摘要:

Stereospecific high-yielding ethynylation of protected dialdoses is described.

ISSN:0732-8303    

DOI:10.1080/07328308808058910

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

An efficient procedure is described for the conversion of digitoxin (2) into 1,3,4-tri-O-benzoyl-2,6-dideoxy-β-D-ribo-hexopyranose (4). This conversion allows digitoxin (2) to become a viable source of 2,6-dideoxy sugars since the tribenzoate 4 is readily converted into synthetically useful derivatives. One type of derivative, exemplified byt-butyl 2,6-dideoxy-β-D-ribo-hexopyranoside (17), is an unprotected glycoside and thus easily permita structural modification at C-3 and C-4. A second type of derivative formed from 4 is one capable of glycosidic coupling at the anomeric carbon atom. Examples of this latter type are 3,4-di-O-benzoyl-2,6-dideoxy-α-D-ribo-hexopyranoayl chloride (7) and ethyl 3,4-di-O-benzoyl-2,6-dideoxy-1-thio-O-D-ribo-hexopyranoside (13).

ISSN:0732-8303    

DOI:10.1080/07328308808058911

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Reduction of sugar aldoximes gave in good yield the corresponding terminal deoxy hydroxyamino sugars. These compounds were found to be reasonably stable (they could be kept for some weeks at 4° C). On standing in the air, these compounds in solution were spontaneously oxidized to the corresponding nitroxide free radicals whose ESR spectra gave useful structural information.

ISSN:0732-8303    

DOI:10.1080/07328308808058912

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The mono- and bis-(p-fluorophenyl)hydrazones of dehydro-L-ascorbic acid were prepared. Oxidation of the bis(hydrazone) afforded 3,6-anhydro-3-C-(p-fluorophenylazo) L-xylo-2-hexul osono-1,4-1 actone-2-(p-fluorophenyl)hydrazone. Rearrangement of the bis(hydrazone) gave T-(p-fluorophenyl)-3-(L-threo-glycerol-1-yl)-pyrazoli n-4,5-di one-4-(p-fluorophenyl)hydrazone, whose periodate oxidation gave 3-formyl-1-(p-fluorophenyl pyrazol in-4.5-dione-3-4-(p-fluorophenyl)hydrazone that upon reduction gave 1-(p-fluorophenyl)-3-hydroxymethyl pyrazol in-4,5-dione-4-(p-fluorophenyl)hydrazone. The compounds were characterized as their acetates and benzoates.

ISSN:0732-8303    

DOI:10.1080/07328308808058913

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

3-[1-(p-Fluorophenylhydrazono)-L-threo-2,3,4-tri hydroxybutyl1-2-quinoxalinowe was prepared and trarrsformed to 3-[5-acetoxymetnyl-1-(p-fluorophenyl)-pyrazol-3-yl]-2-quinoxalinone.N-methylation, followed oy dehydrative cyclisation, gave the M-methyl-derivative of the latter pyrazole. Periodate oxidation gave a glyoxalyl derivative whose aldehyde functionality was confirmed by reduction and oximation.

ISSN:0732-8303    

DOI:10.1080/07328308808058914

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Reaction of 2,3,4,6-tetra-O-acetyl-α-D-galactopyraaosyl bromide (1) with phenyl 2-acetamido-2-deoxy-4,6-O-(4-methoxy-benzylidene)-α-D-galactopyranoside (3) mediated by mercuric salts, followed by removal of the 4-methoxybenzylidene group and O-deacylation afforded phenyl 2-acetamido-2-deoxy-3-O-p-D-galactopyranosyl-α-D-galactopyranoside (6). Compound 6 was used as a substrate for the selective introduction of two neuraminic acid residues with partially purified sialyltrans-ferase preparations. First, disaccharide 6 was treated with CMP-[14c]-NeuAc as donor substrate and CMP-NeuAc: Gal-p(l-3)-GalNac-a(2-3)sialyltransferase from human placenta to afford trisaccharide 7 (yield 85X), sialylated at C-3 of the galactose residue. Treatment of 7 with CMP-[3H]-NeuAc and a micro-somal fraction from regenerating rat liver, containing the CMP-NeuAc: NeuAc-a(2-3)-Gal-p(l-3)GalNAc-α(2-6) sialyltrans-ferase activity, gave the disialylated tetrasaccharide 8 in 10X yield.

ISSN:0732-8303    

DOI:10.1080/07328308808058915

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Invertase-catalysed alcoholysis of sucrose in water - primary alcohol mixtures containing up to 70% organic solvent shows 5-40% alkyl β-D-fructofuranoside formation. No formation of fructosides was observed under anhydrous conditions. The kinetics of the competing reactions of water and primary alcohol as fructosyl acceptors with sucrose as fructosyl donor were studied in order to establish the scope and limitations of the method. On a molar basis, water was a relatively unreactive acceptor. 6-Kestose formation due to sucrose itself as a fructosyl acceptor was suppressed by the presence of aliphatic alcohols. The results have been explained by assuming an nonspecific non-polar binding site to be present in the enzyme cavity near the specific polar binding site for the β-D-fructofuranosyl group of the substrate.

ISSN:0732-8303    

DOI:10.1080/07328308808058916

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

1H NMR signals of H-6proR and H-6proS protons of D-glucoses and their per-O-acylated (acetyl and benzoyl) derivatives were unambiguously assigned by chiral deuteration at the C-6 position. The JH5,H-6proRand JH5,H-6proRvalues thus obtained enabled us to calculate the rotameric distributions ofgg,gtandtgconformers. For the calculations, conventional equations (AandB) and novel equations accounting for possible departure of the three conformers from perfect staggering, were employed. The results showed that D-glucoses irrespective of solvents and protecting groups were predominant in two conformersggandgtin an approximate ratio of 60 and 40, respectively, with a negligibly low population of thetgconformer. These results were in complete accordance with the statistical study of X-ray data of D-glucoses.

ISSN:0732-8303    

DOI:10.1080/07328308808058917

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

1-Deoxy-2,3-hexodiuloses are thought to be key intermediates in the conversion of hexoses to saccharinic acids (in alkaline systems), as well as to furans and related derivatives in acidic systems. The 5,6-O-isopropylidene derivative of the title compound was prepared by condensing 2,3-O-isopropylidene-B-glyceraldehyde with propyne via a Grignard reaction, followed by oxidation of the -O-acetyla-ted epimers to the diketones using a ruthenium catalyst and iodosylbenzene as the oxidant. Yields were in excess of 90% for each step, and no evidence of cleavage of the triple bond to the carboxylic acid was observed. Qualitative tests showed that the -O-isopropylidene-diulose is very unstable to both acids and bases, but that it is moderately stable at elevated temperatures (80 [ddot]C) and toward oxygen in aqueous dioxane solutions.

ISSN:0732-8303    

DOI:10.1080/07328308808058918

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The Fischer glycosylation1is one of the standard reactions in carbohydrate chemistry, in which a reducing sugar is reacted under acid catalysis with a simple alcohol to give a glycoside. Hydrochloric acid is the classical catalyst, but other proton, Lewis acid, or acid form ion echange resins have also been used. Now, the use of trifluoromethanesulfonic acid (triflic acid) as a catalyst is communicated.

ISSN:0732-8303    

DOI:10.1080/07328308808058919

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor