Stereospecific polymerization and chiral initiation,chiral crystallization and chiral nucleation

Helical macromolecules which are configurationally and conformationally specific can now be synthesized. Monomer structures must be selected that demand spacial restriction for monomer addition. High specificity of monomer addition during polymerization has parallels in crystallization of some inorganic salts from aqueous solution. Initiation of highly specific polymerizations with chiral initiators give helical polymers with substantial one-handedness. Nucleation of certain inorganic salts with chiral nucleating agents, the enantiomers of the salts produce enantiomerically pure chiral salts.     

Assessing chiral self-recognition using chiral stationary phases

Chiral stationary phases were synthesized and their ability to separate racemic precursors from which they were derived was assessed. Taken in conjunction with homochiral recognition previously observed in the solid state, the results of this study reveal that a geometrically controlling π-π interaction has a profound influence on molecular recognition.     

Addition of lactate-derived chiral allyltrichlorostannanes to chiral aldehydes

Chiral lactate-derived allyltrichlorostannanes reacted with chiral α-methyl β-alkoxy and syn and anti α-methyl-β-alkoxy aldehydes to give the corresponding homoallylic alcohols with moderate to high 1,4-syn-diastereoselectivities.     

Diastereomeric recognition of chiral foldamer receptors for chiral glucoses

[reaction: see text] Three chiral aromatic hydrazide foldamers have been designed and synthesized, in which two R- or S-proline units were incorporated at the terminals of their backbones. The 1H NMR, circular dichroism (CD), and fluorescent experiments and molecular dynamics simulations revealed that the foldamers adopted a chiral helical conformation and complexed alkylated glucoses in chloroform with a good diastereomeric selectivity.     

Advanced dress-up chiral columns: New removable chiral stationary phases for enantioseparation of chiral carboxylic acids

This paper describes the preparation of new dress-up columns featuring reproducibly removable and replaceable chiral stationary phases. After synthesizing perfluroalkylated quinine and quinidine derivatives as chiral stationary phase compounds (F-CSPs), we adsorbed them reversibly onto a fluorous LC column through pumping of their solutions. Using this dress-up chiral column and fluorophobic elution of aqueous ammonium formate/MeOH mixtures, we could enantioseparate four racemic N-acetyl amino acids, dichlorprop, and sixteen fluorescent 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC)-derivatized amino acids. Dressing and undressing of the coated F-CSPs could be controlled by varying the fluorophilicity and fluorophobicity of the eluent. The relative standard deviations of the retention times, the retention factors, the number of theoretical plates, the enantioseparation factors, and the resolutions of each of four preparations of such dress-up columns were all less than or equal to 5.26% (from 20 repeated analyses); the reproducibilities from four different preparations were all less than or equal to 10.6%. These columns also facilitated highly sensitive and selective analyses of AQC-amino acids when detected using LC–MS/MS.     

Inherently chiral electrodes: the tool for chiral voltammetry

2,2′-Bis[2-(5,2′-bithienyl)]-3,3′-bithianaphthene oligomers are a model case of electroactive films endowed with “inherent chirality”, originating from a stereogenic element coinciding with the whole electroactive backbone, thus resulting in impressive manifestations. This study highlights their applicative potentialities as low-cost and easy-to-prepare artificial enantiopure electrode surfaces, which display an unprecedented ability to pronouncedly separate voltammetry peaks of enantiomers of quite different chiral probes of applicative interest, concurrently with linear dynamic ranges for peak currents, affording enantiomer excess determination. Thus inherently chiral enantiopure electrodes can indeed be regarded as a key to chiral voltammetry.     

双手性选择单元手性固定相的研究进展

手性固定相（chiral stationary phase,CSP）作为手性色谱分离的核心技术,在手性化合物的识别和分离中得到广泛应用。以双手性选择单元结合作为CSP是近些年的研究热点,研究表明,两种手性选择单元相结合的CSP可增加手性识别位点,显著提高分离效果。本文介绍了近几年双手性选择单元手性固定相在手性分离中的研究进展,并对其发展前景进行了展望。     

One-pot synthesis of chiral azetidines from chloroaldehyde and chiral amines

A variety of chiral azetidinepiperidines have been synthesized utilizing an expedient one-pot union of piperidine chloroaldehyde with chiral amines. This two step one-pot procedure provides access to an interesting set of compounds that retain the chiral purity of the starting chiral amine.     

Deepened chiral cavitands

Deep cavitands bearing eight asymmetric centers on their upper rims are prepared from octamino resorcinarenes. The resorcinarenes are acylated with Fmoc d- and l-alanine or Fmoc glycine acid chlorides. The asymmetric centers create a chiral magnetic environment as shown by binding achiral ?-caprolactam. The chiral steric environment shows modest enantioselectivity (55% de) for chiral guests such as pinane diols bound inside the cavitand.     

Inherently chiral calixarenes

Due to the nonplanarity of the basic 1 _n -metacyclophane system, calixarenes and resorcarenes can be transformed into molecules with inherent chirality. Various attempts to achieve this goal are reviewed. Special emphasis is given to derivatives withC _n -symmetry, including derivatives of spherand calixarenes and other calixarene-like macrocycles.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes.     

A chiral furocoumarin

The furocoumarin 1,2‐di­hydro‐2‐(1,2‐di­hydroxy­prop‐2‐yl)‐8H‐furo­[2,3‐h]­benzo­pyran‐8‐one crystallizes from methanol–water as the monohydrate C₁₄H₁₄O₅·H₂O. Both chiral centers have the S configuration. Both OH groups and both H atoms of the water mol­ecule form intermolecular hydrogen bonds with O?O distances in the range 2.7686 (18)–2.8717 (18) Å.     

Reagent controlled addition of chiral sulfur ylides to chiral aldehydes

The degree of reagent and substrate control in the reaction of chiral sulfur ylides with chiral aldehydes has been investigated. Specifically, the reactions of the two enantiomers of the chiral benzyl sulfonium salt 1 with glyceraldehyde acetonide were studied in detail. Of the two new stereogenic centers created, it was found that the C1 stereochemistry was largely controlled by the reagent, whereas control at the C2 center was dependent on the aldehyde used. In one case, the trans isomer was produced via reversible formation of the intermediate betaine, whereas in the alternative case, the C2 center was under Felkin Anh/Cornforth control through non-reversible formation of the betaine. Thus, the aldehyde stereocenter influenced the degree of reversibility in betaine formation, which impacted on the stereocontrol at the C2 position.     

Photosensitive chiral polyisocyanates

The dynamic polyisocyanate helix amplifies changes in the conformation of its side groups. Thereby it acts like a fast responding switch for optical properties. Here we show how the photoisomerization of chiral azo side groups can be used to induce large changes of chirooptical properties. These changes can be detected by CD measurements or by ORD measurements far from the absorption region. Large changes of the optical rotation can be induced reversibly in a multicycle process.     

Comparative studies of various run buffers for chiral capillary electrophoresis using chiral crown ether as a chiral selector

In the capillary electrophoretic separation of primary amine enantiomers using (+)-(18-crown-6)-tetracarboxylic acid (18C6H4) as a chiral selector, the presence of run buffer constituents such as tris(hydroxymethyl)aminomethane (Tris) or Na+ competing with analytes for 18C6H4, diminishes the effectiveness of 18C6H4. In order to determine appropriate buffer systems for 18C6H4, various run buffer cationic components including Tris, 1,3-bis[tris(hydroxymethyl)methylamino]propane, bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane, triethanolamine, tetramethylammonium, and Na+ were compared. Quantitative studies of the effects of the competitive constituents were carried out by measuring the electrophoretic mobilities of histidine as a function of the 18C6H4 concentration. We also derived a simple equation to estimate the optimal chiral selector concentration for a maximum mobility difference in the presence of a competitive inhibitor.     

Rhodium complexes with chiral counterions: achiral catalysts in chiral matrices

The neutral complexes [Rh(I)(NBD)((1S)-10-camphorsulfonate)] (2) and [Rh(I)((R)-N-acetylphenylalanate)] (4) reacted with bis-(diphenylphosphino)ethane (dppe) to form the cationic Rh(I)(NBD)(dppe) complexes, 5 and 6, respectively, accompanied by their corresponding chiral counteranions. Analogously, 4 reacted with 4,4^′-dimethylbipyridine to yield complex 7. Complexes 5 and 6 disproportionated in aprotic solvents to form the corresponding bis-diphosphine complexes 8 and 9, respectively. 8 was characterized by an X-ray crystal structure analysis. In order to form achiral Rh(I) complexes bearing chiral countercations new sulfonated monophosphines 13-16 with chiral ammonium cations were synthesized. Tris-triphenylphosphinosulfonic acid (H₃TPPS, 11) was used to protonate chiral amines to yield chiral ammonium phosphines 14-16. Thallium-tris-triphenylphosphinosulfonate (Tl₃TPPS, 12) underwent metathesis with a chiral quartenary ammonium iodide to yield the proton free chiral ammonium phosphine 13. Phosphines 15 and 16 reacted with [Rh(NBD)₂]BF₄ to afford the highly charged chiral zwitterionic complexes [Rh(NBD)(TPPS)₂][(R)-N,N-dimethyl-1-(naphtyl)ethylammonium]₅ (17) and [Rh(NBD)(TPPS)₂][BF₄][(R)-N,N-dimethyl-phenethylammonium]₆ (18), respectively. Complexes 5, 6, and 18 were tested as precatalysts for the hydrogenation of de-hydro-N-acetylphenylalanine (19) and methyl-(Z)-(α)-acetoamidocinnamate (MAC, 20) under homogeneous and heterogeneous (silica-supported and self-supported) conditions. None of the reactions was enantioselective.     

A concise, modular synthesis of chiral peraza-macrocycles using chiral aziridines

[reaction: see text] Novel chiral peraza-macrocycles were synthesized from chiral aziridines as a common building block. Efficient syntheses of chiral [26]-N(6), [12]-N(4), [9]-N(3), and [14]-N(4) systems were accomplished.     

Stereoselective interactions of chiral dipeptides on amylose based chiral stationary phases

Dipeptides are stereo-specifically involved in several biological functions that are challenging to separate enantiomerically. Elution order of enantiomers is an important issue in chiral chromatography. Amylose tris-(3,5-dimethylphenylcarbamate) chiral stationary phase(CSP) is the best and most-widely-used CSP in chiral separations, but experimental data of enantiomeric separation of dipeptides on this CSP is lacking. Simulation studies were conducted to determine the order of elution and the chiral recognition mechanism of didpetides on this CSP. Results indicated that the docking energy of SR-enantiomers were higher than SS-antipodes. The range of docking energies for SR-enantiomers was -7.44 to -5.92 kcal/mol with CSP, but -7.15 to -5.87 kcal/mol for SS-stereoisomers. Therefore it is predicted that SS-enantiomer will elute first, followed by SR-antipode. Furthermore, hydrogen bondings, van der Waal’s interactions and electrostatic interactions were observed among SR- and SSenantiomers and chiral grooves of CSP. The number of hydrogen bonds was one in each enantiomer binding except S-Ala-R-Tyr, which contained two hydrogen bonds. No hydrogen bond was found in S-Ala-R-Trp, S-Leu-S-Trp, and S-Leu-S-Tyr dipeptides bindings. The chiral recognition mechanisms dictate different strengths of stereoselective bindings of the enantiomers on CSP.     

非均匀取代淀粉衍生物手性固定相的制备及其手性识别能力

通过区域选择性方法制备了两种新型淀粉衍生物,分别为淀粉2-苯甲酸酯-3-(4-甲基苯基氨基甲酸酯)-6-(3,5-二氯苯基氨基甲酸酯)和淀粉2-苯甲酸酯-3-(3,5-二氯苯基氨基甲酸酯)-6-(4-甲基苯基氨基甲酸酯),将二者分别涂覆于氨丙基硅胶后用作液相色谱手性固定相。研究表明:所制备的手性固定相显示出特异的手性识别能力,其手性识别能力明显高于均匀取代淀粉衍生物——淀粉三(3,5-二氯苯基氨基甲酸酯),取代基的性质及在葡萄糖单元上的位置对手性固定相的手性识别能力有较大的影响。一些未在商品化的手性柱Chiralpak AD上得到有效分离的手性化合物在所制备的固定相上得到了更好的分离。所测试的8对对映体在淀粉2-苯甲酸酯-3-(4-甲基苯基氨基甲酸酯)-6-(3,5-二氯苯基氨基甲酸酯)固定相上均得到了分离,因而此固定相的手性识别能力较强,具有潜在的应用价值。