Preparation of α-Halovinyl Sulfides by Eliminative Deoxygenation of α-Halosulfoxides

Abstract

Vinyl sulfides are useful synthetic intermediates¹ which have received increasing attention recently both as masked carbonyl moieties² and in carbon-carbon bond forming reactions.³ With regard to the latter, vinyl sulfide derivatives which are substituted in the α-position with halogen, tin, selenium, etc., are particularly useful due to the ready formation of anions upon treatment with a variety of organometallic reagents.^{3 d ? 1} We report here that synthetically useful halovinyl sulfides can be produced in high yield by the eliminative deoxygenation of the corresponding α-halosulfoxides induced by electrophilic silicon reagents.     

Convenient synthesis of α-diarylmethylphosphonates by HOTf catalyzed Friedel-Crafts arylation of α-aryl α-hydroxyphosphonates

We report a convenient catalytic Friedel-Crafts arylation of α-aryl α-hydroxyphosphonates with various (hetero)aromatic compounds. HOTf (trifluoromethanesulfonic acid) is identified to be the best Brønsted acid catalyst, and the desired α-diarylmethylphosphonates were obtained in up to 41–95% yield.     

Inhibition of dextransucrase by α-D-Glucose derivatives

alpha-D-Glucopyranosyl fluoride was modified at positions 2, 3, or 5 and these analogs were tested as substrates and inhibitors of dextransucrase from Leuconostoc mesenteroides B-512F. The analogs studied were 2-deoxy-2-fluoro-alpha-D-glucopyranosyl fluoride, 3-deoxy-3-fluoro-alpha-D-glucopyranosyl fluoride, 3-deoxy-3-thio-alpha-D-glucopyranosyl fluoride, and 5-thio-alpha-D-glucopyranosyl fluoride. Kinetic constants for alpha-D-glucopyranosyl fluoride were also determined. None of the alpha-D-glucopyranosyl fluorides were accepted as substrates for dextransucrase. 2-Deoxy-2-fluoro-alpha-D-glucopyranosyl fluoride, 3-deoxy-3-fgluoro-alpha-D-glucopyranosyl fluoride, and 3-deoxy-3-thio-alpha-D-glucopyranosyl fluoride were competitive inhibitors with Ki values of 63, 93, and 53 mM, respectively. The Km for alpha-D-glucopyranosyl fluoride was found to be 26 mM. The data indicate that the hydroxyl groups at C2 and C3 are important for proper binding of alpha-D-glucopyranosyl fluoride for the active site of dextransucrase and that the C3-hydroxyl probably acts as a hydrogen-bond donor.     

Conformation Disturbance of CopC by α-Naphthylamine

It is known that urea and guanidine hydrochloride(GuHCl) induce conformational change of proteins in a certain range of molar ratios. In our research,α-naphthylamine(NA) above 10-4 mol/L at pH 7.0 was discovered to perturb the conformation of CopC,a copper resistant protein with a Greek β-barrel motif; this was reflected by the greater fluorescence quenching and red-shifted emission peak of CopC. The conformation change of CopC was also verified in acrylamide collision experiment by comparing quenching leve...     

Determination of α-Amanitin in Serum by HPLC

Abstract

A reverse-phase high-performance liquid chromatographic method for the quantitative determination of α-amanitin in serum of poisoned patients is described and discussed. The methodology developed is simple and rapid with a minimum of sample preparation steps required. Detection is very sensitive, allowing quantitation of 25 ng of α-amanitin/ml of serum. The technique described is a useful tool to determine the severity of Amanita phalloides intoxication during the first 24 h after ingestion of poisonous mushrooms.     

Resolution of α-phenylethylamine by its acidic derivatives

α-Phenylethylamine was resolved by its own derivatives formed with a homologous series of dicarboxylic acids. The structure of the oxalamic acid diastereoisomeric salts was investigated by the single-crystal X-ray diffraction method.     

Hydration of α-pinene catalyzed by acid clays

The hydration reaction of α-pinene in the presence of natural clays treated with monochloroacetic acid as catalyst to obtain oxygenated compounds was studied. Catalysts were characterized using X-ray diffraction, differential thermal analysis, programmed thermal desorption of adsorbed pyridine, and infrared spectroscopic analysis of adsorbed pyridine to determine Brønsted and Lewis acid sites. Catalytic tests revealed that treatment of the natural clay with the acid improved the catalytic activity and the selectivity toward oxygenated products by increasing the acidity of the catalyst. The selectivity toward oxygenated compounds increased with the augment of the α-pinene conversion because of greater contact between water molecules with the remaining α-pinene molecules. The natural clay without treatment produced compounds resulting from α-pinene isomerization, whereas the treated clays produced alcohols and other products in addition to isomerization compounds. After a certain time, the α-terpineol was isomerized into cineols. Studies of the reusability of the JAL catalyst were performed (clay treated with monochloroacetic acid). As the number of reuses increased, the percent conversion decreased; however, the selectivity toward oxygenated compounds increased.      

Polymerization of α-Hydroxyacetylenes by Transition Metal Catalysts

Abstract

α-Hydroxyacetylenes (2-propyn-1-ol, DL-3-butyn-2-ol, 1-octyn-3-ol, 2-phenyl-3-butyn-2-ol) with a hydroxy functional group were polymerized by various Mo- and W-based catalysts. In general, the catalytic activities of Mo-based catalysts were greater than those of W-based catalysts for these polymerizations. In the polymerization of 2-propyn-l-ol, MoCl₅ alone and the MoCl₅-EtAlCl₂ catalyst system gave a quantitative yield of polymer. In the polymerization of 2-propyn-l-ol and its homologues by Mo-based catalysts, the polymer yield decreased as the bulkiness of the substituent increased. On the other hand, the polymer yield increased as the bulkiness of the substituent increased in WCl₆-EtAlCl₂-catalyzed polymerization. Polymers with a bulkier substituent showed better solubility in organic solvents than those without a substituent [e.g., poly (2-propyn-l-ol)]. The structures of the resulting polymers were characterized by various instrumental methods such as ¹H- and ¹³C-NMR, IR, and UV-visible spectroscopies. Thermogravimetric analyses and thermal transitions of the resulting polymers were also studied.     

Enantioselective sulfenylation of α-nitroesters catalyzed by diarylprolinols

The organocatalytic sulfenylation of α-nitroesters mediated by diaryl-l-prolinols was developed. A range of α-sulfenylated α-nitroesters were obtained in good yields with moderate to good enantioselectivities.     

Synthesis of 2-indanones by intramolecular insertion of α-diazoketones

The reaction of α-diazoketones from phenylacetic acid derivatives affords 2-indanones in good yield. Insertion into the aromatic CH bond was found to be favored over insertion into an aliphatic one.     

Membrane Transport of the Zwitterionic Aromatic α-Amino Acids by α-Aminophosphonates

Abstract

Bghly selective biological transport of amino acids is usually mediated by carrier proteins. The application of such membrane systems for the analysis and separation of amino acids has long studied. This work is devoted to the transport of zwitterionic form of aromatic a-amino acids such as d,l-Phe, d,l-DOPA, d,l-His, d,l-Tyr, d,l-Trp, via supported liquid membrane (SLM). The lipophilic α-aminophosphonates (I).

R₁ amyl or 2-ethylhexyl; R₂, R₂-(CH₂)4-(CH₂)5-CH₃ & (CH₃), C₄ H(CH₉) & H; H & H; have been used as carrier in the membrane systems composed of a porous polymeric support (Millipore Type FA) impregnated with 10^?1 M carrier in o-nitrophenyl n-octyl ether (amino acid concentration in source phase is 10^?3 M). The cell for membrane extractions is presented on Fig I.     

Asymmetric synthesis of α-alkyl α-selenocarbonyl compounds catalyzed by bifunctional organocatalysts

A new organocatalytic approach for the synthesis of a variety of α-alkyl, α-phenylselenyl ketones as well as their corresponding esters and amides, by the addition of α-selenocarbonyl derivatives to nitroalkenes catalyzed by thiourea or squaramide cinchona catalysts, is presented. This catalytic system allows the preparation in high yields of enantiomerically enriched selenocarbonyl derivatives bearing two chiral centers with excellent ee's and dr's by using catalytic loadings of 3 mol%.     

Catalytic Asymmetric Synthesis of α-Quaternary Proline Derivatives by 1,3-Dipolar Cycloaddition of α-Silylimines

Going pro: The title reaction between α-silylimines and activated olefins proceeds in the presence of a Cu(I) /DTBM-Segphos catalyst system with excellent diastereoselectivity and enantioselectivity. This process provides straightforward access to highly enantioenriched 5-unsubstituted α-quaternary proline derivatives. TMS=trimethylsilyl, DTBM-Segphos=5,5'-bis[di(3,5-di-tert-butyl-4-methoxyphenyl)phosphino]-4,4'-bi-1,3-benzodioxole.     

Synthesis of α-Phenylsulfonyl cyclopentanones by intramolecular carbenoid cyclization of α-Diazo-β-keto phenylsulfones

Acyclic α-diazo-β-keto phenylsulfones undergo smooth intramolecular carbenoid cyclizations under rhodium (II) catalysis to afford α-phenyl sulfonyl cyclopentanones.     

Synthesis of α-glycosyl thiols by stereospecific ring-opening of 1,6-anhydrosugars

Treatment of 1,6-anhydrosugars with commercially available bis(trimethylsilyl) sulfide in the presence of trimethylsilyl triflate led to the formation of α-glycosyl thiols. All the reactions were highly stereoselective and afforded the α-glycosyl thiols in good to excellent yields. By this procedure, a variety of 1,6-anhydrosugars, differing in their sugar units, glycosidic linkages, and protecting group pattern, were converted smoothly into the corresponding α-glycosyl thiols, which could be of great utility in thioglycoside chemistry. It is noteworthy that 1,6-anhydrosugars carrying the 2-O-acyl group and 1,6-anhydrosugar-containing oligosaccharides could also be ring-opened stereospecifically under the same conditions to give rise to the corresponding 1-thiosugars in high yields. Thus, a very concise and efficient access to α-glycosyl thiols of great value was established.     

Determination of α-tocopherol in Cosmetic Products by Chronopotentiometry

Abstract

In the present study, a rapid chronopotentiometric method was developed for the determination of α-tocopherol in various cosmetic products. Determination of α-tocopherol is based on its irreverse oxidation by constant current at the planar glassy carbon electrode. The influence of the most important experimental parameters of chronopotentiometry was investigated. After optimization, an appropriate procedure for the sample preparation was developed. Under the defined experimental conditions, a detection limit of 7.5 mg L^?1 of α-tocopherol was obtained. The accuracy of the defined method was confirmed by means of recovery assay. The developed method was successfully applied to quantitation of α-tocopherol in various cosmetic products.     

Enantioselective α-hydrazination of α-fluoro-β-ketoesters catalyzed by chiral nickel complexes

The catalytic enantioselective electrophilic α-hydrazination promoted by chiral nickel complexes is described. Treatment of α-fluoro-β-ketoesters with azodicarboxylates as electrophilic amination reagents under mild reaction conditions afforded the corresponding α-amino α-fluoro-β-ketoesters with high yields (80-96%) and enantioselectivities (up to 78% ee).     

Mechanism of membrane interaction and disruption by α-synuclein

Parkinson's disease is a common progressive neurodegenerative condition, characterized by the deposition of amyloid fibrils as Lewy bodies in the substantia nigra of affected individuals. These insoluble aggregates predominantly consist of the protein α-synuclein. There is increasing evidence suggesting that the aggregation of α-synuclein is influenced by lipid membranes and, vice versa, the membrane integrity is severely affected by the presence of bound aggregates. Here, using the surface-sensitive imaging technique supercritical angle fluorescence microscopy and F?rster resonance energy transfer, we report the direct observation of α-synuclein aggregation on supported lipid bilayers. Both the wild-type and the two mutant forms of α-synuclein studied, namely, the familiar variant A53T and the designed highly toxic variant E57K, were found to follow the same mechanism of polymerization and membrane damage. This mechanism involved the extraction of lipids from the bilayer and their clustering around growing α-synuclein aggregates. Despite all three isoforms following the same pathway, the extent of aggregation and their effect on the bilayers was seen to be variant and concentration dependent. Both A53T and E57K formed cross-β-sheet aggregates and damaged the membrane at submicromolar concentrations. The wild-type also formed aggregates in this range; however, the extent of membrane disruption was greatly reduced. The process of membrane damage could resemble part of the yet poorly understood cellular toxicity phenomenon in vivo.     

Synthesis of α-Benzotriazole Sulfides Promoted by Samarium Diiodide

1-(Benzotriazol-1-yl) unsymmetrical diorganyl sulfides were synthesized via replacement of chlorine atom in 1-(benzotriazol-1-yl)-1-chloromethane with thiolate anions promoted by SmI₂.