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21.
Chinmoy Mukherjee 《Journal of carbohydrate chemistry》2013,32(4):213-221
A general, odorless, one‐pot methodology has been developed for the preparation of 1,2‐trans‐thioglycosides and thio‐Michael addition products of carbohydrate derivatives through triphenyl phosphine‐mediated cleavage of disulfides and reaction of the thiolate formed in situ with glycosyl bromides and glycosyl conjugated alkenes. 相似文献
22.
23.
A new simple and sensitive fluorimetric method for the determination of carbohydrates is described. The method is based on the reaction between carbohydrates and Ce(IV) in the presence of sulfuric acid. All the reductive carbohydrates can be detected indirectly by the fluorescence of Ce(III) produced. The addition of sodium triphate enhances the sensitivity of the method by more than 10-folds. Under optimum conditions, an excellent linear relationship was obtained between the fluorescence intensity and the concentration of carbohydrates. The limits of detection lie in the range of 9.3 x 10(-10) - 1.3 x 10(-9) mol/L. As compared to the normal fluorimetric method, the proposed method is faster and more sensitive. 相似文献
24.
The efficiency of microwave irradiation at low temperature for glycosylations is described. Although oligosaccharide synthesis usually requires reactive donors for glycosylations, which have leaving groups on the anomer positions, i.e., trichloroacetoimidates, halogenates, thioalkyl glycosides, etc., the suitable donors in our microwave supported synthesis of Lewis X oligosaccharide were very stable acetate derivatives. Regarding glycosylation with a fucosyl acetate donor and a glucosamine acceptor, microwave irradiation with simultaneous cooling improved yields. Moreover, further synthesis to Lewis X derivatives was achieved only with microwave irradiation at low temperatures. Without microwave irradiation, we could only obtain byproducts and none of the designed product at any reaction temperature. 相似文献
25.
Paul Kosma Martina Strobl Andreas Hofinger Jens Ø. Duus Bent O. Petersen Klaus Bock Helmut Brade 《Monatshefte für Chemie / Chemical Monthly》2002,133(4):561-570
Summary. Methyl glycosides of Kdo and a (2→8)-linked Kdo disaccharide were prepared which contain a deuterium label at C-8 of the reducing unit. The label was introduced in fair
diastereoselectivity upon reduction of an aldehyde group using a chiral borane complex derived from N-benzyloxycarbonyl-(S)-proline which produced the 8-(S)-deuterated derivative as the major isomer. Further coupling with a Kdo bromide gave the α-(2→8)-linked disaccharide in good yield. The deprotected disaccharide serves as a model for NMR spectroscopic
studies on the side chain conformation of a carbohydrate epitope from the bacterial pathogen Chlamydia.
Received September 17, 2001. Accepted October 17, 2001 相似文献
26.
The high-pressure asymmetric Diels-Alder reactions of d-galacto- (1a) and d-manno-3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-nitrohept-1-enitol (1b) with 2,5-dimethylfuran (2) afforded mixtures of cycloadducts, from which the (2S,3R)-3-exo-nitro (3a and 3b), (2R,3S)-3-exo-nitro (4a and 4b), and (2R,3S)-1′,2′,3′,4′,5′-penta-O-acetyl-1′-C-(1,4-dimethyl-3-endo-nitro-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl)-d-galacto-pentitol (5b) were isolated pure. Deacetylation of these compounds led to new chiral mono-, bi-, and tricyclic ethers, being their asymmetric centers arising from the chiral inductor used in the cycloaddition reaction. A ring opening mechanism through a 1-nitro-1,3-cyclohexadiene intermediate has been proposed. 相似文献
27.
Carbohydrate-based low molecular weight gelators are an interesting class of molecules with many potential applications. Previously, we have found that certain esters and carbamates of 4,6-O-benzylidene-α-d-methyl-glucopyranoside are low molecular weight gelators for a variety of solvents, including water. In order to obtain effective and robust sugar-based organogelators and understand the structure and gelation relationship, we extended our studies using 4,6-O-benzylidene-α-d-methyl-2-deoxy-2-amino-glucopyranoside as the headgroup. A series of amides and ureas were prepared from the protected d-glucosamine and the corresponding isocyanates or acid chlorides, in good yields. The self-assembling properties of these compounds were studied in several solvents, including water and aqueous solutions. Comparing to the ester and carbamate derivatives previously prepared from d-glucose, the amides and urea derivatives afforded more robust gels at lower concentrations typically. Most of these compounds were found to be efficient low molecular weight hydrogelators (LMHGs) for aqueous solutions at concentrations lower than 0.5 wt %. The preparation and characterization of these compounds are reported here. 相似文献
28.
Cyanide detection in pure water is important for many applications. We present a novel type of chemodosimeter azo dye developed on the basis of the benzophenone as the electrophilic receptor of the cyanide anion and a saccharidic moiety to render the dye water soluble. This chemodosimeter is found to be highly selective and tunable toward only cyanide in pure water. 相似文献
29.
Treatment of β-d-ribose tetraacetate with trimethylaluminum gives α-3,5-O-acetyl-1,2-O-isopropylidene-d-ribofuranoside in excellent yield. This reaction allows for efficient and high-yielding installation of the 1,2-isopropylidene acetal (acetonide), which is difficult to prepare using more traditional acid-catalyzed methods. The reaction of trimethylaluminum with other per-acetylated carbohydrates is also described. 相似文献
30.
An unprecedented conversion of thioalkyl/aryl glycoside to the corresponding 1‐O‐acetates has been described using acetic anhydride and HClO4‐SiO2 at rt. Although this transformation does not play an important role in the oligosaccharide synthesis in comparison to its reverse transformation, this gives useful information in selecting the reaction condition for the synthesis of oligosaccharides. The yields were excellent in all cases. 相似文献