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Chirality

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https://www.readbyqxmd.com/read/29210117/enantioselective-recognition-of-carboxylic-acids-by-novel-fluorescent-triazine-based-thiazoles
#1
Erkan Halay, Selahattin Bozkurt
Hydrogen bonding and π-π interactions take special part in the enantioselectivity task. In this regard, because of having both hydrogen acceptor and hydrogen donor groups, melamine derivatives become more of an issue for enantioselectivity. In the light of such information, triazine-based chiral, fluorescence active novel thiazole derivatives L1 and L2 were designed and synthesized from (S)-(-)-2-amino-1-butanol and (1S,2R)-(+)-2-amino-1,2-diphenylethanol. The structural establishment of these compounds was made by spectroscopic methods such as FTIR, 1 H, and 13 C NMR...
December 6, 2017: Chirality
https://www.readbyqxmd.com/read/29178302/circular-dichroism-of-surface-complexes-based-on-quantum-dots-and-azo-dye
#2
Evgeny V Kundelev, Anna O Orlova, Vladimir G Maslov, Alexander V Baranov, Anatoly V Fedorov
Chiral properties of surface complexes based on CdSe/ZnS quantum dots (QDs) and 1-(2-pyridylazo)-2-naphthol (PAN) azo dye were investigated by circular dichroism spectroscopy. The use of L-, D-cysteine (Lcys, Dcys) capping ligands allowed us to obtain water-soluble chiral QD-PAN complexes. The characterization of the complexes was performed by UV-vis, FTIR, and CD spectroscopy. Quantum chemical TDDFT calculated CD spectra reproduced the experimentally observed sign patterns, which originate from binding Lcys or Dcys and PAN molecules to the same Zn atom on the QD surface...
November 27, 2017: Chirality
https://www.readbyqxmd.com/read/29154400/a-chiral-enantioseparation-generic-strategy-for-anti-alzheimer-and-antifungal-drugs-by-short-end-injection-capillary-electrophoresis-using-an-experimental-design-approach
#3
Ahmed M Abdel-Megied, Rasha S Hanafi, Hassan Y Aboul-Enein
The present study describes a generic strategy using capillary electrophoretic (CE) method for chiral enantioseparation of anti-Alzheimer drugs, namely, donepezil (DON), rivastigmine (RIV), and antifungal drugs, namely, ketoconazole (KET), Itraconazole (ITR), fluconazole (FLU), and sertaconazole (SRT) in which these drugs have different basic and acidic properties. Several modified cyclodextrins (CDs) were applied for enantioseparation of racemates such as highly sulfated α, γ CDs, hydroxyl propyl-β-CD, and Sulfobutyl ether-β-CD...
November 20, 2017: Chirality
https://www.readbyqxmd.com/read/29139574/an-oxorhenium-complex-bearing-a-chiral-cyclohexane-1-olato-2-thiolato-ligand-synthesis-stereochemistry-and-theoretical-study-of-parity-violation-vibrational-frequency-shifts
#4
Nidal Saleh, Radovan Bast, Nicolas Vanthuyne, Christian Roussel, Trond Saue, Benoît Darquié, Jeanne Crassous
In our effort towards measuring the parity violation energy difference between two enantiomers, a simple chiral oxorhenium complex 5 bearing enantiopure 2-mercaptocyclohexan-1-ol has been prepared as a potential candidate species. Vibrational circular dichroism revealed a chiral environment surrounding the rhenium atom, even though the rhenium is not a stereogenic center itself, and enabled to assign the (1S,2S)-(-) and (1R,2R)-(+) absolute configuration for 5. For both compound 5 and complex 4, previously studied by us and bearing a propane-2-olato-3-thiolato ligand, relativistic calculations predict parity violating vibrational frequency differences of a few hundreds of millihertz, above the expected sensitivity attainable by a molecular beam Ramsey interferometer that we are constructing...
November 15, 2017: Chirality
https://www.readbyqxmd.com/read/29139569/lipase-catalyzed-enantioselective-transesterification-of-prochiral-1-1-3-dihydroxypropan-2-yloxy-methyl-5-6-7-8-tetrahydroquinazoline-2-4-1h-3h-dione-in-ionic-liquids
#5
Renata Kołodziejska, Renata Studzińska, Hanna Pawluk
The application of ionic liquids as solvents for transesterification of prochiral pirymidine acyclonucleoside using lipase (EC 3.1.1.3) Amano PS from Burkholderia cepacia (BCL) is reported. The effect of using medium reaction, acyl group donor, and temperature on the activity and enantioselectivity of BCL was studied. From the investigated ionic solvents, the hydrophobic ionic liquid [BMIM]PF6 ] was the preferred medium for enzymatic reactions. However, the best result was obtained in the mixture [BMIM][PF6 ]:TBME (1:1 v/v) at 50°C...
November 15, 2017: Chirality
https://www.readbyqxmd.com/read/29139568/biomimetic-syntheses-of-racemic-natural-products
#6
REVIEW
Arie Zask, George Ellestad
Racemic natural products are rarely produced in plants and microorganisms and are thought to be the result of nonenzymatic, spontaneous reactions. These compounds are often highly complex with multiple contiguous chiral centers that present a challenge to organic synthesis. Formation of these racemates often occurs by cyclization reactions that can generate multiple stereocenters from achiral precursors. Biomimetic synthesis of these racemic natural products provides support for their proposed nonenzymatic spontaneous biosynthesis...
November 15, 2017: Chirality
https://www.readbyqxmd.com/read/29114933/di-1-naphthyl-methanol-ester-of-carboxylic-acids-for-absolute-stereochemical-determination
#7
Jun Zhang, Wei Sheng, Hadi Gholami, Tatsuo Nehira, Babak Borhan
The absolute stereochemistry of chiral carboxylic acids is determined as a di(1-naphthyl)methanol ester derivative. Computational scoring of conformations favoring either P or M helicity of the naphthyl groups, capable of exciton-coupled circular dichroic coupling, leads to a predicted stereochemistry for the derivatized carboxylic acids.
November 8, 2017: Chirality
https://www.readbyqxmd.com/read/29110401/absolute-configuration-of-the-diterpenoids-icetexone-and-conacytone-from-salvia-ballotaeflora
#8
Baldomero Esquivel, Eleuterio Burgueño-Tapia, Celia Bustos-Brito, Nury Pérez-Hernández, Leovigildo Quijano, Pedro Joseph-Nathan
Detailed literature inspections regarding the diterpenoids icetexone (1) and conacytone (3) reveal that the absolute configuration (AC) of these natural occurring compounds is not rigorously proven, despite they were originally isolated in 1976. This task is now completed by single-crystal X-ray diffraction Flack and Hooft parameters determination after processing data collected with Cu Kα graphite monochromated radiation. The AC of both compounds is further determined by vibrational circular dichroism measurements performed on icetexone acetate (2) and conacytone triacetate (4) since the solubility of 1 and 3 is limited...
November 7, 2017: Chirality
https://www.readbyqxmd.com/read/29110342/production-of-r-1-1-3-benzodioxol-5-yl-ethanol-in-high-enantiomeric-purity-by-lactobacillus-paracasei-bd101
#9
Engin Şahin
Piperonyl ring is found in a number of naturally occurring compounds and possesses enormous biological activities. There are many studies in the literature with compounds containing a piperonyl ring, but there are very few studies on the synthesis of chiral piperonyl carbinol. The objective of this study was to determine the microbial reduction ability of bacterial strains and to reveal the effects of different physicochemical parameters on this reduction ability. A total of 15 bacterial isolates were screened for their ability to reduce 1-(benzo[d][1,3]dioxol-5-yl) ethanone 1 to its corresponding alcohol...
November 7, 2017: Chirality
https://www.readbyqxmd.com/read/29110341/hemin-and-bile-pigments-are-the-secondary-structure-regulators-of-intrinsically-disordered-antimicrobial-peptides
#10
Ferenc Zsila, Tünde Juhász, Szilvia Bősze, Kata Horváti, Tamás Beke-Somfai
The interaction of protoporphyrin compounds of human origin with the major bee venom component melittin (26 a.a., Z +6) and its hybrid derivative (CM15, 15 a.a., Z +6) were studied by a combination of various spectroscopic methods. Throughout a two-state, concentration-dependent process, hemin and its metabolites (biliverdin, bilirubin, bilirubin ditaurate) increase the parallel β-sheet content of the natively unfolded melittin, suggesting the oligomerization of the peptide chains. In contrast, α-helix promoting effect was observed with the also disordered but more cationic CM15...
November 7, 2017: Chirality
https://www.readbyqxmd.com/read/29110336/electronic-and-vibrational-exciton-coupling-in-oxidized-trianglimines
#11
Joanna Szymkowiak, Marcin Kwit
Readily available chiral trianglimine and their (poly)oxygenated congeners represent a unique class of macrocyclic rigid compounds optimal for testing electronic and vibrational circular dichroism exciton chirality methods. Electronic and vibrational circular dichroism spectra of such trianglimines are strongly affected by polar substituents in macrocycle skeletons. Double substitution by OH groups in each aromatic fragment of the macrocycle causes sign reversal of the exciton couplet in the region of the strongest UV absorption...
November 7, 2017: Chirality
https://www.readbyqxmd.com/read/29105860/a-stereodynamic-fluorescent-probe-for-amino-acids-circular-dichroism-and-circularly-polarized-luminescence-analysis
#12
Nadia Alessandra Carmo Dos Santos, Elena Badetti, Giulia Licini, Sergio Abbate, Giovanna Longhi, Cristiano Zonta
The use of stereodynamic probes is becoming one of the leading strategies for the fast and effective determination of enantiomeric excess. Recently, we reported a series of novel molecular architectures based on a modified tris(2-pyridylmethyl)amine complex (TPMA), which are able to amplify the electronic CD, in the case of Zn(II) assemblies and vibrational CD, in the case of Co(II) assemblies. Herein, we report a structural modification of the ligand with the purpose to obtain a fluorescent chiral probe. The study deals with the synthesis of the novel ligand, the formation of the self-assembly system with amino acids, and the study of the electronic CD and circularly polarized luminescence...
November 4, 2017: Chirality
https://www.readbyqxmd.com/read/29105840/stereochemical-analysis-of-%C3%AE-keto-sulfoxides-by-circular-dichroism
#13
Marcin Górecki, Maria Annunziata M Capozzi, Gianluigi Albano, Cosimo Cardellicchio, Lorenzo Di Bari, Gennaro Pescitelli
Three β-keto sulfoxides (1-3) were synthesized in enantiopure form and investigated by means of circular dichroism (CD) spectroscopy, both in electronic and vibrational range (ECD, VCD), in combination with quantum chemical calculations. For compound 2, the X-ray structure was available; thus, the ECD in the solid state was also considered to reveal the differences between the molecular species in both states. Despite the simplicity of all β-keto sulfoxides under investigation (29 atoms), reproducing even the major spectral VCD features failed for two compounds, making the use of VCD not ideal to assign their absolute configuration in a reliable way...
November 4, 2017: Chirality
https://www.readbyqxmd.com/read/29086443/exploring-potentialities-and-limitations-of-stapled-o-oligo-phenyleneethynylene-s-o-opes-as-efficient-circularly-polarized-luminescence-emitters
#14
Pablo Reiné, José Justicia, Sara P Morcillo, Giuseppe Mazzeo, Emilio García-Fernández, Antonio Rodríguez-Diéguez, Luis Álvarez de Cienfuegos, Sergio Abbate, Juan M Cuerva, Giovanna Longhi, Delia Miguel
In this paper, we have studied the chiroptical properties of a family of o-oligo(phenyleneethynylene) (o-OPE) derivatives with different steric hindrance. Experimental results show high dissymmetry factors (gabs and glum up to 1.1 × 10(-2) ) and very similar electronic circular dichroism (ECD) and circularly polarized luminescence (CPL) for all the derivatives that make this basic o-OPE scaffold a robust pure organic emitter. Vibrational circular dichroism spectra are used to characterize conformational properties in solution...
October 31, 2017: Chirality
https://www.readbyqxmd.com/read/29083057/convenient-enzymatic-resolution-of-r-s-2-methylbutyric-acid-catalyzed-by-immobilized-lipases
#15
Mateus Mittersteiner, Bruna Luiza Linshalm, Ana Paula Furlan Vieira, Patrícia Bulegon Brondani, Dilamara Riva Scharf, Paulo Cesar de Jesus
The application of several immobilized lipases has been explored in the enantioselective esterification of (R,S)-2-methylbutyric acid, an insect pheromone precursor. With the use of Candida antarctica B, using hexane as solvent, (R)-pentyl 2-methylbutyrate was prepared in 2 h with c 40%, eep 90%, and E = 35, while Thermomyces lanuginosus leads to c 18%, eep 91%, and E = 26. The (S)-enantiomer was obtained by the use of Candida rugosa or Rhizopus oryzae (2-h reaction, c 34% and 35%, eep 75 and 49%, and E = 10 and 4, respectively)...
October 30, 2017: Chirality
https://www.readbyqxmd.com/read/29083054/on-the-aggregation-of-bilirubinoids-in-solution-as-evidenced-by-vcd-and-ecd-spectroscopy-and-dft-calculations
#16
Simone Ghidinelli, Giovanna Longhi, Giuseppe Mazzeo, Sergio Abbate, Stefan E Boiadjiev, David A Lightner
Vibrational and electronic circular dichroism (VCD and ECD) spectra of 3 optically active bilirubin analogs with propionic acid groups replaced by (1) 1-(S)-methylpropyl groups, (2) 3-acetoxy-1-(S)-methylpropyl groups, and (3) 1-(S)-2-(R)-dimethyl-2-(methoxycarbonyl)ethyl groups have been recorded at different concentrations in chloroform. The aliphatic chains attached to C-8 and C-12 of the 3 chosen mesobilirubins were modified so as to possess no OH group. The variation of the VCD spectra with concentration is consistent with the formation of dimers at high concentration...
October 30, 2017: Chirality
https://www.readbyqxmd.com/read/29083053/transition-dipole-coupling-modeling-of-optical-activity-enhancements-in-macromolecular-protein-systems
#17
Jiří Průša, Petr Bouř
The transition dipole coupling model allows to vary systematically many parameters, such as chromophore geometries and transition dipoles. We used it to explore conditions favorable to chirality enhancement observed in many experiments on protein amyloidal precipitates. Stacking of β-sheet planes has been identified as a particularly powerful mechanism of the enhancement.
October 30, 2017: Chirality
https://www.readbyqxmd.com/read/29080267/synthesis-of-new-c3-symmetric-amino-acid-and-aminoalcohol-containing-chiral-stationary-phases-and-application-to-hplc-enantioseparations
#18
Jeongjae Yu, Daniel W Armstrong, Jae Jeong Ryoo
We recently reported a new C3-symmetric (R)-phenylglycinol N-1,3,5-benzenetricarboxylic acid-derived chiral high-performance liquid chromatography (HPLC) stationary phase (CSP 1) that demonstrated better results as compared to a previously described N-3,5-dintrobenzoyl (DNB) (R)-phenylglycinol-derived CSP. Over a decade ago, (S)-leucinol, (R)-phenylglycine, and (S)-leucine derivatives were used as the starting materials of 3,5-DNB-based Pirkle-type CSPs for chiral separation. In this study, three new C3-symmetric CSPs (CSP 2, 3, and 4) were prepared by combining the ideas and results mentioned above...
October 28, 2017: Chirality
https://www.readbyqxmd.com/read/29064594/exploration-of-the-expeditious-potential-of-pseudomonas-fluorescens-lipase-in-the-kinetic-resolution-of-racemic-intermediates-and-its-validation-through-molecular-docking
#19
Surbhi Soni, Bharat P Dwivedee, Vishnu K Sharma, Gopal Patel, Uttam C Banerjee
A profoundly time-efficient chemoenzymatic method for the synthesis of (S)-3-(4-chlorophenoxy)propan-1,2-diol and (S)-1-chloro-3-(2,5-dichlorophenoxy)propan-2-ol, two important pharmaceutical intermediates, was successfully developed using Pseudomonas fluorescens lipase (PFL). Kinetic resolution was successfully achieved using vinyl acetate as acylating agent, toluene/hexane as solvent, and reaction temperature of 30°C giving high enantioselectivity and conversion. Under optimized condition, PFL demonstrated 50...
October 24, 2017: Chirality
https://www.readbyqxmd.com/read/29024201/enantioseparation-of-racecadotril-using-polysaccharide-type-chiral-stationary-phases-in-polar-organic-mode
#20
Zoltán-István Szabó, Mohammadhassan Foroughbakhshfasaei, Béla Noszál, Gergő Tóth
Enantioseparation of the antidiarrheal drug, racecadotril, was investigated by liquid chromatography using polysaccharide-type chiral stationary phases in polar organic mode. The enantiodiscrimininating properties of 4 different chiral columns (Chiralpak AD, Chiralcel OD, Chiralpak AS, Chiralcel OJ) with 5 different solvents (methanol, ethanol, 1-propanol, 2-propanol, and acetonitrile) at 5 different temperatures (5-40 °C) were investigated. Apart from Chiralpak AS column the other 3 columns showed significant enantioseparation capabilities...
October 11, 2017: Chirality
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