Furan synthesis through AuCl3-catalysed cycloisomerisation of β-alkynyl β-ketoesters

AuCl₃ efficiently catalyses the cycloisomerisation of readily available β-alkynyl β-ketoesters to generate trisubstituted furans. The substrate scope is wide and the reaction is high yielding and operationally simple.     

Synthesis of new β-trifluoromethyl containing GABA and β-fluoromethyl containing N-benzylpyrrolidinones

A whole series of 3-(mono-, di-, trifluoro)methyl-substituted N-benzylpyrrolidinones 5a-c was synthesized by deoxyfluorination of corresponding 3-functionalized N-benzylpyrrolidinones. New β-trifluoromethyl containing GABA 4a was obtained in two alternative ways: by successive hydrolysis and hydrogenolysis of 3-trifluoromethyl N-benzylpyrrolidinone 5a and from trifluoroacetone as starting compound.     

Stereochemistry in alkylations of dianions of β-hydroxysulfoxides and β-hydroxysulfones

Alkylations of dianions of β-hydroxysulfoxides and β-hydroxysulfones have been found to be affected by chelation of a Li cation with a sulfinyl group and by coordination of the cation with tetrahydrofuran rather than a sulfonyl group, respectively.     

Hydrogenation of β-N-substituted enaminoesters in the presence of ruthenium catalysts

β-Aminoesters were prepared in two simple steps from β-ketoesters derivatives and primary amines under mild conditions. Their hydrogenation was performed at 50 °C in the presence of several organometallic catalysts under acidic conditions. The new β-N-substituted aminoesters were isolated in moderate to good yields.     

Computational investigation of enol/keto chloramphenicol with β-cyclodextrin

PM3 and ONIOM2 were carried out to investigate the structures and properties for the inclusion complexes of chloramphenicol tautomers into β-cyclodextrin (at 1:1 stoichiometry). Two possible orientations into host cavity were considered for both enol and keto chloramphenicol. The PM3 results gives that B orientation is more preferred for enol and keto form, the preference is of 0.63 and 1.67 kcal/mol respectively. This preference is greater in the case of ONIOM2 calculations. Finally, the chemical shifts (ppm) of free and complexed chloramphenicol were calculated at B3LYP/6-31G(d) by (GIAO method) and compared with experimental data taken from the literature.     

Influence of β-substituents in aldol reactions of boron enolates of β-alkoxy methylketones

Moderate to good levels of substrate-based 1,5-syn-stereocontrol could be achieved in the boron-mediated aldol reactions of β-tert-butyl methylketones with achiral aldehydes, independent of the nature of the β-alkoxy protecting group (P = PMB or TBS). The analysis of the relative energies of the transition structures by theoretical calculations using the density functional B3LYP shows relative energies favoring the corresponding OUT-1,5-SYN transition structures, explaining the observed 1,5-syn stereoinduction.     

Enantioselective one-pot synthesis of β-sulfonyl ketones and trisubstituted tetrahydrothiophenes via β-elimination/cycloaddition sequence

A mild and efficient enantioselective one-pot synthesis of β-sulfonyl ketones and trisubstituted tetrahydrothiophenes via introducing 1,4-dithiane-2,5-diol to the simple kinetic resolution of β-sulfonyl ketones has been described herein. The one-pot reaction sequence including kinetic resolution and cascade sulfa-Michael/Aldol reaction proceeded successively to afford corresponding sulfonyl ketones and tetrahydrothiophenes with high enantioselectivities (85%–98% ee and 84%–95% ee, respectively).     

Structure determination of glycopeptide of β-momorcharin

The structure of the N-linked oligosaccharide chain of β-momorcharin, a ribosome-inactivating protein from the seeds of Momordica charantia Linn (Cucurbitaceae), was determined. A glycopeptide liberated by pronase digestion of the glycoprotein was subjected to amino acid and neutral carbohydrate analysis to establish the composition of amino acid and sugar residues. The sequences and glycosylation hnkages of the sugar and amino acid residues in the glycopeptide were determined as Manαl-6(XyIβ1-2)-Manβ1-4GlcNAcβ1-4(Fucαl-3)-GlcNAc-Asn-Leu by 2D-NMR spectroscopy and FAB-MS data.     

Study on the Supramolecular Inclusion Complex of β-Cyclodextrin/Lappaconitine

Lappaconitine (Lap) is a diterpenoid akaliamide, naturally occurring in roots and rhizomes of Aconitum and delphinium. Lap reveals bradycardic, hypotensive, antinocieptive activity. However, its application is restrained owing to its poor water solubility, toxicity and side effects on humans. In a number of pharmaceutical studies,CDs have been reported to interact with many drug molecules to form inclusion complexes. These inclusion complexes have been extensively used to improve water solubility of poorly soluble drugs, to reduce their toxicity, and to increase the dissolution rate [1]. In the present work, the β-CD/Lap complex was prepared by kneading method. The products have been characterized by the solubility measurement as well as UV, FTIR, NMR spectroscopy and X-ray powder diffractometry.     

Regioselective synthesis of polysubstituted 4H-thiopyrans from β-oxodithioesters

A simple and efficient method for the synthesis of polyfunctionalized 4H-thiopyrans by highly regioselective cyclocondensation of β-oxodithioesters with 1,1,3-trialkyl or aryl substituted prop-2-yn-1-ols using BF₃·Et₂O as the catalyst is described.     

Evaluation of a molecularly imprinted polymer for the isolation/enrichment of β-estradiol

The selective preconcentration of estradiol was explored using the recognition ability of a molecularly imprinted polymer (MIP) in the solid phase extraction (SPE) format. Polymeric particles were imprinted with 17β-estradiol using methacrylic acid as functional monomer and divinylbenzene as crosslinker. Binding studies of these polymeric particles towards 17β-estradiol showed selectivity over non-imprinted polymers, using acetonitrile as solvent. The imprinted polymer showed a recovery of 88% for β-estradiol in deionized water and 81% in surface water. The selectivity of the MIP over the non-imprinted polymer was relatively low, only 10% higher recovery. The results indicate that the MIP imprinted with 17β-estradiol does not appear to provide a viable approach to be used in a sample clean-up or enrichment step for the determination of estradiol in aqueous systems.     

A New Route for Preparation of β-TCP/PLLA Composite

Bone tissue engineering offers a promising route to repair and replace damaged or diseased tissues in the cases including trauma, congenital and degenerative diseases, cancer, and so on. Polylactic acid(PLLA)-based materials showing bioresorbability are u…     

Salt/current-triggered stabilization of β-cyclodextrins encapsulated host-guest low-molecular-weight gels

Host-guest supramolecular gels were developed via the self-assembly of inclusion complexes(ICs) ofβ-cyclodextrins/phenylboronic acid gelator(PBA).Salts and current were involved in the self-assembly to stabilize the host-guest gels.The stability of the gels was greatly improved after salts were added.The stable time of gels was extended from 2.5 h to 120 h with the addition of NH_4 NO_3 at the concentration of 2.5×10^-2 g/mL.The morphology of the gel was affected by the concentrations of NH_4NO_3.SEM images revealed that the gels were three-dimensional nanofibrous networks,the sizes of fibers decreased with decreasing NH_4NO_3 concentrations,which affected the stability of gels,further proved by the rheological properties of gels.More stable gels were obtained with current stimulation,the stable time of the gel was increased from 2.5 h to 55 h with current by adding NaBF_4.The current also exhibited significant influence on the aggregation as the voltage varied(0-500 mV) with a constant concentration of salts.The result showed the self-assembly process of host-guest gel could be well controlled via the addition of salts and current to desired morphology and stability.     

Preparation of β-fluoro- and β,β-difluoro-histidinols

Nucleophilic attack of azide on 2-bromo-3-fluoro-3-(1-trityl-1H-imidazol-4-yl)-propan-1-ol (1a) in aprotic solvent occurs on the 2-position to give the 2-azido derivative (2a). Reduction of azide and removal of the trityl group produces β-fluorohistidinol (6a). Elimination of HBr from 1a followed by “FBr” addition to the resulting double bond gives 2-bromo-3,3-difluoro-3-(1-trityl-1H-imidazol-4-yl)-propan-1-ol (1b). Nucleophilic attack of azide followed by reduction and removal of the trityl group, as for the preparation of 6a, gives β,β-difluorohistidinol (6b). Initial attempts, under a variety of conditions, to oxidize the fluorinated histidinol precursors to carboxylic acids have not been successful.     

Synthesis of Unsymmetrical β-Arylaminoketones

Azomethines derived from aniline were condensed with acetophenone derivatives to obtain new unsymmetrical -arylaminoketones.     

Regioselective Acetylation of β-Cyclodextrin

One-stage methods of synthesis of water-soluble -cyclodextrins selectively acetylated by primary or secondary hydroxy groups have been found, that make use of acetyl chloride and hydrogen chloride acceptors of different nature.     

New Synthesis of β-Iodostyrenes

A general procedure for the synthesis of -iodostyrenes is proposed. Aromatic aldehyde and ketone hydrazones are converted into the corresponding -iodostyrenes by treatment with CHI₃ in the presence of a catalytic amount of CuCl.     

Selective synthesis of β-alkylpyrroles

β-Alkylpyrroles are key structural motifs found in many natural products and biologically active compounds as well as functional organic materials. For this reason, synthetic chemists continue to be interested in construction of the framework of β-alkylpyrroles. Due to sufficient aromaticity and π-excessive nature of pyrroles, a straightforward approach to β-alkylpyrroles should be electrophilic aromatic substitution (S(E)Ar) toward the pyrrole ring. However, since a primary nucleophilic site of pyrroles is an α-position, some "trick" is required to direct incoming alkyl electrophiles toward a β-position. This Concept article focuses on presenting previous efforts that have been devoted to the synthesis of β-alkylpyrroles, mainly through the S(E)Ar route.