Simultaneous synthesis of enantiomerically pure (S)-amino acids and (R)-amines using α/ω-aminotransferase coupling reactions with two-liquid phase reaction system

An efficient simultaneous synthesis of enantiopure (S)-amino acids and chiral (R)-amines was achieved using α/ω-aminotransferase (α/ω-AT) coupling reaction with two-liquid phase system. As, among the enzyme components in the α/ω-AT coupling reaction systems, only ω-AT is severely hampered by product inhibition by ketone product, the coupled reaction cannot be carried out above 60 mM substrates. To overcome this problem, a two-liquid phase reaction was chosen, where dioctylphthalate was selected as the solvent based upon biocompatibility, partition coefficient and effect on enzyme activity. Using 100 mM of substrates, the AroAT/ω-AT and the AlaAT/ω-AT coupling reactions asymmetrically synthesized (S)-phenylalanine and (S)-2-aminobutyrate with 93% (>99% ee^S) and 95% (>99% ee^S) of conversion yield, and resolved the racemic α-methylbenzylamine with 56% (95% ee^R) and 54% (96% ee^R) of conversion yield, respectively. Moreover, using 300 mM of 2-oxobutyrate and 300 mM of racemic α-methylbenzylamine as substrates, the coupling reactions yielded 276 mM of (S)-2-aminobutyrate (>99% ee) and 144 mM of (R)-α-methylbenzylamine (>96% ee) in 9 h. Here, most of the reactions take place in the aqueous phase, and acetophenone mainly moved to the organic phase according to its partition coefficient.     

Effects of osmotic pretreatments on oxidative stress, antioxidant profiles and cryopreservation of olive somatic embryos

A three-day pretreatment of olive somatic embryos (SE) with 0.75 M sucrose, combined with cryoprotection (0.5 M DMSO, 1 M sucrose, 0.5 M glycerol and 0.009 M proline) and controlled rate cooling, supported regrowth (as 34.6% fresh weight gain) and resumption of embryo development after cryopreservation. Pretreatment with mannitol or sorbitol did not support regrowth. Profiles of sugars, proline, antioxidant enzymes, Reactive oxygen species (ROS), secondary oxidation products and ethylene were constructed for the most successful (0.75 M) pretreatment series. Sucrose was the optimal pretreatment for supporting recovery, it also elevated glutathione reductase (GR) activity compared to controls, whereas superoxide dismutase (SOD), catalase and guaiacol peroxidase activities remained relatively unchanged. Superoxide dismutase activity was higher in SE pretreated with sucrose, compared with those pretreated with polyols; H₂O₂ was enhanced in SE pretreated with sorbitol and sucrose compared to mannitol. The overall trend for ethylene and OH production revealed their levels were highest in SE pretreated with polyols albeit, for individual treatments this was not always the case. Generally, pretreatments did not significantly change embryo secondary oxidation profiles of ThioBarbituric Acid Reactive Substances (TBARS) and Schiff's bases. In combination these studies suggest oxidative processes may influence regrowth of cryopreserved olive SE and that optimal pretreatments could, in part, increase tolerance by an overall enhancement of endogenous antioxidants (particularly GR), proline and sugars.     

异丙甲草胺及其高效体对我国南方潮土微生物的影响Ⅰ-过氧化氢酶

研究了0、5、20和100 mg·kg^-1浓度的异丙甲草胺及其高效体对土壤过氧化氢酶活性的影响.结果表明,不同浓度的异丙甲草胺处理对过氧化氢酶活性的影响不同,20 mg·kg^-1处理的土壤过氧化氢酶受到激活的程度最大,且一直处于激活状态,5 mg·kg^-1处理的土壤过氧化氢酶在前期受到抑制,后期则100 mg·kg^-1处理的土壤过氧化氢酶受激活较强.不同浓度的金都尔对供试土壤过氧化氢酶活性的影响表现为先激活、后抑制、再激活,并且后期100 mg·kg^-1处理的激活程度最大;5 mg·kg^-1和100 mg·kg^-1处理的异丙甲草胺对供试土壤生态环境的影响和危害可能大于金都尔,但20 mg·kg^-1处理则表现出例外.     

METHODOLOGIES FOR THE STEREOSELECTIVE SYNTHESIS OF ADRENERGIC β-BLOCKERS: AN OVERVIEW

The importance of the adrenergic β-blockers with structure of (S) 1-aryloxy-3-amino-2-propanol in the treatment of different diseases has led the development of a variety of stereoselective synthetic methodologies for this stereoisomer. In this review we present several methodologies to obtain this compound using (i) chiral substrates, (ii) chiral catalysts (organometallic or enzymes) and (iii) preparative chiral chromatography, showing the advantages and disadvantages of each methodology.     

Voltammetric discrimination of mandelic acid enantiomers

We report a novel electrochemical biosensor for direct discrimination of d- and l-mandelic acid (d- and l-MA) in aqueous medium. The glassy carbon electrode (GCE) surface was modified with reduced graphene oxide (rGO) and γ-globulin (GLOB). Electrochemical characterization of the modified electrodes was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode surfaces were also characterized by scanning electron microscopy. Electrochemical response of the prepared electrode (GCE/rGO/GLOB) for discrimination of d- and l-MA enantiomers was investigated by cyclic voltammetry and was compared with bare GCE in the concentration range of 2 to 10 mM. Whereas the bare GCE showed no electrochemical response for the MA enantiomers, the GCE/rGO/GLOB electrode exhibited direct and selective discrimination with different oxidation potential values of 1.47 and 1.71 V and weak reduction peaks at potential values of −1.37 and −1.48 V, respectively. In addition, electrochemical performance of the modified electrode was investigated in mixed solution of d- and l-MA. The results show that the produced electrode can be used as electrochemical chiral biosensor for MA.     

RING-EXPANDED ANALOGUES OF NATURAL OXETANOCIN: (+) AND (−) HYDROXYMETHYL ISODIDEOXYADENOSINE

New enantiomeric isonucleoside analogues related to natural oxetanocin have been synthesized from D-glucosamine and D-glucose. The structures of the target compounds were confirmed by NMR, HRMS, UV, single crystal X-ray, and optical rotation data. Stability studies with respect to purine nucleoside phosphorylase and adenosine deaminase show that these compounds are not substrates. Antiviral results are discussed.     

Use of organic modifiers to enhance chiral selectivity in capillary electrophoresis

Summary Using capillary electrophoresis, the enantiomers of a number of dansyl amino acids were resolved using native-cyclodextrin. The neutral chiral host resolved analytes possessing a negative charge at pH 9, the conditions employed in this study. Organic modifiers added to the running buffer were particularly adept at enhancing chiral recognition between the guest and host molecule in capillary electrophoresis. This work examined the effects of methanol, dimethylformamide, and acetonitrile on the resolution, migration time, and efficiency of twelve dansyl amino acids. Examples are given of the separation of racemic dansyl amino acids utilizing this technique and conditions necessary to achieve enantioselectivity.     

New cyclomaltoheptaose (beta-cyclodextrin) derivative 2-O-(2-hydroxybutyl)cyclomaltoheptaose: preparation and its application for the separation of enantiomers of drugs by capillary electrophoresis

A new soluble cyclomaltoheptaose (cyclodextrin) derivative, 2-O-(2-hydroxybutyl)cyclomaltoheptaose [2-O-(2-hydroxybutyl)-beta-cyclodextrin, 2-HB-beta-CD], was prepared and studied as an efficient chiral selector in the separation of racemic mixtures of drugs by capillary electrophoresis (CE). Results showed that 2-HB-beta-CD could provide higher separating capability than that of beta-CD and the similarly substituted 2-HP-beta-CD.     

Syntheses, structure and properties of chiral copper(II) complexes with end-on azide bridge and chiral-bipyridine ligand

A novel one-dimensional chiral copper(II) complex with single end-on (EO) azide bridge and chiral 2,2-bipyridine ligand, [Cu(N₃)₂(L)]_n (1), and a mononuclear chiral copper(II) complex, [Cu(N₃)₂(L)] (2) (L = (1R)-6,6-dimethyl-5,7-methano-2-(2-pyridinyl)-4,5,6,7-tetrahydroquinoline), have been synthesized and characterized. The crystal structure determination shows that complex 1 is a one-dimensional chiral coordination polymer with non-equivalent Cu-N(azide) bonds, in which the central Cu(II) ion is penta-coordinated in the form of a slightly distorted square-based pyramid. Compound 2 is a four-coordinated mononuclear complex where the Cu(II) ion has a highly distorted tetrahedronal environment. Both complexes 1 and 2 crystallize in the chiral space group: P2₁2₁2₁ and P₁, respectively. The magnetic studies show that there exists antiferromagnetic interaction between the copper(II) ions in complex 1.     

Cyclic and high molecular weight chiral binaphthoxy-phosphazene polymers carrying Br or trimethylsilyl-acetylene groups

The new chiral and functionalized cyclic binaphthoxyphosphazenes R,R,R-[N₃P₃(O₂C₂₀H₁₀Br₂)₃] (R-1), R,R,R-[N₃P₃(O₂C₂₀H₁₀(CCSiMe₃)₂)₃] (R-2), and the high molecular weight linear polymers R/S-[NP(O₂C₂₀H₁₀Br₂)]_n (R/S-3), R-[NP(O₂C₂₀H₁₀Br₂)]_n (R-3), and R-{NP[O₂C₂₀H₁₀(CCSiMe₃)₂]}_n, (R-4), with M_w on the order of 10⁶ and very high T_g, have been synthesized and characterized by IR and NMR spectroscopy. The optically active polymer (R-3) was configurationally stable below 300 °C, but at higher temperatures an atropisomerization process took place that became faster near the glass transition temperature (ca. 350 °C).