 1.11.1.10) with H2O2 as the oxidizing agent. Aldehyde dehydrogenases (ALDH) are enzymes that catalyze the oxidation of aldehyde groups to carboxylic acid groups. For the organism Raoultella ornithinolytica BF60, an ALDH is described that can oxidize FFA to FDCA and HMF to HMFA (Hossain et al., 2017). Shortall et al. (2023) also used an aldehyde dehydrogenase (from Thermus thermophilus) to oxidize one aliphatic (hexanal) and three aromatic aldehydes (p-tolualdehyde, benzaldehyde, and terephthalaldehyde) to the corresponding carboxylic acids in a coupled bi-enzymatic flow reactor. For this purpose, the ALDH was immobilized directly from an E. coli cell lysate in one reactor module. In a second reactor module, L-lactate dehydrogenase was immobilized for cofactor regeneration. In another study by Knaus et al. (2018), three different purified aldehyde dehydrogenases (from bovine eye lens, E. coli, and Pseudomonas putida) were tested in combination with a NADH oxidase from Streptococcus mutans for cofactor regeneration on 61 different aliphatic, aryl-aliphatic, benzylic, heteroaromatic, and bicyclic aldehydes. In the oxidation of 20 mM HMF, a 90% yield of HMFA was achieved in 4 h with the ALDH from the bovine eye lens, and a 91% yield was achieved in 24 h with the ALDH from E. coli. The substrate FFA was not tested. In US 10344307 B2 a method for the oxidation of DFF using a commercially available ALDH (in combination with a NAD(P)H oxidase) is described, which, depending on the conditions (DFF concentrations ranging from 10 to 100 mM), yields FFA, FDCA, or mixtures thereof. With the increase of the DFF concentration, more FFA than FDCA is obtained than FDCA (10 mM substrate: 100% FDCA; 50 mM substrate: 80% FDCA, 20% FFA; 100 mM substrate: 20% FDCA, 80% FFA (conversion after 3 h in each case). For the oxidations, US 10344307 B2 uses between 10 and 50 mol% cofactor (relative to the amount of substrate). Yuan et al. (2018) used engineered whole cells (resting cells) of Raoultella ornithinolytica BF60, in which the two genes adhP3 and alkR were deleted to suppress the reduction of HMF to the corresponding diol, to oxidize HMF to FDCA (265 mM; 96% yield) by using a fed-batch method over 144 h. Furthermore, an in vitro conversion of FFA to FDCA is described, which results in lower conversion rates compared to the whole-cell method. The methods known in the prior art generally have disadvantages such as low substrate concentrations or long reaction times. This is where the present invention comes in, with the objective of providing an improved method for the preparation of FDCA. The problem of the invention is solved by oxidizing 5-formyl-2-furan carboxylic acid (FFA), which is present in an aqueous solution, to 2,5-furandicarboxylic acid (FDCA) with a NAD(P)+-dependent oxidoreductase in vitro, wherein the NAD(P)H generated during the oxidation is enzymatically reoxidized to NAD(P)+ by the means of a dehydrogenase, after which the enzymes are removed. The 2,5- furandicarboxylic acid can then be separated from the solution by precipitation. In vitro means that the present method is carried out outside an organism, that is, not in a whole cell and not by fermentation. Sugars, particularly preferred D-fructose, or aldehyde compounds or keto compounds, thereof particularly preferred acetone, are used as substrates for the dehydrogenase to oxidize NAD(P)H to <semantics>NAD(P)+.<annotation encoding="application / x-tex">NAD(P)+.< / annotation>< / semantics> A preferred embodiment of the method according to the invention is schematically illustrated in the attached Figure 1. The NAD(P)+-dependent oxidoreductase for the oxidation of FFA to FDCA is preferably an aldehyde dehydrogenase. An NAD(P)+-dependent oxidoreductase for the oxidation of FFA to FDCA preferably comprises or consists of an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 2, SEQ ID NO: 8, SEQ ID NO: 4, or SEQ ID NO: 6, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 1, SEQ ID NO: 7, SEQ ID NO: 3, or SEQ ID NO: 5, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 1, SEQ ID NO: 7, SEQ ID NO: 3, or SEQ ID NO: 5. SEQ ID NO: 1: ATGTCACGCTATGAACTGCTGATCGATGGTCGCCTGCAGGCGGCCGAGCACTACGACCGGGTGATCGA CCCGGCCAGCGAAGAAATCGTTGGCGAAGCCGCCCGCGCCAGCCTGGAGCAGGTCGACGCGGCGGTG GATGCCGCACACCGCGCCTTCCCGGCCTGGGCCACCGATCTCGACGTCCGCCGCCAGAGCCTGGCCCG AGCCGCCGAACGAGTACGCGAGAATGCCCAGGCGCTGGCCGAGCTGATCACCCGCGAACAGGGTCGC CCACTGCGCTCGACCCTGGAGGAAGTGGCTGGCGTCGCCGCCACTTTCGAGCACCACGCGCAGCTGGA GCTACCCGCCGACACCCAGTTGCGCGACGACGGCGAGCGCCTGGTGCGCATCACCCGCAAACCGCTGG GGGTGGTCGCCGCGATCACCCCGTGGAACGTCCCGCTGATCCTGCTGGTATTGAAGATCGCGCCTGCC CTGCACGCCGGCAACACCGTGGTGGCCAAGCCCTCGGAGCACACGCCGCTGTCTACCCTGCTGGC GCGACTGCTGGGCGATGTTCCCCCGCTGGCGTGTTCAACGTGGTTGCCGGTGCGGGCGAGGTTGGC GAACACCTGGTACGTCATCCGCGGGTGCGCCACGTGACCTTCACCGGCAGCGTCGCCACCGGCAAGCG CCTGTATGCCGGCGCGGGGACGACCTCAAGCGTCTTACCCTGGAACTGGGCGGCAACGACGCCGCG CTGGTACTGGAAGACGCCGACCTCGACGCCATCGTCGAACCGCTGTTCTGGGGCGCCTTCTGGAACAG CGGCCAGGTGTGCTTTGCGATCAAGCGCCTGTACGTGCATGACAGCCTGTTCGAACCGTTACTGGCGA AACTCGCCGAGCGCCCAGCGCACCCGCCTCGGTCATGGGCTCGACCCGCAGACGGAACTGGGGCC GCTGACCAACGCACAGCAACTGGAACGGGTCATCGCCCTGGTGGAAGACGCCAAGGCTCACGGAGCA CGCATCCGCAGCGGCGTACGGCCCGACGGTCCCGGCTACTTCTACCCGCCGACCCTGGTCAGCGG CGTGGCGGCCGCCGCTGGTGGACGAGGAACAGTTCGGCCCGGTGTTGCCGGTGATCTCCTTCC GCAACGAAGAGGCCATTACCCAGGCCAACGCCAGCCACTACGGCCTCGGCGCCTCGGTGTGGACC CGCGACCTGGCGCGCGCGAAGCCATCGCCAGGCGGCTGGAGGCGGGCCTGGCCTGGGTCAACCAGC ACGGCCACATCCAGCCCGGCGCCCCAAGGGCGGCACAAGTGGAGCGGGCTCGGCTACGAAGGCG GGCAGCGCGCTATGAGGCCTTCAGCGAGCTGCAGGTGCTGAACATTTCGCGGCGCTAA SEQ ID No. 2: MSRYELLIDGRLQAAEHYDRVIDPASEEIVGEAARASLEQVDAAVDAAHRAFPAWATDLDVRRQSLARAAE RVRENAQALAELITREQGRPLRSTLEEVAGVAATFEHHAQLELPADTQLRDDGERLVRITRKPLGVVAAITP WNVPLILLVLKIAPALHAGNTVVAKPSEHTPLSTLLLARLLGDVFPAGVFNVVAGAGEVGEHLVRHPRVRHV TFTGSVATGKRLYAGAGDDLKRLTLELGGNDAALVLEDADLDAIVEPLFWGAFWNSGQVCFAIKRLYVHDS LFEPLLAKLAERAQRTRLGHGLDPQTELGPLTNAQQLERVIALVEDAKAHGARIRSGGVRPDGPGYFYPPTL VSGVAAGVALVDEEQFGPVLPVISFRNEEDAITQANASHYGLGASVWTRDLARGEAIARRLEAGLAWVNQ HGHIQPGAPKGGHKWSGLGYEGGQRGYEAFSELQVLNISRR SEQ ID No. 3: ATGAAATCGTATCAGGGATTGGCTGACAAGTGGATTAAGGGCAGTGGGGAAGAATACCTTGATATTAA TCCGGCTGATAAGGATCACGTATTAGCTAAGATAAGATTATATACAAAAGATGACGTTAAAGAAGCTAT AAACAAGGCTGTAGCCAAATTCGACGAATGGTCAAGGACTCCAGCACCTAAAAGAGGCTCAATATTAC TTAAGGCAGGGAATTAATGGAACAAGAAGCCCAAGAGTTTGCGCTATTGATGACATTAGAGGAGGG TAAGACTCTCAAGGATAGTATGTTTGAAGTGACAAGAAGTTATAATTTACTGAAATTTTATGGAGCATT AGCATTTAAGATATCTGGGAAAACGCTTCCTTCAGCAGATCCTAATACTAGGATATTTACAGTAAAAGGA ACCCTTAGGCGTAGTAGCTTTAATTACGCCGTGGAATTTCCCATTATCAATACCAGTATGGAAATTGGCT CCAGCCTTGGCTGCGGTAACACTGCAGTAATAAAACCAGCGACGAAAACACCGTTAATGGTAGCCAA ATTGGTAGAAGTGTTGTCTAAAGCTGGATTGCCAGAGGGTGTCGTGAATTTAGTAGTTGGTAAGGGAA GTGAAGTCGGAGATACCATAGTAAGTGATGATAATATAGCTGCAGTATCATTTACTGGATCAACCGAG GTAGGTAAGAGAATTTACAAACTCGTAGGAAATAAAAATAGAATGACAAGAATTCAACTAGAGCTAGG AGGTAAAAACGCGTTATATGTGGATAAGAGCGCTGACTTAACGTTAGCTGCTGAATTAGCCGTAAGAG GAGGATTTGGACTAACCGGTCAATCATGTACTGCAACTAGTAGGTTAATAATTAACAAGGATGTATATA CTCAATTTAAACAAAGACTACTAGAAAGAGTTAAGAAGTGGAGAGTAGGACCGGGTACTGAAGATGTT GATATGGGTCCAGTTGTAGATGAAGGTCAATTTAAGAAAGA TGTGGGAGCAAAACTAATTTATGGTGGAAATATAATACCAGGGAAGGGATATTTCCTAGAACCTACAA TTTTCGAAGGAGTCACATCTGATATGAGGCTATTTAAAGAAGAGATTTTCGGTCCAGTACTTAGTGTCA CTGAGGCAAAAGATTTAGATGAGGCTATAAGGCTAGTTAACGCTGTAGACTATGGACATACAGCTGGA ATAGTCGCAAGCGATATCAAGGCGATTAACGAGTTCGTTAGTAGGGTAGAGGCAGGAGTTATAAAGG TTAATAAGCCAACAGTCGGACTGGAATTGCAAGCACCATTTGGTGGTTTTAAGAATTCTGGAGCCACTA CGTGGAAAGAGATGGAAAGATGCTTTAGAGTTCTACCTTAAGGAGAAGACAGTATACGAAGGCTG GTAA SEQ ID No. 4: MKSYQGLADKWIKGSGEEYLDINPADKDHVLAKIRLYTKDDVKEAINKAVAKFDEWSRTPAPKRGSILLKAG ELMEQEAQEFALLMTLEEGKTLKDSMFEVTRSYNLLKFYGALAFKISGKTLPSADPNTRIFTVKEPLGVVALIT PWNFPLSIPVWKLAPALAAGNTAVIKPATKTPLMVAKLVEVLSKAGLPEGVVNLVVGKGSEVGDTIVSDDNI AAVSFTGSTEVGKRIYKLVGNKNRMTRIQLELGGKNALYVDKSADLTLAAELAVRGGFGLTGQSCTATSRLII NKDVYTQFKQRLLERVKKWRVGPGTEDVDMGPVVDEGQFKKDLEYIEYGKNVGAKLIYGGNIIPGKGYFLE PTIFEGVTSDMRLFKEEIFGPVLSVTEAKDLDEAIRLVNAVDYGHTAGIVASDIKAINEFVSRVEAGVIKVNKPT VGLELQAPFGGFKNSGATTWKEMGEDALEFYLKEKTVYEGW SEQ ID No. 5: ATGTCGACATTTCATTTACTTATTGATGGCCATCTGCAAGCCAGTGACCAATCCGATGTGGTGATCAACC CCGCGACCGAGCTGGAAGTCGGGCGTGCCCACGTGCCAGCCCACCCA AGCCGCACATCAGGCATTTCATCGCTGGGCATCACAGCCTGAGGTGCGCCAGCAGGCACTGCTGGGCG CGGCCGCCGCCATTCGCCAGCATGCCGATGCCCTGGCACGCCTGATCACGCAAGAGCAGGGGGCGGCCA TTGCACTTTACCCAGGGCGAGGTGGCCGGGGCTGCTGCTACCTTTGAACACTATGCCGGGTTTGCCGCG CCATCGGATGTGGTGCTGCAGCAGGACGAACAAAGCGGGTCAGCATTGAGCGCAGGCCGTTTGGCG TAGTGGCTGCCATTACGCCCTGGAATGTGCCCATCATCCTGCTGGTACTGAAAATCGCCCCGGCCTTGA AGGCTGGCAATACCGTGGTCGCCAAGCCATCGGAATACACCCCGCTTTCTACCTTGTACCTGGGTGAAA TTCTGAAAGATGTATTTCCGCCCGGCGTGCTGAACGTGATAGCCGGTGACGGTCAGGTGGGGGCGCGC CTGGCATCGCATCCGCTGGTGCAGAAGGTGACGTTCACCGGCAGCGTGGCAACCGGAAAAAAACTCTA TGCCAGCGCCGCGCAGGATGTAAAACGCCTGACGCTGGAACTGGGCGGTAACGATGCGGCCATCGTG CTGGACGATGCCAATGTCGATGCCATTGCCGAGAAGATTTTCTGGGGCGCCTTCTGGAATAGCGGTCA GGTGTGCTTTGCCATCAAGCGCCTCTATGTGCACGAGCGTGTTTTCCAGCCCTTGCTCGATGCCCTGGT GAAACGCGCGCAAAAAACCCGCGTGGGCGATGGCCAGCTGCCGGGTACCGAGCTGGGGCCGCTTACC AACAAAGCCCAGTTTGAGCGCGTGATATCGCTGGTGGAAGACGCCAGACGCCATGGCGCCACCATTCA TTCAGGCGGTGCTGCATTGCCTGGCCCCGGCTATTTCTATCCGCCCACCCTGGTCACCGGCATAGGCGC AGGTGTCGCGCTGGTGGATGAAGAGCAGTTCGGACCAGTATTGCCGCTGATTCCTTTCCGTGATGAGC AAGAGGCGGTGCGTCAGGCCAACGACAGTCCGTTTGGTCTGGGCGCTTCGGTTTGGACCGCCAATCCC GAACGCGGCCTGGCGCTACGCCAGCTCCAGGCCGGGCTCGCCTGGGTCAACCAGCATGGCGATAT CCATCCCGGTGCGCCCAAGGGCGGCTACAAATCCAGTGGCCTTGGCTACGAGGGCGGGC ATGACGAGTTCAGCGAGCTGCAAGTCGTCAATGCGGCGCTGGTTTAA SEQ ID No. 6: MSTFHLLIDGHLQASDQSDVVINPATELEVGRAPRASATQVDQAVEAAHQAFHRWASQPEVRQQALLGA AAAIRQHADALARLITQEQGRPLHFTQGEVAGAAATFEHYAGFAAPSDVVLQQDEQKRVSIERRPFGVVAA ITPWNVPIILLVLKIAPALKAGNTVVAKPSEYTPLSTLYLGEILKDVFPPGVLNVIAGDGQVGARLASHPLVQK VTFTGSVATGKKLYASAAQDVKRLTLELGGNDAAIVLDDANVDAIAEKIFWGAFWNSGQVCFAIKRLYVHE RVFQPLLDALVKRAQKTRVGDGQLPGTELGPLTNKAQFERVISLVEDARRHGATIHSGGAALPGPGYFYPPT LVTGIGAGVALVDEEQFGPVLPLIPFRDEQEAVRQANDSPFGLGASVWTANPERGLALVRQLQAGLAWVN QHGDIHPGAPKGGYKSSGLGYEGGLRGYDEFSELQVVNAALV SEQ ID No. 7: ATGAGCGATTCCCGTTATACCGACCTCGGTCTCCAGCCCCTGGCCGGCGAGTGGCGCCACGGCCGGGC CGGCCGCCGGCTGAAGGTGAGCAACCCGTTCGACGGCAGCCTGCTGCTGGAGATCGAGCAGGCCGAC CGCGACGACCTCGATGCCGCCTACGCCAAGGCCGCCGAGGTCCAGCCGGCATGGGCCGCGCTCGGGC CCTCGGCACGCGCGCGGTACTGTACAAGGCGGTGGAGGTGTTCGACCGCCGCCACGAGGAGATCGT CGACTGGATCATCCGCGAGTCCGGCAGCACCCGCCTGAAGGCCGAGATCGAATGGGGCGCGCGC GCGATCACCCTGGAGTCGGCGTCGTTCCCGGCACGGGTGCACGGGCGCATCGTCGAGTCCGACGTGCC GGGCAAGGAAAGCCGGGTCTACCGCAGCGCCATCGGCGTGGTCGGGGTGATCAGCCCGTGGAACTTC CCGCTGCACCTGACCCAGCGTTCCATCGCCCCGGCCCTGGCGCTGGCCAACGCGGTGGTCAAGCC GGCCAGCGACACGCCGGTCTGCGGCGGACTGCTGCTGCCGGATCTTCGAAGAGGCCGGGCTGCCG GCCGGGCTGTTCAGCGTGGTCGGCCCCGGCAGCGAGATCGGCGACGCCTTCGTCGAGCACCCGG TGCCGGGCCTGGTGACCTTCACCGGATCGACCCCGGTGGGCCGCAACATCGGCCGCATCGCCAGCGGC GGCGCGCACCTCAAGCACGTGGCGCTGGAGCTGGGCGGCAACAGTCCGTTCGTGGTGCTCGGCGACG CCGATCTGGAGCAGGCGGTGAATGCCGCGGTGTTCGGCAAGTTCCTCCACCAGGGGCAGATCTGCATG GCGATCAACCGCATCATCGTCGAGGACAGCCTCTACGACGCTTTCGCCGCGCGCG AAGGGTCTCCGGGTCGGCGATCCGCAGCGCCGATACCGCGGTCGGGCCGATCGTCAACGCGCGCC AGCTCGAAGGCCTGCTGGAAAAGATCCGCCTGGCCCGCCAGGAAGGCGCCAAGCCGCTGTACGAGGG CGGCGTCGATGGCAGTTGCTGGCTCCGCACGTATTCGGCGAGGTCACCGCGACGATGGAGATCGCCC GCGATGAAATCTTCGGCCCGCTGGTCGGCCTGCTCCGCGCGCG GCCAACGCCAGCGAATACGGGCTGTCCAGCGCGGTGTTCAGCCGCGACCTGGAACGCGCGGTGCGCTT TGCCCGCCAGCTTCGCGCGGGGATGACCCACGTCAACGACATTCCGGTGAACGACGAGGCCAACGCGC CCTTCGGCGGCGAGAAGAACTCCGGACTTGGCCGCTTCAACGGCGACTGGGCCATCGAGGAATTCACC ACCGACCACTGGATCAGCGTGCAGCACGCGCCGCGCCAGTACCCGTTCTAA SEQ ID No. 8: MSDSRYTDLGLQPLAGEWRHGRAGRRLKVSNPFDGSLLLEIEQADRDDLDAAYAKAAEVQPAWAALGPSA RAAVLYKAVEVFDRRHEEIVDWIIRESGSTRLKAEIEWGAARAITLESASFPARVHGRIVESDVPGKESRVYRS AIGVVGVISPWNFPLHLTQRSIAPALALGNAVVVKPASDTPVCGGLLLARIFEEAGLPAGLFSVVVGPGSEIG DAFVEHPVPGLVTFTGSTPVGRNIGRIASGGAHLKHVALELGGNSPFVVLGDADLEQAVNAAVFGKFLHQG QICMAINRIIVEDSLYDAFAARFVERVKGLRVGDPQRADTAVGPIVNARQLEGLLEKIRLARQEGAKPLYEGG VDGQLLAPHVFGEVTATMEIARDEIFGPLVGLLRARDEAHALELANASEYGLSSAVFSRDLERAVRFARQLR AGMTHVNDIPVNDEANAPFGGEKNSGLGRFNGDWAIEEFTTDHWISVQHAPRQYPF The oxidoreductases listed here for the oxidation of FFA to FDCA preferably comprise an amino acid sequence having an identity to SEQ ID NO. 2, SEQ ID NO. 8, SEQ ID NO. 4, or SEQ ID NO. 6 of at least 80%, more preferably 85%, even more preferably 90%, even more preferably 95%, even more preferably 98%, even more preferably 99%, and in particular 100%. Alternatively, the oxidoreductases for the oxidation of FFA to FDCA preferably comprise an amino acid sequence encoded by a nucleic acid having an identity to SEQ ID NO: 1, SEQ ID NO: 7, SEQ ID NO. 3, or SEQ ID NO. 5 of at least 80%, more preferably 85%, even more preferably 90%, even more preferably 95%, even more preferably 98%, even more preferably 99%, and most preferably 100%. Most preferably, the nucleic acid encoding the oxidoreductase of the invention for the oxidation of FFA to FDCA comprises the nucleic acid sequence SEQ ID NO: 1, SEQ ID NO: 7, SEQ ID NO: 3, or SEQ ID NO: 5, or consist thereof. The term "identity", as used herein, refers to the percentage of identical nucleotide or amino acid matches between at least two nucleotide or amino acid sequences aligned with one another under the use of a standardized algorithm ("alignment"). Such an algorithm may, in a standardized and reproducible manner, insert gaps into the compared sequences to optimize the alignment between two sequences, thereby achieving a more meaningful comparison of the two sequences. The percentage identity between sequences can be determined using one or more computer algorithms or programs known in the prior art or described herein. According to the invention, the Basic Local Alignment Search Tool (BLAST) (Altschul et al., 1990), provided by the National Center for Biotechnology Information (NCBI) is used to determine the identity. The BLAST software suite contains various programs, including a tool called "BLAST 2 Sequences," which is used for the direct pairwise comparison of two nucleotide or amino acid sequences. "BLAST 2 Sequences" can also be accessed and used interactively via the NCBI website on the Internet. The blastn program (for nucleotide sequences) uses a word length (W) of 11, an expectation (E) of 10, <semantics>M=5<annotation encoding="application / x-tex">M = 5< / annotation>< / semantics>, <semantics>N=−4<annotation encoding="application / x-tex">N = -4< / annotation>< / semantics>, and a comparison of both strands as default settings. For amino acid sequences, the blastp program uses a word length of 3 and an expectation (E) of 10, along with the BLOSUM62 scoring matrix (Henikoff & Henikoff, 1989), alignments (B) of 50, expectation (E) of 10, <semantics>M=5<annotation encoding="application / x-tex">M = 5< / annotation>< / semantics>, and <semantics>N=−4<annotation encoding="application / x-tex">N = -4< / annotation>< / semantics> as default settings. Alternatively, the oxidoreductases for the oxidation of FFA to FDCA preferably comprise an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 1, SEQ ID NO: 7, SEQ ID NO: 3, or SEQ ID NO: 5. As used herein, stringent conditions refer to conditions under which so-called specific hybrids, but not nonspecific hybrids, are formed. For example, the stringent conditions include hybridization in 6xSSC (sodium chloride / sodium citrate) at 45 °C, and then washing with 0.2 to 1xSSC, 0.1% SDS at 50 to 65 °C; or such conditions may include hybridization in 1xSSC at 65 to 70 °C, followed by washing with 0.3xSSC at 65 to 70 °C. Hybridization may be performed using conventionally known methods, such as those described by J. Sambrook et al. in Molecular Cloning, A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory (1989). The invention also relates to the use of an oxidoreductase for the oxidation of FFA to FDCA, wherein the oxidoreductase comprises an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 2, SEQ ID NO: 8, SEQ ID NO: 4, or SEQ ID NO: 6, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 1, SEQ ID NO: 7, SEQ ID NO: 3, or SEQ ID NO: 5, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 1, SEQ ID NO: 7, SEQ ID NO: 3, or SEQ ID NO: 5. According to a preferred embodiment, a sugar or an aldehyde compound or a keto compound is used as a substrate for the dehydrogenase in the enzymatic oxidation of NAD(P)H. D-fructose is preferably used as the sugar, and acetone is preferably used as the keto compound. In an alternative embodiment, D-glucose is used as the sugar and acetone as the keto compound. In a variant of the method according to the invention, the enzymatic regeneration of NAD(P)H is accomplished by means of xylitol dehydrogenase (XDH; EC 1.1.1.9) or sorbitol dehydrogenase (EC 1.1.1.14, EC 1.1.1.15), the former being particularly preferred. The xylitol dehydrogenase for the enzymatic oxidation of NAD(P)H via the formation of D-sorbitol from D-fructose preferably comprises or consists of an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 20, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 19, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 19. SEQ ID NO. 19: ATGAGCACACCGGAAAATCTGAGCTTTGTGCTGCAGAAACCGTTTGATGTGAAATTTGAAGATCGTCCGA TTCCGAAACTGAGCGATCCGTATAGCGTTAAAATTCAGGTGAAAAAAACCGGCATTTGCGGTAGTGATGT TCACTATTTCACCCATGGTGCAATTGGTGATTTTGTTGTTAAAGCACCGATGGTTCTGGGTCATGAAAGCA GCGGTGTTGTTCTGGAAGTTGGTAGCGAAGTTAAAAGCCTGAAAGTTGGTGATCGTGTTGCAATGGAAC CGGGTGTTCCGAGCCGTCATAGTGATGAGTATAAAAGCGGTCGTTATAATCTGTGTCCGCACATGGCATT TGCAGCAACCCCTCCGTATGATGGCACCCTGTGTAAATACTATATTCTGCCGGAAGATTTCTGCGTTAAAC TGCCGGAACATGTTAGCCTGGAAGAAGGTGCACTGGTTGAACCGCTGAGCGTTGCAGTTCATAGCAGCA AACTGGGTAACATTAAACCGGGTAGCCATGTTGCAATTTATGGTGCAGGTCCGGTTGGTCTGCTGGTTGC AGCAGTTGCAAGCGCATTTGGTGCAGAAAGCGTTACCATTATTGATCTGGTTGAAAGCCGTCTGAATCTG GCAAAAGAACTGGGTGCAACCGCAACCGTTCAGGTTGATTTTAAAGATACCCCGAAAGAAA AAAGTTGTTGCAGCAAATAATGGCATTGCACCGGATGTTGTTATTGATGCAAGCGGTGCAGAAGCAAGC ATTAATTCAGCCATTAATGCAATTCGTCCGGGTGGCACCTATGTTCAGGTGGGTATGGGTAAACCGGATG TGAGCTTTCCGATTGCAACCCTGATTGGTAAAGAACTGACCGTTAAAGGTAGCTTTCGTTATGGTTATGGT GATTATCCGCTGGCAGTTAGCCTGCTGGCAAGCGGTAAAGTTAATGTGAAAAAACTGATCACCCATGAA GTGAAATTCGAGGATGCAGCAGAAGCATTTCAGCTGGTTCGTGATGGTAAAGCCATTAAATGTATTATCA ACGGTCCGGAATAA SEQ ID No. 20: MSTPENLSFVLQKPFDVKFEDRPIPKLSDPYSVKIQVKKTGICGSDVHYFTHGAIGDFVVKAPMVLGHESSGVV LEVGSEVKSLKVGDRVAMEPGVPSRHSDEYKSGRYNLCPHMAFAATPPYDGTLCKYYILPEDFCVKLPEHVSLE EGALVEPLSVAVHSSKLGNIKPGSHVAIYGAGPVGLLVAAVASAFGAESVTIIDLVESRLNLAKELGATATVQVD FKDTPKESAAKVVAANNGIAPDVVIDASGAEASINSAINAIRPGGTYVQVGMGKPDVSFPIATLIGKELTVKGS FRYGYGDYPLAVSLLASGKVNVKKLITHEVKFEDAAEAFQLVRDGKAIKCIINGPE The xylitol dehydrogenase described herein preferably comprises an amino acid sequence having an identity to SEQ ID NO: 20 of at least 80%, more preferably 85%, even more preferably 90%, even more preferably 95%, even more preferably 98%, and most preferably 99%, in particular has 100%. Alternatively, the xylitol dehydrogenase preferably comprises an amino acid sequence encoded by a nucleic acid having an identity to SEQ ID NO: 19 of at least 80%, more preferably 85%, even more preferably 90%, even more preferably 95%, even more preferably 98%, more preferably 99%, and in particular 100%. Most preferably, the nucleic acid that encodes the xylitol dehydrogenase of the invention comprises or consists of the nucleic acid sequence SEQ ID NO: 19. Alternatively, the xylitol dehydrogenase preferably comprises an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 19. As used herein, stringent conditions refer to conditions under which so-called specific hybrids, but not nonspecific hybrids, are formed. For example, the stringent conditions include hybridization in 6xSSC (sodium chloride / sodium citrate) at 45 °C, and then washing with 0.2 to 1xSSC, 0.1% SDS at 50 to 65 °C; or such conditions may include hybridization in 1xSSC at 65 to 70 °C, followed by washing with 0.3xSSC at 65 to 70 °C. Hybridization may be performed using conventionally known methods, such as those described by J. Sambrook et al. in Molecular Cloning, A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory (1989). The invention also relates to the use of a xylitol dehydrogenase for the enzymatic oxidation of NAD(P)H via the formation of D-sorbitol from D-fructose, wherein the xylitol dehydrogenase comprises an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 20, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 19, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 19. In a further variant of the method according to the invention, the enzymatic oxidation of NAD(P)H is carried out by means of an alcohol dehydrogenase (EC 1.1.1.1 or EC 1.1.1.2). The NAD(P)H-dependent alcohol dehydrogenase for the enzymatic oxidation of NAD(P)H via formation of 2-propanol from acetone or preferably consists of an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 10 or SEQ ID NO: 12, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 9 or SEQ ID NO: 11, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 9 or SEQ ID NO: 11. SEQ ID NO. 9: ATGAAAGCTGCAGTTGTGGAACAATTTAAAAAGCCGTTACAAGTGAAAGAAGTGGAAAAACCTAAGAT CTCATACGGGGAAGTATTAGTGCGCATCAAAGCGTGTGGGGTATGCCATACAGACTTGCATGCCGCAC ATGGCGACTGGCCTGTAAAGCCTAAACTGCCTCTCATTCCTGGCCATGAAGGCGTCGGTGTAATTGAAG AAGTAGGTCCTGGGGTAACACATTTAAAAGTTGGAGATCGCGTAGGTATCCCTTGGCTTTATTCGGCGT GCGGTCATTGTGACTATTGCTTAAGCGGACAAGAAACATTATGCGAACGTCAACAAAACGCTGGCTATT CCGTCGATGGTGGTTATGCTGAATATTGCCGTGCTGCAGCCGATTATGTCGTAAAAATTCCTGATAACTT ATCGTTTGAAGAAGCCGCTCCAATCTTTTGCGCTGGTGTAACAACATATAAAGCGCTCAAAGTAACAGG CGCAAAACCAGGTGAATGGGTAGCCATTTACGGTATCGGCGGGCTTGGACATGTCGCAGTCCAATACG CAAAGGCGATGGGGTTAAACGTCGTTGCTGTCGATTTAGGTGATGAAAAACTTGAGCTTGCTAAACAA CTTGGTGCAGATCTTGTCGTCAATCCGAAACATGATGATGCAGCACAATGGATAAAAGAAAAAGTGGG CGGTGTGCATGCGACTGTCACAGCTGTTTCAAAAGCCGCGTTCGAATCAGCCTACAAATCCATTCG TCGCGGTGGTGCTTGCGTACTCGTCGGATTACCGCCGGAAGAAATACCTATTCCAATTTTCGATACAGT ATTAAATGGAGTAAAAATTATTGGTTCTATCGTTGGTACGCGCAAAGACTTACAAGAGGCACTTCAATT TGCAGCAGAAGGAAAAGTAAAAACAATTGTCGAAGTGCAACCGCTTGAAAACATTAACGACGTATTCG ATCGTATGTTAAAAGGGCAAATTAACGGCCGCGTCGTGTTAAAAGTAGATTAA SEQ ID NO. 10: MKAAVVEQFKKPLQVKEVEKPKISYGEVLVRIKACGVCHTDLHAAHGDWPVKPKLPLIPGHEGVGVIEEVG PGVTHLKVGDRVGIPWLYSACGHCDYCLSGQETLCERQQNAGYSVDGGYAEYCRAAADYVVKIPDNLSFEE AAPIFCAGVTTYKALKVTGAKPGEWVAIYGIGGLGHVAVQYAKAMGLNVVAVDLGDEKLELAKQLGADLV VNPKHDDAAQWIKEKVGGVHATVVTAVSKAAFESAYKSIRRGGACVLVGLPPEEIPIPIFDTVLNGVKIIGSIV GTRKDLQEALQFAAEGKVKTIVEVQPLENINDVFDRMLKGQINGRVVLKVD SEQ ID No. 11: ATGAAAGGTTTTGCAATGCTCAGTATCGGTAAAGTTGGCTGGATTGAGAAGGAAAAGCCTGCTCCTGGC CCATTTGATGCTATTGTAAGACCTCTAGCTGTGGCCCCTTGCACTTCGGACATTCATACCGTTTTTGAAGG CGCCATTGGCGAAAGACATAACATGATACTCGGTCACGAAGCTGTAGGTGAAGTAGTTGAAGTAGGTAG TGAGGTAAAAGATTTTAAACCTGGTGATCGCGTTGTTGTGCCAGCTATTACCCCTGATTGGCGGACCTCT GAAGTACAAAGAGGATATCACCAGCACTCCGGTGGAATGCTGGCAGGCTGGAAATTTTCGAATGTAAAA GATGGTGTTTTTGGTGAATTTTTTCATGTGAATGATGCTGATATGAATTTAGCACATCTGCCTAAAGAAAT TCCATTGGAAGCTGCAGTTATGATTCCCGATATGATGACCACTGGTTTTCACGGAGCTGAACTGGCAGAT ATAGAATTAGGTGCGACGGTAGCAGTTTTGGGTATTGGCCCAGTAGGTCTTATGGCAGTCGCTGGTGCC AAATTGCGTGGAGCCGGAAGAATTATTGCCGTAGGCAGTAGACCAGTTTGTGTAGATGCTGCAAAATAC TATGGAGCTACTGATATTGTAAACTATAAAGATGGTCCTATCGAAAGTCAGATTATGAATCTAACTGAAG GCAAAGGTGTCGATGCCATCATCGCTGGAGGAAATGCTGACATTATGGCTACAGCAGTTAAGATTG TTAAACCTGGTGGCACCATCGCTAATGTAAATTATTTTGGCGAAGGAGAGGTTTTGCCTGTTCCTCGTCTT GAATGGGGTTGCGGCATGGCTCATAAAACTATAAAAGGCGGGCTATGCCCCGGTGGACGTCTAAGAATG GAAAGACTGATTGACCTTGTTTTTTATAAGCGTGTCGATCCTTCTAAGCTCGTCACCTCACGTTTTCCGGGG ATTTGACAATATTGAAAAAGCCTTTATGTTGATGAAAGACCAAAACCAAAAGACCTAATCAAACCTGTTGTA ATATTAGCATAA SEQ ID No. 12: MKGFAMLSIGKVGWIEKEKPAPGPFDAIVRPLAVAPCTSDIHTVFEGAIGERHNMILGHEAVGEVVEVGSEVK DFKPGDRVVVPAITPDWRTSEVQRGYHQHSGGMLAGWKFSNVKDGVFGEFFHVNDADMNLAHLPKEIPLE AAVMIPDMMTTGFHGAELADIELGATVAVLGIGPVGLMAVAGAKLRGAGRIIAVGSRPVCVDAAKYYGATDI VNYKDGPIESQIMNLTEGKGVDAAIIAGGNADIMATAVKIVKPGGTIANVNYFGEGEVLPVPRLEWGCGMA HKTIKGGLCPGGRLRMERLIDLVFYKRVDPSKLVTHVFRGFDNIEKAFMLMKDKPKDLIKPVVILA The alcohol dehydrogenases listed here preferably comprise an amino acid sequence having an identity to SEQ ID NO: 10 or SEQ ID NO: 12 of at least 80%, more preferably 85%, even more preferably 90%, even more preferably 95%, and most preferably 98%, more preferably 99%, and in particular 100%. Alternatively, the alcohol dehydrogenases preferably comprise an amino acid sequence encoded by a nucleic acid having an identity to SEQ ID NO: 9 or SEQ ID NO: 11 of at least 80%, more preferably 85%, even more preferably 90%, even more preferably 95%, more preferably 98%, more preferably 99%, and most preferably 100%. Most preferably, the nucleic acid encoding the alcohol dehydrogenases of the invention comprises or consists of the nucleic acid sequence SEQ ID NO: 9 or SEQ ID NO: 11. Alternatively, the alcohol dehydrogenases preferably comprise an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 9 or SEQ ID NO: 11. As used herein, stringent conditions refer to conditions under which so-called specific hybrids, but not nonspecific hybrids, are formed. For example, the stringent conditions include hybridization in 6xSSC (sodium chloride / sodium citrate) at 45 °C, and then washing with 0.2 to 1xSSC, 0.1% SDS at 50 to 65 °C; or such conditions may include hybridization in 1xSSC at 65 to 70 °C, followed by washing with 0.3xSSC at 65 to 70 °C. Hybridization may be performed using conventionally known methods, such as those described by J. Sambrook et al. in Molecular Cloning, A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory (1989). The invention also relates to the use of an NAD(P)H-dependent alcohol dehydrogenase for the enzymatic oxidation of NAD(P)H via formation of an alcohol from a ketone or aldehyde, wherein the alcohol dehydrogenase comprises an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 10 or SEQ ID NO: 12, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 9 or SEQ ID NO: 11, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 9 or SEQ ID NO: 11. In another variant of the method according to the invention, the enzymatic oxidation of NAD(P)H is carried out using xylose reductase (EC 1.1.1.307, EC 1.1.1.430, EC 1.1.1.431). The xylose reductase for the enzymatic oxidation of NAD(P)H by forming D-sorbitol from D-glucose or L- arabitol from L-arabinose preferably comprises or consists of an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 14 or SEQ ID NO: 16, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 13 or SEQ ID NO: 15, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 13 or SEQ ID NO: 15. SEQ ID NO. 13: ATGGCCACGCCTACTATCAAGCTGAACAGCGGCTATGACATGCCCCTGGTGGGCTTTGGTCTGTGGAAG GTCAACAAGGAAACCTGCGCGGACCAGGTCTACGAGGCTATCAAGGCGGGCTACCGCTTGTTTGACGGT GCGTGCGACTATGGCAACGAAGTTGAGGCCGGCCAGGGTGTCGCTCGC GAAGCGTGAGGACCTCTTCATTGTGTCCAAGCTGTGGAACACGTTCCACGAGGCCGACAAGGTCGAGCC GATCGCGCGGAAGCAGCTGGCCGACTGGGGCCTCGACTACTTTGACCTGTACCTCATCCACTTCCCGATC GCGCTGAAGTACGTCGACCCGGCCGAGATCTACCCGCCGGGCTGGACGGCCACCAAGAAGGAGGTCGA GTTCAGCAACGCGACGATCCAGGAGACGTGGCAGGCCATGGAGACCCTGGTCGACAAGAAGCTGACGC GCAGCATCGGCATCAGCAACTTCAGCGCCCAGCTGATCATGGACCTGCTGCGGTACGCGCGCATCCGCCC CGCGACCTTGCAGATCGAGCACCACCCGTACCTGACGCAGCAGCGCGCTGGTCGAGTACGTGCAGAAGGA GGGCATCGCCGTGACGGCGTACTCGTCCTTCGGCCCACTGAGCTTCCTGGAACTGGGCCACCAGGTCGCC AAGGACACGCCGCTGCTCTTCGAGCACTCGACCGTCAAGTCGATCGCCGAGAAGCACGGCAAGACGCCC GCCCAGGTGCTACTGCGCTGGGCCACCCAGCGCAACATCGCCGTCATCCCCAAGAGCAACAACCCGGGC CGCCTGGCGCAGAACCTGGACGTGACGCGTGGGATCTGGAGCCCGCCGACATTGAGGCCTTGAGCGC GCTGAACAAGAACCTTCGATTCAACAACCCACCTAGCTACGGACTGTACATCCCGATCTTCGCTTAA SEQ ID No. 14: MATPTIKLNSGYDMPLVGFGLWKVNKETCADQVYEAIKAGYRLFDGACDYGNEVEAGQGVARAIKEGIVKRE DLFIVSKLWNTFHEADKVEPIARKQLADWGLDYFDLYLIHFPIALKYVDPAEIYPPGWTGTKKEVEFSNATIQET WQAMETLVDKKLTRSIGISNFSAQLIMDLLRYARIRPATLQIEHHPYLTQQALVEYVQKEGIAVTAYSSFGPLSF LELGHQVAKDTPLLFEHSTVKSIAEKHGKTPAQVLLRWATQRNIAVIPKSNNPGRLAQNLDVTAWDLEPADIE ALSALNKNLRFNNPPSYGLYIPIFA SEQ ID No. 15: ATGACATACCTCGCACCAACAGTTACCTTGAACAATGGATCCAAGATGCCGCTAGTCGGCTTGGGATGCT GGAAAATCCCAAACGAAGTGTGTGCCGAACAGGTGTACGAAGCCATCAAGTTGGGCTACCGCTTGTTCG ACGGCGCGCAGGACTACGCCAACGAAAAAGAGGTGGGCCAAGGTATTAACAGAGCCATCAAGGAAGG ATCGTCAAGAGAGAGACTTGGTCGTCGTTTCTAAGTTGTGGAACAGTTTCCACCACCCAGACAACGTGC GTACCGCAGTCGAAAGAACTTTGAACGACTTGCAATTGGACTACTTGGACTTGTTCTACATCCATTTCCCA TTGGCTTTCAAGTTCGTGCCACTAGACGAGAAGTACCCTCCAGGTTTCTACACAGGTAAGGACAATTTCG CCAAGGAAATCATCGAAGAGGAGCCTGTCCCAATCTTGGACACCTACAGAGCCCTTGAGAAGTTGGTCG ACGAAGGTTTGATCAAATCTTTGGGTATCTCAAACTTTTCGGGTGCATTGATCCAGGACTTGTTGCGTGGC GCCCGTATCAAGCCAGTCGCCTTGCAGATCGAACACCCCCATACTTGGTCCAGGACCGCTTGATCACGT ACGCCCAAAAGGTGGGCTTGCAAGTCGTCGCCTACTCCAGTTTCGGCCCACTATCCTTTGTCGAGTTGAA CAACGAAAAGGCCTTGCACACAAAGACTTTGTTCGAAAACGACACCATCAAGGCCATCGCTCAAAAACAC AACGTCACCCCATCCCACGTCTTGTTGAAGTGGTCCACCCAACGTGGTATCGCCGTCATTCCAAAGTCCTC CAAGAAGGAACGTCTCCTCGAGAACTTGAAGATCGAAGAGACCTTTACCTTGTCCGACGAAGAGATCAA GGAGATCAACGGCTTGGACCAGGGATTGAGATTTAACGACCCATGGGACTGGTTGGGCAACGAATTCCC AACCTTTATCTAA SEQ ID NO. 16: MTYLAPTVTLNNGSKMPLVGLGCWKIPNEVCAEQVYEAIKLGYRLFDGAQDYANEKEVGQGINRAIKEGIVK REDLVVVSKLWNSFHHPDNVRTAVERTLNDLQLDYLDLFYIHFPLAFKFVPLDEKYPPGFYTGKDNFAKEIIEEE PVPILDTYRALEKLVDEGLIKSLGISNFSGALIQDLLRGARIKPVALQIEHHPYLVQDRLITYAQKVGLQVVAYSSF GPLSFVELNNEKALHTKTLFENDTIKAIAQKHNVTPSHVLLKWSTQRGIAVIPKSSKKERLLENLKIEETFTLSDEE IKEINGLDQGLRFNDPWDWLGNEFPTFI The xylose reductases listed here preferably comprise an amino acid sequence having an identity to SEQ ID NO: 14 or SEQ ID NO: 16 of at least 80%, more preferably 85%, even more preferably 90%, even more preferably 95%, and even more preferably 98%, and most preferably 99%, and in particular 100%. Alternatively, the xylose reductases preferably comprise an amino acid sequence encoded by a nucleic acid having an identity to SEQ ID NO: 13 or SEQ ID NO: 15 of at least 80%, more preferably 85%, even more preferably 90%, even more preferably 95%, more preferably 98%, even more preferably 99%, and in particular 100%. Most preferably, the nucleic acid encoding the xylose reductases of the invention comprises or consists of the nucleic acid sequence SEQ ID NO: 13 or SEQ ID NO: 15. Alternatively, the xylose reductases preferably comprise an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 13 or SEQ ID NO: 15. As used herein, stringent conditions refer to conditions under which so-called specific hybrids, but not nonspecific hybrids, are formed. For example, the stringent conditions include hybridization in 6xSSC (sodium chloride / sodium citrate) at 45 °C, and then washing with 0.2 to 1xSSC, 0.1% SDS at 50 to 65 °C; or such conditions may include hybridization in 1xSSC at 65 to 70 °C, followed by washing with 0.3xSSC at 65 to 70 °C. Hybridization may be performed using conventionally known methods, such as those described by J. Sambrook et al. in Molecular Cloning, A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory (1989). The invention also relates to the use of a xylose reductase for the enzymatic oxidation of NAD(P)H, wherein the xylose reductase comprises an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 14 or SEQ ID NO: 16, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 13 or SEQ ID NO: 15, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 13 or SEQ ID NO: 15. In a further variant of the method according to the invention, the enzymatic oxidation of NAD(P)H is carried out using a mannitol dehydrogenase (EC 1.1.1.67; EC 1.1.1.138; EC 1.1.1.255). The mannitol dehydrogenase for the enzymatic oxidation of NAD(P)H via the formation of D-mannitol from D-fructose preferably comprises or consists of an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 18, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 17, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 17. SEQ ID NO. 17: ATGGCTGCCAACGTCCCCAAGACCATGAAGGCTCTCAGATATGAGAAGCCTGAGACGTTCTCCATCGTCG ACATTCCCGTTCCCACTCTGCGTGAGAACGATGTCTTGATCAAGGTCAAGGCTTGCGGTGTCTGTGGTAC CGACCTGCACATTCACGAGGGAGAATTCCTTGCCAAGTTCCCTCTCGTTCCTGGCCACGAGACTGTCGGT GTTGTTGCCGCAGTTGGACCCAAGGTCAAGGGTTTCGAGATCGGTGACCGTGTTGTTGCCGACAACTCCG AGCTTTGCGGCCAATGCTTCTACTGCCGACGAGGAGGAGGAGTTGCTCTGCGAGCACTTCGAAGCTCACG GTGTCACGATGAACGGCGGTTTCGCTGAGTACTGCGCCTACCCTGCCGGCCG CCTCTCTGACGTGGACGCCACTCTGCTTGAGCCCGCGTCCTGCGCCGCTCACGGTCTGGACAAGATTGCC CCCAAGATGGGCTCGTCCTGGTGTTCGGCGCCGGTCCCACCGGTCTGGTCCTTGCTCAGATGCTCC GTCTGAACGGAGGATGCCGCGTCGTCGTCGCTGCGCCCGAGGGTCTGAAGATGGACCTGGCCCAGAAG CTCGGCGCTGGTGATGAATACGTTGCTCTTTCTCGCACGAACCCTCAGGCTCAGTTTGACAAGCTGAAGG CCGACAACCCGTACGGCTTCGACATTGTCGTCGAGGCTACCGGCAATGCCAAGATCCTGGAGGATGCCA TCAACTATGTCCGCCGTGGAGGCAAACTGGTCGTGTACGGTGTGTACGCGAACAAGGACCGCGTCTCGT GGCCCCGAGCAAGATCTTCGGTGACGAAATCACCATTCTGGGTAGCTTCTCCGAGACCTACAAGTTCCC CGCCGCCATCGACTACCTGGACTCCGGCAAGGTGAAGGTCCAGGGCATCGTGAACAAGACCTTCCGGCT GGAGCAGTGGGAGGAGTGTCTGGCGTCGTTGAAGAACAAGAGCGCCATCAAGGCGCGATCGTCTTTG ACTAA SEQ ID No. 18: MAANVPKTMKALRYEKPETFSIVDIPVPTLRENDVLIKVKACGVCGTDLHIHEGEFLAKFPLVPGHETVGVVAA VGPKVKGFEIGDRVVADNSELCGQCFYCRRGEELLCEHFEAHGVTMNGGFAEYCAYPAGRVFKIKNLSDVDA TLLEPASCAAHGLDKIAPKMGSSVLVFGAGPTGLVLAQMLRLNGGCRVVVAAPEGLKMDLAQKLGAGDEYV ALSRTNPQAQFDKLKADNPYGFDIVVEATGNAKILEDAINYVRRGGKLVVYGVYANKDRVSWPPSKIFGDEITI LGSFSETYKFPAAIDYLDSGKVKVQGIVNKTFRLEQWEECLASLKNKSAIKAAIVFD The mannitol dehydrogenase described herein preferably comprises an amino acid sequence having an identity to SEQ ID NO: 18 of at least 80%, more preferably 85%, even more preferably 90%, even more preferably 95%, even more preferably 98%, and most preferably 99%, in particular 100%. Alternatively, the mannitol dehydrogenase preferably comprises an amino acid sequence encoded by a nucleic acid having an identity to SEQ ID NO: 17 of at least 80%, more preferably 85%, even more preferably 90%, even more preferably 95%, even more preferably 98%, even more preferably 99%, and in particular 100%. Most preferably, the nucleic acid that encodes the mannitol dehydrogenase of the invention comprises or consists of the nucleic acid sequence SEQ ID NO: 17. Alternatively, the mannitol dehydrogenase preferably comprises an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 17. As used herein, stringent conditions refer to conditions under which so-called specific hybrids, but not nonspecific hybrids, are formed. For example, the stringent conditions include hybridization in 6xSSC (sodium chloride / sodium citrate) at 45 °C, and then washing with 0.2 to 1xSSC, 0.1% SDS at 50 to 65 °C; or such conditions may include hybridization in 1xSSC at 65 to 70 °C, followed by washing with 0.3xSSC at 65 to 70 °C. Hybridization may be performed using conventionally known methods, such as those described by J. Sambrook et al. in Molecular Cloning, A Laboratory Manual, 2nd Ed., Cold Spring Harbor Laboratory (1989). The invention also relates to the use of a mannitol dehydrogenase, wherein the mannitol dehydrogenase comprises an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 18, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 17, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 17. In further preferred embodiments of the method according to the invention, the concentration of FFA in the aqueous solution is 5–200 g / L, more preferably 5–100 g / L. The preferred temperature range is between 15 and 50 °C, and the particularly preferred temperature range is between 15 and 40 °C. The particularly preferred pH range for the reaction is between pH 5 and pH 9. In a preferred variant of the method according to the invention, the enzymes are present in the homogenate and / or in the lysate of the corresponding cells that produce them, with lysates being particularly preferred. The enzymes may also be present in solid form in the aqueous reaction mixture. In this context, homogenate refers to a physically and / or chemically treated suspension (e.g., treated with pressure, lysozyme, or ultrasound), in which the cellular components are released from the cells. A lysate is obtained when the insoluble cellular components of the homogenate are removed, for example, by filtration or centrifugation (see "Enzyme Production & Lysate Preparation" for details). In a further variant, the enzymes can also be modified at the N-terminus with a water-soluble polymer such as polyethylene glycol, immobilized in or on a solid matrix, or be part of a fusion protein. In a further variant, the enzymes may be present in powder form, in lyophilized form, or in spray-dried form. The following examples describe preferred embodiments of the invention in greater detail. Materials 5-Formyl-2-furancarboxylic acid (FFA) and 2,5-furandicarboxylic acid (FDCA) were obtained from TCI; potassium dihydrogen phosphate, dipotassium hydrogen phosphate, and sodium dodecyl sulfate (SDS) were obtained from Carl Roth; NAD+, NADH disodium salt, NADP+ disodium salt, NADPH tetrasodium salt, and acetonitrile were obtained from PanReac AppliChem (ITW Reagents), and triethanolamine was obtained from Chem-Lab NV. Enzyme Production & Lysate Preparation General Information on the expression of recombinant enzymes in E. coli For recombinant enzyme production in an Escherichia coli strain, the gene to be expressed was first amplified by PCR using genomic DNA or its synthetic equivalent adapted to the codon usage of E. coli as a template, together with specific oligonucleotides that additionally carry recognition sequences for the restriction endonucleases, and isolated from the reaction mixture. Following nucleic acid digestion with the restriction enzymes SphI and HindIII, the gene fragment encoding the target enzyme was ligated into the backbone of the expression vector pQE70-Kan, which had been cut with SphI and HindIII. The ligation product was transformed into chemically competent E. coli cells Top10F, and the resulting colonies were used for plasmid isolation and restriction analysis. The result of the cloning step was verified by restriction enzyme digestion and DNA sequencing. The resulting construct carries the target gene under the IPTG-inducible T5 promoter. For overexpression of the enzyme in E. coli, the resulting expression plasmid was transformed into competent RB791 expression cells. After 24 hours of incubation at 37 °C, the resulting colonies were inoculated into LB-medium for expression assays. The next day, expression cultures with an optical density <semantics>OD550<annotation encoding="application / x-tex">OD_{550}< / annotation>< / semantics> of 0.02 were inoculated and shaken at 37 °C until an OD550 of 0.3 was reached. The temperature was then lowered to 25 °C, and the cultures were induced with 0.1 mM IPTG upon reaching an OD550 of 0.5. After 22 h, the cultures were harvested (separated from the medium by centrifugation to form a cell pellet) and analyzed for expression of the recombinant enzyme using SDS-gel electrophoresis and an activity assay (use in a use test or an optical- enzymatic assay). Preparation of the cell lysates by sonification For the preparation of the cell suspension, the cell pellet produced according to the above method was weighed into a suitable vessel and mixed with buffer and lysozyme (final concentration 0.5 mg / mL) (e.g., triethanolamine (TEA)–HCl) and dissolved under stirring. The mass fraction of biomass is typically 20%; the remainder consists of the buffer. A Branson Sonifier 450 was used for cell lysis. The suspension was treated three times with 15 ultrasonic pulses each (device settings: Timer = 15; Duty Cycle = 50; Output Control = 3–5). The resulting homogenate was centrifuged for 10 minutes at 4 °C and 16,000 rpm (Eppendorf Centrifuge 5417R) to separate the insoluble cell fragments and obtain the lysate. Table 1. Enzyme types and donor organisms for the enzymes used in the examples (ALDH = aldehyde dehydrogenase). [Image disponible dans le document PDF, Image available in the PDF document] [Image disponible dans le document PDF, Image available in the PDF document] *This ALDH is classified in the NCBI Protein Database (entry WP_009990943.1) as 2,5-dioxopentanoate dehydrogenase (catalyzes the oxidation of 2,5-dioxopentanoate to <semantics>α<annotation encoding="application / x-tex">\alpha< / annotation>< / semantics>-ketoglutarate). Analytical Methods High-Performance Liquid Chromatography (HPLC) HPLC (High-Performance Liquid Chromatography) was used to quantify FFA and FDCA. Detection is performed using a UV detector. A Phenomenex Rezex ROA-Organic Acid H+ (8%) column with a corresponding precolumn is used for the measurement and eluted isocratically with 1 mM sulfuric acid. High-Performance Liquid Chromatography (HPLC) was used to quantify D-fructose and D-sorbitol. Detection is performed using a refractive index detector. A Phenomenex Rezex RCM-Monosaccharide Ca2+ column with a corresponding precolumn is used for the measurement, and the sample is eluted isocratically with 3.5% isopropanol. Determination of Enzyme Activities (Optical-Enzymatic Assay) Enzyme activities in the lysates were determined using a Shimadzu UV-1900 spectrophotometer. Therefore, the formation or consumption of NAD(P)H was monitored at a wavelength of 340 nm by measuring changes in absorbance. The measurements were performed using 0.2 mM cofactor (NAD(P) or NAD(P)H). For this purpose, 20 μl of a 10 mM stock solution of the cofactor was placed in a cuvette (Greiner bio-one semi-micro cuvette made of polystyrene), and the desired pH was adjusted with 100 mM TEA-HCl buffer (870 μl). 10 μl of lysate (diluted or undiluted) and 100 μl of substrate solution were added to the cuvette, and the measurement was started immediately thereafter. The measurements were performed at 25 °C as standard. Using the extinction coefficient of NADH / NADPH at 340 nm (<semantics>ε<annotation encoding="application / x-tex">\varepsilon< / annotation>< / semantics> = 6220 L mol-1 cm-1) can be used to determine the enzyme activity of the lysate in U / ml (relative to the volume of the lysate), or U / g (relative to the biomass used for production). Here, 1 U represents 1 <semantics>μ<annotation encoding="application / x-tex">\mu< / annotation>< / semantics>mol of substrate turnover per minute (1 U = 1 <semantics>μ<annotation encoding="application / x-tex">\mu< / annotation>< / semantics>mol / min = 1.67 × 10-8 kat). The following examples describe preferred embodiments of the method according to the invention in greater detail. The lysates used in these examples were prepared according to the methods described above. Example 1 Oxidation of 5-formyl-2-furan carboxylic acid to 2,5-furan dicarboxylic acid – cofactor regeneration using XDH and D-fructose The reaction was carried out in a BioXplorer benchtop bioreactor with a Polyblock (H.E.L.). A stainless- steel reactor (max. volume 400 mL) equipped with a stirrer and a pH electrode was used as the vessel. pH control was achieved by adding 5 M NaOH or 1 M H₂SO4. Initially, 5.5 g of FFA and 16 g of D-fructose (final concentration 600 mM) were added to 100 mL of a 100 mM potassium phosphate buffer (pH 7) and heated to 20 °C with stirring. Subsequently, 20 mL of ALDH I lysate, 13 mL of XDH lysate, and 3 mL of a 10 mM NAD+ solution (final concentration 0.2 mM) were added. The total volume of the reaction mixture was adjusted to 150 mL by adding deionized water. For analysis, 50 µl of the mixture was combined with 200 µl of acetonitrile and incubated in an Eppendorf Thermomixer at 85 °C and 1200 rpm for 15 min. The sample was briefly centrifuged in a centrifuge, mixed with 750 µl of deionized water, vortexed, and then centrifuged for 5 min at max. g. 250 µl of the supernatant was diluted in an HPLC vial with 750 <semantics>μ<annotation encoding="application / x-tex">\mu< / annotation>< / semantics>l of an acetonitrile / water mixture (1 / 4 v / v) and analyzed by HPLC (UV detection). After 4 h, the FFA was completely oxidized to FDCA. For purification, the reactor contents were heated to 70 °C and stirred at this temperature for 1 h. After centrifuging out the denatured protein, the supernatant was filtered through a pleated filter. This yielded a clear solution, which was acidified to a pH < 2 using 10 mL of a 12 M H₂SO₄ solution. Upon cooling to 4 °C, a precipitate formed, which was filtered off. In this manner, 5.1 g of FDCA was isolated as a solid. Example 2 Oxidation of 5-formyl-2-furan carboxylic acid to 2,5-furan dicarboxylic acid – cofactor regeneration using ADH and acetone The reaction was carried out in a Labfors benchtop bioreactor (Infors AG). A glass reactor (volume 3.4 L) equipped with a stirrer and a pH electrode was used as the vessel. pH control was achieved by adding 5 M NaOH or 1 M H2SO4. Initially, 27.7 g of FFA was added to 550 ml of a 100 mM potassium phosphate buffer (pH 7) and heated to 20 °C with stirring. Subsequently, 67 mL of ALDH I lysate, 30 mL of ADH lysate, 10 mL of a 10 mM NAD+ solution (final concentration 0.2 mM), and 15 mL of acetone were added. Additionally, an overpressure of 320 mbar was applied. For analysis, 50 µl of the sample was mixed with 200 µl of acetonitrile and incubated in an Eppendorf Thermomixer at 85 °C and 1200 rpm for 15 min. The sample was briefly centrifuged in a centrifuge, mixed with 750 µl of deionized water, vortexed, and then centrifuged for 5 min at max. g. 250 µl of the supernatant was diluted in an HPLC vial with 750 <semantics>μ<annotation encoding="application / x-tex">\mu< / annotation>< / semantics>l of an acetonitrile / water mixture (1 / 4 v / v) and analyzed by HPLC (UV detection). After 4.5 h, the FFA was completely oxidized to FDCA. FDCA can be isolated as a solid in the same manner as in Example 1. Example 3 Oxidation of 5-formyl-2-furan carboxylic acid to 2,5-furan dicarboxylic acid using aldehyde dehydrogenase II (ALDH II) and cofactor regeneration via XDH and D-fructose The following components were mixed in a glass vial: 300 <semantics>μ<annotation encoding="application / x-tex">\mu< / annotation>< / semantics>l of an FFA solution (11.9 g / l), 10 <semantics>μ<annotation encoding="application / x-tex">\mu< / annotation>< / semantics>l of deionized water, 50 µl of ALDH II lysate, 50 µl of a 1 M potassium phosphate buffer (pH 8), 50 µl of a 1.5 M D-fructose solution, and 40 μl of XDH lysate. The mixture was incubated with continuous shaking (Eppendorf Thermomixer; 20 °C, 800 rpm) for a total of 20 h. For analysis, 50 µl of the mixture was combined with 200 µl of acetonitrile and incubated in the Eppendorf Thermomixer at 85 °C and 1200 rpm for 15 min. The sample was briefly centrifuged in a centrifuge, mixed with 750 µl of deionized water, vortexed, and then centrifuged for 5 min at max. g. 200 µl of the supernatant was transferred to an HPLC vial with an insert and analyzed by HPLC (UV detection). In this manner, 40.8% of the FFA (7.1 g / l) was oxidized to FDCA. Example 4 Oxidation of 5-formyl-2-furan carboxylic acid to 2,5-furan dicarboxylic acid using aldehyde dehydrogenase III (ALDH III) and cofactor regeneration via ADH and acetone The following components were mixed in a glass vial: 5.2 mg FFA, 325 μl deionized water, 35 μl ALDH III lysate, 100 μl of a 500 mM potassium phosphate buffer (pH 8), 15 μl of acetone, 30 μl of ADH lysate, and 5 μl of a 10 mM NAD+ solution. The mixture was incubated under continuous shaking (Eppendorf Thermomixer; 20 °C, 800 rpm) for a total of 24 h. For analysis, 50 µl of the mixture was combined with 200 µl of acetonitrile and incubated in the Eppendorf Thermomixer at 85 °C and 1200 rpm for 15 min. The sample was briefly centrifuged, mixed with 750 μl of deionized water, vortexed, and then centrifuged for 5 min at max. g. 200 μl of the supernatant was transferred to an HPLC vial with an insert and analyzed by HPLC (UV detection). In this manner, 48.0% of the FFA was oxidized to FDCA. Example 5 Oxidation of 5-formyl-2-furan carboxylic acid to 2,5-furan dicarboxylic acid using aldehyde dehydrogenase II (ALDH II) and various dehydrogenases for cofactor regeneration The following components were mixed in 3 glass vials (vials 1–3): 300 µl of an FFA solution (final concentration 7.1 g / l), 50 μl of a 1 M potassium phosphate buffer (pH 8), 50 μl of ALDH II lysate, 5 μl of a 10 mM NADP+ solution, 50 μl of dehydrogenase lysate (see Table 2 below), 50 μl of a 1.5 M substrate solution (see Table 2 below), and 5 μl of deionized water. The mixture was incubated under continuous shaking (Eppendorf Thermomixer; 20 °C, 800 rpm) for a total of 24 h. For analysis, 50 µl of the sample was mixed with 200 µl of acetonitrile and incubated in an Eppendorf Thermomixer at 85 °C and 1200 rpm for 15 min. The sample was briefly centrifuged in a centrifuge, mixed with 750 µl of deionized water, vortexed, and then centrifuged for 5 min at max. g. 200 µl of the supernatant was transferred to an HPLC vial with an insert and analyzed by HPLC (UV detection). The results are shown in Table 2 below. Table 2. [Image disponible dans le document PDF, Image available in the PDF document] The results in Table 2 show that different dehydrogenases are suitable for cofactor regeneration (in this case, NADP+) using different substrates. Example 6 Oxidation of 5-formyl-2-furan carboxylic acid to 2,5-furan dicarboxylic acid using aldehyde dehydrogenase II (ALDH II) and cofactor regeneration via ADH and dihydroxyacetone The following components were mixed in a glass vial: 143 µl of an FFA solution (final concentration 12 g / l), 125 μl of a 250 mM potassium phosphate buffer (pH 7), 10 μl of ALDH II lysate, 10 μl of a 5 mM NADP+ solution, 10 μl of dehydrogenase lysate (see Table 2 below), 50 μl of a 300 g / l dihydroxyacetone solution, and 152 μl of deionized water. The mixture was incubated under continuous shaking (Eppendorf Thermomixer; 30 °C, 800 rpm) for a total of 20 h. For analysis, 50 µl of the mixture was combined with 200 µl of acetonitrile and incubated in the Eppendorf Thermomixer at 85 °C and 1200 rpm for 15 min. The sample was briefly centrifuged in a centrifuge, mixed with 750 µl of deionized water, vortexed, and then centrifuged for 5 min at max. g. 200 μl of the supernatant was transferred to an HPLC vial with an insert and analyzed by HPLC (UV detection). In this manner, 66% of the FFA was oxidized to FDCA. Table 3. [Image disponible dans le document PDF, Image available in the PDF document] Example 7 Oxidation of 5-formyl-2-furan carboxylic acid to 2,5-furan dicarboxylic acid using aldehyde dehydrogenase III (ALDH III) and cofactor regeneration via ADH and acetone The following components were mixed in a glass vial: 143 µl of an FFA solution (final concentration 12 g / l), 187 μl of deionized water, 10 μl of ALDH IV lysate, 125 μl of a 1 M potassium phosphate buffer (pH 7), 15 μl of acetone, 10 μl of ADH II lysate, and 10 μl of a 10 mM NADP+ solution. The mixture was incubated under continuous shaking (Eppendorf Thermomixer; 30 °C, 800 rpm) for a total of 20 h. For analysis, 50 µl of the mixture was combined with 200 µl of acetonitrile and incubated in the Eppendorf Thermomixer at 85 °C and 1200 rpm for 15 min. The sample was briefly centrifuged in a centrifuge, mixed with 750 µl of deionized water, vortexed, and then centrifuged for 5 min at max. g. 200 µl of the supernatant was transferred to an HPLC vial with an insert and analyzed by HPLC (UV detection). In this manner, 85.0% of the FFA was oxidized to FDCA. Example 8 Oxidation of 5-formyl-2-furan carboxylic acid to 2,5-furan dicarboxylic acid using aldehyde dehydrogenase V (ALDH V) and Cofactor regeneration using ADH and acetone The following components were mixed in a glass vial: 85 µl of a substrate solution (final concentration 6.5 g / l FFA), 255 μl of deionized water, 25 μl of ALDH V suspension, 100 μl of a 500 mM potassium phosphate buffer (pH 8), 15 μl of acetone, 30 μl of ADH I lysate, and 5 μl of a 10 mM NAD+ solution. 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Claims

1. A method for the preparation of 2,5-furandicarboxylic acid by oxidizing 5-formyl-2-furancarboxylic acid, which is present in an aqueous solution, to 2,5-furandicarboxylic acid by treating with a NAD(P)+-dependent oxidoreductase in vitro, wherein the NAD(P)H generated during the oxidation is enzymatically reoxidized to NAD(P)+ by the means of a dehydrogenase, after which the enzymes are removed.

2. The method according to claim 1, characterized in that the NAD(P)+-dependent oxidoreductase for the oxidation of 5-formyl-2-furan carboxylic acid to 2,5-furan dicarboxylic acid is an aldehyde dehydrogenase.

3. The method according to any one of claims 1 or 2, characterized in that the NAD(P)+-dependent oxidoreductase for the oxidization of 5-formyl-2-furan carboxylic acid to 2,5-furan dicarboxylic acid has an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 2, SEQ ID NO: 8, SEQ ID NO: 4, or SEQ ID NO: 6, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 1, SEQ ID NO: 7, SEQ ID NO: 4, or SEQ ID NO: 5, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 1, SEQ ID NO: 7, SEQ ID NO: 3, or SEQ ID NO: 5.

4. The method according to any one of claims 1 to 3, characterized in that a sugar or an aldehyde compound or a keto compound is used as a substrate for the dehydrogenase for the enzymatic oxidation of NAD(P)H.

5. The method according to claim 4, characterized in that D-fructose is used as the sugar and acetone is used as the keto compound.

6. The method according to claim 4, characterized in that D-glucose is used as the sugar and acetone is used as the keto compound.

7. The method according to any one of claims 1 to 6, characterized in that a xylitol dehydrogenase is used as the dehydrogenase for the enzymatic oxidation of NAD(P)H, which has an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 20, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 19, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 19.

8. The method according to any one of claims 1 to 6, characterized in that a NAD(P)H-dependent alcohol dehydrogenase is used as the dehydrogenase for the enzymatic oxidation of NAD(P)H via the formation of 2-propanol from acetone, which has an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 10 or SEQ ID NO: 12, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 9 or SEQ ID NO: 11, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 9 or SEQ ID NO: 11.

9. The method according to any one of claims 1 to 6, characterized in that a xylose reductase is used as the dehydrogenase for the enzymatic oxidation of NAD(P)H via the formation of D-sorbitol from D-glucose or L-arabitol from L-arabinose, which has an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 14 or SEQ ID NO: 16, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 13 or SEQ ID NO: 15, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 13 or SEQ ID NO: 15.

10. The method according to any one of claims 1 to 6, characterized in that a mannitol dehydrogenase is used as the dehydrogenase for the enzymatic oxidation of NAD(P)H via the formation of D-mannitol from D-fructose, which has an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO. 18, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 17, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 17.

11. Use of a xylitol dehydrogenase for the enzymatic oxidation of NAD(P)H via the formation of D- sorbitol from D-fructose, wherein the xylitol dehydrogenase comprises an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 20, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 19, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 19.

12. Use of a NAD(P)H-dependent alcohol dehydrogenase for the enzymatic oxidation of NAD(P)H via formation of an alcohol from a ketone or aldehyde, wherein the alcohol dehydrogenase comprises an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 10 or SEQ ID NO: 12, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 9 or SEQ ID NO: 11, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 9 or SEQ ID NO: 11.

13. Use of a xylose reductase for the enzymatic oxidation of NAD(P)H, wherein the xylose reductase comprises an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 14 or SEQ ID NO: 16, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 13 or SEQ ID NO: 15, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 13 or SEQ ID NO: 15.

14. Use of a mannitol dehydrogenase for the enzymatic oxidation of NAD(P)H, wherein the mannitol dehydrogenase comprises an amino acid sequence selected from the group consisting of: i) an amino acid sequence having at least 80% identity to SEQ ID NO: 18, ii) an amino acid sequence encoded by a nucleic acid having at least 80% identity to SEQ ID NO: 17, and iii) an amino acid sequence encoded by a nucleic acid that binds under stringent conditions to a complementary strand of the nucleic acid molecule having the nucleic acid sequence SEQ ID NO: 17.