Regioselective α(2→3)-Sialylation of LeX and Lea by Sialidase-Catalyzed Transglycosylation

Considerable effort has been devoted to the development of new methods for α-selective sialylation due to the growing importance of the synthetic sialoglycoconjugates in glycobiology³. The synthesis of α-sialoside has been establised by chemical routes,⁴ which often involve many steps and are complicated. The promising chemoenzymatic procedure through the use of sialyltransferases has already become a preparative technique.⁵ However, laborious isolation and the pronounced acceptor specificity of the transferases limit their synthetic potential. Recently, a novel procedure for α-sialylation has been reported, which uses sialosides of synthetic substrate as donors and is catalyzed by sialidase in place of sialyltransferase. Thiem et a1.⁶ have reported the enzymatic synthesis of α(2→6)-linked sialyl galactose, glucose, lactose and lactosamine in preference to the corresponding α(2→3)-linked derivatives employing sialidase from vibrio cholerae, while Ajisaka et al.⁷ have synthesized α(2→3)-linked sialyl lactose and lactosamine with sialidase from new castle disease virus.

     

The temperature dependence of the monomer reactivity ratios in the copolymerization of styrene with α-substituted cinnamic acids

Styrene has been copolymerized with α-methyl [carboxyl-¹⁴C]cinnamic acid, α-phenyl [carboxyl-¹⁴C]cinnamic acid and ethyl benzylidene [carboxyl-¹⁴C]cyanoacetate at temperatures between 40 and 130°, using azoisobutyronitrile as initiator. The compositions of the copolymers have been determined by liquid scintillation counting; a simplified form of the copolymer composition equation was used to determine the reactivity ratios of the polystyryl radical. Arrhenius parameters have been derived. With the α-methyl and α-phenyl substituted acids, the pre-exponential factors favour self propagation, which predominates. With the smaller α-cyano substituent, self propagation is also favoured by the pre-exponential factors; however, cross propagation, favoured by the energies of activation, predominates. The effect of substitution by methyl or phenyl groups in the α-position of cinnamic acid is much greater than that found with the methyl or phenyl esters.     

Preparation of a Trans α,β-Epoxysilane by Selective Pyrolysis

α,β-Epoxysilanes have been shown to be useful synthetic intermediates² for the preparation of carbonyl compounds³ and stereoisomerically-pure olefins⁴ and heteroatom-substituted olefins⁵ (vinyl bromides,⁵ enol acetates,⁵ enol ethers,⁵ enamides,⁵ and vinyl mesylates⁶). In many of their reactions, α,β-epoxysilanes serve as stereospecific vinyl cation equivalents;⁴–6 therefore methods to prepare stereoisomerically-pure α,β-epoxysilanes are of considerable importance. Although other methods for preparing α,β-epoxysilanes have recently been developed,⁷ the only general method for preparing stereoisomerically-pure α,β-epoxysilanes is epoxidation of the corresponding vinylsilanes.     

The Synthesis of Diphenyl Phosphonate Analogues of α-Amino Acids as Enzyme Inhibitors

Abstract

α-Aminoalkylphosphonic acids are analogues of natural aminoacids and as such have been the subject of much research effort over past years¹. The diphenyl esters of α- aminoalkylphosphonic acids are particularly potent and show high selectivity as irreversible inhibitors of serine proteinases. Thus far, α-aminoalkylphosphonic acid ester analogues of a number of aliphatic- and aromatic aminoacids have been prepared including valine, phenylalanine, tryptophan, and tyrosine², and the basic aminoacids ornithine, lysine. etc.³. We have now also prepared the a-diphenyl phosphonate analogues of the acidic aminoacids, aspartic and glutamic⁴. These have been examined as potential inactivators of serine proteinases exhibiting a P₁ specificity for aspartate and glutamate, e.g. S. aureus V8 protease and granzyme B.     

Fluorinated anilides of β-keto acids and their Cu(II) complexes

Pentafluoroanilides of acetoacetic and benzoylacetic acids and their α-SCF₃ substituted analogues have been synthesized from the respective β-keto esters. Cu(II) complexes of the compounds obtained as well as of anilide of α-(trifluoromethylthio)acetoacetic acid have been prepared and characterized. The structure of these compounds has been elucidated on the basis of the elemental analysis and IR, MS, ¹H and ¹⁹F NMR spectra.     

β-Ketonitrosamines as Synthetic Equivalents of α-Methinyl Methylamino (R-Chnhch3) and α-Methinyl Alkylamino (R−Chnhr′) Anions

Abstract

β-Ketonitrosamines have been established as anionic synthons of the type (RCO^{+ ?}CHNHR′). The enhanced acidity of protons at the α-carbon, as well as the ease of fragmentation of the title compounds, established them as synthetic equivalents of α-methylenealkylamino anions (^?CH2NHR). We now report the equivalency of β-ketonitrosamines to α-methinyl methylamino (R^?CHNHCH₃) and α-methinyl alkylamino (R ^?CHNHR′) anions.     

Determination of bioactive compounds by catalytic method coupled with planar chromatography

The promoting effect of collagen and inhibiting effect of α-alanine on the catalytic activity of copper(II) in the oxidation of 3,3′,5,5′-tetramethylbenzidine with ammonium persulfate and the reduction of iron(III) with sodium thiosulfate, respectively, have been found. A method combining planar chromatography with the subsequent catalytic determination of collagen after desorption from a plate and methods of sorption-catalytlic determination of histamine and α-alanine directly on the support have been developed with limits of detection 2 × 10^?14, 5 × 10^?7, and 8 × 10^?14 M for histamine, α-alanine, and collagen, respectively. Separation by paper and thin-layer chromatography allowed a substantial increase in the selectivity of catalytic determination. The methods were used to determine histamine in human saliva and collagen and α-alanine in cosmetics.     

Asymmetric transfer hydrogenation of α,β-unsaturated, α-tosyloxy and α-substituted ketones

Asymmetric transfer hydrogenation of cyclic and acyclic α,β-unsaturated ketones catalysed by η⁶-p-cymene/ruthenium(II) and η⁵-pentamethylcyclopentadienyl/rhodium(III) complexes have been investigated. Cyclic α,β-unsaturated ketones appeared to be more suitable substrates for the synthesis of enantiomerically pure allylic alcohols than do acyclic α,β-unsaturated ketones. A proposed mechanism for the formation of 4-phenyl-[1,3]-dioxolan-2-one from α-tosyloxy- and halo-substituted acetophenones is discussed. The results of further investigations into the reduction of a range of α-tosyloxyacetophenones and the dynamic kinetic resolution of α-substituted ketones is presented.     

Synthesis and characterization of some α-naphthyl selenium/tellurium derivatives: X-ray crystal structure of benzyl-1-naphthyl selenide and diphenylmethyl-1-naphthyl selenide

A large number of α-naphthyl selenium and tellurium compounds (1-14) have been prepared through two different methods. The first method involves the alkylation of sodium 1-naphthylselenolate/tellurolate, generated in situ using hydrazine hydrate as reducing agent while the second method involves the reaction of in situ generated α-naphthylseleno/telluromagnesium bromide with an appropriate electrophile. The synthesized alkyl-1-naphthyl selenides/tellurides and some α,ω-bis(1-naphthylseleno)alkanes have been characterized with the help of elemental analysis and using various spectroscopic techniques viz., NMR (¹H, ¹³C, ⁷⁷Se and ¹²⁵Te), IR, UV/vis spectroscopy and mass spectrometry (only in few representative cases). Interpretation of ¹H, ¹³C NMR spectra and assignment of individual resonances for tris(1-naphthylseleno)methane have been done with the help of [¹H-¹H] and [¹H-¹³C] correlation spectroscopy (COSY). X-ray crystallographic results and molecular geometry of benzyl-1-naphthyl selenide, 2 and diphenylmethyl-1-naphthyl selenide, 3 have also been illustrated.     

13C NMR Spectra of tocopherols and 2,2-dimethylchromanols

Carbon-13 NMR signals have been assigned for α-γ- and δ-tocopherols,a nd their model compounds, 2,2-dimethylchromanols. The ¹³C spectra of α-tocopherol-5-CD₃ and ?8-CD₃ afforded the evidence of the assignments of Me-carbon signals. It was found that previous tentative assignments for C-6 and C-8a of α-tocopherol are not correct. Steric compression shifts have been observed at several Me-carbons and at the methylene-carbons of C-4 in their compounds.     

Synthesis,magnetic and spectral studies of chromium(III), manganese(III), iron(III) and cobalt(III) complexes of thiosemicarbazones derived from benzil α-monoxime and unsubstituted/substituted thiosemicarbazides as biological agents

Cr(III), Mn(III), Fe(III) and Co(III) complexes of thiosemicarbazones, derived from benzil α-monoxime and thiosemicarbazides (BMTH₂), benzil α-monoxime and phenyl thiosemicarbazides (BMPTH₂), benzil α-monoxime and 4-bromophenyl thiosemicarbazides (BMBTH₂), benzil α-monoxime and 4-chlorophenyl thiosemicarbazides (BMCTH₂) and benzil α-monoxime and 4-nitrophenyl thiosemicarbazides (BMNTH₂), have been prepared. These complexes have been characterized by elemental analyses, magnetic susceptibilities, molar conductance measurements, electronic, IR, ¹H and ¹³C NMR spectra (in the case of Co(III) complexes), FAB mass spectra and thermogravimetric analysis to arrive at the geometry of the ligand environment around the metal ion and to elucidate the bonding sites of the ligands with the central metal. The complexes contain two monoprotonic tridentate ligands with NNS donor sites. Coordination to metal ion the oxime nitrogen, imine nitrogen and thione sulfur is confirmed in the complexes by IR spectral studies. The antifungal and antibacterial activities of the ligands and complexes have been screened.     

Phase Transfer Catalysed Synthesis of Methyl α-Bromomethylacrylate

Methyl α-bromomethylacrylate 1 is an important intermediate both as a starting material for specifically functionalized polymers and for use in general organic synthesis. As an example of the former it has been used to prepare polymeric anthraquinoid dyes¹. Synthetically, its bifunctional reactivity towards nucleophilic attack has made it useful in the preparation of both spiro² and bicyclic^3,4 ring systems. Several reports of synthetic methods leading to α-methylenelactones, having potential antitumor activity, have also been reported which use α-bromomethylacrylate as a starting point⁵.     

Synthesis of C-Sulfonylcarbohydroximoyl Chlorides from α-Diazosulfones and Nitrosyl Chloride1

Previous investigations in this laboratory have been concerned with reactions of α-diazosulfones² (1) with electrophilic reagents, such as sulfenyl chlorides², t-butyl hypochlorite^2,3 and halogens⁴, which lead to threefold electronegatively substituted methanes (2). As was anticipated, α-diazosulfones closely resemble α-diazoketones in these reactions.⁵     

Chiral,non-racemic α-hydroxyphosphonates and phosphonic acids via stereoselective hydroxylation of diallyl benzylphosphonates

Chiral, non-racemic α-hydroxyphosphonates have been prepared in high enantiomeric excess (96–98% ee), via stereoselective oxaziridine-mediated hydroxylation of diallyl benzylphosphonates. The enantiomeric purity and absolute configuration of the α-hydroxyphosphonates was established from ¹H and ³¹P NMR spectroscopy of the (S)-O-methylmandelate esters. Deprotection of the diallyl α-hydroxyphosphonates under neutral conditions furnished the corresponding free phosphonic acids, retaining a high degree of stereochemical purity (90 to >98% ee).     

Infrared and 1H NMR structural study of 3-tropane, 3-granatane and 3-bicyclo(3.2.1)octane epimeric amino acids

Five amino acids with known configuration: α- and β-3-amino-tropane- and 3-amino-bicyclo(3.2.1)octane-3-carboxylic acids and α -3-amino-granatane-3-carboxylic acid have been studied by i.r. and ¹H NMR spectroscopy. Both α- and γ-zwitterion structures have been found for tropane and granatane amino acids. Equatorial and axial ammonium groups in α-zwitterions can be distinguished by the number and frequencies of the ammonium deformation modes. A chair—boat conformation has been deduced for α-3-amino-granatane-3-carboxylic acid.     

Rate constants for the gas-phase reactions of O3 with a series of Terpenes and OH radical formation from the O3 reactions with Sesquiterpenes at 296 ± 2 K

Rate constants for the gas-phase reactions of O₃ with the sesquiterpenes α-cedrene, α-copaene, β-caryophyllene, α-humulene, and longifolene, and with the monoterpenes limonene, terpinolene, α-phellandrene, and α-terpinene, have been measured using a relative rate technique at 296 ± 2 K and atmospheric pressure of air. The rate constants obtained (in units of 10^?17 cm³ molecule^?1 s^?1) are: limonene, 20.1 ± 5.1; terpinolene, 188 ± 67; α-phellandrene, 298 ± 105; α-terpinene, 2110 ± 770; α-cedrene, 2.78 ± 0.71; α-copaene, 15.8 ± 5.6; β-caryophyllene, 1160 ± 430; α-humulene, 1170 ± 450; and longifolene, <0.07, where the indicated errors include the estimated overall uncertainties in the rate constants for the reference organics. Hydroxyl radical formation yields were also determined for the O₃ reactions with the sesquiterpenes, of 0.67 for α-cedrene, 0.35 for α-copaene, 0.06 for β-caryophyllene, and 0.22 for α-humulene, all with estimated overall uncertainties of a factor of ca. 1.5. The tropospheric lifetimes of the sesquiterpenes due to reaction with O₃ are calculated. © 1994 John Wiley & Sons, Inc.     

Studies concerning charged nickel hydroxide electrodes: Part III. Reversible potentials at low states of charge

Reversible potentials of partially charged α- and β-Ni(OH)₂ electrodes have been measured in both the homogeneous and heterogeneous potential-composition regions. From the points of transition between these regions, nickel oxidation states of the least oxidised coexisting phases U and U¹ have been measured as 2.25.Experimental emf—oxidation state measurements for both the β and α/λ-phase couples are found to be in good agreement with theoretically derived expressions. Direct measurement of the oxidation states of the complementary coexisting phases V and V¹ has not been possible. From considerations of the homogeneous emf—composition regions it is deduced that the oxidised species are dissociated in the host lattice, in both the β- and α/λ-phase systems.     

Acetate anion-selective encapsulation in the ellipsoidal cavity of symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril

Four symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril-based compounds have been prepared and characterised by X-ray crystallography. Their crystal structures displayed the acetate anion-selective encapsulating capability of symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril. The host–guest interaction between the symmetrical α,α′,δ,δ′-tetramethyl-cucurbit[6]uril and the acetate anion in aqueous solution has also been observed by variable temperature ¹H NMR spectroscopy.     

α-substituent effects in 13C NMR of hydrocarbons. Quantum chemical calculations

The ¹³C NMR α-substituent effects within the series methane to neopentane and ethene to isobutene have been calculated using Hartree—Fock perturbation theory with MINDO/3. The sign and order of magnitude of the calculated α-effects are in agreement with new experimental values, including effects of multiple substitution.     

Preparation and spectra of mercuribis (α-diazo ketones)

Bis (α - diazophenacyl) mercury (2a), bis (α - diazo - 2,4,6 - trimethylphenacyl) mercury (2b), bis (1 - diazo - 3,3 - dimethyl - 2 - oxobutyl)mercury (2c), and bis (1 - diazo - 2 - phenylacetonyl) mercury (2d) have been prepared by treatment of the corresponding α-diazo ketones with mercuric oxide. The solution IR, UV, and ¹H NMR spectra of 2a–d and of three other mercuribis (α-diazo ketones) have been compared with the spectra of the corresponding α-diazo ketones, and the similarities between these have led to the conclusion that in solution these mercury derivatives exist with the mercury bonded to carbon. The ¹³C NMR resonance spectra of 2a and of α-diazo - α - methylmercuriacetophenone (9) have been examined for evidence of ¹⁹⁹HgC coupling; this was observed in the case of 9 for the Me carbon, but not detected in either case for the diazo carbon; this is attributed to difficulty of detection and/or ligand exchange. The signals of the diazo carbon in these spectra occur at unusually high field; a similar observation was made in the spectra of several α-diazo ketones, where the chemical shifts were in the range δ 50–70.