Furan carboxylic acids are promising and renewable building blocks in polymer and pharmaceutical industries. In this work, biocatalytic synthesis of furan carboxylic acids was performed from biobased furan aldehydes using recombinant Escherichia coli expressing 3-succinoylsemialdehyde-pyridine dehydrogenase (SAPDH). Particularly, the inhibition and toxicity of furan aldehydes and their carboxylic acid derivatives toward this whole-cell biocatalyst were evaluated. It was found that this biocatalyst displayed the highest tolerance level (200 mM) toward 5-hydroxymethylfurfural (HMF) in the oxidation of furan aldehydes, lower toward 5-methoxymethylfurfural (MMF, 150 mM), and the lowest (75 mM) toward furfural. This may be explained by the less detrimental effects of high concentrations of HMF on the biocatalyst which might be closely related to the low hydrophobicity of this substance. In addition, the presence of furan carboxylic acids resulted in the substantial decrease in both catalytic activities and viability of the cells. The inhibition and toxicity of furan carboxylic acids toward the cells were greatly relieved upon neutralization with a base. Based on the results obtained above, a combined reaction engineering strategy (fed-batch operation coupled with pH controlling) was designed for efficient synthesis of 5-methoxymethyl-2-furancarboxylic acid (MMFCA) from MMF. In addition, the gram-scale preparation of MMFCA was implemented. The desired product was obtained in an isolated yield of 89% and a purity of >98%. Its space-time yield was up to 1.2 g/L h.
challenging, because most of the aerobic alcohol oxidations stop at the aldehyde stage even with noble metals. [4] In addition, many methods suffer from such drawbacks as use of environmentally unfriendly catalysts (e.g., metals) and/ or solvents (e.g., aqueous alkaline solutions and chloroalkanes), harsh reaction conditions, and unsatisfactory selectivities. According to Tojo and Fernández, [1a] approximately 40% of the processes toward carboxylic acids were still performed through a two-step oxidation, with the isolation of the aldehyde intermediates; therefore, this technique for direct access to carboxylic acids is still immature.Nitroxyl radicals are versatile organocatalysts for catalytic oxidations, where they, alone or in combination with other catalysts (e.g., transition metals, NO x and laccase), are used in the presence of oxidants. [5] 2,2,6,6-Tetramethylpiperidinyl-1-oxy (TEMPO) and its derivatives, a type of stable nitroxyl radicals, have been widely used for the production of pharmaceuticals, fragrances and flavors, agrochemicals, and specialty chemicals. [6] To date, few studies on catalytic oxidation of primary alcohols to carboxylic acids by nitroxyl radicals have been reported, [7] although the routes to aldehydes have been well established. [8] In Anelli's oxidation, primary alcohols were oxidized to carboxylic acids by TEMPO and KBr in a biphasic CH 2 Cl 2 /water mixture in the presence of a phasetransfer catalyst (Scheme 1a), with chlorine bleach (NaOCl) as an oxidant. [9] Then a series of modified Anelli's protocols were developed by using alternative oxidants (e.g., NaClO 2 , and bis(acetoxy)iodobenzene (BAIB)). [10] Yakura et al. reported a TEMPO-iodobenzene hybrid catalyst for the synthesis of carboxylic acids in acetic acid in the presence of peracetic acid (Scheme 1b). [11] Stahl and co-workers presented a clean direct electrochemical method to oxidize primary alcohols and aldehydes to carboxylic acids in the presence of 4-acetamido-TEMPO (Scheme 1c). [12] Ma and co-workers found that a threecomponent catalyst (TEMPO, Fe(NO 3 ) 3 •9H 2 O and KCl) enabled room-temperature aerobic oxidation of primary alcohols to carboxylic acids in 1,2-dichloroethane (Scheme 1d), [13] in which Fe(NO 3 ) 3 •9H 2 O catalyzed further oxidation of aldehydes to carboxylic acids. [14] From the perspective of green and sustainable Laccase coupled with 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) is a wellknown catalytic system for the oxidation of alcohols to the carbonyl compounds. In this work, a simple yet effective solvent engineering strategy is developed to enable aromatic alcohols/aldehydes to be efficiently oxidized to carboxylic acids by a laccase-TEMPO system. Citrate buffer (100-300 mm, pH 6) rather than the widely used acetate buffer (pH 4-5) proves to be optimal for this purpose. The roles of citrate are discussed in laccase-TEMPOcatalyzed synthesis of carboxylic acids. 5-Hydroxymethylfurfural (HMF) of 200 mm is oxidized to 2,5-furandicarboxylic acid (FDCA), a top-value biobased chemical in the...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.