摘要:

The cascade of biosynthetic products1,2derived from arachidonic acid involves several oxygenated heterocycles, including thromboxanes A2and B2(in the following TXA2and TXB2, respectively, Scheme 1). In the biological pathway TXA2(1) is produced directly from prostaglandin H2(PGH2, 2), and this same compound is the common precursor of the previously known prostaglandins (i.e. PGE2, PGF2aand PGD2, etc.), as well as of the more recently discovered “beneficial” prostaglandin I2(PGI2, 3). Upon hydrolysis under biological conditions TXA2(1) is converted into the more stable thromboxane B2(TXB2,4).

ISSN:0732-8303    

DOI:10.1080/07328309808005765

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

To evaluate possible chemical strategies for the solid-phase immobilization of sugars, studies on the formation and stability of hydrazones, thiosemicarbazones and azines of D-glucose and 2-acetamido-2-deoxy-D-glucose, and the subsequent release of sugars, were carried out. Hydrazone formation was observed to occur under milder conditions than previously reported, thereby minimising the accompanyingN-deacetylation which occurs withN-acetamido sugars. The cyclic β-pyranosyl structures of the saccharide hydrazones, thiosemicarbazones and azines were the preferred isomers in aqueous solution.

ISSN:0732-8303    

DOI:10.1080/07328309808005766

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Derivatives of the branched amino sugar methyl 3-amino-2,3,6-trideoxy-3-C-methyl-α-L-ribo-hexopyranoside and its 3-nitro analog were coupled with glycosyl donors of 3,4-di-O-acetyl-2,6-dideoxy-L-fucopyranose. Successful glycosylations were developed using the fucosyl bromide, activated with silver triflate, and the fucosyl oxysilane, activated with trimethylsilyl triflate. High stereoselectivities for the desired α-1,4 linkage were observed in both cases. TheN-trifluoroacetamido disaccharide was deacylated and the amino group oxidized to nitro with dimethyldioxirane. An alternate route based on coupling of the fucosyl bromide with the nitro sugar methyl α-L-decilonitroside also gave the α-linked disaccharide, which is related to oligosaccharides found in the antibiotics cororubicin and arugomycin.

ISSN:0732-8303    

DOI:10.1080/07328309808005767

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

N-(2,3,4,6-Tetra-O-acetyl-α-d-gluco-, β-d-gluco- and β-d-mannopyranosyl)-pyridinium salts were obtained and their structures were determined by 2D1H NMR spectroscopy. The compounds obtained were treated with a methanolic solution of sodium methylate. The β-anomer of thed-gluco derivative cyclizesviaBrigl's anhydride but the α anomer is competitively transformed according to the SN2 and SN1 mechanisms. The β-d-manno derivative does not cyclize under the conditions used. Comparison of the qualitative and quantitative results of the reaction studied enabled estimation of the influence of configuration at C-1 and C-2 on the course of cyclization. All product mixtures were separated by capillary gas chromatography (CGC) as exhaustivelyO-acetylated derivatives and their components were identified by coinjection with authentic materials.

ISSN:0732-8303    

DOI:10.1080/07328309808005768

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Treatment of methyl 4-O-benzoyl-3-O-tert-butyldiphenylsilyl-2-O-methanesulfonyl-6-thio-α-d-glucopyranoside (8) and its 6-deoxy analogue (11) with methanolic sodium methoxide, afforded methyl 2,3-anhydro-mannopyranoside derivatives as a consequence of an O3→ O4TBDPS rearrangement. When the protecting group at C-3 was 2-methoxyethoxy methyl ether only deacylation and methanolysis of the methanesulfonyl group occurred.

ISSN:0732-8303    

DOI:10.1080/07328309808005769

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Carbamate derivatives of 3-aminodigitoxose (d-ristosamine) were prepared, with the purpose of synthesizing 3-amino-β-digitoxosyl derivatives of cardioactive steroids. A 1,3 participation procedure, used under acid or mercury salt catalysis, and the imidate procedure were investigated. A careful fine tuning of the glycosylation conditions was necessary in order to obtain significant β-d-stereoselectivity, which proved to be mainly dependent on the polarity of the solvent and the relative reactivity of the sugar and the nucleophile.

ISSN:0732-8303    

DOI:10.1080/07328309808005770

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

With the aim of providing new methods for the regioselective protection at the 2,3 and 4 positions of monosaccharides, we have studied the acetylation of a class of rigid sugars: the 1,6-anhydro-β-d- andl-hexopyranoses (hexopyranosanesD-1toD-5andL-1toL-5), using vinyl acetate as an acyl donor and two common lipases,Candida rugosaandPseudomonas cepacia, as catalysts. Our results indicate that the relative orientation of the hydroxyls governs the regioselectivity of acetylation. In thed-series, when the 3-OH is in the axial position, acetylation occurs mainly at the 4-axial OH, while the 2-axial OH is preferred when the 4-OH is equatorial. Conversely, when the 3-OH is equatorial, a strong selectivity affects the equatorial 2-OH. Compounds of thel-series were shown to be poor substrates for the lipasePseudomonas cepaciaexcept forl-galactosane for which the 2-monoacetyl ester was obtained in good yield. An attempt to rationalize the results by means of molecular modelling is also made to account for the catalytic activity of theCandida rugosalipase on hexopyranosanes1–3.

ISSN:0732-8303    

DOI:10.1080/07328309808005771

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Treatment of 2,3-di-O-benzyl-N-benzyloxycarbonyl-6-O-t-butyldiphenylsilyl-1,5-dideoxy-1,5-imino-D-glucitol (4) with sodium hydride resulted in an intramolecular cyclization concomitant with silyl migration, giving the carbamate derivative5in good yield. This was efficiently converted into 1-deoxymannojirimycin (2)viaregioselectivep-toluenesulfonylation followed by an inversion reaction at the C-2 position. On the other hand, the monochloromethylsulfonate10obtained from4underwent configurational change at the C-4 position by the action of sodium benzoate. The resulting benzoate11was deprotected to afford 1-deoxygalactostatin (3).

ISSN:0732-8303    

DOI:10.1080/07328309808005772

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The monoacetalization of sucrose by citral, α-ionone and β-ionone is reported. Geranial and neral sucrose acetals (EandZisomers of citral acetals) are described. Optimization of the acidic catalysis afforded good yields of acetals directly from unprotected sucrose by transacetalization of dimethyl acetals in dimethylformamide. The influence of microwave irradiation on the reaction outcome was investigated.

ISSN:0732-8303    

DOI:10.1080/07328309808005773

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The glycoside 2-(2-azidoethoxy)ethyl 2-O-benzyl-4,6-O-benzylidene-β-d-glucopyranoside was prepared and then reacted, first with methyl phosphonyl dichloride, then with dimethylaminoethanol, to give the methylphosphonyl diester9.N-Methylation of9with methyl iodide and subsequent catalytic hydrogenation gave the methylphosphonyl diester11. The corresponding phenylphosphonyl diester14was also prepared in a similar way. The phosphonyl diesters11and14are analogs of the transition states for 3-O-acetylation and 3-O-benzoylation of β-d-glucopyranose derivatives with acetyl- and benzoylcholine, respectively. They will be used for generation of catalytic antibodies.

ISSN:0732-8303    

DOI:10.1080/07328309808005774

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor