3,4-Bisthiolated Pyrroles: Concise Construction and Their Electronic Properties.

3,4-Bisthiolated pyrroles constitute key cores in pyrrole-based semiconductors, and their electronic properties could be improved by the bisthio groups via the S-effect. Herein, a convenient method for the synthesis of 3,4-bisthiolated pyrroles has been developed through the AlCl3-catalyzed thiolation/cyclization of homopropargylic azides, and cyclic voltammetry and DFT calculations indicated that the desired 3,4-bisthiolated pyrroles had higher HOMO orbital energies and lower band gaps than the parent unsubstituted 2,5-diphenylpyrrole.

Divergent Synthesis of Fluorinated Alkenes, Allenes, and Enynes via Reaction of 2-Trifluoromethyl-1,3-enynes with Carbon Nucleophiles.

Herein, inorganic base K3PO4 promoted divergent synthesis of CF3-substituted allenes, cyclopentenes, alkynes, and fluorinated enynes via regioselective nucleophilic addition of carbon nucleophiles to 2-trifluoromethyl-1,3-enynes was developed. With the choice of different carbon nucleophiles, various fluorinated compounds could be obtained under K3PO4/DMF reaction system. When malononitriles were used as nucleophiles, CF3-substituted allenes, cyclopentenes, and alkynes could be obtained, respectively. By using 1,3-dicarbonyl compounds as nucleophiles, ring-monofluorinated 4H-pyrans could be prepared, and 1,1-difluoro-1,3-enynes could be furnished with the participation of diethyl malonate. Moreover, these five kinds of fluorinated allenes, alkenes, and enynes are valuable building blocks.

Enantioselective Cascade Biocatalysis for Deracemization of Racemic ß-Amino Alcohols to Enantiopure (S)-ß-Amino Alcohols by Employing Cyclohexylamine Oxidase and ω-Transaminase.

Optically active ß-amino alcohols are very useful chiral intermediates frequently used in the preparation of pharmaceutically active substances. Here, a novel cyclohexylamine oxidase (ArCHAO) was identified from the genome sequence of Arthrobacter sp. TYUT010-15 with the R-stereoselective deamination activity of ß-amino alcohol. ArCHAO was cloned and successfully expressed in E. coli BL21, purified and characterized. Substrate-specific analysis revealed that ArCHAO has high activity (4.15 to 6.34 U mg-1 protein) and excellent enantioselectivity toward the tested ß-amino alcohols. By using purified ArCHAO, a wide range of racemic ß-amino alcohols were resolved, (S)-ß-amino alcohols were obtained in >99 % ee. Deracemization of racemic ß-amino alcohols was conducted by ArCHAO-catalyzed enantioselective deamination and transaminase-catalyzed enantioselective amination to afford (S)-ß-amino alcohols in excellent conversion (78-94 %) and enantiomeric excess (>99 %). Preparative-scale deracemization was carried out with 50 mM (6.859 g L-1 ) racemic 2-amino-2-phenylethanol, (S)-2-amino-2-phenylethanol was obtained in 75 % isolated yield and >99 % ee.

High throughput solid-phase screening of bacteria with cyclic amino alcohol deamination activity for enantioselective synthesis of chiral cyclic ß-amino alcohols.

OBJECTIVES: To screening of bacteria with cyclic amino alcohol deamination activity for enantioselective synthesis of chiral cyclic ß-amino alcohols. RESULTS: A new strain named Arthrobacter sp. TYUT010-15 with the (R)-selective deamination activity of cyclic ß-amino alcohol has been isolated from nature via a high throughput solid-phase screening method. The reaction conditions of TYUT010-15 were optimized. Using the resting cell of TYUT010-15 as the catalyst, kinetic resolution of trans-2-aminocyclopentanol, trans-2-aminocyclohexanol and cis-1-amino-2-indanol was carried out to afford (1S, 2S)-trans-2-aminocyclopentanol, (1S, 2S)-trans-2-aminocyclohexanol and (1R, 2S)-cis-1-amino-2-indanol in > 99% ee and 49.6-50% conversion. Four aromatic ß-amino alcohols and two amines were also resolved, (S)-ß-amino alcohols and (R)-amines were obtained in > 99% ee. Preparation experiment was conducted with 200 mM (23.2 g L-1) racemic trans-2-aminocyclohexanol, yielding the desired (1S, 2S)-trans-2-aminocyclohexanol in 40% isolated yield, > 99% ee and 5.8 g L-1 d-1 space time yields. CONCLUSIONS: This study provides a high throughput solid-phase method for screening of bacteria with cyclic amino alcohol deamination activity and a first example for practical preparation of chiral cyclic ß-amino alcohol by Arthrobacter sp. TYUT010-15.

Synthesis of 4-Sulfenyl Isoxazoles through AlCl3-Mediated Electrophilic Cyclization and Sulfenylation of 2-Alkyn-1-one O-Methyloximes.

An efficient method for the synthesis of 4-sulfenyl isoxazoles has been developed via AlCl3-mediated electrophilic cyclization/sulfenylation of 2-alkyn-1-one O-methyloximes. Remarkably, N-arylsulfanylsuccinimides are employed as electrophiles for the construction of 4-arylsulfanyl isoxazoles, and 4-alkylsulfanyl isoxazoles are accessed with dialkyl disulfides as electrophiles.

Copper(II)-Catalyzed Four-Component Oxysulfonylation/Diazenylation: Synthesis of α-Arylhydrazo-ß-keto Sulfones.

A new and convenient method for one-pot synthesis of α-arylhydrazo-ß-keto sulfones is developed via Cu (II)-catalyzed oxysulfonylation/diazenylation of alkenes. This four-component cascade reaction enables a series of α-arylhydrazo-ß-keto sulfone derivatives accessed from readily available alkenes, sulfinates, and diazonium salts under aerobic conditions. Furthermore, the 3-sulfonyl cinnolin-4(1 H)-one skeleton is successfully constructed from the corresponding α-arylhydrazo-ß-keto sulfone product under basic conditions.

One pot simultaneous preparation of both enantiomer of ß-amino alcohol and vicinal diol via cascade biocatalysis.

OBJECTIVES: To investigate the efficiency of a new cascade biocatalysis system for the conversion of R, S-ß-amino alcohols to enantiopure vicinal diol and ß-amino alcohol. RESULTS: An efficient cascade biocatalysis was achieved by combination of a transaminase, a carbonyl reductase and a cofactor regeneration system. An ee value of > 99% for 2-amino-2-phenylethanol and 1-phenyl-1, 2-ethanediol were simultaneously obtained with 50% conversion from R, S-2-amino-2-phenylethanol. The generality of the cascade biocatalysis was further demonstrated with the whole-cell approaches to convert 10-60 mM R, S-ß-amino alcohol to (R)- and (S)-diol and (R)- and (S)-ß-amino alcohol in 90-99% ee with 50-52% conversion. Preparative biotransformation was demonstrated at a 50 ml scale with mixed recombinant cells to give both (R)- and (S)-2-amino-2-phenylethanol and (R)- and (S)-1-phenyl-1, 2-ethanediol in > 99% ee and 40-42% isolated yield from racemic 2-amino-2-phenylethanol. CONCLUSIONS: This cascade biocatalysis system provides a new practical method for the simultaneous synthesis of optically pure vicinal diol and an ß-amino alcohol.

A high-throughput microtiter plate assay for the discovery of active and enantioselective amino alcohol-specific transaminases.

Chiral vicinal amino alcohols are important chiral building blocks and intermediates in the pharmaceutical industry. The transaminase (TAm) catalyzed kinetic resolution of racemic amino alcohols provides a straightforward approach to access these important compounds. This study describes the development of a novel microtiter plate assay to screen vicinal amino alcohol-specific TAms using a tetrazolium red-based colorimetric assay to monitor the rate of α-hydroxy ketone formation at 510 nm. This approach is the first to determine the Michaelis-Menten parameters for a recombinant TAm (PpbauA) from Pseudomonas putida NBRC14164. The corresponding Vmax and KM values for both enantiomers of 2-amino-1-propanol and 2-amino-1-butanol were obtained, and the calculated kinetic E-factors of PpbauA toward 2-amino-1-propanol and 2-amino-1-butanol are 3 (S) and 6 (R), respectively. The method is sensitive and exhibits low level background coloration. Moreover, this method can be used to detect transaminase activity and enantioselectivity toward amino alcohols in a high-throughput format. Additionally, this simple method is compatible with the most widely used (R)- and (S)-selective transaminases and may be a broadly applicable tool for screening transaminases from a transaminase mutant library.

AlCl3-Catalyzed Intramolecular Cyclization of N-Arylpropynamides with N-Sulfanylsuccinimides: Divergent Synthesis of 3-Sulfenyl Quinolin-2-ones and Azaspiro[4,5]trienones.

Switchable ortho/ipso-cyclization of N-arylpropynamides induced with N-sulfanylsuccinimides as general sulfur reagents is reported. In the presence of MeOH, para-fluoro N-arylpropynamides exclusively undergo the ipso-cyclization to give 3-sulfenyl azaspiro[4,5]trienones. Two kinds of bioactive heterocycles, benzothieno-[3,2-b]quinoline and -[2,3-c]quinolone, have been directly and efficiently prepared from the corresponding sulfenylated products.

Intermolecular sulfenoamination of alkenes with sulfonamides and N-sulfanylsuccinimides to access ß-sulfonylamino sulfides and dihydrobenzothiazines.

An acid-catalyzed intermolecular sulfenoamination reaction of alkenes is developed with sulfonamides as the nitrogen source and N-sulfanylsuccinimides as the sulfur source. This methodology provides a straightforward and general way to synthesize various ß-sulfonylamino sulfides with high regio- and diastereoselectivity. The developed method was coupled with intramolecular C-N coupling in a one-pot procedure to afford a series of dihydrobenzothiazine derivatives, a kind of important heterocycle used as biologically active compounds in medicinal chemistry.

Synthesis of 3-Sulfenylated Coumarins: BF3·Et2O-Mediated Electrophilic Cyclization of Aryl Alkynoates Using N-Sulfanylsuccinimides.

A simple and efficient metal-free sulfenylation/cyclization of aryl alkynoates has been developed, obtaining various 3-sulfenylated coumarins in moderate to excellent yields. In the presence of BF3·Et2O, the stable and readily accessible N-sulfanylsuccinimides were employed as electrophiles to induce the 6-endo-dig electrophilic cyclization of alkynoates. The reaction using substrates bearing a methoxy group on the phenoxy ring proceeded in an exclusively distinct pathway via either ipso sulfenylcyclization or sulfenylation of the phenoxy ring depending on the different locations of the methoxy substituent. The resulting 3-sulfenylated coumarins can be readily transformed to 3-sulfinylated or 3-sulfonylated coumarins under different oxidation conditions.

Cloning and characterization of two distinct water-forming NADH oxidases from Lactobacillus pentosus for the regeneration of NAD.

Two uncharacterized nicotinamide adenine dinucleotide (NADH) oxidases (named as LpNox1, LpNox2) from Lactobacillus pentosus ATCC 8041 were cloned and overexpressed in Escherichia coli BL21 (DE3). The sequence analysis revealed that the two enzymes are water-forming Noxs with 64 % and 52 % identity to LbNox from Lactobacillus brevis DSM 20054. The optimal pH and temperature of the purified LpNox1 and LpNox2 were 7.0 and 8.0 and 35 and 40 °C, respectively, with K M of 99.0 µM (LpNox1) and 27.6 µM (LpNox2), and yielding catalytic efficiency k cat/K M of 1.0 and 0.2 µM(-1) s(-1), respectively. Heat inactivation studies revealed that the two enzymes are relatively instable. The application of LpNox1 for the regeneration of NAD(+) was demonstrated by coupling with a glycerol dehydrogenase-catalyzed oxidation of glycerol to 1,3-dihydroxyacetone. The characteristics of the LpNox1 could prove to be of interest in industrial application such as NAD(+) regeneration in dehydrogenase-catalyzed oxidations.

N-Vinylthio Phthalimides (N-VTPs): Modular Reagents for Vinylthio AIEgen Transfer.

Novel sulfur reagents N-vinylthio phthalimides (N-VTPs) have been employed as modular reagents for vinylthiolation, enabling the construction of aggregation-induced emission (AIE)-active tetraaryldivinyl sulfides (TADVSs) and diarylvinyl sulfides (DAVSs). Notably, TADVSs with sulfur insertion to ethene stators are reported as AIE luminogens (AIEgens) for the first time, and the corresponding photophysical properties and aggregated confirmation have been detailed for the demonstration of the AIE effect. A water-soluble TADVS with a quinolinium salt was prepared for cell imaging.

Suzuki-Miyaura cross-couplings of arenediazonium tetrafluoroborate salts with arylboronic acids catalyzed by aluminium hydroxide-supported palladium nanoparticles.

Suzuki-Miyaura cross-couplings of arenediazonium salts with arylboronic acids catalyzed by highly active aluminium hydroxide-supported palladium nanoparticles catalyst have been investigated for the first time. The reactions are performed at 25 °C in MeOH without any base and ligand to afford biaryls in good to excellent yields under non-anhydrous and non-degassed conditions.

N-Thiohydroxy Succinimide Esters (NTSEs): Versatile Reagents for Selective Acyl and Acylthio Transfer.

Differentiation between similarly reactive sites in molecules represents an ongoing challenge of organic synthesis. Herein we described one kind of versatile reagents, N-thiohydroxy succinimide esters (NTSEs), serving as both acyl and acylthio surrogates for the diverse synthesis of ketones, thioesters, amides, and acyl disulfides by selective cleavage of similarly reactive C-S and N-S bonds.

3-Thiolated pyrroles/pyrrolines: controllable synthesis and usage for the construction of thiolated fluorophores.

Thiolation/cyclization of homopropargylic tosylamides allowed the selective synthesis of 3-thiolated pyrroles and pyrrolines controlled by solvents. Moreover, the desired 3-thiolated pyrroles were readily transformed to organic fluorophores benzothienopyrrole and bisthiolated boron dipyrromethene (S-BODIPY).

N-Alkynylthio Phthalimide: A Shelf-Stable Alkynylthio Transfer Reagent for the Synthesis of Alkynyl Thioethers.

A new kind of electrophilic alkynylthiolating reagent, called N-alkynylthio phthalimide, is designed and synthesized herein. This electrophilic sulfenylating reagent can be easily prepared in three steps from commercially available phthalimide and corresponding silver acetylide. Furthermore, the N-alkynylthio phthalimides are demonstrated to be efficient alkynylthio transfer reagents that can react with various C-nucleophiles, including ß-ketoesters, aryl boronic acids, and Grignard reagents to afford a diverse range of alkynyl thioethers under mild conditions.

Enantioselective synthesis of enantiopure ß-amino alcohols via kinetic resolution and asymmetric reductive amination by a robust transaminase from Mycobacterium vanbaalenii.

Chiral ß-amino alcohols are very important chiral building block for preparing bioactive compounds for use in pharmaceutical and fine chemical industries. Synthesis of chiral ß-amino alcohols by transaminase is big challenging due to the strict substrate specificities and very low activity of the enzyme. In this work, a (R)-selective ω-transaminase (MVTA) from Mycobacterium vanbaalenii was employed as a biocatalyst for the first time for the synthesis of chiral ß-amino alcohol via kinetic resolution and asymmetric reductive amination. The enzyme was purified and characterized. Kinetic resolution of a set of racemic ß-amino alcohols including two cyclic ß-amino alcohols by MVTA was demonstrated, affording (R)-ß-amino alcohols, (1S, 2S)-trans-2-aminocyclopentanol and (1R, 2S)-cis-1-amino-2-indanols in >99% ee and 50-62% conversion. Asymmetric reductive amination of three α-hydroxy ketones (10-300 mM) by MVTA was conducted, (S)-ß-amino alcohols were obtained with >99% ee and 80-99% conversion. Preparation experiment for the reductive amination of 200 mM 2-hydroxyacetophenone by the resting cells of recombinant E. coli (MVTA) was proceeded smoothly and product (S)-2-amino-2-phenylethanol was obtained with 71% isolated yield, >99% ee and 68.6 g/L/d volumetric productivity. The current research proved that the MVTA is a robust enzyme for the preparation of chiral ß-amino alcohol with high volumetric productivity.

Highly efficient bioreduction of 2-hydroxyacetophenone to (S)- and (R)-1-phenyl-1,2-ethanediol by two substrate tolerance carbonyl reductases with cofactor regeneration.

Optically pure 1-phenyl-1,2-ethanediol is a very important chiral building block and intermediate in fine chemical and pharmaceutical industries. Reduction of 2-hydroxyacetophenone provides a straightforward approach to access these important compounds. In this study, two enantiocomplementary carbonyl reductases, BDHA (2,3-butanediol dehydrogenase from Bacillus subtilis) and GoSCR (polyol dehydrogenase from Gluconobacter oxydans) were discovered for the first time to convert 2-hydroxyacetophenone (2-HAP) to (R)-1-phenyl-1,2-ethanediol ((R)-PED) and (S)-1-phenyl-1,2-ethanediol ((S)-PED) with excellent stereochemical selectivity, respectively. The two enzymes were purified and characterized. In vitro bioreduction of 2-HAP catalyzed by BDHA and GoSCR coupled with glucose dehydrogenase (GDH) from Bacillus subtilis for cofactor regeneration were demonstrated, affording both (R)-PED and (S)-PED in>99% ee and 99% conversion. Recombinant Escherichia coli whole cells co-expressing both GDH and BDHA or GoSCR genes were used to asymmetric reduction of 2-HAP to (R)-PED or (S)-PED. Under the optimized conditions, the bioreduction of 400mM (54g/L) substrate was proceeded smoothly without the external addition of cofactor, and the product (R)-PED and (S)-PED were obtained with 99% yield, >99% ee and 18.0g/L/h volumetric productivity. These results offer a practical biocatalytic method for the preparation of both (R)-PED and (S)-PED with high volumetric productivity.

Characterization of Four New Distinct ω-Transaminases from Pseudomonas putida NBRC 14164 for Kinetic Resolution of Racemic Amines and Amino Alcohols.

Four uncharacterized ω-transaminases (ωTAs) from Pseudomonas putida NBRC 14164 have been identified and cloned from the pool of fully sequenced genomes. The genes were functionally expressed in Escherichia coli BL21, and the enzymes were purified and characterized. Four TAs showed highly (S)-selective ωTA activity and converted (S)-α-methylbenzylamine and pyruvate to acetophenone and L-Ala. The maximum activity of cloned enzymes was in the pH range of 8.0-8.5 (Pp36420), 8.5-9.5 (Pp21050), 9.0-9.5 (PpspuC), and 9.5-10.5 (PpbauA), and the optimal temperatures were at 35 °C (Pp36420, Pp21050, and PpspuC) and 50 °C (PpbauA), respectively, with K M of 161.3 mM (Pp21050), 136.7 mM (PpbauA), 398.5 mM (Pp36420), and 130.9 mM (PpspuC) and yielding a catalytic efficiency k cat/K M of 0.015, 0.003, 0.012, and 0.023 mM-1 s-1. Several racemic amines and amino alcohols were resolved by the cloned ωTAs; perfect conversions (48-50 %) were obtained by at least one enzyme, and the residual substrates were left with 97-99 % ee. Kinetic resolution of racemic phenylglycinol was done with PpspuC in a 100-mL scale. Enaniomeric excess of (S)-phenylglycinol reached 99 % with 45 % isolated yield. The high enantioselectivity and large substrate spectra of the cloned PpTAs showed an attractive potency for biotechnology application in production of chiral amines and amino alcohols.