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142 records returned

Interactions between quercetin and Warfarin for albumin binding: A new eye on food/drug interference.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The interaction between quercetin, a popular antioxidant flavonoid, and human serum albumin (HSA) is investigated and characterized by means of induced circular dichroism and saturation transfer difference NMR. These techiques demonstrate the reversible binding of quercetin to the carrier protein, which is responsible for its dissolution in aqueous medium. Competition experiments with two classical probes for HSA binding sites, namely Ibuprofen and Warfarin (a common anticoagulant coumarin), demonstrate that quercetin has a primary binding site located in the subdomain IIA, where coumarins are hosted. The affinity for ...
Source: Chirality - November 9, 2009 Category: Molecular Biology Authors: Di Bari L, Ripoli S, Pradhan S, Salvadori P Tags: Chirality Source Type: journals

Absolute structural elucidation of natural products-A focus on quantum-mechanical calculations of solid-state CD spectra.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this review article we examine state-of-the-art techniques for the structural elucidation of organic compounds isolated from natural sources. In particular, we focus on the determination of absolute configuration (AC), perhaps the most challenging but inevitable step in the whole process, especially when newly isolated compounds are screened for biological activity. Among the many methods employed for AC assignment that we review, special attention is paid to electronic circular dichroism (CD) and to the modern tools available for quantum-mechanics CD predictions, including TDDFT. In this context, we stress that con...
Source: Chirality - November 9, 2009 Category: Molecular Biology Authors: Pescitelli G, Kurtán T, Flörke U, Krohn K Tags: Chirality Source Type: journals

TD-DFT modeling of the circular dichroism for a tryptophan zipper peptide with coupled aromatic residues.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this work, time dependent density functional theory (TD-DFT) is used to provide a reliable basis for interpretation of the electronic spectra of coupled tryptophan (Trp) residues, particularly those in a model Trpzip beta-hairpin peptide. Pairs of isolated indoles form chiral coupled chromophores whose computed electronic ultraviolet circular dichroism (CD) is in excellent agreement with observed transition wavelengths and intensities. The calculations were compared to experimental data for pairwise coupling in mutant Trpzip peptides that are recently available. A study of variation of the basis set, geometry optimi...
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Roy A, Bouř P, Keiderling TA Tags: Chirality Source Type: journals

Structural determination of molecular stereochemistry using VCD spectroscopy and a conformational code: Absolute configuration and solution conformation of a chiral liquid pesticide, (R)-(+)-malathion.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The absolute configuration and solution conformation of (R)-(+)-malathion were determined by using vibrational circular dichroism spectroscopy and a fragment-conformational search with a recently published conformational code. The determination of molecular stereochemistry was carried out without a conformational search using molecular mechanics calculations. Density functional theory calculations of the fragments of (R)-malathion, ethyl propionate, (R)-ethyl 2-(methylthio)propanoate, (R)-diethyl 2-(methylthio)succinate, and O,O,S-trimethyl phosphorodithioate were carried out, and the principal conformational features ...
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Izumi H, Ogata A, Nafie LA, Dukor RK Tags: Chirality Source Type: journals

Stereochemical study of a novel tautomeric furanone, homofuraneol.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A mixture of tautomers with unique keto-enol structures, 5-ethyl-4-hydroxy-2-methylfuran-3(2H)-one or 2-ethyl-4-hydroxy-5-methylfuran-3(2H)-one (EHMF, homofuraneol, 1a or 1b), comprises four structural isomers including their enantiomers. The four isomers were successfully separated by chromatographic optical resolution, and their odor evaluation was performed. Determination of the absolute chemistry of 1a and 1b were accomplished for the first time by direct measurement of the VCD spectra of their methyl ether derivatives 4a and 4b compared with the calculated ones as well as chemical relay reaction. The relationship ...
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Monde K, Nakahashi A, Miura N, Yoshihiro Y, Sugimoto D, Emura M Tags: Chirality Source Type: journals

Determination of the absolute configurations at stereogenic centers in the presence of axial chirality.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Cephalochromin, a homodimeric naphthpyranone natural product, contains both axial chirality due to the hindered rotation along the biaryl axis and central chirality due to the C-2, C-2' stereogenic centers of the fused pyranone ring. For determining the absolute configurations (ACs) of central chirality elements, different chiroptical spectroscopic methods, namely vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and optical rotation (OR), have been used. From these experimental data, in conjunction with corresponding quantum chemical predictions at B3LYP/6-311G* level, it is found that the ECD...
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Polavarapu PL, Jeirath N, Kurtán T, Pescitelli G, Krohn K Tags: Chirality Source Type: journals

Direct enantioselective HPLC monitoring of lipase-catalyzed kinetic resolution of flurbiprofen.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The solvent versatility of Chiralpak IB, a 3,5-dimethylphenylcarbamate derivative of cellulose-based chiral stationary phase, is demonstrated in the direct enantioselective HPLC monitoring of lipase-catalyzed kinetic resolution of flurbiprofen in nonstandard HPLC organic solvents. Nonstandard HPLC organic solvents were used as the reaction media for the lipase-catalysis and in mean time as diluent to dissolve the "difficult to dissolve" enzyme substrate (the acid) and as eluent for the simultaneous enantioselective HPLC baseline separation of both substrate and product in one run without any further derivatization. Chi...
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Ghanem A Tags: Chirality Source Type: journals

Diastereoisomeric assignment in a pacifenol derivative using vibrational circular dichroism.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The configuration of a chiral center in semisynthetic (-)-(2R,5R,5aR,8zeta,9aS)- 2,8-dibromo-2,5,9,9a-tetrahydro-5-hydroxy-5,8,10,10-tetramethyl-6H-2,5a-methano-1-benzoxepin-7(8H)-one (3 or 4), prepared in two steps from (-)-(2R,5R,5aR,7S,8S,9aS)-2, 7-dibromo-8-chloro-2,5,7,8,9,9a-hexahydro-5,8,10,10-tetramethyl-6H-2,5a-methano-1-benzoxepin-5-ol, known as pacifenol 1, has been determined using vibrational circular dichroism (VCD) measurements. The vibrational spectra (IR and VCD) of diastereoisomers 3 and 4 were calculated using density functional theory (DFT) at the B3LYP/DGDZVP level of theory for the two conformers ...
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Muñoz MA, Chamy C, Carrasco A, Rovirosa J, Martín AS, Joseph-Nathan P Tags: Chirality Source Type: journals

Preparation and enantioseparation of a mixed selector chiral stationary phase derived from benzoylated tartaric acid and 1,2-diphenylethylenediamine.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
L-Dibenzoyl tartaric acid was mono-esterified with benzyl alcohol, and then chlorinated with SOCl(2) to give (2S,3S)-1-(benzyloxy)-4-chloro-1,4-dioxobutane-2,3-diyl dibenzoate (Selector 1). (1R,2R)-1,2-Diphenylethylenediamine was mono-functionalized with phenyl isocyanate and phenylene diisocyanate in sequence to give (1R,2R)-1,2-diphenyl-2-(3-phenylureido)ethyl 4- isocyanatophenylurea (Selector 2). Two brush-type chiral stationary phases (CSPs) of single selector were prepared by separately immobilizing selectors 1 and 2 on aminated silica gel. Selectors 1 and 2 were simultaneously immobilized on aminated silica gel t...
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Wei WJ, Deng HW, Chen W, Bai ZW, Li SR Tags: Chirality Source Type: journals

Molecular and supramolecular chirality in gemini-tartrate amphiphiles studied by electronic and vibrational circular dichroisms.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
This contribution presents an application of electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) to study the molecular and supramolecular chirality in assemblies of gemini-tartrate amphiphiles. Nonchiral dicationic n-2-n amphiphiles (n = 14-20) can self-organize into right- or left-handed structures upon interacting with chiral tartrate counterions. Micellar solutions can also be obtained for shorter alkyl chains (n = 12). First, the conformation of tartrate counterions has been investigated in various environments (micellar solutions and chiral ribbons). ECD and VCD spectra recorded in micell...
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Brizard A, Berthier D, Aimé C, Buffeteau T, Cavagnat D, Ducasse L, Huc I, Oda R Tags: Chirality Source Type: journals

Enantioselective interaction with acetylcholinesterase of an organophosphate insecticide fenamiphos.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this study, we used fenamiphos (FAP), an organophosphorus insecticide, to study enantioselectivity in toxicity to arthropods and the inhibition potential towards acetylcholinesterase (AChE) in the rat pheochromocytoma 12 (PC 12) cell line. Furthermore, we carried out molecular docking to help explain the mechanisms of enantioselective toxicity of FAP. The two enantiomers of FAP were successfully separated and identified as R-(+)-FAP and S-(-)-FAP. Toxicological assays revealed that R-(+)-FAP was 2.4-fold more toxic than S-(-)-FAP to Daphnia magna and approximately threefold more to PC12 cells. Based on molecular docking...
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Wang C, Zhang N, Li L, Zhang Q, Zhao M, Liu W Tags: Chirality Source Type: journals

Highly stereoselective hydrogenations-As key-steps in the total synthesis of statins.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Statins are inhibitors of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMG-CoA reductase) and became the standard of care for treatment of hypercholesterolemia because of their efficacy, safety, and long-term benefits. They are administered as diastereo- and enantiomerically pure compounds. We summarize here two new approaches for the total synthesis of the most important representatives, atorvastatin, and rosuvastatin, based on highly stereoselective hydrogenations as key-steps. Chirality 2010. (c) 2009 Wiley-Liss, Inc. PMID: 19899159 [PubMed - as supplied by publisher] (Source: Chirality)
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Andrushko N, Andrushko V, Tararov V, Korostylev A, König G, Börner A Tags: Chirality Source Type: journals

An efficient dipeptide-catalyzed direct asymmetric aldol reaction of equimolar reactants in solid media.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The direct asymmetric aldol reactions of equivalent molar amounts of aldehydes and ketones were carried out at -20 degrees C over alkaline Al(2)O(3) with 20 mol % of Pro-Trp as catalyst and 20 mol % of N-methylmorpholine or 1,4-diazabicyclo[2.2.2]octane as additive. After simple and environmentally friendly work-up, moderate to high isolated yields (up to 95%), good diastereoselectivities (>99:1), and enantioselectivities (up to 98% ee) have been achieved for the reactions of different kinds of ketones with various aldehydes. The catalytic system could be reused without decrease of activity by addition of 10 mol % c...
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Lei M, Xia S, Wang J, Ge Z, Cheng T, Li R Tags: Chirality Source Type: journals

Chiral configuration of the hydration layers of D- and L-alanine in water implied from dilution calorimetry.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this study, we determined by dilution microcalorimetry the fraction of the hydration energy invested in the chiral distortion of the hydration layer surrounding D- and I-alanine in water. The results indicate that in dilute solutions, a multilayered chiral hydration surrounds each of these solutes and amounts to over 100 water molecules. In concentrated solutions, the immediate chiral hydration layer decreases to approximately 30 water molecules. The energy invested in the induction of the chiral twist in the hydration layer is predominantly attributed to TDeltaS, the energy associated with "configurational entropy," wh...
Source: Chirality - November 6, 2009 Category: Molecular Biology Authors: Shvalb A, Mastai Y, Shinitzky M Tags: Chirality Source Type: journals

HPLC-method for determination of permethrin enantiomers using chiral beta-cyclodextrin-based stationary phase.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The liquid chromatographic separation of permethrin enantiomers on chiral beta-cyclodextrin-based stationary phase has been investigated. All four enantiomers are obtained by using simple methanol and water mobile phase, under gradient mode. The method was optimized and validated. The relationship between temperature and chromatographic parameters: k' (capacity factor), alpha (separation factor) and Rs (resolution factor) was studied. Van't Hoff's curves for each enantiomer were plotted for temperature range 288-318 K. It was noticed that the response factor ratio of permethrin isomers differ and calculated value is fo...
Source: Chirality - November 2, 2009 Category: Molecular Biology Authors: Shishovska M, Trajkovska V Tags: Chirality Source Type: journals

New applications and challenges for computational ROA spectroscopy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this article, applications of quantum chemical methods in calculations of the vibrational Raman optical activity (ROA) spectra are reviewed and new developements are discussed. Modeling of ROA spectra of amino acids and peptides and applications for establishing absolute configuration are briefly outlined. Particular attention is paid to the modeling of solvent effects on ROA spectra, anharmonicity in ROA, resonance and pre-resonance ROA spectra, and ROA spectra of molecules adsorbed on metal surfaces or metal nanoparticles (surface-enhanced Raman optical activity, SEROA). Remaining challenges in computational ROA s...
Source: Chirality - November 2, 2009 Category: Molecular Biology Authors: Pecul M Tags: Chirality Source Type: journals

Channel-like crystal structure of cinchoninium L-O-phosphoserine salt dihydrate.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Studies on the interactions between L-O- phosphoserine, as one of the simplest fragments of membrane components, and the Cinchona alkaloid cinchonine, in the crystalline state were performed. Cinchoninium L-O-phosposerine salt dihydrate (PhSerCin) crystallizes in a monoclinic crystal system, space group P2(1), with unit cell parameters: a = 8.45400(10) A, b = 7.17100(10) A, c = 20.7760(4) A, alpha = 90 degrees , beta = 98.7830(10) degrees , gamma = 90 degrees , Z = 2. The asymmetric unit consists of the cinchoninium cation linked by hydrogen bonds to a phosphoserine anion and two water molecules. Intermolecular hydroge...
Source: Chirality - November 2, 2009 Category: Molecular Biology Authors: Wesełucha-Birczyńska A, Oleksyn BJ, Wątroba J Tags: Chirality Source Type: journals

Factors influencing the interconversion of a new class of dibenzodiazepine sulfonamide atropisomers.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A novel family of atropisomers based on a conformationally constrained seven membered ring system is investigated using a combination of preparative chiral chromatography, circular dichroism, and other analytical techniques. The influence of structure on the rate of atropisomer interconversion was explored with a series of analogs showing a range of interconversion rates ranging from very fast (undetectable on the HPLC timescale) to very slow (half life of many days). Chirality 2010. (c) 2009 Wiley-Liss, Inc. PMID: 19885821 [PubMed - as supplied by publisher] (Source: Chirality)
Source: Chirality - November 2, 2009 Category: Molecular Biology Authors: Welch CJ, Gong X, Schafer W, Chobanian H, Lin L, Biba M, Liu P, Guo Y, Beard A Tags: Chirality Source Type: journals

Molecular tweezers for enantiodiscrimination in NMR: Di-(R,R)-1-[10-(1-hydroxy-2,2,2-trifluoroethyl)-9-anthryl]-2,2,2-trifluoroethyl benzenedicarboxylates.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A series of new chiral molecular tweezers, di-(R,R)-1-[10-(1-hydroxy-2,2,2-trifluoroethyl)-9-anthryl]-2,2,2-trifluoroethyl phthalate (2), isophthalate (3) and terephthalate (4), were synthesized and their structure studied by NMR and molecular mechanics. Their effectiveness as chiral solvating agents for the determination of the enantiomeric purity of chiral compounds using NMR was demonstrated. Chirality 2010. (c) 2009 Wiley-Liss, Inc. PMID: 19885822 [PubMed - as supplied by publisher] (Source: Chirality)
Source: Chirality - November 2, 2009 Category: Molecular Biology Authors: Gil S, Palomino-Schätzlein M, Burusco KK, Jaime C, Virgili A Tags: Chirality Source Type: journals

Experimental and computational studies of enantioseparation of structurally similar chiral compounds on amylose tris(3,5-dimethylphenylcarbamate).Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The enantioseparation of 14 structurally similar chiral solutes, with one or two chiral centers, are studied for a commercially important polysaccharide-based chiral stationary phase, amylose tris(3,5-dimethylphenylcarbamate) (ADMPC). Among these solutes, only two solutes show significant enantioresolutions of 2 to 2.5 in n-hexane/2-propanol (90/10, v/v) at 298 K. The retention factors of the chiral solutes vary significantly from 0.7 to 7.0, and they are compared with those of simpler nonchiral solutes having similar but fewer functional groups. The sorbent-solute H-bonding interactions between the solute functional g...
Source: Chirality - November 2, 2009 Category: Molecular Biology Authors: Kasat RB, Franses EI, Wang NH Tags: Chirality Source Type: journals

Circular dichroism spectra, optical rotations and absolute configurations of cis-dihydrodiol metabolites of quinoline and derivatives: The role of the nitrogen atom.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The absolute configurations of cis-dihydrodiol bacterial metabolites derived from quinoline substrates and their quinolinium salts have been determined by comparison of experimental and calculated chiroptical data (circular dichroism spectra and optical rotations). The role of intramolecular H-bonding and other interactions in the preferred conformations has been investigated, including the effect of protonation of several cis-dihydrodiols. The presence of a strong intramolecular OH...N bond in several cis-dihydrodiol metabolites suggests that such species have a residually chiral oxygen atom. Chirality 2009. (c) 2009 ...
Source: Chirality - September 10, 2009 Category: Molecular Biology Authors: Kwit M, Gawronski J, Sbircea L, Sharma ND, Kaik M, Boyd DR Tags: Chirality Source Type: journals

Characterization of folded conformations in a tetrapeptide containing two tryptophan residues by vibrational circular dichroism.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The intramolecularly hydrogen bonded conformations of the tetrapeptide Boc-Trp-Aib-Gly-Trp-OMe (WUGW) are investigated using experimental and quantum chemical predictions of vibrational circular dichroism (VCD) in the 1800-1550 cm(-1) region. The predicted VCD spectrum, for a conformation (conformer A) obtained from optimization of crystal structure, reproduced the dominant negative VCD band observed experimentally in CH(3)OH and CHCl(3) solvents. However, the predicted VCD spectrum of Conformation A also has an extra positive band which is not seen in the experimental spectra. This mismatch appears to be due to the la...
Source: Chirality - September 10, 2009 Category: Molecular Biology Authors: Petrovic AG, Polavarapu PL, Mahalakshmi R, Balaram P Tags: Chirality Source Type: journals

Theoretical approaches to the calculation of Raman optical activity spectra.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this article, we will give a brief account of the different approaches that have been presented in the literature for calculating Raman optical activity (ROA) spectra by ab initio methods. We will also outline the general structure of a self-consistent-field-based approach for analytic calculations of ROA spectra, including also contributions from London orbitals. The use of London orbitals ensures that the relevant ROA parameters are gauge origin independent. We will also give an outlook on the future of ab initio calculations of Raman optical activity spectra. Chirality 2009. (c) 2009 Wiley-Liss, Inc. PMID: 19...
Source: Chirality - September 10, 2009 Category: Molecular Biology Authors: Ruud K, Thorvaldsen AJ Tags: Chirality Source Type: journals

Use of (S)-BINOL as NMR chiral solvating agent for the enantiodiscrimination of omeprazole and its analogs.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The application of (S)-1,1'-binaphthyl-2,2'-diol as NMR chiral solvating agent (CSA) for omeprazole, and three of its analogs (lanso-, panto-, and rabe-prazole) was investigated. The formation of diastereomeric host-guest complexes in solution between the CSA and the racemic substrates produced sufficient NMR signal splitting for the determination of enantiomeric excesses by (1)H- or (19)F-NMR spectroscopy. Using of hydrophobic deuterated solvents was mandatory for obtaining good enantiodiscrimination, thus suggesting the importance of intermolecular hydrogen bonds in the stabilization of the complexes. The method was ...
Source: Chirality - September 10, 2009 Category: Molecular Biology Authors: Redondo J, Capdevila A, Latorre I Tags: Chirality Source Type: journals

Imaging chiroptical artifacts.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
It is well-known that circular dichroism (CD) measurements of anisotropic media may contain artifacts that result from mixed linear anisotropies. Such artifacts are generally considered a nuisance. However, systematic artifacts, carefully measured, may contain valuable information. Herein, polycrystalline spherulites of D-sorbitol grown from the melt were analyzed with a Mueller matrix microscope, among other differential polarization images devices. As spherulites grew into one another they developed strong apparent optical rotation and CD signals at the boundaries between spherulites. These signals are shown not to h...
Source: Chirality - September 8, 2009 Category: Molecular Biology Authors: Freudenthal JH, Hollis E, Kahr B Tags: Chirality Source Type: journals

Bile acids in asymmetric synthesis and chiral discrimination.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An overview on the use of bile acid-based compounds able to catalyze transformations, control the stereochemical course of a given reaction, recognize and bind other molecules, is presented. The recent developments in inclusion discrimination of chiral and achiral guests and enantioselective recognition achieved by bile acid are described with suitable examples. Chirality 2009. (c) 2009 Wiley-Liss, Inc. PMID: 19743483 [PubMed - as supplied by publisher] (Source: Chirality)
Source: Chirality - September 8, 2009 Category: Molecular Biology Authors: Bortolini O, Fantin G, Fogagnolo M Tags: Chirality Source Type: journals

Production of (R)-1-phenylethanols through bioreduction of acetophenones by a new fungus isolate Trichothecium roseum.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A total of 120 fungal strains were isolated from soil samples and evaluated in the bioreduction of substituted acetophenones to the corresponding (R)-alcohols. Among these strains, isolate Trichothecium roseum EBK-18 was highly effective in the production of (R)-alcohols with excellent enantioselectivity (ee > 99%). Gram scale preparation of (R)-1-phenylethanol is reported. Chirality 2009. (c) 2009 Wiley-Liss, Inc. PMID: 19743484 [PubMed - as supplied by publisher] (Source: Chirality)
Source: Chirality - September 8, 2009 Category: Molecular Biology Authors: Zilbeyaz K, Taskin M, Kurbanoglu EB, Kurbanoglu NI, Kilic H Tags: Chirality Source Type: journals

High-performance liquid chromatography separation of enantiomers of mandelic acid and its analogs on a chiral stationary phase.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The enantiomers of mandelic acid and its analogs have been chromatographically separated on a chiral stationary phase (CSP) derived from 4-(3,5-dinitrobenzamido) tetrahydrophenanthrene. The rationale of separations of these compounds is discussed with respect to the method development for determining enantiomeric purity and possibility of obtaining enantiomerically pure materials by high-pressure liquid chromatography. The relationship of analyte structure to the extent of enantiomeric separation has been examined and separation factors (alpha) are presented for various groups of structurally related compounds. Chiral ...
Source: Chirality - September 8, 2009 Category: Molecular Biology Authors: Aneja R, Luthra PM, Ahuja S Tags: Chirality Source Type: journals

Determination of the absolute configuration of the natural product klaivanolide via density functional calculations of vibrational circular dichroism (VCD).Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The absolute configuration (AC) of the antiprotozoal lactone, Klaivanolide, 1, from Uvaria klaineana, has been determined using Vibrational Circular Dichroism (VCD) spectroscopy. The experimental VCD spectrum of the (+) enantiomer of 1 was measured. To analyze the AC of (+)-1, the conformationally-averaged VCD spectrum of 7-S-1 was calculated using density functional theory (DFT) and the GAUSSIAN 03 program. The B3PW91/TZ2P conformationally-averaged VCD spectrum of 7-S-1 proves that the AC of 1 is 7-S-(+). Chirality 2009. (c) 2009 Wiley-Liss, Inc. PMID: 19743486 [PubMed - as supplied by publisher] (Source: Chirality)
Source: Chirality - September 8, 2009 Category: Molecular Biology Authors: Devlin FJ, Stephens PJ, Figadère B Tags: Chirality Source Type: journals

Gas phase optical rotation calculated from coupled cluster theory with zero-point vibrational corrections from density funcional theory.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Molecular vibrations can have a significant influence on gas phase specific optical rotations. Mainly due to the large number of nuclear degrees of freedom in most chiral molecules, theoretical predictions of vibrational corrections quickly become prohibitively expensive. Here, we investigate an approach in which the purely electronic contribution is calculated at the coupled cluster singles and doubles level, while the zero-point vibrational correction is computed using the less demanding density functional theory (B3LYP functional). By comparing to experimental gas phase results for seven molecules and two wavelength...
Source: Chirality - September 8, 2009 Category: Molecular Biology Authors: Pedersen TB, Kongsted J, Crawford TD Tags: Chirality Source Type: journals

Synthesis, chiroptical properties, and their theoretical simulation of some highly rotating benzotricamphor derivatives.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The large molecules 1-3 (69, 90, and 102 atoms, respectively), prepared by cyclotrimerization of enantiomerically pure derivatives of (-)-bornyl acetate, show intense ECD spectra, high optical rotation (OR) values (200-1300, in absolute value) dominated in sign and order of magnitude by the lowest-energy Cotton effects, that is, they are the ideal candidates to test the reliability of our "approximate" (TDDFT/B3LYP/6-31G* or smaller basis set) approach to the calculation of chiroptical properties. As a matter of fact, a correct simulation of the OR values and ECD spectra of 1 and 2 can be obtained even using STO-3G bas...
Source: Chirality - August 31, 2009 Category: Molecular Biology Authors: Mazzeo G, Giorgio E, Rosini C, Fabris F, Fregonese E, Toniolo U, De Lucchi O Tags: Chirality Source Type: journals

Vibrational and electronic optical activity of the chiral disulphide group: Implications for disulphide bridge conformation.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Using dihydrogendisulphide (H(2)S(2)), dimethyl- ((CH(3))(2)S(2)), and diethyldisulphide ((CH(3)CH(2))(2)S(2))as model molecules, theoretical ECD, VCD, and ROA spectra of nonplanar disulphides were calculated by DFT methods. Most of the calculated electronic and vibrational chiroptical features suffer an equivocal relation between calculatedsigns of ECD, VCD, or ROA and the sense of disulphide nonplanarity as noted earlier for low-lying ECD bands. This is a consequence of local C(2) symmetry of a disulphide group causing most electronic and vibrational transitions to occur as pairs falling to alternative A, B symmetry ...
Source: Chirality - August 31, 2009 Category: Molecular Biology Authors: Bednárová L, Bouř P, Maloň P Tags: Chirality Source Type: journals

Experimental aspects of solid state circular dichroism.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The interest of circular dichroism in the solid state is stimulated by several needs, such as the desire to get solvent free spectra, the insolubility of the sample or the intrinsic process in which the sample itself is prepared or manipulated. We approach the argument on the basis of the sampling technique, since each different case calls for specific care in getting proper results. Chirality, 2009. (c) 2009 Wiley-Liss, Inc. PMID: 19722271 [PubMed - as supplied by publisher] (Source: Chirality)
Source: Chirality - August 30, 2009 Category: Molecular Biology Authors: Castiglioni E, Biscarini P, Abbate S Tags: Chirality Source Type: journals

Evaluation of dalbavancin as chiral selector for HPLC and comparison with teicoplanin-based chiral stationary phases.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Dalbavancin is a new compound of the macrocyclic glycopeptide family. It was covalently linked to 5 mum silica particles using two different binding chemistries. Approximately 250 racemates including (a) heterocyclic compounds, (b) chiral acids, (c) chiral amines, (d) chiral alcohols, (e) chiral sulfoxides and sulfilimines, (f) amino acids and amino acid derivatives, and (g) other chiral compounds were tested on the two new chiral stationary phases (CSPs) using three different mobile phases. As dalbavancin is structurally related to teicoplanin, the same set of chiral compounds was screened on two commercially availabl...
Source: Chirality - August 11, 2009 Category: Molecular Biology Authors: Zhang X, Bao Y, Huang K, Barnett-Rundlett KL, Armstrong DW Tags: Chirality Source Type: journals

A computationally inspired investigation of the solid forms of (R)-1-phenylethylammonium-(S)-2-phenylbutyrate.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Following the computation of a lattice energy landscape which predicted that there should be more stable, denser forms of (R)-1-phenylethylammonium-(S)-2-phenylbutyrate, crystallizations from a range of solvents were performed to search for other polymorphs and investigate the possibility that the known P4(1) structure could be a hydrate. Extensive crystallization experiments from a wide range of solvents gave fine needles or microcrystalline samples. A redetermination of the P4(1) structure by powder X-ray diffraction located all protons, and in conjunction with other experimental and computational evidence showed tha...
Source: Chirality - July 29, 2009 Category: Molecular Biology Authors: Antoniadis CD, D'Oria E, Karamertzanis PG, Tocher DA, Florence AJ, Price SL, Jones AG Tags: Chirality Source Type: journals

On circular dichroism and the separation between chromophore and chiral center: The near carbon K-edge X-ray absorption and circular dichroism spectra of noradrenaline and L-DOPA.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The near carbon K-edge X-ray absorption and circular dichroism spectra of noradrenaline (neutral and protonated forms) and L-DOPA (protonated form) have been determined with use of the complex polarization propagator method in conjunction with Kohn-Sham density functional theory. A Coulomb attenuated exchange-correlation functional and London atomic orbitals have been employed to address the issues of hole-electron interactions and gauge-origin dependence of the magnetic-dipole operator, respectively. Results show that the characteristics of the chromophore part of the circular dichroism spectra are shared for all thre...
Source: Chirality - July 29, 2009 Category: Molecular Biology Authors: Villaume S, Norman P Tags: Chirality Source Type: journals

Determination of enantiomerization barriers of hypericin and pseudohypericin by dynamic high-performance liquid chromatography on immobilized polysaccharide-type chiral stationary phases and off-column racemization experiments.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Direct enantiomer separation of hypericin, pseudohypericin, and protohypericin was accomplished by high-performance liquid chromatography (HPLC) using immobilized polysaccharide-type chiral stationary phases (CSPs). Enantioselectivities up to 1.30 were obtained in the polar-organic elution mode whereby for hypericin and pseudohypericin Chiralpak IC [chiral selector being cellulose tris(3,5-dichlorophenylcarbamate)] and for protohypericin Chiralpak IA (chiral selector being the 3,5-dimethylphenylcarbamate of amylose) gave favorable results. Enantiomers were distinguished by on-line electronic circular dichroism detectio...
Source: Chirality - July 29, 2009 Category: Molecular Biology Authors: Ciogli A, Bicker W, Lindner W Tags: Chirality Source Type: journals

Stereoselective metabolism of propranolol glucuronidation by human UDP-glucuronosyltransferases 2B7 and 1A9.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Stereoselective metabolism of propranolol side-chain glucuronidation was studied for two recombinant human uridine diphosphate glucuronosyltransferases (UGTs), UGT1A9 and UGT2B7. The S- and R-propranolol side-chain glucuronides produced in the incubation mixtures were assayed simultaneously by RP-HPLC with fluorescent detector. The excitation and emission wavelengths were set at 310 nm and 339 nm, respectively. UGT1A9 prefers catalyzing S-enantiomer to R-enantiomer and the intrinsic clearance (CL(int)) ratios of S-enantiomer to R-enantiomer are 3.8 times and 6.5times for racemic propranolol and individual enantiomers, ...
Source: Chirality - July 29, 2009 Category: Molecular Biology Authors: Yu L, Qian M, Liu Y, Yao T, Zeng S Tags: Chirality Source Type: journals

The pyrolysis of (-)-(S)-nicotine: Racemization and decomposition.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The pyrolytic behaviour of (-)-(S)-nicotine in methanol was investigated using on-line pyrolysis GC/MS to establish whether racemization to the R(+) antipode occurs and to identify other products of pyrolysis. The conditions used included pyrolysing the sample for 15 seconds in an atmosphere of 9% oxygen in nitrogen (275ml/min total flow) across the temperature range of 200 degrees C-1000 degrees C. A chiral Cyclodex-B analytical column (30m x 0.25mm i.d. x 0.25 mum film thickness) was used to separate the enantiomers of nicotine, although the two enantiomer peaks were not baseline resolved. The results of the experime...
Source: Chirality - July 29, 2009 Category: Molecular Biology Authors: Clayton P, Lu A, Bishop L Tags: Chirality Source Type: journals

Supramolecular dynamics of thalidomide and its derivatives in water-sediment system.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The contamination of drug residues, including chiral ones, is not acceptable in earth's ecosystem. The dynamicity of enantiomers of thalidomide and its derivatives (3-methyl thalidomide, 3-ethyl thalidomide, and 3-butyl thalidomide) was ascertained at supramolecular level in water-sediment system using solid phase extraction (SPE) and stereoselective HPLC. Enantiomeric separation of these drugs was carried out on Ceramosphere RU-2 (25 cm x 0.46 cm, particle size 50 mum) chiral column using pure ethanol (1.0 ml/min) as eluent at 230 nm detection. Retention times, capacity, separation, and resolution factors of the enant...
Source: Chirality - July 16, 2009 Category: Molecular Biology Authors: Ali I, Gupta VK, Aboul-Enein HY Tags: Chirality Source Type: journals

Recyclable Merrifield resin-supported organocatalysts containing pyrrolidine unit through A(3)-coupling reaction linkage for asymmetric Michael addition.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Merrifield resin-supported pyrrolidine-based chiral organocatalysts A-D through A(3)-coupling reaction linkage have been developed and found to be highly effective catalysts for the Michael addition reaction of ketones with nitrostyrenes. The reactions generated the corresponding products in good yields (up to 92%), excellent enantioselectivities (up to 98% ee), and high diastereoselectivities (up to 99:1 dr). In addition, the catalysts can be reused at least five times without a significant loss of catalytic activity and stereoselectivity. Chirality, 2009. (c) 2009 Wiley-Liss, Inc. PMID: 19618421 [PubMed - as supp...
Source: Chirality - July 16, 2009 Category: Molecular Biology Authors: Liu J, Li P, Zhang Y, Ren K, Wang L, Wang G Tags: Chirality Source Type: journals

Self-assembly and chiral recognition of quartz crystal microbalance chiral sensor.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A novel chiral sensor based on the self-assembled monolayer of (6(A)-omega-mercaptoethylureado-6(A)-deoxy)heptakis(2,3-di-o-phenylcarbamoyl)-6(B), 6(C), 6(D), 6(E), 6(F), 6(G)- hexa-o-phenylcarbamoyl-beta-cyclodextrin (Ph-beta-CD-SH) on a quartz crystal transducer for chiral recognition was set up. (R,S)-(+/-)-(3-Methoxyphenyl)ethylamine were recognized by this QCM chiral sensor with a QCM chiral discrimination factor of 1.33. Furthermore, UV spectroscopy was used to investigate the mechanism of host-guest interactions between (6(A)-azido-6(A)-deoxy)heptakis(2,3-di-o-phenylcarbamoyl)-6(B), 6(C), 6(D), 6(E), 6(F), 6(G)-...
Source: Chirality - July 13, 2009 Category: Molecular Biology Authors: Luo ML, Zhang WG, Zhang S, Fan J, Su WC, Yin X Tags: Chirality Source Type: journals

Ultrasound-mediated synthesis of camphoric acid-based chiral salens for the enantioselective trimethylsilylcyanation of aldehydes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
New chiral salen ligands were prepared by the ultrasound-irradiated condensation of optically active (1R, 3S)-1,2,2-trimethyl-1,3-diaminocyclopentane with aromatic 1-hydroxyaldehydes. The ultrasound-mediated process is more convenient due to shorter reaction times, energy economy, and easier isolation of the products. The in situ formed Ti(IV)(salen) complexes, evaluated as catalysts in the enantioselective trimethylsilylcyanation of benzaldehyde, were found to be efficient for this process, originating the corresponding product in high yields (72-99%) and selectivities of up to 79%. The lowest energy transition states...
Source: Chirality - July 13, 2009 Category: Molecular Biology Authors: Serra ME, Murtinho D, Goth A, Rocha Gonsalves AM, Abreu PE, Pais AA Tags: Chirality Source Type: journals

Stereoselective synthesis and characterization of new enantiomerically pure phosphoric acids.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Starting from (R)-6,6'-dimethyldiphenyl-2,2'-dicarboxylic acid, a novel class of enantiomerically pure cyclic dialkyl phosphates was synthesized and properly characterized. The absolute configuration was determined by 2D NOESY experiments. The catalytic behavior of the new chiral Bronsted acids was investigated in the stereoselective addition of a silyl keteneacetal to aldimines. The Mannich-type reaction was promoted in up to 94% yields and enantioselectivities up to 55%. On the basis of preliminary molecular mechanic calculations, a model of stereoselection was also proposed to explain the sense of the enantioselecti...
Source: Chirality - July 6, 2009 Category: Molecular Biology Authors: Biaggi C, Benaglia M, Annunziata R, Rossi S Tags: Chirality Source Type: journals

Enantiodiscrimination of methamphetamine by circular dichroism using a porphyrin tweezer.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Using exciton-coupled circular dichroism (ECCD) spectroscopy, our lab was able to differentiate between the two enantiomers of methamphetamine using a commercially available porphyrin tweezer as an achiral host. The host-guest complex formed with (+)-(S)-methamphetamine produced a negative bisignate-shaped ECCD spectrum, whereas the complex formed with (-)-(R)-methamphetamine produced a positive one. This sensitive technique could serve as an alternative method for the enantiodiscrimination of chiral methamphetamine, a commonly abused drug in the United States. Chirality 2009. (c) 2009 Wiley-Liss, Inc. PMID: 195754...
Source: Chirality - July 1, 2009 Category: Molecular Biology Authors: Anderson M, Wilcox K, Guericke M, Chu H, Wilson MV, Wilson E, Lucas K, Holmes AE Tags: Chirality Source Type: journals

Stereoselective transport and uptake of propranolol across human intestinal Caco-2 cell monolayers.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The transport and uptake of individual propranolol (PPL) enantiomers were studied in human intestinal Caco-2 cell monolayers, and a reversed-phase HPLC-UV assay was used for quantitative analysis. S-PPL and R-PPL across Caco-2 cell monolayers was determined in the concentrations range of 10-500 muM in both apical (AP) to basolateral (BL) and BL to AP directions. S-PPL exhibited greater permeability than R-PPL in the AP to BL direction, whereas in the BL to AP direction S-enantiomer transported less than R-enantiomer. Uptake of R-PPL was significantly higher than that of S-PPL either from AP side or from BL side. The st...
Source: Chirality - July 1, 2009 Category: Molecular Biology Authors: Wang Y, Cao J, Wang X, Zeng S Tags: Chirality Source Type: journals

Simultaneous determination of enantiomerization and hydrolysis kinetic parameters of chiral N-alkylbenzothiadiazine derivatives.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
On-column stopped flow multidimensional HPLC (sfMDHPLC) and dynamic high-performance liquid chromatography were applied to investigate the influence of alkyl substituents at the sulfonamidic and amino moieties of benzothiadiazine 1,1-dioxide derivatives on hydrolysis and enantiomerization rate constants. The data obtained indicate the presence of pyrrolo substituent at the 3,4 positions on benzothiadiazine rings inhibits the hydrolysis, whereas the enantiomerization occurs in acidic medium. Hydrolysis rates are quite similar for the two benzothiadiazines methyl substituted to nitrogen at 2- and 4-positions. Conversely,...
Source: Chirality - July 1, 2009 Category: Molecular Biology Authors: Carrozzo MM, Cannazza G, Battisti U, Braghiroli D, Parenti C Tags: Chirality Source Type: journals

Effect of the substrate and catalyst chirality on the diastereoselective epoxidation of limonene using Jacobsen-type catalysts.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Chiral and achiral Jacobsen's catalysts in their homogeneous form or immobilized on Al-MCM-41 exhibit similar catalytic activity during diastereoselective epoxidation of limonene when in situ generated dimethyldioxirane is used as oxidizing agent. Experimental observations suggest that not only the catalyst chiral center but also the substrate chiral center participates in the preferential formation of most diastereomers. Remarkable turnover numbers (TON), up to 288, was achieved over the heterogeneous catalysts in comparison to their homogeneous counterparts (TON up to 46). Catalyst leaching rather than catalyst oxida...
Source: Chirality - June 28, 2009 Category: Molecular Biology Authors: Cubillos J, Vargas M, Reyes J, Villa A, De Correa CM Tags: Chirality Source Type: journals

Chiral separation of phospine-containing alpha-amino acid derivatives using two complementary cellulosic stationary phases in supercritical fluid chromatography.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Enantiomeric separations of six amino-acid derivatives have been studied using packed-column supercritical fluid chromatography with two polysaccharide-based enantioselective stationary phases: cellulose tris(3,5-dimethylphenylcarbamate) and cellulose tris(3-chloro-4-methylphenylcarbamate) (Lux Cellulose-1 and -2). The effect of analyte structure on retention and separation was studied. Varied mobile phase compositions were investigated: alcohol modifier percentage was increased from 3 to 40% but smaller amounts were most effective in separating these compounds. Besides, ethanol was preferred to methanol or isopropanol...
Source: Chirality - June 22, 2009 Category: Molecular Biology Authors: West C, Bouet A, Gillaizeau I, Coudert G, Lafosse M, Lesellier E Tags: Chirality Source Type: journals

Fast chiral separation of drugs using columns packed with sub-2 mum particles and ultra-high pressure.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The use of columns packed with sub-2 mum particles in liquid chromatography with very high pressure conditions (known as UHPLC) was investigated for the fast enantioseparation of drugs. Two different procedures were evaluated and compared using amphetamine derivatives and beta-blockers as model compounds. In one case, cyclodextrins (CD) were directly added to the mobile phase and chiral separations were carried out in less than 5 min. However, this strategy suffered from several drawbacks linked to column lifetime and low chromatographic efficiencies. In the other case, the analysis of enantiomers was carried out after...
Source: Chirality - June 17, 2009 Category: Molecular Biology Authors: Guillarme D, Bonvin G, Badoud F, Schappler J, Rudaz S, Veuthey JL Tags: Chirality Source Type: journals