摘要:

The thermal Claisen rearrangement of theZ-isomer (5-Z) of 3,5,6-trideoxy-1,2-O-isopropylidene-3-C-methyl-α-D-ribo-hept-5-eno-1,4-furanose with triethyl orthoacetate in the presence of propionic acid gave two rearrangement products with a high level of diastereoselectivity (approximately 8.5 to 1). On the other hand, the re-arrangement executed by using theE-isomer resulted in the formation of the products without significant stereoselectivity (approximately 1.6 to 1 ratio). TheS-configuration for the newly introduced stereogenic center in the major product was secured by chemical correlation with our previously reported compound, which was the major rearrangement product of 5,6-dideoxy-1,2-O-isopropylidene-α-D-ribo-hept-5-eno-1,4-furanose. The transition state argument applied to the similar models accounts well for the stereoselectivity observed in the case of 5-Z.

ISSN:0732-8303    

DOI:10.1080/07328309108543886

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The platinum catalyzed oxidation of sucrose by oxygen has been studied. With platinum on carbon at 100°C and at constant neutral pH, the oxidation is highly specific for the primary hydroxyls at the 6- and 6′-positions of sucrose. There was no evidence of oxidation of the 1′ hydroxyl. The 6,6′-dicarboxysucrose was resistant to attack by invertase. The 6- and 6′-carboxysucroses could not be resolved from each other, but the former component was hydrolysed rapidly by invertase and subsequently the 6′-carboxysucrose was isolated. The13C spectrum of 6-carboxysucrose was then assigned by difference.

ISSN:0732-8303    

DOI:10.1080/07328309108543887

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

1-Deoxynojirimycin (1,5-dideoxy-1,5-imino-D-glucitol) was converted, via epoxide intermediates, into a series of N-acetyl-hexosamine analogs, i. e., 2-acetamido-1,2,5-trideoxy-1,5-imino-D-glucitol, 2-acetamido-1,2,5-trideoxy-1,5-imino-D-mannitol, 2-acetamido-1,2,5-trideoxy-1,5-imino-D-galactitol, and their isomers. The cyclic 5-N,6-O-carbamoyl derivatives of 1-deoxynojirimycin were also prepared.

ISSN:0732-8303    

DOI:10.1080/07328309108543888

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

O-Glycosyl phosphotothioates can be conveniently prepared by treatment of reducing monosaccharides with p-tolylsulfonyl chloride and the triethylammonium salt of phosphorothioic acid under phase-transfer catalysed conditions.

ISSN:0732-8303    

DOI:10.1080/07328309108543889

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The preparation of an amphiphilic lipodigalactosyl hemiacetal is described. Use of benzoyl protecting groups and mild conditions for detritylation allow preparation of a 1-α-C-allyl galactosyl acceptor without intramolecular acyl transfer. Condensation with a lipogalactosyl donor and cleavage of the protecting groups gave aC-allyl disaccharide. Reductive ozonolysis of the double bond yielded an aldehyde which spontaneously formed a cyclic hemiacetal with the C-2 hydroxyl group. In the Lewis acid catalyzed allylation of the penta-O-acetyl galactose with allyltrimethylsilane, the reactivity of the β-anomer is much higher than that of the α-anomer.

ISSN:0732-8303    

DOI:10.1080/07328309108543890

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Ammonium 2,3,6-trideoxy-2,6-epithio-D-manno-2-octenoate (8), ammonium 2,3,6-trideoxy-2,6-epithio-D-glycero-D-talo-octanoate (10a), ammonium 2,3,6-trideoxy-2,6-epithio-D-glycero-D-galacto-octanoate (10b) and ammonium 2,3,6-trideoxy-2,6-epithio-oxa-D-glycero-D-galacto-octanoate (13) have been synthesised as potential inhibitors of the enzyme CMP-KDO synthetase. The key step in the synthesis of8was the elimination of water from methyl 3,6-dideoxy-4,5:7,8-di-O-isopropylidene-6-thio-D-manno-2-octulosonate (4) using chlorodiphenylphosphine, imidazole and bromine to give the unsaturated methyl 2,3,6-trideoxy-2,6-epithio-4,5:7,8-di-O-isopropylidene-D-manno-2-octenoate (5). For the synthesis of10aand10b, zinc reduction of methyl 3,6-dideoxy-4,5:7,8-di-O-isopropylidene-6-S-(4-methoxybenzyl)-6-thio-2-O-(trichloro-tert-butoxycarbonyl)-D-manno-2-octenoate (2) gave an epimeric mixture of an α-hydroxyester6which was ring closed by insituactivation of the hydroxyl group using triphenylphosphine and tri-iodoimidazole followed by cleavage of thep-methoxybenzyl group to give7aand7b, which then were deprotected to give10aand10b.

ISSN:0732-8303    

DOI:10.1080/07328309108543891

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Heating galactitol, D-glucitol, D-mannitol and L-iditol in a 5% aqueous sulfuric acid solution at 200 °C for 30 min afforded 1, 4-, 3, 6-, 1,5-, 2,6- and 1,6-monoanhydrohexitols with retained configuration as well as 2,5-monoanhydrohexitols with inverted configuration at C-2 or C-5. 1, 4;3,6-, 1,5;2,6- and 1,4;2,6- ß 1,5;3,6-Dianhydrohexitols were also identified. Cyclization of the hexitolsviatheirO-tosyl derivatives in pyridine gave products completely free of 2,5-anhydrohexitols but with increased amounts of dianhydrohexitols. All mixtures were separated by capillary GC (CGC) and their components identified by CGC-MS and by co-injection with standards.

ISSN:0732-8303    

DOI:10.1080/07328309108543892

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Doxorubicin and daunorubicin are clinically important antitumor antibiotics but their use is restricted, especially for long-term treatment by their toxicity.1Hence the cardiotoxic side effects associated with these drugs have stimulated the search for analogues with lower cardiotoxicity, improved antitumor activity and lack of cross-resistance.

ISSN:0732-8303    

DOI:10.1080/07328309108543893

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The “formose reaction” is the generic name for the base-catalyzed condensation of formaldehyde to give “formose” which is a complex mixture of sugars, alditols, organic acids, etc.2Increasing attention has been recently given to this reaction because of its possible importance in the manufacture of edible carbohydrates from a simple material and its possible role in the prebiotic synthesis of carbohydrates.3In our recent study4on the reaction catalyzed by triethylamine (TEA) and thiamine HCl in N,N-dimethylformamide (DMF)-water mixed solvent, the formation of 3-pentulose (GP-11-1 corresponding to GLC peak number 11-1) was suggested. P. Decker et al.5also reported that at the end of formaldehyde consumption the concentration of 3-pentuloses became smaller because of their higher reactivity (these carbohydrates cannot form stable furanoses or pyranoses) compared to tetroses, pentoses, and hexoses. Although the isolation of 3-pentuloses was not described in that report,5erythro-3-pentulose and threo-3-pentulose in a formose were identified by comparison of GLC retention times and mass spectra with those of authentic samples.

ISSN:0732-8303    

DOI:10.1080/07328309108543894

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Le récent article de S. Oscarson et M. Szõnyilarappelle qu′en milieu acide un orthoester de type 1,3-dioxolane s'ouvre préférentiellement en dirigeant le groupement acyle sur l'hydroxyle axial, c'est à dire, l'hydroxyle anomérique dans le cas des 1,2-orthoesters de configurationgluco, en accord avec les règles de contrôle stéréoélectronique démontrées par P. Deslongchamps dès 1975,1bl'ester équatorial étant produit par d'autres méthodes1davec une éventuelle régiosélectivité induite.1e

ISSN:0732-8303    

DOI:10.1080/07328309108543895

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor