摘要:

Muscarosides D, E, and F, three new 27-norlanostane tetra-, penta-, and hexasaccharides, respectively, isolated from the bulbs ofMuscaricomosum, were respectively shown to be (23S,24S)-3-O-{α-L-arabinopyranosyl(1→3)[β-D-apio-D-furanosyl(1→2)]-β-D-glucopyranosyl(1→2)-α-L-arabinopyranosyl(1→6)-β-D-glucopyranosyl}-17,23-epoxy-3β,24,30,31-tetrahydroxy-27-nor-5α-lanost-8-ene4, (23R)-3-O-{α-L-arabinofuranosyl(1→2)-α-L-arabinopyranosyl(1→3)[α-L-rhamnopyranosy(1→2)]-β-D-glucopyranosyl(1→2)-α-L-arabinopyranosyl(1→6)-β-D-glucopyranosyl}-17,23-epoxy-3β,31-dihydroxy-27-nor-5α-lanost-8-en-15,24-dione5, and (23S)-3-O-[β-D-apio-D-furanosyl(1→2)-β-D-glucopyranosyl(1→2)-α-L-arabinopyranosyl(1→6)-β-D-glucopyranosyl]-17,23-epoxy-3β,31-dihydroxy-27-nor-5α-lanost-8-en-15,24-dione6. The structural details were elucidated by a combination of fast-atom-bombardment mass spectroscopy, one- and two-dimensional nuclear magnatic resonance spectroscopy, and comparison to model compounds expressly synthesized.

ISSN:0008-4042    

DOI:10.1139/v87-387

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

An efficient acetylation of alcohols and aliphatic amines promoted by the AlPO4–Al2O3/ethyl acetate system is described. The solid catalyst acts, at least in part, as the acetyl carrier.

ISSN:0008-4042    

DOI:10.1139/v87-388

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The oxidation of glycine by permanganate ion in aqueous phosphate buffers is autocatalyzed by the soluble form of colloidal manganese dioxide formed as a reaction product. Both the noncatalytic and the catalytic reaction pathways are first order in permanganate, the noncatalytic pathway is also first order in glycine, whereas the catalytic pathway has a kinetic order unity for the autocatalytic agent and a non-integral order (1.31) for glycine. Both reaction pathways are accelerated by an increase in the pH of the medium, whereas an increase in the buffer concentration at constant pH results in an increase in the rate of the noncatalytic pathway and a decrease in the rate of the catalytic one. Additions of potassium chloride to the solutions have no kinetic effect on the reaction. The apparent activation energies of the noncatalytic and catalytic reaction pathways are 64.5 and 62.0 kJ mol−1, respectively. On the other hand, manganese(II), thiosulfate, and hexacyanoferrate(II) ions, as well as benzyltriethylammonium chloride and arabic gum, have all been found to increase the initial reaction rate. Mechanisms in concordance with the experimental findings are proposed.

ISSN:0008-4042    

DOI:10.1139/v87-389

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Formation of hydroxyl radicals, in relatively large quantities, by oxygen reduction due to the surface activity of asbestos in a cell-free system is demonstrated, using electron spin resonance and a spin trapping agent. The quantity of OH•produced (in general, above 1014 mg−1for a Canadian chrysotile) is a function of activation or passivation of the electron donor surface sites of the minerals. The role of these radicals in oxidative stress in relation to the toxic properties of these minerals is discussed.

ISSN:0008-4042    

DOI:10.1139/v87-390

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Pulsed picosecond laser photolysis of the diphenyliodonium cation indicates that excitation of the allowed transition is followed by rapid (ps) deactivation to a homolytically dissociative state, presumablyT1. Steady-state photolysis yields iodobenzene and biphenyl from the primary radical products. Iodobiphenyl is also observed. We infer in-cage recombination of these radical products, with intervention of a carbocationic intermediate. Laser flash photolysis of diphenyliodonium iodide in its charge transfer band yields an initial transient with a lifetime of ca. 200 ps. A strongly absorbing secondary transient is observed on the nanosecond time scale. Iodobenzene is the exclusive reaction product. We infer that it is not formed directly from the primary photoproduct, but through in-cage recombination of phenyl cation with iodide anion, as in benzenediazonium iodide.

ISSN:0008-4042    

DOI:10.1139/v87-391

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The title compounds1and2, the first examples of peroxides polysubstituted at the α and α′ positions by alkoxy groups, are formed by benzophenone sensitized photooxygenation of trimethoxymethane and 1,1,1-trimethoxyethane, respectively. No peroxide was formed from tetramethoxymethane. Allowing 98% hydrogen peroxide and trimethoxymethane to stand results in an 80% yield of1, so that1and2are probably formed by such a disproportionation reaction during photooxygenation. Compound1is converted quantitatively to methanol, methyl formate, and dimethyl carbonate in pyridine solution at 60 °C. In acidic methanol both1and2undergo solvolysis rapidly with exclusive cleavage of the carbon – peroxy oxygen bond. Signals for the ether and peroxy oxygens of1appear at 34 and 263 ppm and those of2appear at 40 and 264 ppm in the17O nuclear magnetic resonance spectrum. Luminescence results when1and2are heated to 150 °C.

ISSN:0008-4042    

DOI:10.1139/v87-392

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

A new and improved procedure for the preparation of (R)-2-alkoxycarbonyl-1-formyl-1,2,3,4-tetrahydro-6,7-dimethoxyisoquinolines has been developed beginning fromD-(−)-tartaric acid. The utility of these aldehydes in the asymmetric synthesis of isoquinoline alkaloids of high enantiomeric purity has been extended to the synthesis of phenylethylisoquinolines, which have been further transformed in straightforward steps into the homoprotoberberine and homoaporphine ring systems. In this manner, (S)-homolaudanosine, (S)-5′-methoxyhomolaudanosine, (S)-2,3,9,10,11-pentamethoxyhomoprotoberberine, and (S)-O-methylkreysigine have been synthesized. The conversion of (S)-laudanosine to (S)-glaucine, an aporphine alkaloid, has also been realized.

ISSN:0008-4042    

DOI:10.1139/v87-393

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

It is shown that 3,4-dihydroisoquinolines are activated toward nucleophilic attack by reaction with trimethylsilyl trifluoromethanesulfonate. The complex so formed reacts readily with the lithio derivative of 3-cyano-4-methyl-5-vinylpyridine, affording in a single step a tetracyclic amidine from which a lactam is obtained by hydrolysis. These reactions have been applied to the synthesis of theAlangiumalkaloids, (±)-alangimaridine and alangimarine.

ISSN:0008-4042    

DOI:10.1139/v87-394

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Two previously unreported antibiotic metabolites, 2′,3′,4″-triacetoxy-3,4,5′,6′-tetrahydroxy-p-terphenyl (10) and 2′,3′-diacetoxy-3,4,5′,6′,4″-pentahydroxy-p-terphenyl (11), have been isolated from the basidiomyceteSarcodonleucopus. Their structures have been determined by chemical transformations and spectral analysis, including heteronuclear two-dimensional nuclear magnetic resonance methods.

ISSN:0008-4042    

DOI:10.1139/v87-395

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The oxidation of methylamine by permanganate ion in aqueous phosphate buffers is autocatalyzed by a soluble form of colloidal manganese dioxide temporarily stabilized in solution by adsorption of phosphate ions on its surface. The dependence of the rate constants of both the noncatalytic and catalytic mechanisms on the concentrations of both methylammonium and hydroxyl ions and on temperature has been determined. The activation parameters have been obtained. Mechanisms in agreement with the experimental data are proposed.

ISSN:0008-4042    

DOI:10.1139/v87-396

出版商:NRC Research Press    

年代:1987

数据来源: NRC