Concise Stereoselective Synthesis of ß-Hydroxy-γ-lactones: (4R,5R)-4-Hydroxy-γ-decalactone from the Japanese Orange Fly and Enantiomers of Arachnid Harvestmen Isolates.

The naturally occurring (4R,5R)-4-hydroxy-γ-decalactone from the Japanese orange fly and the antipode of (4S,5R)-4-hydroxy-γ-dodecalactone from the harvestmen arachnid and their stereoisomers are synthesized from the chiral pool material d-glucono-δ-lactone in a few steps. The one-pot conversion of the latter to γ-vinyl-ß-hydroxy-γ-lactone, cross-metathesis with requisite olefin, and hydrogenation enabled the synthesis of syn-lactones in just a two-pot operation. An additional efficient Pd-catalyzed allylic isomerization of γ-vinyl-ß-hydroxy-γ-lactone led to the anti-lactones in high yields.

Design of enzymatic cascade processes for the production of low-priced chemicals.

While the application of enzymes to synthetic and industrial problems continues to grow, the major development today is focused on multi-enzymatic cascades. Such systems are particularly attractive, because many commercially available enzymes operate under relatively similar operating conditions. This opens the possibility of one-pot operation with multiple enzymes in a single reactor. In this paper the concept of modules is introduced whereby groups of enzymes are combined in modules, each operating in a single reactor, but with the option of various operating strategies to avoid any complications of nonproductive interactions between the enzymes, substrates or products in a given reactor. In this paper the selection of modules is illustrated using the synthesis of the bulk chemical, gluconic acid, from lignocellulosic waste.

Preparation of restricted-access material precolumns by grafting δ-gluconolactone onto a hybrid silica monolithic column for on-line solid-phase extraction of tetracycline residues from milk.

A restricted-access material-hybrid monolithic column was prepared based on single-component organosiloxane and dynamic grafting of δ-gluconolactone for on-line solid phase extraction of tetracycline antibiotic residues from milk. The hybrid monolithic column was prepared in a stainless-steel chromatographic column using methyltrimethoxysilane as the single precursor. δ-Gluconolactone was covalently coupled to aminopropyl derivatized hybrid monolithic column, which formed hydrophilic structures on the surface of the pore of the restricted-access material-hybrid monolithic column. The columns were characterized by scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, nitrogen adsorption, contact angle analysis, dynamic adsorption, and chromatographic performance evaluation. The restricted-access material-hybrid monolithic column was applied to the on-line extraction of tetracycline residues from milk. An enrichment factor of 15.8 and a good sample clean-up effect were obtained under the optimized conditions. The recoveries of the three spiked milk samples were between 81.7 and 102.5% with relative standard deviations (n = 3) in the range of 2-5%. The limits of detection (S/N = 3) for target compounds were in the range of 3.80-9.03 µg/kg. The results show that the on-line extraction using the restricted-access material-hybrid monolithic column was powerful for food sample pretreatment with high selectivity and good clean-up effect.

Enzyme-immobilized metal-organic framework nanosheets as tandem catalysts for the generation of nitric oxide.

An enzyme-immobilized metal-organic framework (MOF) nanosheet system was developed as a tandem catalyst, which converted glucose into gluconic acid and H2O2, and sequentially the latter could be used to catalyze the oxidation of l-arginine to generate nitric oxide in the presence of porphyrinic MOFs as artificial enzymes under physiological pH, showing great potential in cancer depleting glucose for starving-like/gas therapy.

Stratiform Protein Microtube Reactors Containing Glucose Oxidase Layer.

This paper describes the synthesis and catalytic activities of stratiform protein microtube reactors containing a glucose oxidase (GOD) enzyme layer. The microtubes were fabricated by layer-by-layer assembly using a microporous polycarbonate membrane with human serum albumin (HSA), poly(l-arginine) (PLA), and GOD. The GOD component was introduced into the tube wall as the innermost layer, the intermediate layer, or all internal protein layers. SEM observations revealed the formation of uniform hollow cylinders with ca. 1.17 µm outer diameter and ca. 135 nm wall thickness. In aqueous medium, each microtube catalyzed ß-d-glucose oxidation with high efficiency. We first ascertained the enzyme parameters (Km and kcat ) of these microtube reactors. Different catalytic activities that have dependent on the GOD layer position in the cylindrical wall have been elucidated.

Impact of ultrasound on galactooligosaccharides and gluconic acid production throughout a multienzymatic system.

Galactooligosaccharides (GOS), recognised prebiotic, can be industrially produced from lactose and commercial ß-galactosidase (ß-gal) from Kluyveromyces lactis. Residual lactose and glucose limit GOS applications. To handle this problem, a multienzymatic system, with ß-gal and glucose oxidase (Gox), was proposed to reduce glucose content in reaction media through its oxidation to gluconic acid (GA). Besides, ultrasound (US) probe effect over the multienzymatic system to produce GOS and GA has been evaluated. A production around 40% of GOS was found in all treatments after the first hour of reaction. However, glucose consumption and GA production was significantly higher (P < 0.05) for sequential reaction assisted by US, obtaining the best production of GOS (49%) and GA (28%) after 2 h of reaction. The conformational and residual activity changes of enzymes under US conditions were also evaluated, Gox being positively affected whereas in ß-gal hardly any change was found.

Modeling and simulation of enzymatic gluconic acid production using immobilized enzyme and CSTR-PFTR circulation reaction system.

OBJECTIVES: Production of gluconic acid by using immobilized enzyme and continuous stirred tank reactor-plug flow tubular reactor (CSTR-PFTR) circulation reaction system. RESULTS: A production system is constructed for gluconic acid production, which consists of a continuous stirred tank reactor (CSTR) for pH control and liquid storage and a plug flow tubular reactor (PFTR) filled with immobilized glucose oxidase (GOD) for gluconic acid production. Mathematical model is developed for this production system and simulation is made for the enzymatic reaction process. The pH inhibition effect on GOD is modeled by using a bell-type curve. CONCLUSIONS: Gluconic acid can be efficiently produced by using the reaction system and the mathematical model developed for this system can simulate and predict the process well.

Efficient Aerobic Oxidation of Glucose to Gluconic Acid over Activated Carbon-Supported Gold Clusters.

The catalytic performance of the atomically precise gold cluster-Au38 (PET)24 (PET=2-phenylethanethiolate), immobilized on activated carbon (AC), was investigated for the aerobic oxidation of glucose to gluconic acid. The Au38 (PET)24 /AC-120 catalysts, annealed at 120 °C in air, exhibited high catalytic activity and significantly better performance than the corresponding catalysts Au38 /AC-150 and Au38 /AC-300 (treated at 150 and 300 °C to remove the protecting thiolate ligands). The high activity of the robust Au cluster was a result of the partial ligand removal, providing catalytically active sites, which were evidenced by TEM, X-ray photoelectron spectroscopy, thermogravimetric analysis, and Fourier-transform IR spectroscopy. Au38 (PET)24 /AC-120 also showed excellent recyclability (up to seven cycles). The turnover frequency for the Au38 (PET)24 /AC-120 catalyst was 5440 h-1 , which is higher than for the Pd/AC, Pd-Bi/AC, and Au/AC under identical reaction conditions. This new ultra-small gold nanomaterial is expected to find wide application in other catalytic oxidations.

Characterization of a continuous agitated cell reactor for oxygen dependent biocatalysis.

Biocatalytic oxidation reactions employing molecular oxygen as the electron acceptor are difficult to conduct in a continuous flow reactor because of the requirement for high oxygen transfer rates. In this paper, the oxidation of glucose to glucono-1,5-lactone by glucose oxidase was used as a model reaction to study a novel continuous agitated cell reactor (ACR). The ACR consists of ten cells interconnected by small channels. An agitator is placed in each cell, which mixes the content of the cell when the reactor body is shaken by lateral movement. Based on tracer experiments, a hydrodynamic model for the ACR was developed. The model consisted of ten tanks-in-series with back-mixing occurring within and between each cell. The back-mixing was a necessary addition to the model in order to explain the observed phenomenon that the ACR behaved as two continuous stirred tank reactors (CSTRs) at low flow rates, while it at high flow rates behaved as the expected ten CSTRs in series. The performance of the ACR was evaluated by comparing the steady state conversion at varying residence times with the conversion observed in a stirred batch reactor of comparable size. It was found that the ACR could more than double the overall reaction rate, which was solely due to an increased oxygen transfer rate in the ACR caused by the intense mixing as a result of the spring agitators. The volumetric oxygen transfer coefficient, kL a, was estimated to be 344 h-1 in the 100 mL ACR, opposed to only 104 h-1 in a batch reactor of comparable working volume. Interestingly, the large deviation from plug flow behavior seen in the tracer experiments was found to have little influence on the conversion in the ACR, since both a plug flow reactor (PFR) model and the backflow cell model described the data sufficiently well. Biotechnol. Bioeng. 2017;114: 1222-1230. © 2017 Wiley Periodicals, Inc.

Genipin Cross-Linked Glucose Oxidase and Catalase Multi-enzyme for Gluconic Acid Synthesis.

In this work, glucose oxidase (GOD) and catalase (CAT) were used simultaneously to produce gluconic acid from glucose. In order to reduce the distance between the two enzymes, and therefore improve efficiency, GOD and CAT were cross-linked together using genipin. Improvements in gluconic acid production were due to quick removal of harmful intermediate hydrogen peroxide by CAT. GOD activity was significantly affected by the proportion of CAT in the system, with GOD activity in the cross-linked multi-enzyme (CLME) being 10 times higher than that in an un-cross-linked GOD/CAT mixture. The glucose conversion rate after 15 h using 15 % glucose was also 10 % higher using the CLME than was measured using a GOD/CAT mixture.

Heterogeneously Catalyzed Hydrothermal Processing of C5-C6 Sugars.

Biomass has been long exploited as an anthropogenic energy source; however, the 21st century challenges of energy security and climate change are driving resurgence in its utilization both as a renewable alternative to fossil fuels and as a sustainable carbon feedstock for chemicals production. Deconstruction of cellulose and hemicellulose carbohydrate polymers into their constituent C5 and C6 sugars, and subsequent heterogeneously catalyzed transformations, offer the promise of unlocking diverse oxygenates such as furfural, 5-hydroxymethylfurfural, xylitol, sorbitol, mannitol, and gluconic acid as biorefinery platform chemicals. Here, we review recent advances in the design and development of catalysts and processes for C5-C6 sugar reforming into chemical intermediates and products, and highlight the challenges of aqueous phase operation and catalyst evaluation, in addition to process considerations such as solvent and reactor selection.

Enhancement of 5-keto-d-gluconate production by a recombinant Gluconobacter oxydans using a dissolved oxygen control strategy.

The rapid and incomplete oxidation of sugars, alcohols, and polyols by the gram-negative bacterium Gluconobacter oxydans facilitates a wide variety of biological applications. For the conversion of glucose to 5-keto-d-gluconate (5-KGA), a promising precursor of the industrial substance L-(+)-tartaric acid, G. oxydans DSM2343 was genetically engineered to strain ZJU2, in which the GOX1231 and GOX1081 genes were knocked out in a markerless fashion. Then, a secondary alcohol dehydrogenase (GCD) from Xanthomonas campestris DSM3586 was heterologously expressed in G. oxydans ZJU2. The 5-KGA production and cell yield were increased by 10% and 24.5%, respectively. The specific activity of GCD towards gluconate was 1.75±0.02 U/mg protein, which was 7-fold higher than that of the sldAB in G. oxydans. Based on the analysis of kinetic parameters including specific cell growth rate (µ), specific glucose consumption rate (qs) and specific 5-KGA production rate (qp), a dissolved oxygen (DO) control strategy was proposed. Finally, batch fermentation was carried out in a 15-L bioreactor using an initial agitation speed of 600 rpm to obtain a high µ for cell growth. Subsequently, DO was continuously maintained above 20% to achieve a high qp to ensure a high accumulation of 5-KGA. Under these conditions, the maximum concentration of 5-KGA reached 117.75 g/L with a productivity of 2.10 g/(L·h).

One-step synthesis of 2-keto-3-deoxy-d-gluconate by biocatalytic dehydration of d-gluconate.

2-Keto-3-deoxy-sugar acids are key intermediates of central metabolism and integral constituents of bacterial (lipo)polysaccharides and cell wall components and are therefore continuously and highly demanded in related research fields. The stereospecific chemical synthesis of chiral 2-keto-deoxy-sugar acids involves a multitude of reaction steps, while in metabolic pathways only few conversions lead to the same 2-keto-3-deoxy sugar acids from easily available carbohydrate precursors. Here we present a straightforward and highly economic one-step biocatalytic synthesis procedure of 2-keto-3-deoxy-d-gluconate (KDG) from d-gluconate using recombinant gluconate dehydratase (GAD) from the hyperthermophilic crenarchaeon Thermoproteus tenax. This method is highly advantageous to KDG production schemes described so far for several reasons: (i) the d-gluconate is completely converted to stereochemically pure D-KDG without side-product formation, (ii) the final KDG yield is approximately 90%, (iii) the newly developed quantitative and qualitative LC-MS analysis method enabled the simultaneous detection of d-gluconate and KDG and (iv) the T. tenax GAD as biocatalyst can be provided by a simple and rapid procedure involving only two precipitation steps. The described utilization of dehydratases for 2-keto-3-deoxy sugar acid syntheses represents a highly resource-efficient one-step preparation and offers potential short synthetic routes toward a broad range of 2-keto-3-deoxy sugar acids and their derivatives.

Novel organic salts based on fluoroquinolone drugs: synthesis, bioavailability and toxicological profiles.

In order to overcome the problems associated with low water solubility, and consequently low bioavailability of active pharmaceutical ingredients (APIs), novel organic salts containing fluoroquinolones (e.g. ciprofloxacin and norfloxacin) were prepared, using an optimized synthetic procedure based on direct protonation, with different biocompatible counter ions such as mesylate, gluconate and glycolate. All the prepared organic salts were characterized by spectroscopic techniques, mass spectrometry and thermal analysis. Solubility studies in water and simulated biological fluids at 25°C and 37°C were also performed. Additionally, octanol-water and phospholipid-water partition coefficients were measured at 25°C. The cytotoxicity and anti-inflammatory efficacy using an human cell model of intestinal epithelia (Caco-2 cells) were also evaluated and compared to those of the parent APIs. The adequate selection of the biocompatible anions allows the tuning of important physical, thermal and toxicological properties.

Simultaneous saccharification of inulin and starch using commercial glucoamylase and the subsequent bioconversion to high titer sorbitol and gluconic acid.

A new bioprocess for production of sorbitol and gluconic acid from two low-cost feedstocks, inulin and cassava starch, using a commercially available enzyme was proposed in this study. The commercial glucoamylase GA-L NEW from Genencor was found to demonstrate a high inulinase activity for hydrolysis of inulin into fructose and glucose. The glucoamylase was used to replace the expensive and not commercially available inulinase enzyme for simultaneous saccharification of inulin and starch into high titer glucose and fructose hydrolysate. The glucose and fructose in the hydrolysate were converted into sorbitol and gluconic acid using immobilized whole cells of the recombinant Zymomonas mobilis strain. The high gluconic acid concentration of 193 g/L and sorbitol concentration of 180 g/L with the overall yield of 97.3 % were obtained in the batch operations. The present study provided a practical production method of sorbitol and gluconic acid from low cost feedstocks and enzymes.

Synthesis and evaluation of D-gluconamides as green mineral scales.

A series of 13 D-gluconamides were synthesized in moderate to good yields and evaluated as green scale inhibitors. The crystal structures of two compounds were determined by X-ray crystallography. The compounds 6c and 6d showed a reasonable inhibition of BaSO(4) precipitation from aqueous solution (47% and 51%, respectively) that indicated the potential for these derivatives of δ-gluconolactone.

Selective conversion of cellobiose and cellulose into gluconic acid in water in the presence of oxygen, catalyzed by polyoxometalate-supported gold nanoparticles.

Gold nanoparticles loaded onto Keggin-type insoluble polyoxometalates (Cs(x)H(3-x)PW(12)O(40)) showed superior catalytic performances for the direct conversion of cellobiose into gluconic acid in water in the presence of O(2). The selectivity of Au/Cs(x)H(3-x)PW(12)O(40) for gluconic acid was significantly higher than those of Au catalysts loaded onto typical metal oxides (e.g., SiO(2), Al(2)O(3), and TiO(2)), carbon nanotubes, and zeolites (H-ZSM-5 and HY). The acidity of polyoxometalates and the mean-size of the Au nanoparticles were the key factors in the catalytic conversion of cellobiose into gluconic acid. The stronger acidity of polyoxometalates not only favored the conversion of cellobiose but also resulted in higher selectivity of gluconic acid by facilitating desorption and inhibiting its further degradation. On the other hand, the smaller Au nanoparticles accelerated the oxidation of glucose (an intermediate) into gluconic acid, thereby leading to increases both in the conversion of cellobiose and in the selectivity of gluconic acid. The Au/Cs(x)H(3-x)PW(12)O(40) system also catalyzed the conversion of cellulose into gluconic acid with good efficiency, but it could not be used repeatedly owing to the leaching of a H(+)-rich hydrophilic moiety over long-term hydrothermal reactions. We have demonstrated that the combination of H(3)PW(12)O(40) and Au/Cs(3.0)PW(12)O(40) afforded excellent yields of gluconic acid (about 85%, 418 K, 11 h), and the deactivation of the recovered H(3)PW(12)O(40)-Au/Cs(3.0)PW(12)O(40) catalyst was not serious during repeated use.

Uncatalysed wet oxidation of D-glucose with hydrogen peroxide and its combination with hydrothermal electrolysis.

An increasing interest in biomass as a renewable feedstock for the chemical industry has risen over the last decades, and glucose, the monomer unit of cellulose, has been widely studied as a source material to produce value-added products such as carboxylic acids, mainly gluconic and formic. In this work, the non-catalysed wet oxidation of glucose using hydrogen peroxide has been analysed, obtaining molar yields to gluconic and formic acids up to 15% and 64%, respectively. Glucose conversion was generally between 40 and 50%, reaching over 80% under the highest temperature (200°C). An appropriate choice of temperature can tune product distribution as well as reaction rates. The interaction of the wet oxidation with an electrolytic reaction was also analysed.

Synthesis of a chitosan derivative soluble at neutral pH and gellable by freeze-thawing, and its application in wound care.

Conventional chitosan hydrogels exhibit an acidic nature and contain unfavorable additives because (i) chitosan is soluble only in acidic solutions and (ii) toxic chemicals or proteins of non-human origin that serve as antigens are necessary for preparing chitosan hydrogels. These characteristics of the chitosan hydrogels limit their possibilities as wound dressings. In this study, a chitosan-gluconic acid conjugate is developed, soluble in an aqueous solution at neutral pH and gellable by freeze-thawing (cryogelation) without using additives. The viability of L929 fibroblasts cultured in the presence of the chitosan derivative for 24 h was >96%. The degradation rate of the corresponding chitosan cryogels by lysozyme was tunable via the derivative concentration in the gels. The gels had low cellular adhesiveness. The gels promoted the accumulation of inflammatory cells such as polymorphonuclear leukocytes, which have the potential to release chemical mediators effective for wound healing, in full-thickness skin wounds in rats and accelerated the healing of the wounds. These results demonstrate that cryogels are promising for wound care.

Carbon nanotube-supported gold nanoparticles as efficient catalysts for selective oxidation of cellobiose into gluconic acid in aqueous medium.

Gold nanoparticles loaded on nitric acid-pretreated carbon nanotubes are efficient for the selective oxidation of cellobiose by molecular oxygen to gluconic acid in aqueous medium without pH control; a gluconic acid yield of 80% has been obtained at 145 degrees C.