Hafnium Chloride Catalyzed Polycondensation of α,ω-Alkanediol with Dicarboxylic Acids or Succinic Anhydride

Three different kinds of polycondensation were preformed and the usefulness of HfCl₄.2THF as estrification and polycondensation catalyst was evaluated. It was compared with HfCl₄, BiCl₃, LaCl₃ and SnCl₂. In polycondensations of 1,6-hexandiol, and 1,10-decandiol with various dicarboxylic acids all catalysts failed to give satisfactory results. However, in polycondensations of 1,4-butanediol with succinic anhydride in refluxing decalin good results were obtained, and HfCl₄.2THF was the most effective catalyst after SnCl₂. The MALDI-TOF mass spectra revealed that cyclization made a significant contribution to the limitation of the chain growth.     

“One-Pot” Synthesis of Disymmetrically α,α′-Disubstituted Succinic Anhydrides Precursors

A “one-pot” synthesis for disymmetrically α,α′-disubstituted succinic anhydrides precursors is reported in the present paper. Substituents are aryl, primary or secondary alkyl groups. This reaction represents a simple and quick method with fair yields.     

Interaction of Rose Bengal with α-chymotrypsin and α- chymotrypsinogen-A

Absorption spectra of aqueous solutions of Rose Bengal—(α-chymotrypsin) and Rose Bengal—(α- chymotrypsinogen-A) measured at different pHs showed that both proteins formed the same complexes. The binding constants for the formation of RB/CHT and RB/CHTGA complexes were of the same order of magnitude. The binding isotherms showed that stoichiometry of RB complexes was 3:1 at pH 4.6 and 1:1 at pH 7.2 for both RB/CHT and RB/CHTGA, respectively. Equal binding between the dye and both proteins eliminated the possibility that RB could interact selectively with the active site of α-chymotrypsin.Charge-charge interaction between the carboxylic group of the dye and the positively charged protein surface was essential for the stability of the complexes. The binding reached its minimum when the pH of aqueous solution was equal to the pI of the protein. The complexes exhibited no CD at any pH and at any KCl concentration varied from 0.0 to 0.5 M, which showed that the complexes were achiral. At pH < 4, both proteins trapped the acidic form of RB in a temperature dependent process.     

The Molecular Basis of the Interaction of Cyclophilin A with α-Synuclein

Peptidylprolyl isomerases (PPIases) catalyze cis/trans isomerization of prolines. The PPIase CypA colocalizes with the Parkinson's disease (PD)-associated protein α-synuclein in cells and interacts with α-synuclein oligomers. Herein, we describe atomic insights into the molecular details of the α-synuclein/CypA interaction. NMR spectroscopy shows that CypA catalyzes isomerization of proline 128 in the C-terminal domain of α-synuclein. Strikingly, we reveal a second CypA-binding site formed by the hydrophobic sequence ⁴⁷GVVHGVATVA⁵⁶, termed PreNAC. The 1.38 Å crystal structure of the CypA/PreNAC complex displays a contact between alanine 53 of α-synuclein and glutamine 111 in the catalytic pocket of CypA. Mutation of alanine 53 to glutamate, as found in patients with early-onset PD, weakens the interaction of α-synuclein with CypA. Our study provides high-resolution insights into the structure of the PD-associated protein α-synuclein in complex with the most abundant cellular cyclophilin.     

The Preparation of 1H-Pyrazole-5-propanoic and 1H-Pyrazole-5-butanoic Acids from Dilithiated C(α),N-Carboalkoxyhydrazones and Succinic or Glutaric Acid Anhydrides

C(α),N-Carboalkoxyhydrazones were dilithiated with excess lithium diisopropylamide, condensed with succinic or glutaric acid anhydride, and cyclized to 1H-pyrazole-5-propanoic or 1H-pyrazole-5-butanoic acids.     

Cationic Copolymerization with Depropagation. The Copolymerization of α-Methylstyrene and Styrene

ABSTRACT

To evaluate the existence of the depropagation reaction in the copolymerization of vinyl monomers, the cationic copolymerization of α-methylstyrene with styrene was studied. The copolymer composition exhibited an extensive dependency on the temperature of polymerization and the monomer concentration, this fact not being explained by the Mayo-Lewis equation. Treatment of the copolymerization in terms of the depropagation reaction led to an estimate of the monomer reactivity ratio and the equilibrium constant between the polymer and the monomer of α-methylstyrene. A comparison of the equilibrium constants thus obtained with those reported in the literature indicates that the magnitude of the equilibrium constants depends on the sequence length of α-methylstyrene units. By extrapolation to long sequence length, the equilibrium constants approach the values which are reported for high molecular weight poly(α-methylstyrene).     

Interaction of hydroxyaryl aldehydes with α-hydroxyethyl radicals

The effect of some hydroxylated aromatic aldehydes on the radiation-chemical transformations of deaerated ethanol during continuous radiolysis has been studied. The data obtained show that these compounds effectively inhibit radiation-induced processes involving α-hydroxyethyl radicals (α-HER). Benzaldehyde and its hydroxylated derivatives (II, III) predominantly oxidize, and compounds containing the cinnamic moiety, (IV–VI), add α-HER to a carbonyl group or -C=C bond.     

Ring cleavage reactions of methyl α-D-allopyranoside derivatives with phenylboron dichloride and triethylsilane

In the course of our studies on the regioselective carbon-oxygen bond cleavage of the benzylidene acetal group of hexopyranosides with a reducing agent, we found that a combination of a Lewis acid and a reducing agent triggered a ring-opening reaction of the pyranose ring of methyl α-D-allopyranosides. The formation of an acyclic boronate ester by the attachment of a hydride ion at C-1 indicated that the unexpected endocyclic cleavage of the bond between the anomeric carbon atom and the pyranose ring oxygen atom proceeded via an oxacarbenium ion intermediate produced by the chelation between O5/O6 of the pyranoside and the Lewis acid, followed by nucleophile substitution with a hydride ion at C1.     

Interaction of α,α-difluoroazides with trivalent phosphorus compounds and triphenylantimony

α,α-Difluoroazides react with triphenylantimony and various compounds of trivalent phosphorus according to the oxidative fluorination scheme. In the case of trivalent phosphorus compound the primary products are phosphazenes, phosphazides or difluorophosphoranes that may undergo further transformations to the corresponding fluorine derivatives of pentavalent phosphorus.     

Reaction of nitroalkanes with levoglucosenone and its α-bromo and α-iodo derivatives. Cyclopentaannulation of α-halocyclenones

Michael reactions of levoglucosenone and its α-bromo and α-iodo derivatives with α,ω-dinitroalkanes were studied under conditions of chemical and electrochemical generation of base. Procedures were developed for stereospecific fusion of a cyclopentane ring to α-bromo- and α-iodolevoglucosenones, 2-iodocyclopent-2-en-1-one, and 2-iodocyclohex-2-en-1-one by the action of 2,2-dimethyl-1,3-dinitropropane.     

The Interaction of β-Cyclodextrin with Benzoic Acid

The interaction of β-cyclodextrin with benzoic acid was studied by UV and IR spectroscopy, X-ray diffraction, and thermogravimetry. The introduction of the benzoic acid molecule into the internal hydrophobic β-cyclodextrin cavity and additional stabilization by weak H-bonds caused the formation of 1: 1 axial inclusion complexes of the host—guest type. The degree of crystallinity of the inclusion complex decreased compared with the initial compounds, whereas its thermal stability increased.     

Interaction of aminoquinolines with unsaturated carboxylic acids. 1. Synthesis of N-quinolyl-β-alanines and their biological activity

N-Quinolyl--alanines, and -methyl- and-methyl-N-quinolyl--alanines were prepared by reaction of aminoquinolines and acrylic, methacrylic, and crotonic acids. The corresponding hydrazides and benzylidenehydrazides were obtained. 4-Aminoquinoline with unsaturated acids in water gave betaines. The biological activity of sodium salts of -alanines was investigated.Kaunas University of Technology, Kaunas LT-3028, Lithuania; Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 504–511, April, 2000.     

Synthesis with organoboranes. 21. Synthesis of α- and gd-bamascone

Selective syntheses of α- and gd-damascone, using allylic organoboranes as the key intermediates, are described.     

The Synthesis of α-DDB, β-DDB and Theoretical Study with AM1

Biphenyl units are present in a wide range of compounds both natural and synthetic, and many of them have pharmacological activity1. Xie Jingxi et al. found that dimethyl 4,4'-dimethoxy-5,6,5',6'-dimethylenedioxybiphenyl-2,2'-dicarboxylate((-DDB) as an important intermediate for the synthesis of Schizandrin C analogue which is effective in lowering elevated SGPT level2-3. Two isomers dimethyl 6,6'-dimethoxy-4,5,4',5'-dimethylenedioxybiphenyl-2,2'-dicarboxylate ((-DDB) and 6,4,-dimethoxy-4…     

The 1:1 adduct of 2,5-dihydroxy-1,4-benzoquinone with 4,4′-bipyridine

2,5-Di­hydroxy-1,4-benzo­quinone (DHBQ) and 4,4′-bi­pyridine (BPY) crystallize in a 1:1 ratio as a neutral molecular adduct, C₆H₄O₄·C₁₀H₈N₂, in space group C2/c, with half of each mol­ecule in the asymmetric unit. The mol­ecules are linked by a strong O—H⃛N hydrogen bond [O⃛N 2.6323 (15) Å] and a weak C—H⃛O hydrogen bond [C⃛O 3.2082 (17) Å] to form infinite stacks of parallel one-dimensional hydrogen-bonded ribbons. The two rings of the bi­pyridine are twisted at 28.3° with respect to each other, and the benzo­quinone ring is inclined at an angle of 18.3° with respect to the plane of the neighbouring pyridine ring. The 4,4′-bi­pyridine mol­ecule lies on a twofold axis and the benzo­quinone mol­ecule lies across an inversion centre.     

The Reaction of (Phenyldimethylsilyl)dichloromethyllithium with Organoboranes. A Synthesis of α-Hydroxyorganosilanes and Ketones

The α-transfer reaction of organoboranes has been utilized to great advantage in the employment of organoboranes in synthesis.² We report here that this process can be used as illustrated in eq 1 to generate α-hydroxyorganosilanes, which can be converted to ketones. This procedure serves to incorporate two of the groups of the organoborane into the product as well as generating the hydroxyl group via oxidation of the newly formed carbon-boron bond.     

Interaction of 2-Aminoindoles with Tetracyanoethylene. 1. 2-Amino-3,4-dicyano-α-carbolines and Related Compounds

2-Aminoindoles are subject to attack by tetracyanoethylene at position 3 with, when possible, subsequent ring closure.