Chirality (CHIRALITY)

Publications in this journal

• Article: Synthesis and Structural Elucidation of Novel Camphor-Derived Thioureas

  UROŠ GROŠELJ, ALEN SEVŠEK, SEBASTIJAN RIČKO, AMALIJA GOLOBIČ, JURIJ SVETE, BRANKO STANOVNIK
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  ABSTRACT: Two novel 4-substituted camphidine derivatives 10a,b have been prepared from (+)-camphor (1) in five steps, the Beckmann rearrangement being the bottleneck of the synthesis. Isoborneol derivative 5b, formed as a side product during the hydrogenation of arylidene ketone 3b, under Beckmann rearrangement conditions yielded interesting novel rearrangement products 11 and 12. (1S)-(+)-Camphorquinone (13) was transformed into diamines 15 and 16 in two steps, the former being cyclized into an imidazoline salt 17, an N-heterocyclic carbene precursor. The structures of all novel compounds have been meticulously characterized using NMR techniques and/or single crystal X-ray analysis.
  Chirality 06/2012; 24:778–788.
• Article: Synthesis and Structural Elucidation of Novel Camphor-Derived Thioureas

  UROSˇ GROSˇELJ, AMALIJA GOLOBIC, KATARINA STARE, JURIJ SVETE, BRANKO STANOVNIK
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  ABSTRACT: Nine novel (1)-camphor-derived thioureas have been prepared. 3-((Dimethylamino) methylene)camphor (2) served as the common precursor for the preparation of both, 2- thiourea 15–20 and 3-thiourea functionalized camphor derivatives 6, 7/70, respectively. Starting from 2, the latter were prepared in two or three steps whereas the former in five steps, respectively. Configuration of all novel compounds has been meticulously determined using NMR techniques and/or single crystal X-ray crystallography.
  Chirality 02/2012; 24:307–317.
• Article: Lipase-catalyzed enantioselective access to flurbiprofen

  Ashraf Ghanem
  Chirality 01/2010; 22:597.
• Article: Comparison of separation performances of amilose- and cellulose-based stationary phases in the high-performance liquid chromatographic enantioseparation of stereoisomers of beta-lactams

  Z. Patai; R. Berkecz; I. Ilisz; E. Forró; F. Fülöp; A. Péter
  Chirality 01/2010; 22:120-128.
• Article: Chiroptical properties and racemization behavior of highly distorted donor-acceptor tetracyanoanthraquinodimethane with interconvertible planar chirality.

  Hideaki Saito, Tadashi Mori, Yumi Origane, Takehiko Wada, Yoshihisa Inoue
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  ABSTRACT: Absolute configuration of optically active 7,12-bis(dicyanomethylene)-7,12-dihydrobenz[a]anthracene (1) with interconvertible planar chirality was determined by a comparison of experimental and theoretical circular dichroism (CD) spectra. Upon standing at ambient temperatures, 1 was found to spontaneously racemize, the rates of which were assessed through the separation profiles of chiral HPLC at 5-20 degrees C and also from the CD spectral decay profiles at the same temperatures. Mechanism of the racemization was discussed.
  Chirality 04/2008; 20(3-4):278-81.
• Article: Species-dependent stereoselective drug binding to albumin: a circular dichroism study.

  Marco Pistolozzi, Carlo Bertucci
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  ABSTRACT: Drug binding to albumins from different mammalian species was investigated to disclose evidence of species-dependent stereoselectivity in drug-binding processes and affinities. This aspect is important for evaluating the reliability of extrapolating distribution data among species. The circular dichroism (CD) signal induced by drug binding to the albumins [human serum albumin (HSA), bovine serum albumin (BSA), rat serum albumin (RSA), and dog serum albumin (DSA)] were measured and analyzed. The binding of selected drugs and metabolites to HSA significantly differed from the binding to the other albumins in terms of affinity and conformation of the bound ligands. In particular, phenylbutazone, a marker of site one on HSA, showed a higher affinity for binding to BSA with respect to RSA, HSA, and DSA, respectively. In the case of diazepam, a marker of site two on HSA, the affinity decreased in order from HSA to DSA, RSA, and BSA. The induced CD spectra were similar in terms of energy and band signs, suggesting almost the same conformation for the bound drug to the different albumins. Stereoselectivity was high for the binding of ketoprofen to HSA and RSA. A different sign was observed for the CD spectra induced by the drug to the two albumins because of the prevalence of a different conformation of the bound drug. Interestingly, the same induced CD spectra were obtained using either the racemic form or the (S)-enantiomer. Finally, significant differences were observed in the affinity of bilirubin, being highest for BSA, then decreasing for RSA, HSA, and DSA. A more complex conformational equilibrium was observed for bound bilirubin.
  Chirality 04/2008; 20(3-4):552-8.
• Article: Investigation of the stereoselectivity of an anti-amino acid antibody using molecular modeling and ligand docking.

  Daniel I Ranieri, Danielle M Corgliano, Elliott J Franco, Heike Hofstetter, Oliver Hofstetter
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  ABSTRACT: The structure of the binding site of the stereoselective anti-D-amino acid antibody 67.36 was modeled utilizing web antibody modeling (WAM) and SWISS-MODEL. Although docking experiments performed with an aromatic amino acid as model ligand were unsuccessful with the WAM structure, ligand binding was achieved with the SWISS-MODEL structure. Incorporation of side-chain flexibility within the binding site resulted in a protein structure that stereoselectively binds to the D-enantiomer of the model ligand. In addition to four hydrogen bonds that are formed between amino acid residues in the binding site and the ligand, a number of hydrophobic interactions are involved in the formation of the antibody-ligand complex. The aromatic side chain of the ligand interacts with a tryptophan and a tyrosine residue in the binding site through pi-pi stacking. Fluorescence spectroscopic investigations also suggest the presence of tryptophan residues in the binding site, as ligand binding causes an enhancement of the antibody's intrinsic fluorescence at an emission wavelength of 350 nm. Based on the modeled antibody structure, the L-enantiomer of the model ligand cannot access the binding site due to steric hindrance. Additional docking experiments performed with D-phenylalanine and D-norvaline showed that these ligands are bound to the antibody in a way analogous to the D-enantiomer of the model ligand.
  Chirality 04/2008; 20(3-4):559-70.
• Article: Enantioselective HPLC of potentially CNS-active acidic amino acids with a Cinchona carbamate based chiral stationary phase.

  Roccaldo Sardella, Michael Lämmerhofer, Benedetto Natalini, Wolfgang Lindner
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  ABSTRACT: A tert-butylcarbamoylquinine-based chiral stationary phase (Chiralpak QN-AX) has been employed for the enantiomer separation of underivatized chiral acidic amino acids, viz. 4-carboxyphenylalanine (4-CPHE), 1-aminoindan-1,5-dicarboxylic acid (AIDA), 2-(5-carboxy-3-methyl-2-thienyl)glycine (3-MATIDA), 2-(4-carboxy-5-methyl-2-thienyl)glycine (5-MATIDA), and 2-(2'-carboxy-3'-phenylcyclopropyl)glycine (PCCG). Some of the acidic amino acids have potential activity on the central nervous system and are thus of great interest. A stereoselective HPLC method that allows the baseline resolution of all the five test solutes has been developed. For that purpose the mobile phase composition (pH, organic modifier, and type) and flow rate were optimized. The final method makes use of mild elution conditions, namely methanol - 0.8 M ammonium acetate buffer (97.5:2.5; v/v) pH 5.5 which are also compatible with mass spectrometric detection.
  Chirality 04/2008; 20(3-4):571-6.
• Article: Measured and calculated CD spectra of G-quartets stacked with the same or opposite polarities.

  Donald M Gray, Jin-Der Wen, Carla W Gray, Rudolf Repges, Charlotte Repges, Gerhard Raabe, Jörg Fleischhauer
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  ABSTRACT: Circular dichroism (CD) spectroscopy is widely used to characterize the structures of DNA G-quadruplexes. CD bands at 200-300 nm have been empirically related to G-quadruplexes having parallel or antiparallel sugar-phosphate backbones. We propose that a more fundamental interpretation of the origin of the CD bands is in the stacking interactions of neighboring G-quartets, which can have the same or opposing polarities of hydrogen bond acceptors and donors. From an empirical summation of CD spectra of the d(G)5 G-quadruplex and of the thrombin binding aptamer that have neighboring G-quartets with the same and opposite polarities, respectively, the spectra of aptamers selected by the Ff gene 5 protein (g5p) appear to arise from a combination of the two types of polarities of neighboring G-quartets. The aptamer CD spectra resemble the spectrum of d(G3T4G3), in which two adjacent quartets have the same and two have opposite polarities. Quantum-chemical spectral calculations were performed using a matrix method, based on guanine chromophores oriented as in d(G3T4G3). The calculations show that the two types of G-quartet stacks have CD spectra with features resembling experimental spectra of the corresponding types of G-quadruplexes.
  Chirality 04/2008; 20(3-4):431-40.
• Article: Chirality sensing of fullerenes using cyclic hosts having a chiral N-substituted porphyrin: a remote substituent effect.

  Yoshiaki Shoji, Kentaro Tashiro, Takuzo Aida
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  ABSTRACT: Cyclic host molecules 1 2H and 2 2H, having a chiral N-methylporphyrin unit, include C76 in their asymmetrically distorted pi-electronic cavity and are capable of spectral discrimination of the enantiomers of C76 by means of 1H NMR. Although the only structural difference between 1 2H and 2 2H is in the para-substituents R on their meso-phenyl groups, the association constant of C76 with 1 2H is more than twice as large as that with 2 2H. The Delta H values for the association of C76 with these hosts are hardly different from one another, but a rather big difference exists in their DeltaS values (1 2H, -17.7 +/- 0.7 J mol(-1); 2 2H, -26.3 +/- 1.0 J mol(-1)). The difference in DeltaS is most likely due to a steric effect of the substituents on the conformational freedom of the hexamethylene linkers. Although the R groups are topologically remote from the binding site, they also affect the resolution of the diastereoisomerically split N-Me signals in the 1H NMR spectra of the hosts upon inclusion of C76.
  Chirality 04/2008; 20(3-4):420-4.
• Article: Chirality sensing with synthetic pores.

  Hiroyuki Tanaka, Stefan Matile
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  ABSTRACT: A concept to determine enantiomeric excess with synthetic multifunctional pores is introduced. To do so, the poor stereoselectivity of molecular recognition by stimuli-responsive pores is coupled with the stereospecificity of enzymes. With substrates as good and products as poor pore blockers, enzymatic conversion of one enantiomer is shown to readily reveal the concentration of the other one. Calculations suggest that high substrate/product discrimination by the synthetic pores may provide access to the accurate detection of the extreme enantiomeric excess that is of interest in chemistry, pharmacology, and medicine, but otherwise possibly problematic to detect. Validity of the introduced concept is experimentally confirmed with poly-L-glutamate and poly-D-glutamate as enantiomeric substrates with high blockage efficiency, L-glutamate and D-glutamate as enantiomeric products with poor blockage efficiency, subtilisin A as enzyme, and a classical rigid-rod beta-barrel as synthetic pore.
  Chirality 04/2008; 20(3-4):307-12.
• Article: Discrimination of enantiomers of alpha-amino acids by chiral derivatizing reagents from trans-1,2-diaminocyclohexane.

  Magdalena Kaik, Jadwiga Gajewy, Jakub Grajewski, Jacek Gawronski
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  ABSTRACT: New chiral derivatizing reagents (CDAs) derived from trans-1,2-diaminocyclohexane, having an electron-deficient aromatic substituent (either an aromatic imide or 3,5-dinitrobenzamide) and rigid structure (either an amide or a urea linker), are reported. Significant shift differences of diastereotopic protons in the 1H NMR signals are observed for enantiomers of suitably protected alpha-amino acids, linked to CDA by a covalent bond. A simple, general model rationalizing the observed enantiomer discrimination and based on semiempirical conformational search is presented.
  Chirality 04/2008; 20(3-4):301-6.
• Article: Enantioseparation using urea- and imide-bearing chitosan phenylcarbamate derivatives as chiral stationary phases for high-performance liquid chromatography.

  Chiyo Yamamoto, Mari Fujisawa, Masami Kamigaito, Yoshio Okamoto
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  ABSTRACT: Completely deacetylated chitosan was prepared by the treatment of commercial chitosan with 50% aqueous NaOH, and then derivatized into several new chitosan phenylcarbamate derivatives having a urea and an imide moiety at the 2-position of the glucosamine ring by the reaction with isocyanate and phthalic anhydride/isocyanate, respectively. The chitosan derivatives were coated on macroporous silica gel and evaluated as chiral stationary phases (CSPs) for high-performance liquid chromatography. The chiral recognition ability of the chitosan derivative was improved using the completely deacetylated chitosan. Among the novel chitosan derivatives, the 3,5-dimethyl-, 3,5-dichloro-, and 3,4-dichlorophenylcarbamate derivatives were found to possess relatively high chiral resolution abilities. The CSPs based on the chitosan phenylcarbamate-urea and -imide derivatives were stable in the presence of chloroform and ethyl acetate as a component of the eluents, and some racemates were better resolved by such eluents. The dichlorophenylcarbamate-imide derivatives showed a high chiral recognition for metal acetylacetonate complexes. The enantiomerization of Al(acac)3 was performed on the chitosan 3,5-dichlorophenylcarbamate-imide derivative CSP and the resulting chromatogram showed a 26% (+)-isomer enrichment.
  Chirality 04/2008; 20(3-4):288-94.
• Article: Intermolecular chiral recognition processes probed by chiroptical luminescence.

  Todd A Hopkins, David H Metcalf, Frederick S Richardson
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  ABSTRACT: Enantiopreferential energy transfer processes between dissymmetric lanthanide and transition metal complexes dissolved in acetonitrile are studied using chiroptical luminescence techniques. The energy donors (luminophores) in this study are a racemic mixture of Ln(dpa)3 (3-) complexes (where Ln = Eu3+ or Tb3+ and dpa = 2,6-pyridinedicarboxylate), and the energy acceptors (quenchers) are an enantiomerically-resolved population of Co(R,R-chxn)3 3+ (where R,R-chxn = trans-1R,2R-diaminocyclohexane) complexes. The luminophores are dissolved in acetonitrile as (NEt4)3[Ln(dpa)3] (where NEt(4) = tetraethlylammonium) and (NBu4)[Ln(dpa)3] (where NBu4 = tetrabutylammonium) salts. The unquenched luminescence lifetimes are reported for both Eu(dpa)3 (3-) and Tb(dpa)3 (3-) in acetonitrile over the range 263-333 K, and these results are compared to luminescence lifetimes in aqueous solution. Time-resolved chiroptical luminescence measurements of enantiopreferential quenching kinetics are reported for samples with Eu(dpa)3 (3-) and Co(R,R-chxn)3 3+ in acetonitrile over 263-333 K range. These results are analyzed using a phenomenological quenching kinetics model, and the results are compared to results in aqueous solution. These comparisons show that the overall Eu-Co luminescence quenching efficiency is reduced in acetonitrile vs. aqueous samples, because the salts of (NX4)3[Eu(dpa)3] are not completely dissociated in acetonitrile. However, the enantiopreference exhibited is identical in acetonitrile vs. aqueous solution.
  Chirality 04/2008; 20(3-4):511-23.
• Article: Entropy production in chiral symmetry breaking transitions.

  Dilip Kondepudi, Lauren Kapcha
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  ABSTRACT: It is now well known that nonequilibrium chemical systems may reach conditions that spontaneously generate chiral asymmetry. One can find a host of model reactions that exhibit such behavior in the literature. Among these, models based on one originally devised by Frank have been studied extensively. Though the kinetic aspects of such model reactions have been discussed in great detail, the behavior of entropy in such systems is rarely discussed. In this article, the rate of entropy production per unit volume, sigma, in a modified Frank model is discussed. It is shown that the slope of sigma changes at the point at which the asymmetric states appear, behavior similar to that observed in second-order phase transitions.
  Chirality 04/2008; 20(3-4):524-8.
• Article: Synthesis and chiroptical properties of a helical poly(phenylacetylene) bearing optically active pyrene pendants.

  Hongzhen Lin, Kazuhide Morino, Eiji Yashima
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  ABSTRACT: A novel poly(phenylacetylene) derivative bearing optically active pyrene moieties as the pendant groups (poly-(R)-1) was prepared by the polymerization of the corresponding monomer (R)-1 in the presence of a rhodium catalyst, and its chiroptical property was investigated. Poly-(R)-1 exhibited an induced circular dichroism (ICD) in the polymer backbone region due to the predominantly one-handed helical conformation. The ICD pattern dramatically changed and was accompanied by inversion of the Cotton effect sign in response to a change in the temperature and solvent, indicating that poly-(R)-1 underwent a helix-helix transition in response to the external stimuli.
  Chirality 04/2008; 20(3-4):386-92.
• Article: Recent advances in spirochalcogenurane stereochemistry--a mini review.

  Stig Allenmark
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  ABSTRACT: A summary of the present knowledge of the stereochemistry of the hypervalent spirochalcogenuranes, especially the role of the central atom (S, Se, Te) for the chemical and configurational stability and the chiroptical and X-ray crystallographic techniques available for the determination of absolute configuration, is given.
  Chirality 04/2008; 20(3-4):544-51.
• Article: Chiral memory: induction, amplification, and switching in porphyrin assemblies.

  Lauceri Rosaria, Alessandro D'urso, Angela Mammana, Roberto Purrello
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  ABSTRACT: The interaction between the tetra-anionic porphyrin H2TPPS and its copper derivative, CuTPPS, with the tetra-cationic porphyrin H2T4 and its copper derivative, CuT4, leads, in aqueous solution, to the formation of remarkably stable and kinetically inert heteroaggregates. The aggregation process is under hierarchic control and, in the presence of a suitable chiral mold, leads to the formation of chiral porphyrin heteroassemblies as stable and inert as the achiral ones. Because of these properties, the chirality of the porphyrin "imprinted" heteroaggregates not only survives the disruption of the template, but also to its complete removal from the solution. Notably, the template-free chiral porphyrin system is an excellent mold for its own self-replication. The relevant characteristics of these chiral heteroaggregates together with the knowledge of the forces that guide the aggregation processes permitted us to design a new but similar system. This system not only is able to store chiral information, but also is capable to release and restore it reversibly, in a cyclic manner. This has been achieved by modulating the charges carried by one of the two coupled porphyrins through protonation under various pH conditions. The role of the central metal ion and the template-free chiral structure of the CuT4-H2TPPS heteroaggregate, determined through EDXD analysis, are also presented.
  Chirality 04/2008; 20(3-4):411-9.
• Article: Factors determining the pattern of a hydrogen-bonding network in the diastereomeric salts of 1-arylethylamines with enantiopure P-chiral acids.

  Yuka Kobayashi, Hiroaki Handa, Jin Maeda, Kazuhiko Saigo
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  ABSTRACT: In order to clarify factor(s) determining the pattern of a hydrogen-bonding network in the diastereomeric salts of 1-arylethylamines (1) with enantiopure P-chiral acids, three kinds of enantiopure P-chiral alkylphenylphosphinothioic acids (3) were synthesized, and their chiral recognition abilities for racemic 1 were examined. The characteristics of the diastereomeric salt crystals of 1 with 3 were then studied on the basis of their X-ray crystallographic analyses. Statistical analysis on the molecular conformations observed in the diastereomeric salts with 3 as well as those with P-chiral O-alkyl arylphosphonothioic acids (2), which have a chemical structure similar to that of 3, and molecular orbital calculations for 2 and 3 in a gas phase revealed that the torsion angle between the aromatic plane and the P--O(alkoxy in 2) or P--C(alkyl in 3) plays an important role in determining the pattern of a hydrogen-bonding network in the diastereomeric salts, either a closed globular cluster or an infinite 2(1) column type. The calculations also indicated that there is a hydrogen-bonding-like interaction between the ammonium hydrogen atom of 1-arylethylammonium cations and the P--O(alkoxy) oxygen atom of phosphonothioate anions in the clusters.
  Chirality 04/2008; 20(3-4):577-84.