摘要:

1-Desacetylwilfordine,8, 1-desacetylwilfortrine,9, and 2-debenzoyl-2-nicotinoylwilforine,10, have been isolated from root extracts of the Chinese medicinal and insecticidal plantTripterygiumwilfordii. Analysis of the1H and13C NMR spectra of8and10, with the aid of COSY, HCCOSY, and COLOC experiments, has allowed unambiguous chemical shift assignments of all protons and carbons of these alkaloids.Keywords: alkaloids, sesquiterpene, Celastraceae,Tripterygium, NMR.

ISSN:0008-4042    

DOI:10.1139/v90-056

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Laser flash photolysis in aqueous basic solutions of the ortho acid derivatives 1-(phenyldimethoxymethyl)benzimidazole2and 4-bromo-1-(phenyldimethoxymethyl)imidazole3results in production of the phenyldimethoxymethyl cation, which has λmaxat 260 nm. The cation decays in reactions with water (k = 9.9 × 104 s−1) and hydroxide ion (2.5 × 108 M−1 s−1) to finally yield methyl benzoate, whose formation was monitored at 234 nm. In solutions with pH 10–12, rate constants measured at this wavelength are the same as those obtained at 260 nm, but with pH > 13 and pH < 9, rate constants at 234 nm are smaller. With pH 9–10 and pH 12–13, single exponential kinetics are not observed at 234 nm. This behavior is interpreted in terms of a scheme where at each pH there are two consecutive first-order reactions, cation → phenyldimethoxyhydroxymethane (5) → ester, and the pH dependencies of the rate constants are such that they cross twice over the pH range of this study. The intermediate5is the tetrahedral intermediate formed in the methanolysis of methyl benzoate, and the 234-nm buildup at pH > 13 and pH < 9 directly measures its breakdown. At pH > 13 the rate constant is independent of pH withk = 9 × 106 s−1. This represents the rapid expulsion of methoxide from the conjugate base of5. At pH < 9 the rate constants are proportional to hydroxide ion concentration, with. In these solutions the neutral intermediate predominates and the dependence on [OH−] of its rate of conversion to ester is interpreted in terms of breakdown of the anion and protonation of this species by water occurring at comparable rates. Thus,represents a situation where there is partial rate-limiting deprotonation of the neutral intermediate by hydroxide. The intermediate of this study bears a close resemblance to the tetrahedral intermediate of the hydrolysis of methyl benzoate. The observation that the anionic forms of such intermediates undergo breakdown at rates similar to those associated with the establishment of proton transfer equilibrium explains why the ester undergoes carbonyl oxygen exchange in base at a rate slower than hydrolysis.Keywords: tetrahedral intermediate, flash photolysis, ester hydrolysis.

ISSN:0008-4042    

DOI:10.1139/v90-057

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Preparation and properties of the bacteriorhodopsin (bR) analogue having the 3,7-dimethyl-9-(9-anthryl)-2E,4E,6E,8E-nonatetraenal (12) chromophore is described. Synthesis of the chromophore has been achieved by successive introduction of C5units to 9-anthraldehyde (3) via the Horner reaction. The all-transchromophore has been characterized by its ultraviolet–visible and1H nuclear magnetic resonance spectra. Incubation of12with bacterioopsin suspension (prepared by photobleaching of bR isolated fromHalobacteriumhalobium) at ambient temperature in the dark gave the new bR analogue15, which showed an absorption band at 545 nm, and an opsin shift of 5575 cm−1. The new pigment is stable to hydroxylamine in the dark. It showed light–dark adaptation with the light-adapted form absorbing at a slightly red-shifted value of 550 nm. All-trans-retinal did not replace the anthryl chromophore in competitive bindings. Photolysis of the bR analogue15, followed by difference spectrophotometric analysis, indicated formation of a photoproduct with an absorption band near 400 nm. The results are discussed in terms of the stereoelectronic requirements of the bR reaction centre.Keywords: bacteriorhodopsin (bR), retinal analogue, reconstitution, opsin shift (OS), external point charge model (EPC).

ISSN:0008-4042    

DOI:10.1139/v90-058

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Irradiation of an acetonitrile solution ofpara-dicyanobenzene (1), 3,3-diphenyltetrahydrofuran (2), and magnesium perchlorate leads to the formation of 4,4-diphenyl-1,3-dioxane (7). Similarly, irradiation of an acetonitrile solution of1, methyl 2,2-diphenylcyclopentyl ether (5), and magnesium perchlorate leads to the formation of 6,6-diphenyl-2-methoxytetrahydropyran (8). The mechanism proposed for these reactions involves formation of the radical cationsandwith the first excited singlet state of1acting as the photosensitizer (electron transfer). The radical cationsandthen cleave to give 1,5 radical cations. Reaction of the cationic site with water, followed by futher oxidation of the radical site by the perchlorate anion, gives the diphenylalkyl carbocation that can cyclize via a six-membered intermediate to the observed products7and8. While the addition of other perchlorate salts (lithium and tetra-n-butylammonium) also lead to the formation of7and8, lithium trifluoroacetate is ineffective. The proposal that water is involved as the nucleophile is supported by incorporation of17O in the products7and8when17O-enriched water was added to the reaction mixture.Keywords: photosensitization, electron transfer, radical cations, bond cleavage, 2,2-diphenylethyl ether.

ISSN:0008-4042    

DOI:10.1139/v90-059

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Abietinarins A (1) and B (2), two new 1-[4H]-anthracenone derivatives, have been isolated from the Northeastern Pacific marine hydroidAbietinariasp. The proposed structures for abietinarins A (1) and B (2) are based on spectroscopic analysis. Abieitinarin A (1) exhibited significant cytotoxicity in an in vitro L1210 bioassay.Keywords: cytotoxic, hydroid, abietinarins, metabolites, marine.

ISSN:0008-4042    

DOI:10.1139/v90-060

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Chlorination of isobutyrophenone in alkaline aqueous solution leads to formation of α-hydroxyisobutyrophenone as the first detectable intermediate; a slow subsequent oxidation gives benzoate. From the rates of the initial chlorinations we have been able to determine the pKavalue for the ketone as 18.18 ± 0.50. α-Chloroisobutyrophenone undergoes surprisingly rapid alkaline hydrolysis,kOH = 71.9 ± 1.5 M−1 s−1.Keywords: isobutyrophenone, chlorination, enolization, pKa, hydrolysis.

ISSN:0008-4042    

DOI:10.1139/v90-061

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The syntheses of the acyclic trienetrans–trans–cis27andtrans–trans–trans31are described. Macrocyclization and concomitant transannular Diels–Alder reaction were performed with the chloride derivative obtained from thetrans–trans–cistriene alcohol27yielding a mixture of the tricyclic compoundstrans–syn–trans33andcis–syn–cis34. On the other hand, macrocyclization of the chloride derived fromtrans–trans–transtriene31was not successful.Keywords: transannular process, Diels–Alder reaction, macrocyclic triene, macrocyclization, tricyclic compounds, organic synthesis.

ISSN:0008-4042    

DOI:10.1139/v90-062

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Methylammonium lead(II) halides, CH3NH3PbX3(X = Cl, Br, I), have been investigated by single-crystal X-ray diffraction,2H and14N nmr, adiabatic calorimetry, and other methods. The chloride (CL) has transitions at 171.5 and 177.4 K, the bromide (BR) at 148.4, 154.2, and 235.1 K, and the iodide (IO) at 162.7 and 326.6 K. The respective entropies of transition (J K−1 mol−1) are 11.0 and 5.1 for CL; 8.7, 3.4, and 5.3 for BR; and 16.1 and 1.9 for IO. The highest-temperature phase, phaseI, of each halide is of the cubic (Pm3m) perovskite type. The cation in CL(I) and BR(I) could not be localized in the electron density maps; the thermal motion of the halogen atom is highly anisotropic. The lnT1(2H) vs.T−1plots (N-deuterated samples as well as CD3NH3PbCl3) show significant departures from linearity: the temperature variation ofT1(2H) in BR(II) and IO(II) can be represented by functions of the type lnT1(H) = k0 − k2T−2, which give adequate analytical representations ofT1(2H) andT1(14N) in phaseIas well. On cooling, BR(II) and IO(II) exhibit small quadrupole splittings QS(2H), which can be represented to a high degree of correlation by QS(2H) = k(Ttr − T)n, i.e. they appear to exhibit critical behaviour with respect toT. The14N nmr results indicate that the C—N bond in phaseIreorientates in an isotropic potential at a rate approaching that of the freely rotating methylammonium ion. Below phaseIthis motion takes place in an increasingly anisotropic potential in BR(II) and IO(II) and is essentially arrested in CL(II), BR(III), and IO(III). The temperature dependence of the activation energyEafor the cation reorientation and other aspects of the non-Arrhenius behaviour are discussed, and the CH3NH3PbX3perovskites are compared with the corresponding (CH3NH3)2TeX6halides, utilizing preliminary2H nmr results on (CH3ND3)2TeBr6. The electrical conductivity, between 0 and 95 °C, of CH3NH3PbI3increases with temperature and exhibits no discontinuity atTtr = 326.6 K; the activation energy for the conduction process is estimated as ~0.4 eV.Keywords: crystal structure, MeNH3PbCl3and MeNH3PbBr3; heat capacity, MeNH3PbX3(X = Cl, Br, I); methylammonium lead halides; solid-state NMR,2H and14N; spin-lattice relaxation, non-Arrhenius behaviour.

ISSN:0008-4042    

DOI:10.1139/v90-063

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The electrochemical oxidation of a sacrificial anode (M = Zn, Cd, Hg, In, Sn) in non-aqueous solutions of 3-hydroxyflavone, 1′-hydroxy-2′-acetonaphthone, or 2-ethoxyphenol (= HL) gives ZnL2, CdL2, HgL, InL3, or SnL2(not all combinations). Adducts with 2,2′-bipyridine (bpy) orN,N,N′,N′-tetramethylethanediamine (tmen) have also been prepared in some cases. Certain zinc and cadmium compounds produce paramagnetic species on exposure to the atmosphere. The structure of Zn(C15H9O3)2tmen has been determined; the crystals are orthorhombic, space groupPbcn, cell dimensionsa = 18.817(2) Å,b = 13.886(3) Å,c = 12.567(3) Å,Z = 4,R = 0.0758 for 773 unique observed reflections. The corresponding data for Cd(C12H9O2)2bpy are orthorhombic, space groupPbca, cell dimensionsa = 20.338(4) Å,b = 30.473(5) Å,c = 9.316(2) Å,Z = 8,R = 0.0457 for 2623 unique observed reflections. Both molecules have MO4N2kernels, but each shows significant differences in the two M—O bond lengths to the dioxo ligand, and there are concomitant effects in the C—O and C—C bond distances in the ligands.Keywords: electrochemical synthesis,d10metal ions, X-ray crystallography, zinc complex, cadmium complex.

ISSN:0008-4042    

DOI:10.1139/v90-064

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Nine symmetrical aliphatic dicarboxylic acids, namely oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, and sebacic acids, were titrated conductimetrically with tetrabutylammonium hydroxide in pyridine and pyridine–benzene mixtures ((2 + 1), (1 + 1), (1 + 2), (1 + 3), and (1 + 4)). Titration curves of the acids exhibited two distinct and stoichiometric end-points in media of dielectric constants 13.5, 10.0, 8.2, 6.3, 5.3, and 4.7, respectively. The closer investigations of the titration curves revealed that three factors mainly influence the shapes of the titration curves: dielectric constant of the medium, number of the methylene groups in the acid, and formation of hydrogen bonds between several species. As dielectric constant of the medium decreases, conductivity of the medium also decreases at any point in the titration curve. Increase in the number of methylene groups from one to five decreases conductivity of the medium linearly at the first end-points of the acids, from then the conductivity becomes practically constant in acids having five to eight methylene groups in pyridine and pyridine–benzene mixtures of 2 + 1 and 1 + 1 ratios.Keywords: conductimetric titration in pyridine, conductimetric titration in pyridine–benzene mixtures, symmetrical aliphatic dicarboxilic acids.

ISSN:0008-4042    

DOI:10.1139/v90-065

出版商:NRC Research Press    

年代:1990

数据来源: NRC