Chiral Α-hydroxy Carboxylic Acids Research Articles

Complexation of Boronic Acid with Chiral α-Hydroxycarboxylic Acids and the Ability of the Complexes to Catalyze α-Hydroxycarboxylic Acid Esterification.

The complexation of boric acid (BA) with various α-hydroxycarboxylic acids (HCAs) was examined by analyzing the change in the optical rotation after the addition of BA to aqueous HCA solutions, and the catalytic properties of the complexes were examined by catalyzing the esterification of the HCAs. The absolute values of the optical rotation of the HCAs increased with increasing BA-to-HCA molar ratio, and the rate of change of the optical rotation gradually decreased as the BA-to-HCA molar ratio increased, reaching a minimum value at a molar ratio of approximately three. As a catalyst, BA could catalyze the acetylation of hydroxyl groups in addition to the esterification of HCAs. Compared to the conventional synthesis routes of ATBC and ATOC, a synthesis route with BA as the catalyst allowed for a lower frequency of catalyst separation and replacement while providing light-colored products. BA could catalyze the formation of triethyl citrate, and the yield of triethyl citrate reached 93.8%. BA could also catalyze the reaction between malic acid and pinene to produce borneol malate. After saponification of borneol malate, borneol was obtained with a yield of 39%.

Enantioselective [2,3]-Wittig Rearrangement of Carboxylic Acid Derived Enolates by Tetradentate Chiral Lithium Amide

AbstractA chiral lithium amide mediated enantioselective [2,3]-Wittig rearrangement of carboxylic acid enolate has been developed. The reaction proceeds through the formation of a chiral mixed aggregate that shields one enantioface of enolate anion to give a highly functionalized chiral α-hydroxycarboxylic acid.

Selective Crystal Growth Regulation by Chiral α-Hydroxycarboxylic Acids Improves the Strength and Toughness of Calcium Sulfate Cements.

Natural biominerals, such as bones and teeth, use acidic matrix biomolecules to control growth, morphology, and organization of the brittle hydroxyapatite crystals. This interplay provides biominerals with outstanding mechanical properties. Recently, we reported that the l-enantiomer of chiral tartaric acid has a potent regulatory effect on the crystal structure and mechanical performance of brushite cement, a mineral with a monoclinic crystal system. We hypothesized that this strategy could be applied using various chiral α-hydroxycarboxylic acids to enhance the mechanical performance of calcium sulfate dihydrate cements, another mineral belonging to the monoclinic crystal system. Calcium sulfate cements are widely used in dentistry, medicine, and construction, but these cements have low mechanical properties. In this work, we first determined the impact of different chiral α-hydroxycarboxylic acids on the properties of calcium sulfate cements. After that, we focused on identifying the regulation effect of chiral tartaric acid on gypsum crystals precipitated in a supersaturated solution. Here, we show that the selective effect of α-hydroxycarboxylic acid l-enantiomers on calcium sulfate crystals improved the mechanical performance of gypsum cements, while d-enantiomer had a weak impact. Compare to the calcium sulfate cements prepared without additives, the presence of l-enantiomer enhanced the compressive strength and the fracture toughness of gypsum cements by 40 and 70%, respectively. Thus, these results prove the generalizability of this approach and help us to fabricate high-strength cements.

Recent advances of BINOL-based sensors for enantioselective fluorescence recognition.

Enantioselective fluorescent sensors show large potential for fast, real-time, and highly sensitive measurement of the concentration and enantiomeric composition of chiral molecules. Among all of the sensors, BINOL-based sensors have been actively investigated and extensively used to carry out highly enantioselective, sensitive recognition of chiral α-hydroxycarboxylic acids, amino acids, amino acid derivatives, amino alcohols and amines. In this manuscript, the recent progress of chiral BINOL-based sensors for enantioselective fluorescence recognition of different substrates is reviewed and discussed. The structure of BINOL is tuned by introducing various groups or molecules which systematically changed its fluorescence properties and offered potential for rapid assays of chiral organic molecules. From the development of this area, we gain fresh insight into the challenges and chances of BINOL-based sensors.

Chiral Guanidines-catalyzed Nucleophilic Addition Reactions Using 5<i>H</i>-Oxazol-4-ones: Development of Catalytic Asymmetric Syntheses of Chiral α-Tetrasubstituted Hydroxycarboxylic Acid Derivatives

Chiral α-hydroxycarboxylic acids and their derivatives bearing a tetrasubstituted α-carbon atom are well-recognized chiral synthons and components of various pharmaceuticals and biologically active natural products. Despite their high demand, preparative methods of these compounds are quite limited due to the difficulty in achieving stereoselective construction of the tetrasubstituted carbon stereogenic center at the α-position. To address this issue, we developed asymmetric nucleophilic addition reactions of 5H-oxazol-4-ones to carbon electrophiles using chiral bicyclic guanidine catalysts containing a hydroxyl group at the appropriate position as a preparative method of α-tetrasubstituted hydroxycarboxylic acid derivatives. In this article, we introduce the nucleophilic addition reactions with several types of electrophiles, such as aldehydes, alkynyl carbonyl compounds, allenyl carbonyl compounds, vinyl ketones, dienones, and 2-chloroacrylnitrile. Derivatizations of the products of these reactions into corresponding α-hydroxycarboxylic acid derivatives and their application to a natural product synthesis are also described.

Enantioselective Recognition of α-Hydroxycarboxylic Acids and N-Boc-Amino Acids by Counterion-Displacement Assays with a Chiral Nickel(II) Complex

A new chiral sensor based on an N,N'-dioxide nickel(II) complex was prepared, which could visually recognize a series of chiral α-hydroxycarboxylic acid enantiomers by coordination and self-assembly forming into nanospheres or nanofibers. With the help of various techniques, the morphology structures of the colloid or suspension were obtained and the counterion-displacement assays were also confirmed. In addition, this metal complex could act as a highly enantioselective fluorescence sensor to recognize N-Boc-amino acids and chiral α-hydroxycarboxylic acids.

Macrocyclic Bisbinaphthyl Fluorophores and Their Acyclic Analogues: Signal Amplification and Chiral Recognition.

A series of optically active macrocyclic and acyclic bisbinaphthyls have been synthesized and characterized. The structure of one of the bisbinaphthyl macrocycles has been established by a single-crystal X-ray analysis. The UV and fluorescence spectra of these chiral compounds in various solvents and at different concentrations are studied. Formation of excimers is observed for the macrocyclic bisbinaphthyl compounds. Introduction of conjugated substituents to the 6,6‘-positions of the binaphthyl units in the macrocycles leads to greatly amplified fluorescence signals. Using the 6,6‘-substituted bisbinaphthyl macrocycles in place of the unsubstituted macrocycles allows a 2 orders of magnitude reduction in the sensor concentration for the fluorescence measurements. These macrocycles have exhibited highly enantioselective fluorescent enhancements in the presence of chiral α-hydroxycarboxylic acids and N-protected α-amino acids. They are useful as fluorescent sensors for chiral recognition. The macrocycles s...

Chiral sulfonated phosphines. Rhodium(I)-catalyzed asymmetric hydrogenolysis of epoxides

Rhodium(I) complexes of sulfonated (−)-(2S,4S)-2,4-bis(diphenylphosphino)pentane ((S,S)-(BDPP)) are effective as catalyst for asymmetric hydrogenolysis of sodium cis-epoxysuccinate to sodium hydroxysuccinate in aqueous-organic two phase solvent system or in aqueous solution. It has been shown by deuterium labelling studies that both hydrogen and water participate in the aqueous hydrogenolysis as reactants and the reaction proceeds via the direct CO bond cleavage of the epoxy group. High pressure NMR studies show the presence of rhodaoxetane-BDPP complexes as catalytic intermediates, which are formed by the oxidative addition of the epoxide to unsaturated Rh(I) species. Accordingly, a reaction mechanism has been proposed for the aqueous catalytic process. The use of a racemic substrate, sodium trans-phenylglycidate with the aqueous Rh-sulfonated (S,S)-BDPP system results in the kinetic resolution of the (2S,3R)-epoxide enantiomer. Thus, asymmetric aqueous catalytic hydrogenolysis could be a useful synthetic approach not only to chiral α-hydroxycarboxylic acid derivatives but also to chiral trans-substituted epoxides.

HPLC Resolution of Hydroxyl Carboxylic Acid Enantiomers Using 2-Quinoxaloyl Chloride as a New Precolumn Derivatizing Agent

Abstract Chiral α-hydroxy carboxylic acids were reacted using 2-quinoxaloyl chloride to form UV and fluorescent derivatives. Under mild conditions either in aqueous or non-aqueous conditions reaction proceeds quickly and without racemisation. The labelled compounds have been resolved into enantiomers on β-cyclodextrin bonded stationary phase operated with polar organic eluents. The high sensitivity and selectivity of the method has been used for the determination of low levels of enantiomeric impurities in commercial “pure” samples.

ChemInform Abstract: CIRCULARLY POLARIZED LUMINESCENCE STUDIES OF THE EUROPIUM(III) BIS(PYRIDINE‐2,6‐DICARBOXYLATE) COMPLEXES WITH CHIRAL α‐HYDROXYCARBOXYLIC ACIDS

Chemischer InformationsdienstVolume 13, Issue 52 Physical Organic Chemistry ChemInform Abstract: CIRCULARLY POLARIZED LUMINESCENCE STUDIES OF THE EUROPIUM(III) BIS(PYRIDINE-2,6-DICARBOXYLATE) COMPLEXES WITH CHIRAL α-HYDROXYCARBOXYLIC ACIDS M. RANSOM, M. RANSOMSearch for more papers by this authorH. G. BRITTAIN, H. G. BRITTAINSearch for more papers by this author M. RANSOM, M. RANSOMSearch for more papers by this authorH. G. BRITTAIN, H. G. BRITTAINSearch for more papers by this author First published: December 28, 1982 https://doi.org/10.1002/chin.198252058AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume13, Issue52December 28, 1982 RelatedInformation

Circularly polarized luminescence studies of the Eu(III) bis(pyridine-2,6-dicarboxylate) complexes with chiral α-hydroxycarboxylic acids

Circularly polarized luminescence studies of the Eu(III) bis(pyridine-2,6-dicarboxylate) complexes with chiral α-hydroxycarboxylic acids