Synthesis of p-Trifluoroacetamidophenylethyl O-(2-Acetamido-2-Deoxy-β-D-Galactopyranosyl)-(1→4)-O-β-D- Galactopyanosyl-(1→4)-O-β-D-Glucopyranoside,Containing the Trisaccharide Portion of the Asialo-GM2 Glycolipid

ABSTRACT

The p-trifluoroacetamidophenylethyl β-glycoside 9 of the trisaccharide O-(2-acetamido-2-deoxy-β-D-galactopyranosyl)-(1→4)-O-β-D-galactopyranosyl-(1→4)-D-glucopyranose (gangliotriose, asialo-GM2) was synthesised. The key step was coupling of a suitably protected lactose derivative with a galactosamine thioglycoside derivative using sulfuryl chloride/trifluoromethanesulfonic acid activation.     

Reaction of arylidene-2-naphthylamines with the ethyl ester of (2-quinolyl)-β-oxopropionic acid

The reaction of arylidene-2-naphthylamines with the ethyl ester of (2-quinolyl)--oxopropionic acid results in the synthesis of ethyl esters of 1-(2-quinolyl)-3-arylbenzo[f]quinoline-2-carboxylic acids. All the theoretically possible intermediate reaction products were isolated: the amino esters of 2-quinoline--oxopropionic acid, the hydroxy esters of tetrahydro- and esters of dihydrobenzo[f]quinoline-2-carboxylic acid, as well as the by-products — the ethyl ester of 2-quinolyl--(R-benzylidene)--oxopropionic acid. The IR, UV, and mass spectra of the synthesized compounds are discussed.Institute of Physical Organic Chemistry, Belorussian Academy of Sciences, Minsk 220603. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1406–1410, October, 1994. Original article submitted October 5, 1994.     

Dependence of the chemical properties of macrocyclic [Ni(II)(2)L(μ-O(2)CR)](+) complexes on the basicity of the carboxylato coligands (L(2-) = macrocyclic N(6)S(2) ligand)

The dependence of the properties of mixed ligand [Ni(II)(2)L(μ-O(2)CR)](+) complexes (where L(2-) represents a 24-membered macrocyclic hexaamine-dithiophenolato ligand) on the basicity of the carboxylato coligands has been examined. For this purpose 19 different [Ni(II)(2)L(μ-O(2)CR)](+) complexes (2-20) incorporating carboxylates with pK(b) values in the range 9 to 14 have been prepared by the reaction of [Ni(II)(2)L(μ-Cl)](+) (1) and the respective sodium or triethylammonium carboxylates. The resulting carboxylato complexes, isolated as ClO(4)(-) or BPh(4)(-) salts, have been fully characterized by elemental analyses, IR, UV/vis spectroscopy, and X-ray crystallography. The possibility of accessing the [Ni(II)(2)L(μ-O(2)CR)](+) complexes by carboxylate exchange reactions has also been examined. The main findings are as follows: (i) Substitution reactions between 1 and NaO(2)CR are not affected by the basicity or the steric hindrance of the carboxylate. (ii) Complexes 2-20 form an isostructural series of bisoctahedral [Ni(II)(2)L(μ-O(2)CR)](+) compounds with a N(3)Ni(μ-SR)(2)(μ-O(2)CR)NiN(3) core. (iii) They are readily identified by their ν(as)(CO) and ν(s)(CO) stretching vibration bands in the ranges 1684-1576 cm(-1) and 1428-1348 cm(-1), respectively. (iv) The spin-allowed (3)A(2g) → (3)T(2g) (ν(1)) transition of the NiOS(2)N(3) chromophore is steadily red-shifted by about 7.5 nm per pK(b) unit with increasing pK(b) of the carboxylate ion. (v) The less basic the carboxylate ion, the more stable the complex. The stability difference across the series, estimated from the difference of the individual ligand field stabilization energies (LFSE), amounts to about 4.2 kJ/mol [Δ(LFSE)(2,18)]. (vi) The "second-sphere stabilization" of the nickel complexes is not reflected in the electronic absorption spectra, as these forces are aligned perpendicularly to the Ni-O bonds. (vii) Coordination of a basic carboxylate donor to the [Ni(II)(2)L](2+) fragment weakens its Ni-N and Ni-S bonds. This bond weakening is reflected in small but significant bond length changes. (viii) The [Ni(II)(2)L(μ-O(2)CR)](+) complexes are relatively inert to carboxylate exchange reactions, except for the formato complex [Ni(II)(2)L(μ-O(2)CH)](+) (8), which reacts with both more and less basic carboxylato ligands.     

β-Cyclodextrin Facilitates the Cleavage of Cobalt-Carbon Bonds during the Electrochemical Reduction of Alkylaquabis(dimethylglyoximato)Cobalt(Ⅲ)

HomolysisoftheCo-CbondisakeystePincoempeB12dependentenZymecatalyticCycle[l].Howevr,whytheempmeacceleratestherateofCo-Cbondcleavage2lO1otimesisstillunknown[21.Therefre,effortShaVebeenmadeforinvestigahononalargenumberofcoempeBl2modelsencomPassingtheStrUctUreandfunchonrelahonshipforthecoeap'meBl2.ButmoStformerinVestigationsincludingtheelectrochendsnyweredoneontheisolatedcoempeB12oritSmodelsl3].Recenhy,therehasbeenanincreasingintereStinusingcyClodextrins(CDs)asaamcialempeduetoCDscanfOr…     

Magnetic,spectroscopic and biological properties of copper(II) complexes of the tridentate ligand, α-N-methyl-S-methyl-β-N-(2-pyridyl)methylenedithiocarbazate(NNS) and the X-ray crystal structure of the [Cu(NNS)I2] complex

Copper(II) complexes of general formula, Cu(NNS)X ₂ · nH₂O (NNS = the 2-formylpyridine Schiff base of N-methyl-S-methyldithiocarbazate; X = Cl^–, Br^–, I^–, NCS^–; n = 0, 2) have been synthesized and characterized by elemental analysis and by magnetic and spectroscopic techniques. Based on magnetic and spectroscopic data, a monomeric five-coordinate square-pyramidal structure is assigned to these complexes. The crystal and molecular structure of [Cu(NNS)I₂] has been determined by X-ray diffraction. The complex has a monomeric square-pyramidal structure with the ligand coordinated to the copper(II) ion via the pyridine nitrogen atom, the azomethine nitrogen atom and the thione sulfur atom. The fourth and fifth coordination sites are occupied by the iodide ligands. Antimicrobial tests indicate that Schiff base is inactive against the bacteria, Bacillus subtilis (mutant defective DNA repair), Pseudomonas aeruginosa, methicillin resistant Staphylococcus aureus and Bacillus subtilis (wild type) and weakly active against the fungi, Candida albicans, Candida lypolytica, Saccharomyces cereviseae and Aspergillus ochraceous but its copper(II) complexes, Cu(NNS)X ₂ are strongly active against these organisms. A cytotoxicity study of the compounds against leukemic and cervical cancer cells showed that the Schiff base is inactive, but the complexes, [Cu(NNS)I₂] and [Cu(NNS)(NCS)₂] · 2H₂O exhibit significant activity against cervical cancer cells with CD₅₀ values of 4.8 and 4.2 g, respectively.     

β-Ketoaldehydes in the synthesis of 6-alkyl-3-cyano-2(1H)-pyridinethiones

An efficient synthesis of 6-alkyl-3-cyano-2(1H)-pyridinethiones by the reactions of the sodium salts of -ketoaldehydes with cyanothioacetamide was developed. Pyridinethiones undergo selectiveS-alkylation with haloacetonitriles and haloacetophenones followed by cyclization to the corresponding thieno[2,3-b]pyridines.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 727–731, April, 1995.This study was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-08-823).     

New Fluoroaryl-containing β,β'-Dioxoesters in the Synthesis of Fluorobenzopyran-2(4)-ones

For the first time were obtained ethyl 2-(2-methoxy-3,4,5,6-tetrafluorobenzoyl)-3-oxobutanoate and ethyl 2-pentafluorobenzoyl-3-oxobutanoate and their copper chelates. The compounds were prepared by acylation of ethyl acetoacetate with 2-methoxy-3,4,5,6-tetrafluoro- and pentafluorobenzoyl chlorides. Cyclization of these ,'-dioxoesters afforded substituted chromones. 2-Methyl-5-methoxy-6,7,8-trifluoro-3-ethoxycarbonylchromone hydrolyzes depending on reaction conditions either to 5-hydroxy-2-methyl-6,7,8-trifluorochromone or to 5-hydroxy-2-methyl-6,7,8-trifluorochromone-3-carboxylic acid. Reaction with morpholine provided 7-substituted product, and with aqueous ammonia as a result of rearrangement forms 3-acetimidoyl-4-hydroxy-5-methoxy-6,7,8-trifluorocoumarin. Hydrolysis of the latter yields 3-acetyl-4-hydroxy-5-methoxy-6,7,8-trifluorocoumarin.     

Extrathermodynamic relations in the binding of charged and neutral substrates to sulfobutylether-β-CDs (SBE-β-CDs) and a 2-hydroxypropyl-β-CD (HP-β-CD)

The thermodynamics of binding of various neutral, cationic and anionic substrates to β-cyclodextrin, a hydroxylpropyl-β-cyclodextrin (HP_4M-β-CD) and three sulfobutyl-β-cyclodextrins with varying degrees of total substitution (SBE_1M-β-CD, SBE_7M-β-CD, and SBE_12M-β-CD) were determined by estimating binding constants, using a UV spectrophotometric technique, and temperature variation. linear free energy relation (LFER) plots and enthalpy–entropy Compensation (EEC) plots provided insight into the mechanisms of complexation as did carbon T ₁ relaxation times using NMR. LFER plots for charged molecules with HP_4M-β-CD deviate from the neutral substrates suggesting differences in interaction modes. LFER plots for SBE_7M-β-CD show that cationic substrates surprisingly fall within the same linear relationship for neutral substrates while anionic substrates deviate. The EEC plots for HP_4M-β-CD show the largest loss of motion and degree of desolvation upon complexation. The interaction with SBE_1M-β-CD was similar to that for β-CD. SBE_7M-β-CD, and SBE_12M-β-CD EEC plots are similar with the least loss of motion upon complex formation, suggesting a more organized and less flexible structure. This is supported by the T ₁ relaxation times for SBE_1M-β-CD, SBE_7M-β-CD, and SBE_12M-β-CD, which show a critical distance at which the mobility of the side chain is reduced to form an extended cavity. No such evidence was seen with HP_4M-β-CD, although the effect of varying of hydroxypropyl substitution was not studied.     

Kinetics of the single-electron chemical oxidation of rhenium(V) meso-phenyl-β-octaethylporphyrinate

The states and reactions of rhenium(V) complexes with meso-monophenyl-β-octaethylporphines containing Cl^? and OPh^? as axial ligands O=Re(Cl)MPOEP and O=Re(OPh)MPOEP in concentrated sulfuric acid at 298–348 K are studied via spectral and kinetic methods. While stable along M-N bonds, O=Re(Cl)MPOEP is found to undergo slow oxidation after transforming into axial hydrosulfate complex O=Re(HSO₄)MPOEP. It is shown that the sole electron oxidizing agent is atmospheric oxygen (with the assistance of highly concentrated protons) and the sites of reduction are aromatic ligands. The reaction product was identified as π-radical cation O=Re(HSO₄)MPOEP^·+. Forward and inverse chemical kinetics solutions are used to obtain a full kinetic equation and the reaction rate parameters of elementary steps, and to establish the stoichiometric mechanism of the composite oxidation of the complex. Complex O=Re(OPh)MPOEP in the form O=Re(OPh)(O₂)MPOEP with coordinated oxygen is shown experimentally to be stable with respect to oxidation. The obtained results are important for identifying intermediates in processes catalyzed by stable metal porphyrins.     

The mechanisms of the acid-catalysed dissociation of tris-β-diketonatoruthenium(III) complexes

Summary The reactions of four -diketonatoruthenium(III) complexes in the presence of HNO₃ andp-MeC₆H₄SO₃H in the 45° and 57° range were followed spectrophotometrically in Me₂COH₂O mixtures. Dissociation of Ru(acac)₃ follows [H⁺]-dependent and [H⁺]²-dependent paths, whereas the bzac and F₃acacF₃ complexes follow only the [H⁺]-dependent path. The bzbz (Dibenzoylmethanate) complex is inert. Protonation of the bound ligand leads to its rupture from the metal ion. The bzac complex is kinetically more inert than the acac complex, because of extra stability arising from interaction of the (bzac) benzene ring with the pseudo-aromatic diketonate ring of the complex. Considering the kinetic labilities, the complexes may be arranged in the order Ru(F₃acacF₃)₃>Ru(acac)₃>Ru(bzac)₃>Ru(bzbz)₃.Activation parameters for [H⁺] dependent path are: H ₁ 86.5±7, 69±5, 121±7 kJ mol^–1, S ₂ –52±10, –107±10, 57±8 JK^–1 mol^–1 for acac, bzac and F₃acacF₃ complexes respectively and H ₂ 67±5 kJ mol^–1, S ₂ –92±8 JK^–1 mol^–1 for the acac complex only.     

Facile synthesis of nanoparticles of the molecule-based superconductor κ-(BEDT-TTF)2Cu(NCS)2

Well-dispersed roughly spherical nano-objects of the molecule-based superconductor κ-(BEDT-TTF)₂Cu(NCS)₂ have been prepared in an organic solution by using an easy synthetic route. Long alkyl-chain aconitate esters have been used as growth controlling agents. Nano-objects exhibiting sizes in the 35–120 nm range are made of aggregated individual smaller nanoparticles ranging from 3 to 10 nm. Nanoparticle powders have been studied by X-ray diffraction, high resolution electron microscopy and atomic force microscopy in the conductivity mode.     

Accessibility and Selective Stabilization of the Principal Spin States of Iron by Pyridyl versus Phenolic Ketimines: Modulation of the (6)A(1) ↔ (2)T(2) Ground-State Transformation of the [FeN(4)O(2)](+) Chromophore

Several potentially tridentate pyridyl and phenolic Schiff bases (apRen and HhapRen, respectively) were derived from the condensation reactions of 2-acetylpyridine (ap) and 2'-hydroxyacetophenone (Hhap), respectively, with N-R-ethylenediamine (RNHCH(2)CH(2)NH(2), Ren; R = H, Me or Et) and complexed in situ with iron(II) or iron(III), as dictated by the nature of the ligand donor set, to generate the six-coordinate iron compounds [Fe(II)(apRen)(2)]X(2) (R = H, Me; X(-) = ClO(4)(-), BPh(4)(-), PF(6)(-)) and [Fe(III)(hapRen)(2)]X (R = Me, Et; X(-) = ClO(4)(-), BPh(4)(-)). Single-crystal X-ray analyses of [Fe(II)(apRen)(2)](ClO(4))(2) (R = H, Me) revealed a pseudo-octahedral geometry about the ferrous ion with the Fe(II)-N bond distances (1.896-2.041 ?) pointing to the (1)A(1) (d(π)(6)) ground state; the existence of this spin state was corroborated by magnetic susceptibility measurements and M?ssbauer spectroscopy. In contrast, the X-ray structure of the phenolate complex [Fe(III)(hapMen)(2)]ClO(4), determined at 100 K, demonstrated stabilization of the ferric state; the compression of the coordinate bonds at the metal center is in accord with the (2)T(2) (d(π)(5)) ground state. Magnetic susceptibility measurements along with EPR and M?ssbauer spectroscopic techniques have shown that the iron(III) complexes are spin-crossover (SCO) materials. The spin transition within the [Fe(III)N(4)O(2)](+) chromophore was modulated with alkyl substituents to afford two-step and one-step (6)A(1) ? (2)T(2) transformations in [Fe(III)(hapMen)(2)]ClO(4) and [Fe(III)(hapEen)(2)]ClO(4), respectively. Previously, none of the X-salRen- and X-sal(2)trien-based ferric spin-crossover compounds exhibited a stepwise transition. The optical spectra of the LS iron(II) and SCO iron(III) complexes display intense d(π) → p(π)* and p(π) → d(π) CT visible absorptions, respectively, which account for the spectacular color differences. All the complexes are redox-active; as expected, the one-electron oxidative process in the divalent compounds occurs at higher redox potentials than does the reverse process in the trivalent compounds. The cyclic voltammograms of the latter compounds reveal irreversible electrochemical generation of the phenoxyl radical. Finally, the H(2)salen-type quadridentate ketimine H(2)hapen complexed with an equivalent amount of iron(III) to afford the μ-oxo-monobridged dinuclear complex [{Fe(III)(hapen)}(2)(μ-O)] exhibiting a distorted square-pyramidal geometry at the metal centers and considerable antiferromagnetic coupling of spins (J ≈ -99 cm(-1)).     

Synthesis of the 4-Deoxy-2-Deutero-4-Fluoro Analog of Methyl O-β-D-Galactopyranosyl-(1→6)-β-D-Galactopyranoside

ABSTRACT

Methyl 4-deoxy-4-fluoro-6-O-(β-D-galactopyranosyl)-(2-²H)-β-D-galactopyranoside was prepared by the condensation of 2,3,4,6-tetra-O-benzoyl-α-D-galactopyranosyl bromide and methyl 2-O-benzoyl-3-O-benzyl-4-deoxy-4-fluoro-(2-²H)-β-D-galactopyranoside (17), followed by deprotection. The introduction of deuterium at C-2 in an intermediate methylhexopyranoside was achieved by a double inversion, brought about by oxidation of C-2 of a derivative of methyl α-D-glucopyranoside, to give the corresponding ketone, and subsequent reduction thereof with NaBD₄, to give a derivative with the D-manno configuration (8). Inversion of the configuration at C-2 of the latter was achieved by displacement with sodium benzoate of the O-trifluoromethanesulfonyl (triflyl) group in the 2-O-triflyl derivative of 8. The resulting synthon was converted, conventionally, to methyl 2-O-benzoyl-3-O-benzyl-6-O-trityl-(2-²H)-β-D-glucopyranoside. Its conversion into the 6-O-trityl derivative of 17, unsuccessful by treatment with dimethylaminosulfur trifluoride, was readily accomplished by the displacement of the triflyl group with fluoride ion contained in an ion-exchange resin.     

Application of the Ru(bipy)2(dpp)2+ / C2O4 2− electrochemiluminescence reaction to the determination of phenol

The electrochemiluminescence (ECL) of the ruthenium di(2,2′-bipyridine)- (4,7-diphenyl-1,10-phenanthroline) complex (Ru-bipy-dpp) produced on a glassy carbon electrode was studied by cyclic voltammetry. The anodic oxidation of Ru-bipy-dpp produces ECL in the presence of oxalate in oxygen-free aqueous solutions. Threefold ECL efficiencies were obtained for Ru-bipy-dpp relative to Ru(bipy)₃ as a standard. The ECL of Ru-bipy-dpp is quenched by both oxygen and phenol. The luminescence intensity was proportional to the concentration of phenol in the range of 5–100 μM. At a phenol concentration of 100 μM, the ECL of Ru-bipy-dpp peaking at 597 nm was completely quenched. Correspondence: Dan Xiao, College of Chemistry and Chemical Engineering, Sichuan University, Chengdu 610065, P.R. China     

Functionalized 3(2H)-furanones via photooxygenation of (β-keto)-2-substituted furans: application to the biomimetic synthesis of merrekentrone C

Photooxygenation of (β-keto)-2-substituted furans leads, in a one pot operation, to functionalized 3(2H)-furanones with good to excellent yields. This methodology was applied as a key-step to the concise and biomimetic synthesis of the sesquiterpene merrekentrone C. The precursor to merrekentrone C, keto difuran, was synthesized using a cross coupling of α-iodo-3-acetylfuran with an alkenyl furan under Fenton-type conditions.     

Electrochemical study of the thermodynamic properties of matildite (β-AgBiS2) in different temperature and compositional ranges

Thermodynamic properties of matildite (β-AgBiS₂) in equilibrium with sulfur and bismuth have been studied by an EMF method, using the fast Ag⁺ ion-conducting solid electrolytes AgI and RbAg₄I₅. The ternary phases were synthesized from the pure binary compounds. Properties of the electrolytes used have been reviewed, and their usage as pure conductors of Ag⁺ ions in the temperature ranges of the electrochemical cells employed was well defined. The EMF measurements were carried out using the solid-state electrochemical cells Pt(?)|Ag|RbAg₄I₅|β‐AgBiS₂?+?AgBi₃S₅?+?S|Pt(+) and Pt(?)|Ag|AgI|β‐AgBiS₂?+?AgBi₃S₅?+?Bi|C|Pt(+), in the temperature range 325–464 K. Based on the obtained results, thermodynamic functions for the formation of matildite (β-AgBiS₂) at sulfur and bismuth saturation have been determined. The obtained experimental values have been compared with the available literature values. New experimentally determined thermodynamic properties of the bismuth-saturated matildite (β-AgBi_1?+?x S₂) and sulfur-saturated matildite (β-AgBiS_2?+?y ) were generated and analyzed in detail.     

Preparation of the N-(2-Bromo-2-Nitroethenyl) Benzenamine: The First One-Pot Synthesis of a β-Halo-β-Nitroenamine

Bromonitromethane, triethyl orthoformate and aniline react together, in a one-flask procedure, to afford the title compound.     

Synthesis ofβ-glycosides of n-acetylglucosamine in the presence of HgI2

The use of HgI₂ as catalyst in the synthesis oftrans-glycosides of N-acetylglucosamine is described. Using this catalyst, -glycosides of N-acetylglucosamine with aglycons of different structures and lyophilicities have been synthesized. The possibility of performing oligosaccharide synthesis has been demonstrated.     

Electrochemical and Theoretical Investigations of the Role of the Appended Base on the Reduction of Protons by [Fe(2) (CO)(4) (κ(2) -PNP(R) )(μ-S(CH(2) )(3) S] (PNP(R) ={Ph(2) PCH(2) }(2) NR, R=Me, Ph)

The behavior of [Fe(2) (CO)(4) (κ(2) -PNP(R) )(μ-pdt)] (PNP(R) =(Ph(2) PCH(2) )(2) NR, R=Me (1), Ph (2); pdt=S(CH(2) )(3) S) in the presence of acids is investigated experimentally and theoretically (using density functional theory) in order to determine the mechanisms of the proton reduction steps supported by these complexes, and to assess the role of the PNP(R) appended base in these processes for different redox states of the metal centers. The nature of the R substituent of the nitrogen base does not substantially affect the course of the protonation of the neutral complex by CF(3) SO(3) H or CH(3) SO(3) H; the cation with a bridging hydride ligand, 1?μH(+) (R=Me) or 2?μH(+) (R=Ph) is obtained rapidly. Only 1?μH(+) can be protonated at the nitrogen atom of the PNP chelate by HBF(4) ?Et(2) O or CF(3) SO(3) H, which results in a positive shift of the proton reduction by approximately 0.15?V. The theoretical study demonstrates that in this process, dihydrogen can be released from a η(2) -H(2) species in the Fe(I) Fe(II) state. When R=Ph, the bridging hydride cation 2?μH(+) cannot be protonated at the amine function by HBF(4) ?Et(2) O or CF(3) SO(3) H, and protonation at the N atom of the one-electron reduced analogue is also less favored than that of a S atom of the partially de-coordinated dithiolate bridge. In this situation, proton reduction occurs at the potential of the bridging hydride cation, 2?μH(+) . The rate constants of the overall proton reduction processes are small for both complexes 1 and 2 (k(obs) ≈4-7?s(-1) ) because of the slow intramolecular proton migration and H(2) release steps identified by the theoretical study.