Chirality
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 P21, with unit cell parameters: a = 8.45400(10) Å, b = 7.17100(10) Å, c = 20.7760(4) Å, α = 90°,...
The direct asymmetric aldol reactions of equivalent molar amounts of aldehydes and ketones were carried out at −20 °C over alkaline Al2O3 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...
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 2010. © 2009...
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...
L‐Dibenzoyl tartaric acid was mono‐esterified with benzyl alcohol, and then chlorinated with SOCl2 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)...
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...
The size and configuration of the hydration layer of solutes play a major role in their thermodynamic features. With respect to amino acids in water, a series of indirect evidence strongly suggest that their hydration layer acquires a chiral configuration induced by their chiral centers. Such a chiral hydration may act as a recognition factor in the various biochemical interactions, but information...
Flecainide, an antiarrythmic agent, and its analogs were resolved on a high performance liquid chromatographic chiral stationary phase (CSP) based on (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid with the use of a mobile phase consisting of methanol‐acetonitrile‐trifluoroacetic acid‐triethylamine (80/20/0.1/0.3, v/v/v/v). The chiral resolution was quite successful, the separation factors (α) and...
Practical, cheap, and stereoselective synthetic methods were applied to the preparation of novel 1‐(aminoalkyl)naphthol and γ‐aminoalcohol tridentate ligands. The ligands obtained were conveniently applied with good results as catalytic sources in the borane‐mediated enantioselective reduction of acetophenone with borane dimethylsulfide. Conformational analysis through molecular modeling allows the...
The reduction of the axially chiral N‐(o‐aryl)‐5,5‐dimethyl‐2,4‐oxazolidinediones by NaBH4 yielded axially chiral N‐(o‐aryl)‐4‐hydroxy‐5,5‐dimethyl‐2‐oxazolidinone enantiomers having a chiral center at C‐4, with 100% diastereoselectivity as has been shown by their 1H and 13C NMR spectra and by enantioselective HPLC analysis. The resolved enantiomeric isomers were found to interconvert thermally through...
Although chiral distinction plays a pervasive role in chemistry, a complete understanding of how this takes place is still lacking. In this work, we expand the earlier described minimal requirement of so called four‐point interactions (vide infra). We focus on chiral point charge model systems as a means to aid in the dissection of the underlying, operative principles. We also construct models with...
Modification of dimethyl tartrate has been investigated through transesterification with aminoalcohols to provide reactive functionalities for the covalent bonding of chiral tartrate to polyhedral oligomeric silsesquioxanes. The transesterification of dimethyl tartrate has been widely studied using different catalytic systems and reaction conditions. Through the proper selection of both the catalytic...
The aim of this study was to explore potential transport mechanisms of cetirizine enantiomers across Caco‐2 cells. Cetirizine displayed polarized transport at concentrations ranging from 4.0 to 80.0 μM, with the permeability in the secretory direction being 1.4‐ to 4.0‐fold higher than that in the absorptive direction. Cetirizine enantiomers were transported distinctively different from each other...
A simple, efficient, and economical method based on the combination of the exceptional behavior of o,o′‐dibenzoyl‐ or o,o′‐di‐p‐toluyl‐(2R,3R)‐tartaric acid in chiral recognition processes, and the coordination ability of calcium or magnesium ion was developed for the resolution of phospholene oxides 1. The calcium or magnesium salt of (−)‐o,o′‐dibenzoyl‐(2R,3R)‐tartaric acid 2,4‐6 or calcium hydrogen...
The purpose of this study was to investigate whether CYP2C19 activity can be estimated from plasma concentrations of lansoprazole enantiomers 4 h (C4h) after single administration by oral and enteral routes. Sixty‐nine subjects, 22 homozygous extensive metabolizers (homEMs), 32 heterozygous EMs (hetEMs), and 15 poor metabolizers (PMs), participated in the study. After a single oral or enteral dose...
Although the organocatalytic direct asymmetric Michael reactions of carbonyl compounds to nitroalkenes have been investigated intensely, the Michael reaction of the thioether‐based donors remains a rather undeveloped field. This work concerns the asymmetric Michael addition of aryl sulfanyl‐propan‐2‐one to nitroalkenes with benzoic acid as an additive, and chiral amine‐thiourea as a bifunctional organocatalyst...
The optical spectroscopic characterization of γ‐turns in solution is uncertain and their distinction from β‐turns is often difficult. This work reports systematic ECD and vibrational circular dichroism (VCD) spectroscopic studies on γ‐turn model cyclic tetrapeptides cyclo(Ala‐β‐Ala‐Pro‐β‐Ala) (1), cyclo(Pro‐β‐Ala‐Pro‐β‐Ala) (2) and cyclo(Ala‐β‐Ala‐Ala‐β‐Ala) (3). Conformational analysis performed...
A new set of optically active 2,3,3‐ and 2,7,7‐trimethyl‐substituted γ‐aminonorbornan‐2‐ols have been obtained from 2‐methylenenorbornane‐1‐carbonitriles derived from (+)‐camphor and (−)‐fenchone and probed as chiral ligands for the enantioselective addition of diethylzinc to benzaldehyde. This has allowed the study of the structural factors influencing the chirality transfer, such as variation of...
When catechins are found in plant extracts, they are almost always identified as catechin and/or epicatechin probably due to stereoselectivity of the enzymes involved in the biosynthesis of these substances. However, the lack of reports regarding to ent‐catechin as well as ent‐epicatechin does not necessarily mean that these compounds have not been produced. In fact, most of the previous reports used...
The racemic and enantioselective synthesis of a novel glyceric acid derivative, namely, 2,3‐dihydroxy‐3‐(3,4‐dihydroxyphenyl)‐propionic acid as well as the antioxidant activities is described. The virtually pure enantiomers, (+)‐(2R,3S)‐2,3‐dihydroxy‐3‐(3,4‐dihydroxyphenyl)‐propionic acid and (−)‐(2S,3R)‐2,3‐dihydroxy‐3‐(3,4‐dihydroxyphenyl)‐propionic acid were synthesized for the first time via Sharpless...