Chirality
The effect of nonchromophoric additives on supramolecular exciton intensity was tested. Fatty acids and 1‐dodecanol decreased exciton intensity of the tightly packed aggregate of 6′R‐capsanthol‐3′‐on, whereas all esters studied increased exciton intensity. These results apparently confirm the validity of the treatment of Harada for supramolecular systems too. Chirality 2010. © 2010 Wiley‐Liss, Inc.
The compounds I–IV derived from α‐D‐cyclodextrin moiety by bridging and/or interconnecting with various patterns of disulfide bonds were chosen as models for the spectroscopic study of conformation of the disulfide bridge. The energy gap between the disulfide and cyclodextrin's electronic transitions allows us to investigate absorption and electronic circular dichroism spectra without disturbing spectral...
Density Functional Theory (DFT) calculations of optical rotation (OR) and vibrational circular dichroism (VCD) have been used to assign the absolute configuration (AC) of a recently prepared (3‐phenyloxirane‐2,2‐diyl)bis(phenylmethanone), 3, by asymmetric epoxidation of the corresponding 2‐arylidene‐1,3‐diketone. The experimental OR at 589.3 nm and the VCD spectrum of the (+)‐ and (−)‐enantiomer of...
The intense circular dichroism (CD) phenomena, as induced in amorphous samples of syndiotactic polystyrene (s‐PS) by cocrystallization with nonracemic volatile guest molecules (carvone and limonene), have been investigated by Vibrational Circular Dichroism (VCD) measurements and X‐ray diffraction characterizations. Moreover, the stability of these CD phenomena after thermal and solvent treatments,...
We describe herein the use of a flexible biphenyl moiety as efficient chirality probe in the assignment of the absolute configuration (AC) of aliphatic, non‐chromophoric diols. The diols are transformed in the corresponding biphenyl dioxolanes in which the biphenyl system has either a P or M torsion depending on the chirality of the diol. As the correlation between biphenyl torsion and diol AC has...
Two peptide nucleic acids (PNAs) containing three adjacent modified chiral monomers (chiral box) were synthesized. The chiral monomers contained either a C2‐ or a C5‐modified backbone, synthesized starting from D‐ and L‐arginine, respectively (2D‐ and 5L‐PNA). The C2‐modified chiral PNA was synthesized using a submonomeric strategy to avoid epimerization during solid‐phase synthesis, whereas for the...
Despite that a number of experimental and theoretical investigations have been carried out to determine the structure of trialanine in water, the reported populations of polyproline II (PPII) and β‐strand conformers vary and were found to be dependent on which spectroscopic method was used. Such discrepancies are due to limitations of different spectroscopic methods used. Here, the temperature‐ and...
Chiral symmetry breaking occurs during vortex‐assisted crystallization of several simple compounds leading to a stochastically determined emergence of an enantiomeric excess of one chiral isomer. This article summarizes recent developments in studies of a similar phenomenon observed in agitated solutions of aggregating insulin, when a phase transition—precipitation of insoluble amyloid fibrils from...
Tamburro and coworkers have demonstrated that some elastin‐derived polypeptide sequences are able to give rise, in vitro, to amyloid‐like fibers. The biological relevance of this finding could be explained by the recent detection of some amyloidogenic material found in arteries of old patients affected by atherosclerosis and demonstrated to be elastin derived. In this context, the comprehension of...
(R,R)‐formoterol was synthesized in seven steps with 4‐hydroxyl‐3‐nitro‐acetophenone as the starting material. The key intermediate, the chiral secondary alcohol 4, was prepared via Rh‐catalyzed asymmetric transfer hydrogenation with (S,S)‐PEGBsDPEN as the ligand and sodium formate as the hydrogen donor under mild conditions. With a mixture of PEG 2000 and water as the reaction media, the catalyst...
The stereoselective degradation of triadimenol in different cucumber plant tissues (root, stem, leaf, and fruit) has been investigated. Rac‐triadimenol was applied to cucumber plants by root irrigation mode under field conditions. The degradation kinetics and the enantiomer fraction were determined by normal‐phase high‐performance liquid chromatography with diode array detector and on‐line optical...
The parallel kinetic resolution of racemic 2‐aryl‐2‐deuterio‐propionic and butanoic acids using an equimolar combination of quasi‐enantiomeric oxazolidin‐2‐ones is discussed. The levels of diastereoselectivity were high leading to enantiomerically pure D‐labeled products in good yield. Chirality, 2010. © 2009 Wiley‐Liss, Inc.
The acetylcholinesterase inhibition by enantiomers of exo‐ and endo‐2‐norbornyl‐N‐n‐butylcarbamates shows high stereoselelectivity. For the acetylcholinesterase inhibitions by (R)‐(+)‐ and (S)‐(−)‐exo‐2‐norbornyl‐N‐n‐butylcarbamates, the R‐enantiomer is more potent than the S‐enantiomer. But, for the acetylcholinesterase inhibitions by (R)‐(+)‐ and (S)‐(−)‐endo‐2‐norbornyl‐N‐n‐butylcarbamates, the...
Optically active 3,3′‐dimethyl‐2,2′‐diamino‐1,1′‐binaphthyl (DM‐DABN) and 3,3′‐dimethyl‐2‐amino‐2′‐hydroxybinaphthyl (DM‐NOBIN) derivatives were synthesized by Cu‐(−)‐sparteine complex‐catalyzed enantioselective homo‐ and hetero‐coupling of 2‐naphthylamine, respectively. The difference in enantioselectivity was observed by changing the concentration of oxygen. Chirality, 2010. © 2009 Wiley‐Liss, Inc.
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...
A convenient method for the generation of (+)‐sedamine and (+)‐allosedamine in high optical purity has been elaborated. The key steps are the highly stereoselective 1,2‐nucleophilic addition to SAMP hydrazones allowing the installation of the stereogenic center at C2 and ring closing metathesis. Chirality, 2010. © 2009 Wiley‐Liss, Inc.
The binding of the (R)‐ and (S)‐enantiomers of amlodipine to bovine serum albumin (BSA), human serum albumin (HSA), α1‐acid glycoprotein (AGP), and human plasma (HP) was studied by equilibrium dialysis over the concentration range of 75–200 μM at a protein concentration of 150 μM. Unbound drug concentrations were determined by enantioselective capillary electrophoresis using 50 mM phosphate buffer,...
In this study, a new Pirkle‐type chiral column stationary phase for resolution of β‐methylphenylethyl amine was described by using activated Sepharose 4B as a matrix, L‐tyrosine as a spacer arm, and an aromatic amine derivative of L‐glutamic acid as a ligand. The binding capacities of the stationary phase were determined at different pH values (pH = 6, 7, and 8) using buffer solutions as mobile phase,...
The absolute configuration of semisynthetic (−)‐3α,6β‐acetoxytropane 1, prepared from (−)‐6β‐hydroxyhyoscyamine 2, has been determined using vibrational circular dichroism (VCD) spectroscopy. The vibrational spectra (IR and VCD) were calculated using DFT at the B3LYP/DGDZVP level of theory for the eight more stable conformers which account for 99.97% of the total relative abundance in the first 10...
Triadimefon is a systemic agricultural fungicide of the triazole class whose major metabolite, triadimenol, also a commercial fungicide, provides the majority of the actual fungicidal activity, i.e., inhibition of steroid demethylation. Both chemicals are chiral: triadimefon has one chiral center with two enantiomers while its enzymatic reduction to triadimenol produces a second chiral center and...