摘要:

We have studied the reaction of bothD- andL-penicillamine with pyridoxal hydrochloride and examined the products by single crystal X-ray diffraction. The structure of the title compound,A, formed by the reaction ofD-penicillamine and pyridoxal was determined. Crystals are orthorhombic,P212121, with cell dimensionsa = 9.507(5),b = 19.185(5),c = 7.766(2) Å andZ = 4. The structure was solved by standard methods and refined toR = 0.088,Rw = 0.079 for 2433 independent reflections.Aexists as a zwitterion, and bond lengths and angles are normal. In the solid state,Aand the corresponding product obtained fromL-penicillamine,B, have identical geometrical structure but are of opposite chirality; that is,D-penicillamine produces the 2R,4Sdiastereomer andL-penicillamine produces the 2S,4Rdiastereomer (with noS,SandR,Rcomponents). In solution, however, NMR spectra show the presence of both pairs of diastereomers (2R,4Sand 2S,4S; 2S,4Rand 2R,4R). In neutral or alkaline solution there appears to be a rapid epimerization at the thiazolidine carbon atom attached to the pyridoxal moiety. Features of the mass,1H NMR, vibrational, and electronic spectra are also discussed.Keywords:D-penicillamine, vitamin B6, pyridoxal hydrochloride, therapeutic uses, bischemical reactions, structures.

ISSN:0008-4042    

DOI:10.1139/v91-001

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The fractionation by solvents of the contents of the seeds ofAnnonamuricata(Annonaceae), guided by the toxic activity towards the brine shrimp larva and the KB cancer cells, has enabled us to isolate two new cytotoxic mono-tetrahydrofuran γ-lactones: corossolone1and corossolin2. The structure of these two cytotoxic acetogenins was determined by analysis of the spectral data, NMR and MS in particular. The chemical correlation between1and2was established by the NaBH4reduction of corossolone.1and2constitute the first examples of mono-tetrahydrofuran acetogenins with an unfunctionalized C-4.Keywords: Annonaceae, acetogenins, cytotoxicity, soursop,Annonamuricata.

ISSN:0008-4042    

DOI:10.1139/v91-002

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The synthesis of crown ethers derived frommeso-tartaric acid was investigated. The sodium salt of the bis(dimethylamide) ofmeso-tartaric acid reacted with diethylene glycol ditosylate to give a mixture of 18-crown-6 tetraamide and 27-crown-9 hexaamide crown ethers. The 2R,3S,11S,12R18-crown-6 isomer crystallized in triclinic space group(a = 7.557(2),b = 8.866(2),c = 10.4133(13) Å, α = 94.13(2), β = 95.86(2), γ = 99.26(2)°,R = 0.040 for 2090 observed of 3129 unique reflections). The structures of the remaining products were then assigned from the NMR spectra. The solution conformations of the amide crown ethers were examined by NMR, and provide a rationale for the product distribution obtained. One of the 18-crown-6 isomers and a mixture of the two 27-crown-9 isomers were hydrolyzed to the respective crown ether carboxylic acids, and the stability constants for complexation of cations were determined by potentiometric titration. Themesotetra- and hexacarboxylates are remarkably nonselective and inefficient cation complexing agents, compared to related crown ethers fromR,R-(+)-tartaric acid, due to the unfavorable conformational control exerted by the tartaro units.Keywords: crown ether synthesis, complexation, crown ether conformation,meso-tartaric acid, crystal structure.

ISSN:0008-4042    

DOI:10.1139/v91-003

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The structure of imbricatine (1), a cytotoxic metabolite of the starfishDermasteriasimbricata, has been determined by spectroscopic analysis and chemical degradation. Synthesis of model compounds7and18provided evidence for the absolute configuration and constitution of the benzyltetrahydroisoquinoline substructure of imbricatine.Keywords: imbricatine, asteroid, alkaloid.

ISSN:0008-4042    

DOI:10.1139/v91-004

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Hydrolysis of aluminum(III) ion in 3.0 M(Na)NO3medium was studied by emf method at 25° C. Data cover the range 1–78 mMAl(III) within the pH range of 2.0–4.5. At a definite pH, the extent of hydrolysis increases with increasing aluminium concentration, thereby indicating the presence of polynuclear hydrolysis products. The least squares treatment of the data indicates the formation of polynuclear hydrolytic complexesandWith the reactions written in the formthe stability constants obtained were log (β2,2 = −7.55 ± 0.21, log β2,4 = −16.41 ± 0.13, and log (β3,4 = −13.24 ± 0.08. Distribution curves indicate that the complexis predominant.Keywords: hydrolysis, aluminum(III) ion, hydrolytic complexes, aluminum(III) ion hydrolysis.

ISSN:0008-4042    

DOI:10.1139/v91-005

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Some ferrospinels act as catalysts for the decomposition of H2O2, their effectiveness is dependent on the composition of the catalyst. This study is to find the most effective catalyst of stoichiometry MIIFe2IIIO4. A set of ferrites of different composition MIIFe2II04(MII = Mn, Co, Ni, Cu, Zn, Cd) was synthesized by co-precipitation and characterized by chemical analysis, X-ray diffractometry, and B.E.T. technique. A comparative assessment of the catalytic power of these ferrites from investigations of their influence on the kinetics of H2O2decomposition in a neutral medium was made. An analysis of the data on specific rate, and the Eyrings activation parameters for the reaction sharply reveal the following: (a) The catalytic power follows the order MnFe2O4 > CoFe2O4 > CuFe2O4 > NiFe2O4 > CdFe2O4 > ZnFe2O4, MnFe2O4is much more highly effective than the others (50–100 fold). (b) A compensation effect has been noted from the observed linearity with slightly less than unity slope betweenTΔ≠S0and Δ≠H0over the entire series.Keywords: Ferrospinels, catalysis, hydrogen peroxide decomposition kinetics.

ISSN:0008-4042    

DOI:10.1139/v91-006

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Mixtures of ethylene and methane have been pyrolyzed in the temperature range 925–1023 K for the purpose of converting methane to higher hydrocarbons. Addition of methane to thermally-reacting ethylene increases the rate of formation of propylene but decreases the rates of formation of the other major products, ethane, acetylene, and butadiene. Hydrogen abstraction from methane is a major propagation reaction and causes a shift in the radical distribution from ethyl and vinyl radicals, the main radicals in the pyrolysis reactions of ethylene alone, to methyl radicals, which lead to the formation of propylene. At 1023 K with a pressure of ethylene of 6.5 Torr and of methane of 356 Torr, 1.5 mol of methane is converted to higher molecular weight products for every mole of ethylene reacted. The rate of conversion of methane in the homogeneous system is lower than in catalytic reactions but the product is entirely hydrocarbon and no methane is lost to carbon monoxide or carbon dioxide.Keywords: methane, ethylene, kinetics, pyrolysis, fuels.

ISSN:0008-4042    

DOI:10.1139/v91-007

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

An experimental study of the homogeneous gas phase oxidation of propane at 350 °C and subatmospheric pressure has been performed in order to identify and to measure the major primary products of the reaction. The experimental results have been interpreted by a chain radical mechanism, deduced from these results and from estimates of the rate constants for the elementary steps obtained by the methods of Thermochemical Kinetics. The proposed elementary steps are discussed and compared with the experimental observations. The results that we have obtained and their interpretation are compared with a similar detailed investigation performed on the oxidation of isobutane. As in the case of isobutane, two parallel reaction pathways appear, a dominant one leading to the conjugated alkene (propylene) and another one leading to the epoxide of this olefin (here propylene oxide). The oxidation of isobutane and that of propane appear to be quite similar, which corroborates the results that we have obtained.Keywords: oxidation, kinetics, reaction mechanism, propane, thermochemical kinetics.

ISSN:0008-4042    

DOI:10.1139/v91-008

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Homochiral α-substituted γ-lactols3and4derived from (R)-pantolactone1were used in 2-lithio-1,3-dithiane additions to afford very high controls in diastereoselectivities arising from 1,2-asymmetric inductions. Thus non-chelation controlled nucleophilic addition on3gave theantidiastereomer5as the major product (92% de), while the chelation controlled addition on4furnished thesyndiastereomer7(96% de) as the almost exclusive product. The stereochemical outcomes of these reactions were proven unambiguously by locking the conformation of thesyn- andanti-triol adducts7and8through their respective acetonides and by nuclear Overhauser enhancement measurements. The lack of 1,3-dioxolane formation in the case of theanti-triol8was taken as a further confirmation of the absolute configuration at the newly created stereocenter.Keywords: byrostatin, pantolactone, α-hydroxylactol, dithiane.

ISSN:0008-4042    

DOI:10.1139/v91-009

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The title compound (10) was prepared, along with the 4-cyano isomer (11), by the direct irradiation of 5-cyanobenzocyclooctatetraene (9); the yields were 82% (Φ10 = 0.0030) and 12% (Φ11 = 0.0004) respectively. Triene10was thermally and photochemically reactive. Heating solutions of10at 150 °C for 1 h gave COT9quantitatively. On direct irradiation10forms 5-cyanobenzosemibullvalene (12; 5%, Φ = 0.019), COT9(70%, Φ = 0.56), and 1-cyanonaphthalene (14%, Φ = 0.078). Sensitized irradiation of10gave9exclusively (92%, Φ = 0.88). COT9was also produced by the direct irradiation of semibullvalene12(75%, Φ = 0.13). Studies with deuterium labelled10suggest that the photoformation of COT9involves a simple electrocyclic opening of the cyclobutene ring of the triene. Additionally, the labelling results indicate that the formation of semibullvalene12from10derives from the operation of two reaction pathways, the major one of which appears to be a Zimmerman di-π-methane rearrangement. The mechanism proposed for the minor pathway to12has not been observed in other bicyclo[4.2.0]octatrienes.Keywords: mechanisms, rearrangements, photochemistry, di-π-methane.

ISSN:0008-4042    

DOI:10.1139/v91-010

出版商:NRC Research Press    

年代:1991

数据来源: NRC