摘要:

New macrocycle polyether 18-crown-6 complexes of stoichiometry [(H3O+•18-crown-6)2(MC42−)] have been synthesized for M = Zn and Mn. The two complexes are isostructural and crystallize in the monoclinic system, space groupC2/c. The unit cell dimensions are as follows:a = 16.229(9),b = 11.535(3),c = 20.134(8) Å, β = 97.55(4)° anda = 16.255(6),b = 11.625(3),c = 20.122(8) Å, β = 96.54(3)° for the Zn and Mn complexes respectively. In both crystal structures (finalRw = 0.048 with 1817 reflections for Zn andRw = 0.074 with 728 reflections for Mn), the crown ether molecule and the H3O+cation to which it is hydrogen-bonded are disordered over two sites. The MCl42−anions, which have tetrahedral coordination, are on crystallographic twofold axes of rotation. The Mn—Cl and Zn—Cl distances average 2.270 and 2.361 Å respectively. The hydronium cation, H3O+, has pyramidal coordination. Of the two disordered crown ether molecules in the Zn and the Mn complexes, one has a slightly deformed (ttg)6conformation while the other one may be described as having the distorted (ttg)5(ttc) conformation. These observations are in agreement with the infrared analyses of the complexes.Keywords: 18-crown-6 complexes, hydronium ion, ZnCl42−, MnCl42−, crystal structure.

ISSN:0008-4042    

DOI:10.1139/v90-127

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

4,4-Dimethyl-2-oxabicyclo[3.2.1]octan-3-one (10), obtained in two steps from norcamphor, was converted to 3-(1,1-dimethyl-2-oxopropyl)cyclopentanone (14), then selectively ketalized. The ketal function underwent Lewis acid catalysed spiro-annulation with 1,2-bis)trimethylsiloxy)cyclobutene (4) yielding 7-(1,1-dimethyl-2-oxopropyl)spiro[4.4]nonane-1,4-dione (21), and intramolecular titanium-induced ketone–ketone coupling and oxidation afforded (±)-isokhusimone (3) in an overall yield of 35% from norcamphor. In an alternative approach, the ethylene ketal of methyl 2-mefhyl-2-(3-oxocyclopentyl)propanoate (27) was prepared from10. Spiro-annulation proceeded in good yield, but subsequent titanium-induced ketone–ester coupling failed to provide the desired tricyclic product, 7,7-dimefhyltricyclo[6.2.1.01,5]undecane-2,6-dione (30).Keywords: annulation, carbonyl coupling, isokhusimone, terpene.

ISSN:0008-4042    

DOI:10.1139/v90-128

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Diphenylmethyl radicals have been generated by 266 nm laser excitation of 1,1,3,3-tetraphenylacetone adsorbed on silica gel and included in NaX and Silicalite zeolites and have been studied using diffuse reflectance laser flash photolysis techniques. The spectrum for the radical shows λmaxat ~335 nm in all three supports and is similar to that in solution. The radicals decay over time scales that vary from hundreds of nanoseconds to minutes and there are indications that some radicals may be decaying on shorter time scales than we can monitor. The efficiency of oxygen quenching increases in going from Silicalite to NaX to silica gel, consistent with the greater accessibility of oxygen to silica gel pores as compared to the narrow channels in Silicalite. Laser dose and ketone loading effects were also examined for the various supports. Potential applications of a kinetic treatment of the data based on dispersive reaction kinetics are also discussed as a means of dealing with the problem of decay kinetics that occur over a wide range of time scales.Keywords: zeolites, kinetics, diphenylmethyl radicals, laser photolysis.

ISSN:0008-4042    

DOI:10.1139/v90-129

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Computer simulations of the hydration of the tetrasaccharide αLFuc(1 → 2)βDGal(1 → 3) αLFuc(1 → 4) βDGlcNAc-OMe and one of its deoxy derivatives were carried out as a first step toward an understanding of the role of water in the recognition of oligosaccharides by proteins. The model consisted of one solute molecule in one of its low-energy conformations, surrounded by 250 water molecules. The solute–water and water–water interaction energies were evaluated with Clementi's potentials. Ensemble states for the derivation of average properties were generated by Monte Carlo methods. As expected, the strength of interaction between water and the amphiphilic solute was found to be considerably greater at hydrophilic than at hydrophobic sites. Furthermore, the average distance between the solvation shell and the solute surface was about 1 Å greater near hydrophobic than around hydrophilic groups. There is also a definitive alignment of the water dipole around the hydroxyl groups of the saccharide, which is not evident over the hydrophobic regions. Finally, in a parallel investigation the tetrasaccharides were solvated by adding water to the solute at sites of minimum energy of association, in order to explore less-CPU-time-consuming alternatives to Monte Carlo simulations. While the patterns of interaction energies, distances, and dipole orientations were found to be similar to Monte Carlo results, the time savings were not as significant as hoped.Keywords: Monte Carlo simulations, numerical solvation studies, solvation simulations of oligosaccharides, molecular recognition, carbohydrate solvation.

ISSN:0008-4042    

DOI:10.1139/v90-130

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The disaccharides β-D-GlcNAOC-(1 → 2)-D-Man, β-D-GlcNAOC-(1→ 4)-D-Man, the trisaccharide β-D-GlcNAOC-(1 → 2)-[β-D-GlcNAOC-(1→ 4)]-D-Man, and the tetrasaccharide β-D-GlcNAOC-(1 → 2)-[β-D-GlcNAOC-(1→ 3)]-[β-D-GlcNAOC-(1 → 4)]-D-Man have been synthesized in their peracetylated form, using the Lewis acid catalyzed condensations of 1,3,4,6-tetra-O-acetyl-2-N-allyloxycarbonylamino-2-deoxy-β-D-glucopyranose1with properly substituted 1,6-anhydro-β-D-mannopyranose derivatives. The anhydro glycosylation products obtained were then easily transformed into the4C1peracetylated derivatives by acetolysis. TheN-allyloxycarbonyl groups could be converted intoN-acetyl groups in the presence of Pd(0) complexes, followed by reacetylation of the free amino function in high yields.Keywords:N-allyloxycarbonyl, glycosylation, glucosamine, glycan fragments.

ISSN:0008-4042    

DOI:10.1139/v90-131

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The three-dimensional structure of the antiviral agent 5-methoxymethyl-2′-deoxycytidine (MMdCyd) was deduced by X-ray crystallographic analysis. MMdCyd crystallized in space groupP21witha = 7.9255(6) Å;b = 16.1505(15) Å,c = 10.1861(5) Å, β = 103.801(5)°, andZ = 4 (2 molecules per asymmetric unit);R = 0.044 (Rw = 0.046) for 2560 observed reflections with netI > 3σ(I). The furanose ring adopts the C(3′)-exoenvelope conformation (3E) in molecule A and the C(2′)-endoenvelope conformation (2E) in molecule B. In the sugar ring of both crystallographically independent molecules A and B, the side chain at C(5′) has the g+conformation. This appears to be a preferred geometry required for antiherpes activity in 2′-deoxyribonucleosides. The glycosyl linkage isantiwith χ = 213.7° for the A molecule and 222.2° for the B molecule. With respect to thisanticonformation, the methoxy group at C(5) in molecules A and B exhibits different conformations; it is on the same side of the pyrimidine plane as the deoxyribofuranose ring oxygen (O4′) in molecule B and on the opposite side in molecule A.Keywords: antiherpes agent, conformation, 5-methoxymethyl-2′-deoxycytidine, crystal structure.

ISSN:0008-4042    

DOI:10.1139/v90-132

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The condensation of various iminophosphoranes witho-phthalaldehyde led directly toN-substituted isoindoline-1-ones and 3-acylisoquinolines. Three different mechanisms, depending on the nature of the iminophosphorane and reaction conditions, are proposed. All the compounds have been fully characterized, particularly by one- and two-dimensional nuclear magnetic resonance spectroscopy.Keywords: isoindolones, isoquinolines, iminophosphoranes.

ISSN:0008-4042    

DOI:10.1139/v90-133

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The dichlorodithionitronium cation, ClSNSCl+, undergoes symmetry-allowed, concerted, cycloaddition reactions with alkynes and alkenes in liquid sulphur dioxide. With ethyne and propyne it gives corresponding 1,3,2-dithiazolium salts in quantitative yield. Cycloaddition with alkenes yields (hitherto unknown) 1,3-dichloro-1,3,2-dithiazolidinium cations. The reactions are sensitive to substituents, and only the cycloaddition with ethene occurs quantitatively on a preparative scale. Cycloadditions with propyne andE- andZ-2-butene have been observed in solution. The preparation, characterization, and X-ray crystal structure of the product of the reaction of CISNSCl+with ethene, 1,3-dichloro-1,3,2-dithiazolidinium hexafluoroarsenate(V), are reported. Crystals of 1,3-dichloro-1,3,2-dithiazolidinium hexafluoroarsenate(V) are monoclinic, of space groupP21/c,a = 6.3161(6) Å,b = 17.1724(23) Å,c = 19.1558(18) Å, and β = 98.143(8)°;Z = 4 andR = 0.061. The 1,3-dichloro-1,3,2-dithiazolidinium cation consists of a five-memberedring, axially substituted at the sulphurs by chlorine (average bond lengths: S—N 1.603(8) Å, S—Cl 2.025(4) Å, S—C 1.822(10) Å, and C—C 1.504(13) Å). Two crystallographically unique cations are linked by weak S..N contacts into pseudo-dimers. These data are used, together with structural comparisons with related SNS-containing cations and the sulphoxides and the14N chemical shift, to show that the bonding in the SNS region of the cation is best represented by the valence canonicalsand, such that the sulphur and nitrogen atoms respectively carry absolute positive and negative charges. This picture is also supported by the fluoride contacts to the cation from the AsF6−anion, which are exclusively to sulphur. Nuclear magnetic resonance data were consistent with the retention of the solid state structure ofin solution.Keywords: sulphur-nitrogen chloride, sulphur-nitrogen cations, 1,3-dichloro-1,3,2-dithiazolidinium, cycloaddition reactions, X-ray crystallography.

ISSN:0008-4042    

DOI:10.1139/v90-134

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The previously suggested mechanism of the condensation–rearrangement reaction of a Reissert compound hydrofluoroborate salt with reactive olefins was reexamined in the case of methyl methacrylate, itaconate, citraconate, and mesaconate. Addition of triethylamine to the reaction medium leads to the isolation of a presumed intermediate8. Spectrometric (proton magnetic resonance) data of the compounds8allow us to specify their stereochemistry and in two cases to point out an isomerization equilibrium.Keywords: Reissert compound fluoroborate salt, [4 + 2] cycloaddition, stereochemistry.

ISSN:0008-4042    

DOI:10.1139/v90-135

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The reaction of Li[Fe(CO)4(PCy2)] withtrans-PtCl(H)(PEt3)2results in the formation of the hydride complex (CO)3Fe((μ-H)((μ-PCy2)Pt(PEt3)2,1. This heterobimetallic, phosphido-bridged complex reacts with one equivalent of HBF4•Et2O to give the complex [(CO)3Fe(μ-H)2((μ-PCy2)Pt(PEt3)2][BF4],2, which contains two bridging hydride ligands. This species is isolated and fully characterized by31P{1H} and1H NMR and infrared spectroscopy. In contrast,1reacts with one equivalent of HCl•DMA (DMA = dimethylacetamide) to give the complex (CO)3ClFe(μ-PCy2)Pt(PEt3)2,3. This species is the result of oxidative addition of HCl with subsequent reductive elimination of H2(g). This complex is fully characterized by31P{1H} and1H NMR, infrared spectroscopy and an X-ray crystal structure determination.3crystallizes in the space groupwitha = 10.037(4) Å,b = 10.644(3) Å,c = 17.137(9) Å, α = 102.80(3)°, β = 76.74(3)°, γ = 103.99(3)°,V = 1702(1) Å3, andZ = 2. The structure was refined toR = 2.54% andRw = 2.73% for 4056 reflections with Fo2 > 3σ(Fo2).Keywords: heterobimetallic, hydride, phosphide, protonation.

ISSN:0008-4042    

DOI:10.1139/v90-136

出版商:NRC Research Press    

年代:1990

数据来源: NRC