Production of (S)-β-Nitro Alcohols by Enantioselective C−C Bond Cleavage with an R-Selective Hydroxynitrile Lyase

Hydroxynitrile lyase (HNL)-catalysed stereoselective synthesis of β-nitro alcohols from aldehydes and nitroalkanes is considered an efficient biocatalytic approach. However, only one S-selective HNL—Hevea brasiliensis (HbHNL)—exists that is appropriate for the synthesis of (S)-β-nitro alcohols from the corresponding aldehydes. Further, synthesis catalysed by HbHNL is limited by low specific activity and moderate yields. We have prepared a number of (S)-β-nitro alcohols, by kinetic resolution with the aid of an R-selective HNL from Arabidopsis thaliana (AtHNL). Optimization of the reaction conditions for AtHNL-catalysed stereoselective C−C bond cleavage of racemic 2-nitro-1-phenylethanol (NPE) produced (S)-NPE (together with benzaldehyde and nitromethane, largely from the R enantiomer) in up to 99 % ee and with 47 % conversion. This is the fastest HNL-catalysed route known so far for the synthesis of a series of (S)-β-nitro alcohols. This approach widens the application of AtHNL for the synthesis not only of (R)- but also of (S)-β-nitro alcohols from the appropriate substrates. Without the need for the discovery of a new enzyme, but rather by use of a retro-Henry approach, it was used to generate a number of (S)-β-nitro alcohols by taking advantage of the substrate selectivity of AtHNL.     

One-Pot Preparation of <Emphasis Type="SmallCaps">d</Emphasis>-Amino Acids Through Biocatalytic Deracemization Using Alanine Dehydrogenase and ω-Transaminase

d-Amino acids are pharmaceutically important building blocks, leading to a great deal of research efforts to develop cost-effective synthetic methods. Preparation of d-amino acids by deracemization has been conceptually attractive owing to facile synthesis of racemic amino acids by Strecker synthesis. Here, we demonstrated biocatalytic deracemization of aliphatic amino acids into d-enantiomers by running cascade reactions; (1) stereoinversion of l-amino acid to a d-form by amino acid dehydrogenase and ω-transaminase and (2) regeneration of NAD⁺ by NADH oxidase. Under the cascade reaction conditions containing 100 mM isopropylamine and 1 mM NAD⁺, complete deracemization of 100 mM dl-alanine was achieved after 24 h with 95% reaction yield of d-alanine (>?99% ee^D, 52% isolation yield).

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Stereodivergent Biocatalytic Formal Reduction of α-Angelica Lactone to (R)- and (S)-γ-Valerolactone in a One-Pot Cascade

The formal asymmetric and stereodivergent enzymatic reduction of α-angelica lactone to both enantiomers of γ-valerolactone was achieved in a one-pot cascade by uniting the promiscuous stereoselective isomerization activity of Old Yellow Enzymes with their native reductase activity. In addition to running the cascade with one enzyme for each catalytic step, a bifunctional isomerase-reductase biocatalyst was designed by fusing two Old Yellow Enzymes, thereby generating an unprecedented case of an artificial enzyme catalyzing the reduction of nonactivated C=C bonds to access (R)-valerolactone in overall 41 % conversion and up to 91 % ee. The enzyme BfOYE4 could be used as single biocatalyst for both steps and delivered (S)-valerolactone in up to 84 % ee and 41 % overall conversion. The reducing equivalents were provided by a nicotinamide recycling system based on formate and formate dehydrogenase, added in a second step. This enzymatic system provides an asymmetric route to valuable chiral building blocks from an abundant bio-based chemical.     

Enantioselective Separation of Racemic Amlodipine by Two-Phase Chiral Extraction Containing O,O′-Dibenzoyl-(2S,3S)-Tartaric Acid as Chiral Selector

A two-phase chiral extraction system containing O,O′-dibenzoyl-(2S,3S)-tartaric acid ((+)-DBTA) in 1-decanol organic phase and aqueous phase was developed for the chiral resolution of amlopidine. The effects of extractant concentration, equilibrium time, and pH of the aqueous phase on the separation performance were investigated. The results indicated that the system afforded a strong chiral separation ability; the (+)-DBTA showed a higher recognition ability toward (S)-amlodipine than the (R)-amlodipine. Upon a single extraction, the enantiomeric excess (%) of (S)-amlodipine could be enriched to 24.27%. The product recovery ratio was 0.74. The distribution ratios for (S)-amlodipine (D _S ), (R)-amlodipine (D _R ) and separation factor (α) were 1.28, 0.78, and 1.64, respectively. Therefore, the pH and concentration of the extractant have the great effects on chiral separation ability. Two-phase chiral extraction has great significance for preparative separation of (S)-amlodipine; it can also be used to design and scale up the enantioselective separation process.     

Oxidation of Aliphatic and Benzylic Alcohols by Oxone®, Catalysed by 12-Tungstocobaltate (II)

$R_1 R_2 CH_2 OH\xrightarrow[{50\% {\text{ }}Aqueous{\text{ }}acetonitrile}]{{[Co^{II} (W_{12} O_{40} )]^{6 - } /Oxone}}R_1 R_2 CHO$ A Keggin-type polyoxometalate (POM) 12-tungstocobaltate (II) ([Co^II(W₁₂O₄₀)]^6?) has been used as a catalyst for the oxidation of aliphatic and benzylic alcohols to the corresponding carbonyl compounds. The reduced (POM) formed in the oxidation of alcohols is re-oxidized by potassium peroxomonopersulphate.     

Enantioselective Extraction of Racemic Mandelic Acid by Di(2‐ethylhexyl) Phosphoric Acid and Tartaric Acid Derivatives as Mixed Complex Chiral Selectors

The distribution behavior of mandelic acid (MA) enantiomers was examined in a two‐phase system containing di(2‐ethylhexyl) phosphoric acid (D2EHPA) with two tartaric acid derivatives as complex chiral selectors in n‐octanol. Factors affecting the extraction were investigated, including the structure and concentration of tartaric acid as well as the concentration of D2EHPA and D,L‐MA. The results showed that both the distribution ratio and enantioselectivity were greatly improved by using a complex chiral selector rather than using the tartaric acid derivative by itself. Finally, it was found that the formation of mixed complex chiral selectors by mixing two tartaric acid derivatives with D2EHPA can improve the capacity of enantioselective extraction.     

Assessing Glycinin (11S) and β-Conglycinin (7S) Fractions of Soybean Storage Protein by Near-Infrared Spectroscopy

Soybean breeding programs underway today are addressing the goal of improving the protein profile to benefit the human diet as well as that of livestock. Glycinin, a globulin storage protein of the meal and designated as the 11S size fraction by ultracentrifugation, is desirable because of its relative abundance of sulfur-containing amino acids, such as methionine and cysteine. The current study examined the feasibility of near-infrared (NIR) measurement of glycinin and the other prevalent protein fraction, β-conglycinin (7S size fraction), as well as the electrophoretically separable sub fractions that comprise these two components. From a population of 101 F₆-derived recombinant inbred lines in a field replicated trial, single whole soybeans were scanned in transmittance (800–1,798 nm, 24 beans/sample × 197 samples total). Additional scanning of the ground meal was performed in reflectance (1,100–2,498 nm). Partial least squares (PLS) calibrations were developed, using the 24-bean average log(1/T) spectrum for each sample, as well as the average spectrum from duplicate packs of log(1/R) spectra of the meal. The results indicate that NIR prediction of 11S and 7S, as well as the sub fractions thereof, is at best limited to screening purposes in soybean breeding programs for probable reasons of an inherent lack of spectral specificity of the protein fractions and a non-constant proportion of soluble-to-total protein.

Quantitative trait loci for β-conglycinin (7S) and glycinin (11S) fractions of soybean storage protein

Glycinin (11S) and β-conglycinin (7S) are important seed storage proteins in soybean [Glycine max (L.) Merr.]. A major limitation of soybean seed storage proteins is their low levels of the sulfur-containing amino acids, methionine and cysteine, which are important nutritional components of protein mea. Glycinin contains significantly more S-containing amino acids than does β-conglycinin. Thus, detection of quantitative trait loci (QTL) that govern 11S may provide marker-assisted selection (MAS) opportunities to improve soybean total S-containing amino acids. The objective of this study was to detect and map QTL governing 7S and 11S fractions of soybean seed storage proteins. To achieve this objective, 101 F₆-derived recombinant inbred lines (RIL) developed from a cross of N87-984-16 ×TN93-99 were used. Storage proteins were extracted from all RIL and separated in 10–20% linear gradient polyacrylamide gels. Dried gels were scanned for individual subunits of storage protein with a densitometer equipped with a He−Ne laser light source. Data were converted to concentration for each subunit component and analyzed using SAS software. A significant (P<0.05) difference among genotypes was found for glycinin and β-conglycinin. A total of 94 polymorphic simple sequence repeat molecular genetic markers were used in screening all RIL. Three QTL for glycinin (Satt461, Satt292, and Satt156) were distributed on linkage group (LG) D2, I, and L, respectively, whereas two QTL for conglycinin (Satt461 and Satt249) were distributed on LG D2 and J. Phenotypic variation explained by individual QTL ranged from 9.5 to 22%. These QTL may provide useful MAS opportunities for improvement of nutritional quality in soybean.     

Molecular dynamics simulations of α- to β-poly(vinylidene fluoride) phase change by stretching and poling

The mechanism of inducing a phase change from α-poly(vinylidene fluoride) (α-PVDF) to β-PVDF is addressed using molecular dynamics simulations based on a molecular mechanics force field. The effect of applying a strain to the α-PVDF crystal along the axis of the molecules is investigated, as well as poling the crystal before or after stretching. Rather large (at least 10¹⁰ V/m) electric fields that are perpendicular to the axis of the PVDF molecules are required to induce α- to β-PVDF phase change when no strain is applied to the α-PVDF crystal. However, at a strain of 1.0475 (i.e., when the crystal is stretched by 4.75%) α-PVDF changes to a β-PVDF like structure, where the β-PVDF molecules orientate anti-parallel relative to each other. Transformation of the anti-parallel β-PVDF to β-PVDF can be induced by poling (even at the lowest electric field of 10⁵ V/m studied here) or by thermal annealing.     

The synthesis of a homochiral methacrylate macromonomer by polymerisation of (R)- or (S)-methyl β-hydroxyisobutyrate

Summary Polymerisations of either enantiomer of commercially available methyl -hydroxyisobutyrates 1a and 1b were carried out. Ti(OBuⁿ)₄ catalysed transesterification of the neat monomer generated either polymer 3 at lower temperatures (100°C) or homochiral macromonomer 2 at higher temperatures. Under optimal conditions for the preparation of the macromonomer 2, a soluble material (Mn 3600, Mw 7000) was produced which displayed high crystallinity as judged by X-ray powder diffraction analysis.     

Transformation of β-damascone to (+)-(S)-4-hydroxy-β-damascone by fungal strains and its evaluation as a potential insecticide against aphids Myzus persicae and lesser mealworm Alphitobius diaperinus Panzer

Microbial conversion of β-damascone (1) into 4-hydroxy-β-damascone (2) was studied. The results showed the potential of the tested biocatalysts for the regio- and enantioselective hydroxylation of substrate 1. The highest enantioselectivity was exhibited by strain Mortierella isabellina AM212. β-Damascone (1) was a relatively good deterrent towards Alphitobius diaperinus and it was behaviorally inactive to Myzus persicae. The racemic compound 2 and its (+)-(S)-enantiomer were stronger antifeedants against A. diaperinus than β-damascone (1), in the case of M. persicae only (+)-(S)-(2) exhibited the deterrent properties.     

A Simple and Highly Selective Biomimetic Oxidation of Alcohols with Hypervalent Iodine(III) Reagent Catalyzed by β-Cyclodextrin in Water

Abstract  

A simple, mild and highly efficient biomimetic oxidation of alcohols to the corresponding aldehydes or ketones with hypervalent iodine(III) reagent catalyzed by β-cyclodextrin was reported. β-cyclodextrin serves as a biological catalyst to enhance the reaction remarkably. The oxidation proceeded in water to afford aldehydes or ketones in excellent yields and high selectivity without remarkable over-oxidation to carboxylic acids. Selective oxidation of primary alcohols in the presence of secondary alcohols was also achieved. A possible mechanism for the oxidation was proposed.     

Stereospecific formation of a ternary complex of (S)-α,β-fluoromethylene-dATP with DNA pol β

The influence of water: crystallization of (R/S)-α,β-CHF-dATP with the preorganized pol β-DNA complex shows that (S)-α,β-CHF-dATP is preferentially bound to the active site with the C=F fluorine proximal to a structural water bound to Asp276.     

Selective Photo-epoxidation of (R)-(+)- and (S)-(−)-Limonene by Chiral and Non-Chiral Dioxo-Mo(VI) Complexes Anchored on TiO2-Nanotubes

Topics in Catalysis - Selective epoxidation of the (R) and (S) isomers of limonene by dioxomolybdenum(VI) complexes anchored covalently on TiO2 nanotubes using UV–Vis light and O2 as the...     

Oxidation of α- and β-pinene catalyzed by MnIII (Salen) Cl·H2O

The cationic complex Mn^III (Salen) is a very effective catalyst for the oxidation of both- and-pinene. The higher selectivity towards epoxide formation supports the rebound oxygen mechanism. A turnover of 40 was obtained for both compounds after 16 h of reaction with a molar ratio 10.011 (feedstock: catalyst: iodosobenzene) and conversions between 50 and 60% were observed. A very high selectivity (55%) was determined for epoxide formation from -pinene. The good selectivity observed for myrtanal isomers (6.5 and 23.2%) from-pinene is related to the prior formation of the 1,2-epoxides.     

Synthesis of stereoisomers of 6β- and 7β-(benzylthio)-3-(p-tolyl) tropane-2-carboxylic acid methyl ester

To develop new ^99mTc-labelled agents to evaluate dopamine transporters (DAT) involved in Parkinson's disease, by in vivo SPECT imaging, we have synthesized six new sulfur-containing ligands with the tropane skeleton. We have introduced the complexing sulfur atom far from the three sites of recognition by DAT of these tropane derivatives. The 6β-substituted tropinone has been obtained by a double Mannich condensation followed by the introduction of the moieties for molecular interactions at the binding site on C2 and C3, leading to the six stereoisomers.     

Measurement and Correlation for Solubility of (S)-(+)-2,2-Dimethyl-cyclopropane Carbox Amide in Different Solvents

1 INTRODUCTION (S)-(+)-2,2-dimethylcyclopropane carbox amide [(+)-DMCPCA, Fig.1] is a key intermediate of Cilas- tatin, an inhibitor of dehydropeptidase-I. As the syner- gist of imipenem (an antibiotic drug), cilastatin is widely used in clinical applications and has prosper- ous prospects[1]. In industrial manufacture[2―6], as the optical intermediate, the chemical and optical purity of (+)-DMCPCA would affect the quality of cilastatin. So, the separation and purification are impo…     

Oxidation of catechol catalyzed by β-cyclodextrin-Cu(Ⅱ) complexes and its reaction kinetics

以β-环糊精(β-CD)作为骨架,经磺酰化反应、卤代反应和与L-组氨酸的亲核取代反应,得到了两种β-环糊精-组氨酸衍生物配体,再将配体与Cu(Ⅱ)配位,合成了具有多酚氧化酶催化活性的β-环糊精-Cu(Ⅱ)配合物。采用元素分析、傅里叶变换红外光谱、核磁共振波谱和原子吸收光谱等方法对配体和配合物的结构进行了表征。以O₂为氧化剂,用分光光度法测定了它们催化邻苯二酚氧化反应的性能,并考察了反应温度、pH值等因素对催化反应速率的影响。结果表明：β-环糊精-Cu(Ⅱ)配合物具有良好的催化性能;C-2位修饰得到的环糊精类金属衍生物因为活性基团与反应中心之间相对位置适宜,表现出较大的加速效果;反应动力学表明组胺基配位Cu(Ⅱ) 、β- CD疏水空腔和碱催化作用是反应加速的3个因素。