Stereoselective Interaction between DNA and Stable Chiral Surfaces Modified with 1,2‐Diphenylethylenediamine Enantiomers

This work described an interesting phenomenon of the stereoselective adsorption behaviors of DNA on stable chiral surfaces which were modified with 1,2‐diphenylethylenediamine enantiomers on gold electrodes. The modification process and electrochemical characterization of the chiral surfaces were measured by cyclic voltammetry (CV). The stereoselective adsorption behaviors of DNA on the two chiral surfaces were investigated via atomic force microscopy (AFM), CV, electrochemical impedance spectroscopy (EIS) and quartz crystal microbalance (QCM). All results confirmed that (1R,2R)‐1,2‐diphenylethylenediamine modified surface had stronger interaction with DNA molecules than (1S,2S)‐1,2‐diphenylethylenediamine modified surface, and the chirality of the surfaces created an different effect on the morphology and adsorption quantity of DNA.     

基于杯[4]芳烃的对N-乙酰基-天冬氨酸盐对映选择性识别的荧光传感器

合成了携带有丹磺酰基荧光团和（1R,2R）- 或（1S,2S）-1,2-二苯基乙二胺键合单元的双臂杯[4]芳烃手性阴离子受体（1和2）。通过荧光光谱检测了受体对手性氨基酸阴离子的键和能力。非线型曲线拟合的结果表明受体（1或2）与N-乙酰基-L或D－天冬氨酸盐通过多重氢键的相互作用形成了1：1的络合物。并且展现了对N-乙酰基天冬氨酸盐对映体良好的对映选择性的荧光识别（受体1： K_ass(D)/ K_ass(L)=6.74;受体2： K_ass(L)/ K_{ass (D)}=6.48）。明显不同的荧光响应说明受体1和2能被用作为对N-乙酰基天冬氨酸盐的荧光化学传感器。     

Catalytic asymmetric 1,2‐Addition/Lactonization tandem reactions for the syntheses of chiral 3‐Substituted phthalides using organozinc reagents

Using chiral phosphoramide ligand 2d‐ Zn (II) complex derived from (1R,2R)‐1,2‐diphenylethylenediamine as the catalyst, we have developed efficient catalytic asymmetric 1,2‐addition/lactonization tandem reactions of diverse organozinc reagents with varied methyl 2‐formylbenzoates for the construction of optically enriched 3‐aryl or alkyl substituted phthalides, which are significant building blocks of many important chiral pharmaceuticals and natural products. The corresponding products could be afforded with good to excellent yields (up to 95%) and moderate to good enantioselectivities (up to 89%).     

Comparison of HPLC enantioseparation of substituted binaphthyls on CD‐, polysaccharide‐ and synthetic polymer‐based chiral stationary phases

Retention and enantioseparation behavior of ten 2,2′‐disubstituted or 2,3,2′‐trisubstituted 1,1′‐binaphthyls and 8,3′‐disubstituted 1,2′‐binaphthyls, which are used as catalysts in asymmetric synthesis, was investigated on eight chiral stationary phases (CSPs) based on β‐CD, polysaccharides (tris(3,5‐dimethylphenylcarbamate) cellulose or amylose CSPs) and new synthetic polymers (trans‐1,2‐diamino‐cyclohexane, trans‐1,2‐diphenylethylenediamine and trans‐9,10‐dihydro‐9,10‐ethanoanthracene‐(11S,12S)‐11,12‐dicarboxylic acid CSPs). Normal‐, reversed‐phase and polar‐organic separation modes were employed. The effect of the mobile phase composition was examined. The enantiomeric separation of binaphthyl derivatives, which possess quite similar structures, was possible in different enantioselective environments. The substituents and their positions on the binaphthyl skeleton affect their properties and, as a consequence, the separation system suitable for their enantioseparation. In general, the presence of ionizable groups on the binaphthyl skeleton, substitution with non‐identical groups and a chiral axis in the 1,2′ position had the greatest impact on the enantiomeric discrimination. The 8,3′‐disubstituted 1,2′‐binaphthyl derivatives were the most easily separated compounds in several separation systems. From all the chiral stationary phases tested, cellulose‐based columns were shown to be the most convenient for enantioseparation of the studied analytes. However, the polymeric CSPs with their complementary behavior provided good enantioselective environments for some derivatives that could be hardly separated in any other chromatographic system.     

Biomolecule‐Doped Organic/Inorganic Hybrid Nanocomposite Film for Label‐Free Electrochemical Immunoassay of α‐1‐Fetoprotein

A new electrochemical immunosensor for the detection of α‐1‐fetoprotien (AFP) was developed based on AFP antibody (anti‐AFP)‐functionalized organic/inorganic hybrid nanocomposite membrane. To fabricate such a hybrid composite membrane, 3,4,9,10‐perylenetetracarboxylic acid‐bound thionine molecules (PTCTH) were initially doped into titania colloids (TiO₂), and then gold nanoparticles and anti‐AFP were immobilized onto the composite film in turn. Comparison with the electrode fabricated only with thionine not 3,4,9,10‐perylenetetracarboxylic acid, the immunosensor with PTCTH exhibited high sensitivity and fast electron transfer. The presence of gold nanoparticles provided a good microenvironment for the immobilization of biomolecules, enhanced the surface coverage of protein, and improved the sensitivity of the immunosensor. The modified process was characterized by scanning electron microscope (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The surface topography of the membrane was investigated by scanning electron microscopy (SEM). Under optimal conditions, the proposed immunosensor exhibited a wide linear range from 2.5 to 200.0 ng/mL towards AFP with a detection limit of 0.5 ng/mL (S/N=3). The stability, reproducibility and precision of the immunosensor were acceptable. Comparison with the conventional enzyme‐linked immunosorbent assay (ELISA), the present method did not require more labeled procedures and washing steps. Significantly, the detection methodology provides a promising approach for other proteins or biosecurities.     

New Route to Stabilize Ruthenium Nanoparticles with Non‐Isolable Chiral N‐Heterocyclic Carbenes

Ru nanoparticles (RuNPs) stabilized by non‐isolable chiral N‐heterocyclic carbenes (NHCs), namely SIDPhNp ((4S,5S)‐1,3‐di(naphthalen‐1‐yl)‐4,5‐diphenylimidazolidine) and SIPhOH ((S)‐3‐((1S,2R)‐2‐hydroxy‐1,2‐diphenylethyl)‐1‐((R)‐2‐hydroxy‐1,2‐diphenylethyl)‐4,5‐dihydro‐3H‐imidazoline), have been synthesized through a new procedure that does not require isolation of the free carbenes. The obtained RuNPs have been characterized by state‐of‐the‐art techniques and their surface chemistry has been investigated by FTIR and solid‐state MAS NMR upon the coordination of CO, which indicated the presence of free and reactive Ru sites. Their catalytic activity has been tested in various hydrogenation reactions involving competition between different sites, whereby interesting differences in selectivity were observed, but no enantioselectivity.     

Preparative enantioseparation of loxoprofen precursor by recycling countercurrent chromatography with hydroxypropyl‐β‐cyclodextrin as a chiral selector

Recycling countercurrent chromatography was successfully applied to the resolution of 2‐(4‐bromomethylphenyl)propionic acid, a key synthetic intermediate for synthesis of nonsteroidal anti‐inflammatory drug loxoprofen, using hydroxypropyl‐β‐cyclodextrin as chiral selector. The two‐phase solvent system composed of n‐hexane/n‐butyl acetate/0.1 mol/L citrate buffer solution with pH 2.4 (8:2:10, v/v/v) was selected. Influence factors for the enantioseparation were optimized, including type of substituted β‐cyclodextrin, concentration of hydroxypropyl‐β‐cyclodextrin, separation temperature, and pH of aqueous phase. Under optimized separation conditions, 50 mg of 2‐(4‐bromomethylphenyl)propionic acid was enantioseparated using preparative recycling countercurrent chromatography. Technical details for recycling elution mode were discussed. The purities of both the S and R enantiomers were over 99.0% as determined by high‐performance liquid chromatography. The enantiomeric excess of the S and R enantiomers reached 98.0%. The recovery of the enantiomers from eluted fractions was 40.8–65.6%, yielding 16.4 mg of the S enantiomer and 10.2 mg of the R enantiomer. At the same time, we attempted to enantioseparate the anti‐inflammatory drug loxoprofen by countercurrent chromatography and high‐performance liquid chromatography using a chiral mobile phase additive. However, no successful enantioseparation was achieved so far.     

HPLC enantioseparation of β2‐homoamino acids using crown ether‐based chiral stationary phase

RP high‐performance liquid chromatographic methods were developed for the enantioseparation of eleven unusual β²‐homoamino acids. The underivatized analytes were separated on a chiral stationary phase containing (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid as chiral selector. The effects of organic (alcoholic) and acidic modifiers, the mobile phase composition and temperature on the separation were investigated. The structures of the substituents in the α‐position of the analytes substantially influenced the retention and resolution. The elution sequence was determined in some cases: the S enantiomers eluted before the R enantiomers.     

Enantiomeric separation of oxybutynin by recycling high‐speed counter‐current chromatography with hydroxypropyl‐β‐cyclodextrin as chiral selector

Recycling high‐speed counter‐current chromatography was successfully applied to the preparative separation of oxybutynin enantiomers. The two‐phase solvent system consisted of n‐hexane, methyl tert‐butyl ether, and 0.1 mol/L phosphate buffer solution (pH = 5.0) with the volume ratio of 6:4:10. Hydroxypropyl‐β‐cyclodextrin was employed as the chiral selector. The influence of factors on the chiral separation process, including the concentration of chiral selector, the equilibrium temperature, the pH value of the aqueous phase were investigated. Under optimum separation conditions, 15 mg of oxybutynin racemate was separated with the purities of both the enantiomers over 96.5% determined by high‐performance liquid chromatography. Recovery for the target compounds reached 80–82% yielding 6.00 mg of (R)‐oxybutynin and 6.15 mg of (S)‐oxybutynin. Technical details for recycling elution mode were discussed.     

Synthesis of Chiral 2‐Aroyl‐1‐tetralols: Asymmetric Transfer Hydrgenation of 2‐Aroyl‐1‐tetralones via Dynamic Kinetic Resolution

The dynamic kinetic resolution of 2‐aroyl‐1‐tetralones was achieved via asymmetric transfer hydrogenation using (S,S)‐RuCl(p‐cymene)TsDPEN (TsDPEN=N‐(tosyl)‐1,2‐diphenylethylenediamine) in formic acid/triethyl‐ amine (5:2, molar ratio), afforded the desired products in good yields (up to 85%) with diastereomeric ratio up to >99:1 and high enantiomeric excesses (up to >99%). The absolute configuration of major the product was confirmed by X‐ray crystal structure analysis.     

A Reagentless Amperometric Immunosensor for Alpha‐Fetoprotein Based on Gold Nanoparticles/TiO2 Colloids/Prussian Blue Modified Platinum Electrode

A novel reagentless amperometric immunosensor for the determination of alpha‐fetoprotein (AFP) was prepared by immobilizing TiO₂ colloids on Prussian blue (PB) modified platinum electrode, which yielded a positively charged interface with strong adsorption to deposit gold nanoparticles for immobilization of alpha‐fetoprotein antibody (anti‐AFP). The factors influencing the performance of the proposed immunosensors were studied in detail. Under the optimized conditions, cyclic voltammograms determination of AFP showed a specific response in two concentration ranges from 3.0 to 30.0 ng/mL and from 30.0 to 300.0 ng/mL with a detection limit of 1.0 ng/mL at a signal‐to‐noise ratio of 3. The proposed immunosensor exhibited high selectivity, good reproducibility, long‐term stability (>2 months) and good repeatability.     

Electrochemical Immunoassay for Carbohydrate Antigen‐125 Based on Polythionine and Gold Hollow Microspheres Modified Glassy Carbon Electrodes

A new electrochemical immunosensor for the detection of carbohydrate antigen‐125 (CA125), a carcinoma antigen, was developed by immobilization CA125 antibody (anti‐CA125) on gold hollow microspheres and porous polythionine (PTH) modified glassy carbon electrodes (GCE). The gold hollow microspheres provided a biocompatible microenvironment for proteins, and greatly amplified the coverage of anti‐CA125 molecules on the electrode surface. The performance and factors influencing the immunosensor were investigated in detail. The detection is based on the current change before and after the antigen‐antibody interaction. Under optimal conditions, the amperometric changes were proportional to CA125 concentration ranging from 4.5 to 36.5 U/mL with a detection limit of 1.3 U/mL (at 3σ). The CA125 immunosensor exhibited good precision, high sensitivity, acceptable stability, accuracy and reproducibility. The as‐prepared immunosensors were used to analyze CA125 in human serum specimens. Analytical results suggest that the developed immunoassay has a promising alternative approach for detecting CA125 in the clinical diagnosis.     

HPLC法拆分(-)-2(S)-苄基-4-酮-4-(顺式-全氢化异吲哚-2-基)丁酸钙对映体

目的：建立刺激胰岛素分泌的新型降糖药物(-)-2 (S)-苄基-4-酮-4-(顺式-全氢化异吲哚-2-基)丁酸钙对映体的HPLC拆分方法。方法：采用Sumichiral OA-3300手性柱(250 × 4.6 mm I.D., 5 μm), 柱温35℃,以0.05 mol·L-1醋酸铵的甲醇溶液为流动相,检测波长为210 nm。结果：本品两对映体在22分钟内实现良好分离,分离度达3以上,S－异构体分别在0.028 ~ 5.6 μg mL-1和0.03 ~ 6.0 μg mL-1范围内线性关系良好,回归方程分别为：Y=1.32×103x-2.54 (r=0.9997)和Y=1.15×103x-1.78 (r=0.9998),最低检测限分别为0.15 ng和0.10 ng,方法精密度RSD低于1.0% (n=5)。结论：建立的对映体分离方法可用于本品光学异构体的质量控制。     

Preparative enantioseparation of propafenone by counter‐current chromatography using di‐n‐butyl l‐tartrate combined with boric acid as the chiral selector

This paper extends the research of the utilization of borate coordination complexes in chiral separation by counter‐current chromatography (CCC). Racemic propafenone was successfully enantioseparated by CCC with di‐n‐butyl l ‐tartrate combined with boric acid as the chiral selector. The two‐phase solvent system was composed of chloroform/ 0.05 mol/L acetate buffer pH 3.4 containing 0.10 mol/L boric acid (1:1, v/v), in which 0.10 mol/L di‐n‐butyl l ‐tartrate was added in the organic phase. The influence of factors in the enantioseparation of propafenone were investigated and optimized. A total of 92 mg of racemic propafenone was completely enantioseparated using high‐speed CCC in a single run, yielding 40–42 mg of (R)‐ and (S)‐propafenone enantiomers with an HPLC purity over 90–95%. The recovery for propafenone enantiomers from fractions of CCC was in the range of 85–90%.     

Asymmetric Mannich‐Type Synthesis of N‐Phosphinyl α‐Aminophosphonic Acid Monoesters

A convenient diastereoselective synthesis of diisopropyl (2R,3R)‐3‐{{{(R/S)‐aryl[(diethoxyphosphinyl)amino]methyl}hydroxyphosphinyl}oxy}‐2‐hydroxybutanedioate through Mannich‐type reactions is reported. The reactions take place under mild conditions in good yields, and this makes it possible to introduce various substituents at the α‐position to the P‐atom of α‐aminophosphonates. The chiral diisopropyl (4R,5R)‐2‐chloro‐1,3,2‐dioxaphospholane‐4,5‐dicarboxylate ( 3 ) was found to be a good phosphonylating agent in this stereoselective reaction.     

Enantioseparation of hydroxyeicosatetraenoic acids by hydroxypropyl‐γ‐cyclodextrin‐modified micellar electrokinetic chromatography

Complete resolution of hydroxyeicosatetraenoic acid (HETE) enantiomers was achieved using hydroxypropyl‐γ‐cyclodextrin (HP‐γ‐CD)‐modified MEKC. The optimum running conditions were determined to be utilizing a 30 mM phosphate–15 mM borate buffer (pH 9.0) containing 30 mM HP‐γ‐CD and 75 mM SDS as the BGE, application of +30 kV as the effective voltage, and carrying out the experiment at 15°C. The eluents were detected at 235 nm. The method was used successfully for the simultaneous separations of (S)‐ and (R)‐enantiomers of regioisomeric 8‐, 11‐, 12‐, and 15‐HETEs. Subsequently, the optimized method was applied to evaluate the stereochemistry of 8‐ and 12‐HETEs from the marine red algae, Gracilaria vermiculophylla and Gracilaria arcuata, respectively. The 8‐HETE was found to be a mixture of 98% (R)‐enantiomer and 2% (S)‐enantiomer, while the 12‐HETE was a mixture of 98% (S)‐enantiomer and 2% (R)‐enantiomer. The present study demonstrates that the HP‐γ‐CD‐modified MEKC method is simple and sensitive and provides unambiguous information on the configuration of natural and synthetic HETEs.     

Comparative study on the liquid chromatographic enantioseparation of cyclic β‐amino acids and the related cyclic β‐aminohydroxamic acids on Cinchona alkaloid‐based zwitterionic chiral stationary phases

The enantiomeric pairs of cis and trans stereoisomers of cyclic β‐aminohydroxamic acids and their related cis and trans cyclic β‐amino acids containing two chiral centers were directly separated on four structurally related chiral stationary phases derived from quinine and quinidine modified with (R,R)‐ and (S,S)‐aminocyclohexanesulfonic acids. Applying these zwitterionic ion‐exchangers as chiral selectors, the effects of the composition of the bulk solvent, the acid and base additives, the structures of the analytes, and temperature on the enantioresolution were investigated. To study the effects of temperature and obtain thermodynamic parameters, experiments were carried out at constant mobile phase compositions in the temperature range 5–50°C. The differences in the changes in standard enthalpy Δ(ΔH°), entropy Δ(ΔS°), and free energy Δ(ΔG°) were calculated from the linear van't Hoff plots derived from the ln α versus 1/T curves in the studied temperature range. Results thus obtained indicated enthalpy‐driven separations in all cases. The sequence of elution of the enantiomers was determined and found to be reversed when ZWIX(–)™ was changed to ZWIX(+)™ or ZWIX(–A) to ZWIX(+A).     

Sensitive amperometric pyridoxine sensor based on self‐assembled Prussian blue nanoparticle‐modified poly(o‐phenylenediamine)/glassy carbon electrode

Prussian blue nanoparticles (PBNPs) were prepared by a self‐assembly process on a glassy carbon electrode (GCE) modified with poly(o‐phenylenediamine) (PoPD) film. The stepwise fabrication process of PBNP‐modified PoPD/GCE was characterized using scanning electron microscopy and electrochemical impedance spectroscopy. The prepared PBNPs showed an average size of 70 nm and a homogeneous distribution on the surface of the modified electrode. The PBNPs/PoPD/GCE showed electrocatalytic activity towards the oxidation of pyridoxine (PN) and was used as an amperometric sensor. The modified electrode exhibited a linear response for PN oxidation over the concentration range 3–38.5 μM with a detection limit of ca 6.10 × 10^?7 M (S/N = 3) and sensitivity of 2.79936 × 10³ mA M^?1 cm^?2 using an amperometric method. The mechanism and kinetics of the catalytic oxidation reaction of PN were investigated using cyclic voltammetry and chronoamperometry. The values of α, k_cat and D were estimated as 0.36, 1.089 × 10² M^?1 s^?1 and 8.9 × 10^?5 cm² s^?1, respectively. This sensor also exhibited good anti‐interference and selectivity. Copyright © 2016 John Wiley & Sons, Ltd.     

Development of a high‐performance liquid chromatography method for the simultaneous determination of chiral impurities and assay of (S)‐clopidogrel using a cellulose‐based chiral stationary phase in methanol/water mode

A simple reversed‐phase high‐performance liquid chromatography method for the chiral separation of the active pharmaceutical ingredient (S)‐clopidogrel has been developed on the cellulose‐based Chiralcel OJ‐RH chiral stationary phase. The S enantiomer was baseline resolved from its R impurity (impurity C) with a mobile phase consisting of methanol/water (100:15) without any interference coming from the other two potential chiral impurities A and B. The enantio‐ and chemoselective method was partially validated and compared with that reported in the United States Pharmacopoeia for the drug product. The versatility of the Chiralcel OJ‐RH allowed separating the enantiomers of the impurity B also under normal phase and setting up an efficient strategy to convert the racemic sample into the enantiomeric S form on a semipreparative scale.     

Asymmetric Synthesis of All Four Isomers of an Unusual Heterocycle‐Containing Amino Acid: 2‐Amino‐3‐furan‐2‐yl‐pentanoic Acid

All four isomers of a novel β‐branched unusual amino acid were designed and synthesized with high stereoselectivity (>90% de) and in 33% –44% overall yields by the use of 4(R/S)‐5,5‐dimethyl‐4‐phenyl‐oxazolidin‐2‐one as the chiral auxiliary via asymmetric 1,4‐Michael addition, direct or indirect azidation, hydrolysis and hydrogenation reactions.