Synergistic Extraction of Thorium by β-Hydroxy Naphthaldoxime in Presence of Neutral Donors

The effects of neutral organophosphorous compounds on the extraction of thorium by -hydroxy naphthaldoxime in xylene are reported. Enhancement of the extraction is explained by a complex adduct formation in the organic phase. Synergistic coefficients and apparent formation constant of complex adducts are calculated.     

Highly Regioselective Conversion of Epoxides to β-Hydroxy Nitriles with Cyanide Exchange Resin

Abstract

A simple and regioselective method is described for the efficient conversion of epoxides to β-hydroxy nitriles using Amberlite IRA-400 supported cyanide. The reactions occur in the absence of catalyst and furnish the corresponding β-hydroxy nitriles in high yields.     

Enantioselective Construction of 3-Hydroxy Oxindoles via Decarboxylative Addition of β-Ketoacids to Isatins

The first highly enantioselective decarboxylative addition of β-ketoacids to isatins mediated by a bifunctional tertiary amine-thiourea catalyst has been developed, allowing facile synthesis of biologically important 3-hydroxy oxindoles in good yields and excellent enantioselectivities. The method reported represents a valuable approach of utilizing β-ketoacids as synthetic equivalents of aryl/alkyl methyl ketone enolates.     

ATP-Independent and Cell-Free Biosynthesis of β-Hydroxy Acids Using Vinyl Esters as Smart Substrates

In vitro biosynthetic pathways that condense and reduce molecules through coenzyme A (CoASH) activation demand energy and redox power in the form of ATP and NAD(P)H, respectively. These coenzymes must be orthogonally recycled by ancillary reactions that consume chemicals, electricity, or light, impacting the atom economy and/or the energy consumption of the biosystem. In this work, we have exploited vinyl esters as dual acyl and electron donor substrates to synthesize β-hydroxy acids through a non-decarboxylating Claisen condensation, reduction and hydrolysis stepwise cascade, including a NADH recycling step, catalyzed by a total of 4 enzymes. Herein, the chemical energy to activate the acyl group with CoASH and the redox power for the reduction are embedded into the vinyl esters. Upon optimization, this self-sustaining cascade reached a titer of (S)-3-hydroxy butyrate of 24 mM without requiring ATP and simultaneously recycling CoASH and NADH. This work illustrates the potential of in vitro biocatalysis to transform simple molecules into multi-functional ones.     

Palladium(O) Catalysed Isomerisation of 2,3-Epoxy Alcohols to α and β-Hydroxy Ketones

Isomerisation of 2,3-epoxy alcohols possessing an arylgroupat1 and/or 3 position, with Pd(PPh₃)₄ leads to formation of α and β-hydroxy ketones.     

Catalyst-Free,Efficient, and Facile Conversion of Epoxides to β-Hydroxy Thiocyanates Under Neutral Conditions

Epoxides are efficiently and easily converted to their corresponding β-hydroxy thiocyanates by NH₄SCN in refluxing acetonitrile in a regio- and chemoselective manner under neutral conditions without using a catalyst, in spite of the use of many different catalysts reported in the literature for this purpose.     

Highly Stereoselective Aldol Reactions by Memory of Chirality: Synthesis of Quaternary β-Hydroxy α-Amino Acids

We describe here an asymmetric aldol reaction based on the principle of Memory of Chirality. From α-amino acids such as leucine and methionine, we have synthesized in two steps quaternary α-amino acid derivatives with high diastereoselectivity and enantioselectivity, using the chirality of the initial α-amino acid as the only chirality source. Furthermore, we were able to determine the relative and absolute configurations of the aldol products thanks to crystallographic structures and thus showed that the relative configuration depended on the aldehyde employed. We proposed a stereoselectivity explanation and obtained also quaternary β-hydroxy α-amino acids after acidic hydrolysis.     

Photo-isomerization of Aromatic α-Hydroxy Hydrazone

Photo-isomerization of aromatic α-hydroxy hydrazone was reported. We investigated the structures of salicylaldehyde phenylhydrozone(SP) in the ground state using density functional theory(DFT) with the B3LYP functional and the 6-311+G(d) basis set. All nine possible isomers of SP in the ground state consist of seven phenol forms and two ketone forms. Intrisic reaction coordinate(IRC) analysis discloses the existence of a cycle driven by the two proton transfer processes in the ground and excited states of SP, which suggests that no ketonic form could exist in the ground state. Further theoretical studies of the potential energy surfaces support a trans-cis conversion followed by a relaxation to the stable form of SP in the excited states.     

Asymmetric Synthesis of Some Chiral Aryl and Hetero Aryl-Substituted β-, γ-, δ-Hydroxy Esters

Sixteen chiral β-, γ-, and δ-hydroxy esters with aryl, substituted aryl, and heteroaryl groups 2a–2s were synthesized by the asymmetric reduction of their corresponding keto esters 1a–1s as chiral pure reference compounds and starting materials. The asymmetric reduction was achieved by (R)-Me-CBS-oxazaborolidine. Ten new chiral γ- and δ-hydroxy esters 2d, 2e, and 2j–2s were obtained with high ee values and characterized by infrared, NMR (¹H and ¹³C), mass spectrometry, chiral high-performance liquid chromatography, and specific rotation.     

Unusual Reaction of β-Hydroxy α-Diazo Carbonyl Compounds with Trichloroacetonitrile (CI3CCN) and Sodium Hydride

In the process of preparing α-diazo carbonyl compound 2 by imidation of 1, we unexpectedly observed a direct conversion of the hydroxyl group into trichloroacetylamino group. In this presentation, we report this unprecedented reaction, as well as the Rh2(OAc)4-catalyzed reaction of the resulting β-(trichloroacetyl)amino β-diazo carbonylcompounds 3. [ 1]     

Asymmetric Syntheses XXVI: Catalytic Enantioselective Syntheses of β-Hydroxy Esters via Double Chiral Induction in Asymmetric Reformatsky Reactions

Catalytic asymmetric Reformatsky reactions of benzaldehyde with optically active menthyl bromoacetates in the presence of Zn-Cu couple were performed using 0.25 equiv. of (1R,2S) or (1S,2R)-dimethyl-2-amino-1,2-diphenyl ethanol as chiral ligand to obtain β - hydroxy esters with enantioselectivities up to 60.2%. The obvious double chiral induction effect was observed while chiral ligands matched with optically active substrates.     

Isothiourea-Catalyzed Acylative Kinetic Resolution of Tertiary α-Hydroxy Esters

A highly enantioselective isothiourea-catalyzed acylative kinetic resolution (KR) of acyclic tertiary alcohols has been developed. Selectivity factors of up to 200 were achieved for the KR of tertiary alcohols bearing an adjacent ester substituent, with both reaction conversion and enantioselectivity found to be sensitive to the steric and electronic environment at the stereogenic tertiary carbinol centre. For more sterically congested alcohols, the use of a recently-developed isoselenourea catalyst was optimal, with equivalent enantioselectivity but higher conversion achieved in comparison to the isothiourea HyperBTM. Diastereomeric acylation transition state models are proposed to rationalize the origins of enantiodiscrimination in this process. This KR procedure was also translated to a continuous-flow process using a polymer-supported variant of the catalyst.     

α-Hydroxy ketones as useful templates in asymmetric reactions

Approaching the Nature's efficiency in controlling both reactivity and stereoselectivity of organic reactions by means of a catalyst species remains a formidable challenge for chemists to face. Despite impressive advances in the design of novel catalysts and activation modes, current catalytic and asymmetric methodologies rarely meet desirable standards of robustness, substrate scope, and selectivity altogether. One trick to improve catalyst behaviour is to identify adequate substrate template-catalyst combinations so that optimum performance of the reaction system could be achieved. During the last couple of years α-hydroxy ketones, and most particularly α'-hydroxy enones, have emerged as useful templates with applications in a number of metal-catalyzed as well as organocatalyzed C-C and C-X bond-forming stereoselective reactions. The first review of these accomplishments is presented here along with a brief historical introduction.     

Hydroxyapatite For Poly(α-Hydroxy Esters) Biocomposites Applications

This article focuses on providing a systematic review on various fundamental properties of composite based on poly(α-hydroxy esters) and hydroxyapatite (HAp) for application in bone tissue engineering. Poly(α-hydroxy esters), a well-known synthetic biopolymer has attracted considerable interest to be employed for synthesis of bone graft substitute material with HAp mainly due to its bioresorbability, variable biodegradation rate and melt-processibility. Such features are simultaneously attractive for both biomedical application and industrial-scale productions. Besides the main function of hydroxyapatite as bioactive ceramic filler in composite to induce new bone formation upon polymer bioresorption, HAp can also serve as reinforcement for matrix polymer by providing sufficient mechanical support for cell attachment. Moreover, HAp plays a significant role in determining other composite properties, such as resistance to ingress of body fluid, body temperature ageing, relaxation movement of polymer segment, and in vivo biodegradation. These properties constitute as the fundamental requirements in field of bone tissue regeneration which is desirable to be achieved by unique composite system based on poly(α-hydroxyesters) and HAp particles.     

Synthesis and Antimicrobial Evaluation of Novel N-Substituted β-Hydroxy Benzimidazole Sulfone Fluoroquinolones by Selective Oxidation Using Ticl4-H2O2

Abstract

The synthesis of N-substituted β-hydroxy benzimidazole sulfones containing 8-methoxy fluoroquinolone has been described and they were evaluated for antimicrobial activities. The compounds of N-substituted β-hydroxy benzimidazole sulfides (4a–e) and N-substituted β-hydroxy benzimidazole sulfones (5a–e) at C-7 of fluoroquinoline exhibited superior activity in vitro. 8-Methoxy fluoroquinolone carboxylic acid (1), reaction with piperizine in acetonitrile in presence of triethylamine under reflux gives 7-piperazinyl-8-methoxyfluoroquinolone (2). The latter is reacted with epichlorohydrine in presence of NaOH in acetone yielded N-substituted epoxide (3), which on treatment with 5-substituted-2-mercaptobenzimidazoles gives N-substituted β-hydroxy benzimidazole sulfides (4). Further, 4 on treatment with TiCl₄-H₂O₂ and in DCM yielded the corresponding N-substituted β-hydroxy benzimidazole sulfone (5).     

Spectrofluorimetric Determination of Zirconium Based on the Inclusion Complex of 8-Hydroxy 7 Iodo Quinoline Sulfonic Acid with β-Cyclodextrin As Ligand

Abstract

Ferron form inclusion complex with β-cyclodextrin in aqueous media at pH 3.2 with an association constant of 25 M^?1. This ligand has been used for the fluorimetric determination of zirconium at trace levels. The limit of detection is 0.07 μg/ml and the RSD is 5.2%. A significant improvement in selectivity is gained in the β-CD method compared to the method in absence of cyclodextrin.     

Mono-2, 3 or 6-Hydroxy Methylated β-Cyclodextrin (Eicosa-O-methyl-β-cyclodextrin) Isomers as Chiral Stationary Phases for Capillary GC

This work deals with the evaluation of three monohydroxy methylated β-cyclodextrin isomers as chiral selectors for capillary gas chromatography. Chromatographic properties of these stationary phases have been investigated in terms of efficiency, inertness and polarity. Injections of homologous series of hydantoin derivatives and 1-phenylethan-1-ol have highlighted the predominant influence of hydroxyl groups in 2 or 3 positions on chiral discrimination. By contrast, presence of hydroxyl groups in 6-O-position did not significantly influence the enantioseparation ability. Moreover, T _iso calculated on TRIMEB-2-OH in OV1701-OH and on pure TRIMEB-2-OH for 5-methyl-5-alkyl hydantoin derivatives were notably different indicating that polysiloxan–selector interactions could not be neglected.     

(Bromodimethyl)sulfonium Bromide–Mediated Thiolysis of Epoxides: An Easy Access to β-Hydroxy Sulfides and Benzoxathiepinones in Solvent-Free Conditions

A mild, rapid and highly regioselective opening of epoxides by mercaptans to β-hydroxy sulfides and benzoxathiepinones has been achieved in excellent yields, using catalytic amount of (bromodimethyl)sulfonium bromide in solvent free reaction conditions.     

Synthesis of 14-Bromo and 14-Hydroxy Baccatin III Derviatives

Numerous efforts towards synthesis of anticancer drug paclitaxel (Taxol(r), 1a) with improved activities led to the modification at 13-phenylisoserine side chain and different positions of its core structure-baccatin III 1c1. At the same time, the activities of searching new taxoids for starting materials of new semi-synthetic paclitaxel analogs from Taxus spp. plant have not ever been stopped. Among these taxoids, 14?-hydroxy-10-deacetylbaccatin III 22 and 13-acetyl-9-dihydrobaccatin III …