β‐Hydroxyamide‐Based Ligands and Their Use in the Enantioselective Borane Reduction of Prochiral Ketones

Hydroxyamide‐based ligands have occupied a considerable place in asymmetric synthesis. Here we report the synthesis of seven β‐hydroxyamide‐based ligands from the reaction of 2‐hydroxynicotinic acid with chiral amino alcohols and test their effect on the enantioselective reduction of aromatic prochiral ketones with borane in tetrahydofuran (THF). They produce the corresponding secondary alcohols with up to 76% enantiomeric excess (ee) and good to excellent yields (86‐99%). Chirality 26:21–26, 2013. © 2013 Wiley Periodicals, Inc.     

Scale‐up and intensification of (S)‐1‐(2‐chlorophenyl)ethanol bioproduction: Economic evaluation of whole cell‐catalyzed reduction of o‐Chloroacetophenone

Escherichia coli cells co‐expressing genes coding for Candida tenuis xylose reductase and Candida boidinii formate dehydrogenase were used for the bioreduction of o‐chloroacetophenone with in situ coenzyme recycling. The product, (S)‐1‐(2‐chlorophenyl)ethanol, is a key chiral intermediate in the synthesis of polo‐like kinase 1 inhibitors, a new class of chemotherapeutic drugs. Production of the alcohol in multi‐gram scale requires intensification and scale‐up of the biocatalyst production, biotransformation, and downstream processing. Cell cultivation in a 6.9‐L bioreactor led to a more than tenfold increase in cell concentration compared to shaken flask cultivation. The resultant cells were used in conversions of 300 mM substrate to (S)‐1‐(2‐chlorophenyl)ethanol (e.e. >99.9%) in high yield (96%). Results obtained in a reaction volume of 500 mL were identical to biotransformations carried out in 1 mL (analytical) and 15 mL (preparative) scale. Optimization of product isolation based on hexane extraction yielded 86% isolated product. Biotransformation and extraction were accomplished in a stirred tank reactor equipped with pH and temperature control. The developed process lowered production costs by 80% and enabled (S)‐1‐(2‐chlorophenyl)ethanol production within previously defined economic boundaries. A simple and efficient way to synthesize (S)‐1‐(2‐chlorophenyl)ethanol in an isolated amount of 20 g product per reaction batch was demonstrated. Biotechnol. Bioeng. 2013; 110: 2311–2315. © 2013 Wiley Periodicals, Inc.     

Asymmetric Allylation of α‐Ketoester‐Derived N‐Benzoylhydrazones Promoted by Chiral Sulfoxides/N‐Oxides Lewis Bases: Highly Enantioselective Synthesis of Quaternary α‐Substituted α‐Allyl‐α‐Amino Acids

Chiral sulfoxides/N‐oxides (R)‐ 1 and (R,R)‐ 2 are effective chiral promoters in the enantioselective allylation of α‐keto ester N‐benzoylhydrazone derivatives 3a , 3b , 3c , 3d , 3e , 3f , 3g to generate the corresponding N‐benzoylhydrazine derivatives 4a , 4b , 4c , 4d , 4e , 4f , 4g , with enantiomeric excesses as high as 98%. Representative hydrazine derivatives 4a , 4b were subsequently treated with SmI₂, and the resulting amino esters 5a , 5b with LiOH to obtain quaternary α‐substituted α‐allyl α‐amino acids 6a , 6b , whose absolute configuration was assigned as (S), with fundament on chemical correlation and electronic circular dichroism (ECD) data. Chirality 25:529–540, 2013. © 2013 Wiley Periodicals, Inc.     

Stereoselective Synthesis of (3R)‐3‐Alkyl‐4,1‐Benzoxazepine‐2,5‐Diones

Novel 3‐alkyl‐4,1‐benzoxazepine‐2,5‐diones were synthesized in good ee exploiting the chiral pool methodology, an economical way of asymmetric synthesis. Various anthranilic acids are coupled with different α‐haloacids to afford N‐acylated anthranilic acid intermediates which undergo cyclization to (3R)‐3‐alkyl‐4,1‐benzoxazepines‐2,5‐diones. Chirality 25:865–870, 2013. © 2013 Wiley Periodicals, Inc.     

Application of NMR spectroscopy for assignment of the absolute configuration of 8‐tert‐butyl‐2‐hydroxy‐7‐methoxy‐8‐methyl‐9‐oxa‐6‐azaspiro[4.5]dec‐6‐en‐10‐one

In order to assign the absolute configurations of 8‐tert‐butyl‐2‐hydroxy‐7‐methoxy‐8‐methyl‐9‐oxa‐6‐azaspiro[4.5]dec‐6‐en‐10‐one ( 2a , 2b ), their esters ( 5a , 5b , 5c , 5d ) with (R)‐ or (S)‐2‐methoxyphenylacetic acid ( 4a , 4b ) have been synthesized. The absolute configurations of these compounds have been determined on the basis of NOESY correlations between the protons of the tert‐butyl group and the cyclopentane fragment of the molecules. The crucial part of this analysis was assignment of the absolute configuration at C‐5. Additionally, by calculation of the chemical shift anisotropy, δ^RS, for the relevant protons, it was also possible to confirm the absolute configurations at the C‐2 centres of compounds 2a , 2b and 5a , 5b , 5c , 5d . Chirality, 25:422–426, 2013.© 2013 Wiley Periodicals, Inc.     

Recovery of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) from Ralstonia eutropha cultures with non‐halogenated solvents

Reduced downstream costs, together with high purity recovery of polyhydroxyalkanoate (PHA), will accelerate the commercialization of high quality PHA‐based products. In this work, a process was designed for effective recovery of the copolymer poly(hydroxybutyrate‐co‐hydroxyhexanoate) (P(HB‐co‐HHx)) containing high levels of HHx (>15 mol%) from Ralstonia eutropha biomass using non‐halogenated solvents. Several non‐halogenated solvents (methyl isobutyl ketone, methyl ethyl ketone, and butyl acetate and ethyl acetate) were found to effectively dissolve the polymer. Isoamyl alcohol was found to be not suitable for extraction of polymer. All PHA extractions were performed from both dry and wet cells at volumes ranging from 2 mL to 3 L using a PHA to solvent ratio of 2% (w/v). Ethyl acetate showed both high recovery levels and high product purities (up to 99%) when using dry cells as starting material. Recovery from wet cells, however, eliminates a biomass drying step during the downstream process, potentially saving time and cost. When wet cells were used, methyl isobutyl ketone (MIBK) was shown to be the most favorable solvent for PHA recovery. Purities of up to 99% and total recovery yields of up to 84% from wet cells were reached. During polymer recovery with either MIBK or butyl acetate, fractionation of the extracted PHA occurred, based on the HHx content of the polymer. PHA with higher HHx content (17–30 mol%) remained completely in solution, while polymer with a lower HHx content (11–16 mol%) formed a gel‐like phase. All PHA in solution could be precipitated by addition of threefold volumes of n‐hexane or n‐heptane to unfiltered PHA solutions. Effective recycling of the solvents in this system is predicted due to the large differences in the boiling points between solvent and precipitant. Our findings show that two non‐halogenated solvents are good candidates to replace halogenated solvents like chloroform for recovery of high quality PHA. Biotechnol. Bioeng. 2013; 110: 461–470. © 2012 Wiley Periodicals, Inc.     

Green Asymmetric Synthesis: β‐Amino Alcohol‐Catalyzed Direct Asymmetric Aldol Reactions in Aqueous Micelles

The ability of chiral β‐amino alcohols to catalyze the direct asymmetric aldol reaction was evaluated for the first time in aqueous micellar media. A family of cheap and easily accessible β‐amino alcohols, obtained in one step from naturally occurring amino acids, was shown to successfully catalyze the asymmetric aldol reaction between a series of ketones and aromatic aldehydes. These aldol reactions furnished the corresponding β‐hydroxy ketones with up to 93% isolated yield and 89% ee. (S)‐2‐phenylglycinol and Triton X‐100 proved to be the best organocatalyst and surfactant, respectively. Chirality 25:119–125, 2013. © 2012 Wiley Periodicals, Inc.     

Crystal structure of decaprenylphosphoryl‐β‐ D‐ribose 2'‐epimerase from Mycobacterium smegmatis

Decaprenylphosphoryl‐β‐D ‐ribose 2'‐epimerase (DprE1) is an essential enzyme in the biosynthesis of cell wall components and a target for development of anti‐tuberculosis drugs. We determined the crystal structure of a truncated form of DprE1 from Mycobacterium smegmatis in two crystal forms to up to 2.35 Å resolution. The structure extends from residue 75 to the C‐terminus and shares homology with FAD‐dependent oxidoreductases of the vanillyl‐alcohol oxidase family including the DprE1 homologue from M. tuberculosis. The M. smegmatis DprE1 structure reported here provides further insights into the active site geometry of this tuberculosis drug target. Proteins 2013. © 2012 Wiley Periodicals, Inc.     

Determination of the enantiomeric purity of the selective dopamine transporter inhibitor (+)‐R,R‐4‐(2‐benzhydryloxyethyl)‐1‐(4‐fluorobenzyl)piperidin‐3‐ol

(+)‐R ,R ‐D‐84 ((+)‐R ,R ‐4‐(2‐benzhydryloxyethyl)‐1‐(4‐fluorobenzyl)piperidin‐3‐ol) is a promising pharmacological tool for the dopamine transporter (DAT), due to its high affinity and selectivity for this target. In this study, an analytical method to ascertain the enantiomeric purity of this compound was established. For this purpose, a high‐performance liquid chromatographic (HPLC) method, based on a cellulose derived chiral stationary phase (CSP) was developed. The method was characterized concerning its specificity, linearity, and range. It was shown that the method is suitable to determine an enantiomeric excess of up to 99.8%. With only a few adjustments, this analytical CSP‐HPLC method is also well suited to separate (+)‐R ,R ‐D‐84 from its enantiomer in a semipreparative scale.     

(S)‐6‐Bromo‐BINOL‐based phosphoramidite ligand with C1 symmetry for enantioselective hydrogenation and allylic substitution

(S)‐6‐Br‐BINOL‐derived phosphoramidite, a s imple monodentate ligand with a stereogenic center at the phosphorus atom, was synthesized for the first time. This stereoselector generated a high level of enantioselectivity (80–95% ee) in the rhodium‐catalyzed hydrogenation of α‐dehydrocarboxylic acid esters and was also successfully employed in the asymmetric palladium‐catalyzed allylic substitution of (E)‐1,3‐diphenylallyl acetate. The optical yield also showed significant dependence with reaction type: up to 70% ee for allylic amination, up to 75% ee for allylic sulfonylation, and up to 90% ee for allylic alkylation. Chirality, 2010. © 2010 Wiley‐Liss, Inc.     

Whole‐cell biocatalytic of Bacillus cereus WZZ006 strain to synthesis of indoxacarb intermediate: (S)‐5‐Chloro‐1‐oxo‐2,3‐dihydro‐2‐hydroxy‐1H‐indene‐2‐carboxylic acid methyl ester

In this study, a newly isolated strain screened from the indoxacarb‐rich agricultural soils, Bacillus cereus WZZ006, has a high stereoselectivity to racemic substrate 5‐chloro‐1‐oxo‐2,3‐dihydro‐2‐hydroxy‐1H‐indene‐2‐carboxylic acid methyl ester. (S)‐5‐chloro‐1‐oxo‐2,3‐dihydro‐2‐hydroxy‐1H‐indene‐2‐carboxylic acid methyl ester was obtained by bio‐enzymatic resolution. After the 36‐hour hydrolysis in 50‐mM racemic substrate under the optimized reaction conditions, the e.e._s was up to 93.0% and the conversion was nearly 53.0% with the E being 35.0. Therefore, B cereus WZZ006 performed high‐level ability to produce (S)‐5‐chloro‐1‐oxo‐2,3‐dihydro‐2‐hydroxy‐1H‐indene‐2‐carboxylic acid methyl ester. This study demonstrates a new biocatalytic process route for preparing the indoxacarb chiral intermediates and provides a theoretical basis for the application of new insecticides in agricultural production.     

6‐Methyl 3‐chromonyl 2,4‐thiazolidinedione/2,4‐imidazolidinedione/2‐thioxo‐imidazolidine‐4‐one compounds: novel scavengers of reactive oxygen species

The benefits of antioxidants on human health are usually ascribed to their potential ability to remove reactive oxygen species providing protection against oxidative stress. In this paper the free radicals scavenging activities of nine 6‐methyl 3‐chromonyl derivatives (CMs) were evaluated for the first time by the chemiluminescence, electron paramagnetic resonance, spin trapping and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH^?) methods. The total antioxidant capacity was also measured using a ferric‐ferrozine reagent. Compounds having a hydrogen atom at the N3‐position of the β‐ring were effective in quenching CL resulted from the KO₂/18‐crown‐6‐ether system (a source of superoxide anion radical, ) in a dose‐dependent manner over the range of 0.05–1 mmol/L [IC₅₀ ranged from 0.353 (0.04) to 0.668 (0.05) mmol/L]. The examined compounds exhibited a significant scavenging effect towards hydroxyl radicals (HO^? HO^?), produced by the Fenton reaction, and this ranged from 24.0% to 61.0%, at the concentration of 2.5 mmol/L. Furthermore, the compounds examined were also found to inhibit DPPH^? and this ranged from 51.9% to 97.4% at the same concentration. In addition, the use of the total antioxidant capacity assay confirmed that CM compounds are able to act as reductants. According to the present study, CM compounds showed effective in vitro free radical scavenging activity and may be considered as potential therapeutics to control diseases of oxidative stress‐related etiology. Copyright © 2013 John Wiley & Sons, Ltd.     

Asymmetric Addition of Triethylaluminium to Aromatic Aldehydes Catalyzed by Titanium‐(5,5’‐Biquinoline‐6,6’‐Diol) Complexes

A novel convenient procedure for the resolution of 5,5’‐biquinoline‐6,6’‐diol (BIQOL) was achieved by separating the corresponding diastereomeric mixture of (S)‐(+)‐camphorsulfonates on a semiprepared XDB‐C8 column followed by hydrolysis. The efficient asymmetric addition of triethylaluminium to aromatic aldehydes catalyzed by Ti‐(+)/(–)BIQOL complexes under mild conditions is described. The reactions led to the formation of 1‐arylpropan‐1‐ol in up to 87.5% ee. Chirality 26:268‐271, 2014. © 2014 Wiley Periodicals, Inc.     

A Highly Enantioselective Access to Chiral 1‐(β‐Arylalkyl)‐1H‐1,2,4‐triazole Derivatives as Potential Agricultural Bactericides

A series of chiral 1‐(β‐arylalkyl)‐1H‐1,2,4‐triazole derivatives has been designed as potential antifungal agents. The target triazoles have been synthesized by using a chiral auxiliary as a controlling reagent. All of the compounds were obtained with high ee values, reaching up to 99%. Preliminary bioassay results have revealed that most of the synthesized compounds display significantly higher fungicidal activities against the species Fusarium oxysporium, Rhizoctonia solani, Botrytis cinereapers, Gibberella zeae, Dothiorella gregaria, and Colletotrichum gossypii than the commercial agent triadimefon. Moreover, some of the enantiomers have been found to display significant differences in activity.     

Asymmetric Borane Reduction of Prochiral Ketones Catalyzed By Helical Poly[(S)‐3‐vinyl‐2,2'‐dihydroxy‐1,1'‐binaphthyl]

The application of helical poly[(S)‐3‐vinyl‐2,2'‐dihydroxy‐1, 1'‐binaphthyl] ( L* ) in the asymmetric borane reduction of prochiral ketones was studied. The results showed that L* had excellent catalytic activity as well as enantioselectivity, giving up to 96% yield and up to 99% enantiomeric excess (ee) of the corresponding secondary alcohol at 25 °C. Moreover, L* can be easily recovered and reused without loss of catalytic activity. Chirality 27:422–424, 2015. © 2015 Wiley Periodicals, Inc.     

Enantioselective Synthesis and Antimicrobial Activities of Tetrahydro‐Β‐Carboline Diketopiperazines

A series of single isomers tetrahydro‐β‐carboline diketopiperazines were stereoselectively synthesized starting from l ‐tryptophan methyl ester hydrochloride and six aldehydes through a four‐step reaction including Pictet‐Spengler reaction, crystallization‐induced asymmetric transformations (CIAT), Schotten‐Baumann reaction, and intramolecular ester amidation. The chemical structures were characterized by nuclear magnetic resonance (NMR) and elemental analysis, among which two compounds were determined by x‐ray single crystal diffraction. Moreover, antimicrobial activities of all the compounds were also tested. Chirality 25:656–662, 2013. © 2013 Wiley Periodicals, Inc.     

An efficient and enantioselective Michael addition of aromatic oximes to α,β‐unsaturated aldehydes promoted by a chiral diamine catalyst derived from α,α‐diphenyl prolinol

Chiral diamine catalysts 11a–e derived from α ,α ‐diphenyl prolinol were prepared and successfully applied to the Michael addition of aromatic oximes to α ,β ‐unsaturated aldehydes in mediocre to good yields (up to 78%) and good to high enantioselectivities (up to 93% ee ).     

Engineering Escherichia coli for renewable production of the 5‐carbon polyamide building‐blocks 5‐aminovalerate and glutarate

Through metabolic pathway engineering, novel microbial biocatalysts can be engineered to convert renewable resources into useful chemicals, including monomer building‐blocks for bioplastics production. Here we describe the systematic engineering of Escherichia coli to produce, as individual products, two 5‐carbon polyamide building blocks, namely 5‐aminovalerate (AMV) and glutarate. The modular pathways were derived using “parts” from the natural lysine degradation pathway of Pseudomonas putida KT2440. Endogenous over‐production of the required precursor, lysine, was first achieved through metabolic deregulation of its biosynthesis pathway by introducing feedback resistant mutants of aspartate kinase III and dihydrodipicolinate synthase. Further disruption of native lysine decarboxylase activity (by deleting cadA and ldcC) limited cadaverine by‐product formation, enabling lysine production to 2.25 g/L at a glucose yield of 138 mmol/mol (18% of theoretical). Co‐expression of lysine monooxygenase and 5‐aminovaleramide amidohydrolase (encoded by davBA) then resulted in the production of 0.86 g/L AMV in 48 h. Finally, the additional co‐expression of glutaric semialdehyde dehydrogenase and 5‐aminovalerate aminotransferase (encoded by davDT) led to the production of 0.82 g/L glutarate under the same conditions. At this output, yields on glucose were 71 and 68 mmol/mol for AMV and glutarate (9.5 and 9.1% of theoretical), respectively. These findings further expand the number and diversity of polyamide monomers that can be derived directly from renewable resources. Biotechnol. Bioeng. 2013; 110: 1726–1734. © 2013 Wiley Periodicals, Inc.     

Planar Chiral Iridium Complexes with the Δ‐TRISPHAT Anion: Toward the First Enantiopure o‐Quinone Methide π‐Complex

We describe the resolution of a planar chiral cationic iridium complex [Cp*Ir(η⁵‐2‐methyl‐oxodienyl)][OT f] ( 2 ) following the counterion strategy, where anion metathesis by Δ‐TRISPHAT generates the two diastereomers (pR, pS)‐[Cp*Ir(η⁵‐2‐methyl‐oxodienyl)][Δ‐TRISPHAT] ( 3a , 3a' ). Upon fractional crystallization both compounds were separated as confirmed by ¹H nuclear magnetic resonance (NMR) and circular dichroism studies recorded in solution. The latter represents the key‐complex precursors for the enantioselective synthesis of metallated o‐quinone methide complexes ( 4a , 4a' ). Chirality 25:449–454, 2013. © 2013 Wiley Periodicals, Inc.     

Syntheses and anti‐tubercular activity of β‐substituted and α,β‐disubstituted peptidyl β‐aminoboronates and boronic acids

Tuberculosis is still affecting millions of people worldwide, and new resistant strains of Mycobacterium tuberculosis are being found. It is therefore necessary to find new compounds for treatment. In this paper, we report the synthesis and in vitro testing of peptidyl β‐aminoboronic acids and β‐aminoboronates with anti‐tubercular activity. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.