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1.
ABSTRACT Synthesis of the terminal trisaccharide sequence of the ganglioside GD3, α-D-Neup5Ac-(2→8)-α-D-Neup5Ac-(2→3)-β-D-Galp-(1→4)-β-D-Glcp-(1→1)-Cer (2) was achieved by employing an α-(2→8) disialyl glycosyl donor (1). Condensation of 1 with the glycosyl acceptor 6, propyl 4,6-O-benzylidene-β-D-galactopyranoside, gave the desired protected trisaccharide 10 (14%) as well as the elimination and hydrolysis products of 6, compounds 8 and 9 respectively. O-Deacetylation and debenzylation of 10 gave the final trisaccharide 11, as its propyl glycoside. 相似文献
2.
《Tetrahedron: Asymmetry》2003,14(16):2381-2386
The α(1→2)-l-galactosyltransferase from Helix pomatia transfers an l-fucosyl residue from GDP-l-Fucose to a terminal, non-reducing d-galactopyranosyl moiety of an oligosaccharide. The extent of the enzyme's specificity towards the stereochemistry at the d-galactopyranosyl anomeric centre, the site of interglycosidic linkage and the nature of the subterminal oligosaccharide residue has been investigated using HPAEC-PAD and MALDI-TOF technology. This α(1→2)-l-galactosyltransferase is specific for d-galactopyranosyl β-linkages, independent of the site of the interglycosidic linkage and aglycone configuration and with limited specificity for the nature of the subterminal sugar residue. 相似文献
3.
L. Balsanova D. Mikhailova A. Senyshyn D. Trots H. Fuess W. Lottermoser H. Ehrenberg 《Solid State Sciences》2009,11(6):1137-1143
Silver diiron tris(oxomolybdate), α-AgFe2(MoO4)3, was synthesized in sealed silica tubes at 1050 K and is isostructural to α-NaFe2(MoO4)3, determined by single-crystal X-ray diffraction (space group P?1, a = 6.9320(7) Å, b = 6.9266(6) Å, c = 10.9732(13) Å, α = 81.197(8)°, β = 83.456(9)°, γ = 81.352(8)° at 300 K, Z = 2). The crystal structure is built up from both monomers and edge-sharing dimers of [FeO6]-octahedra, which are linked with each other by isolated [MoO4]-tetrahedra to a three-dimensional network. Ag ions are situated on a site with four near oxygen neighbours. Thermal expansion is most pronounced along the c-axis, while the angle α decreases with increasing temperature. Antiferromagnetic ordering is indicated by a sharp maximum in the temperature dependence of magnetization at 21.5(5) K, and a magnetic moment of 5.36(1) μB per Fe-ion was derived from the Curie constant in the paramagnetic region. The collinear antiferromagnetic structure with propagation vector k = (0,½,½) and an ordered magnetic moment of 4.62(9) μB per Fe-ion were deduced from neutron powder diffraction data and give evidence for an underlying magnetic interaction mechanism, resulting in rather strong and long-ranged couplings. Mössbauer spectroscopy shows a change in the electronic configuration on the two distinct Fe sites between room temperature and 150 K, accompanied by an increase of the average Fe–O distance for one site and a shrinking one for the other as expected for charge ordering in a mixed valence compound with Fe(II) and Fe(III). 相似文献
4.
《Mendeleev Communications》2021,31(4):490-492
Glycosylation of lactosamine acceptors with Kdn thioglycoside donors in the presence of NIS/TfOH as a promoter affords products with both α- and β-ketosidic linkage (2–6' or 2–3') between the Kdn and Gal residues. After deprotection, the synthesized trisaccharides and glycans containing Neu5Ac were printed to a chip and their comparative interaction with human serum antibodies was explored. 相似文献
5.
Zhenjiang Qiu Mingxiang Zhu Lu Zheng Jingya Li Dapeng Zou Yangjie Wu Yusheng Wu 《Tetrahedron letters》2019,60(19):1321-1324
An efficient protocol for the synthesis of α-benzyl azetidines starting from benzylboronic acid pinacol ester derivatives and 3-iodoazetidine was developed. A wide range of α-benzyl azetidine derivatives were obtained in moderate to good yields with high regioselectivity (>99%). 相似文献
6.
《Tetrahedron: Asymmetry》2000,11(18):3647-3651
Supported lipase from Candida antarctica (Chirazyme®) was employed for a regioselective protection of the 2-azido derivatives 1 and 2, synthetic equivalents of β-d-Gal(1→3)-d-GlcNAc and β-d-Gal(1→4)-d-GlcNAc (N-acetyl lactosamine), respectively. The selectivity of the enzyme towards 1 and 2 was also exploited for an easy separation of the mixture of the two compounds obtained from a straightforward synthetic approach. 相似文献
7.
8.
Xing Xian ZHANG Wei Dong Z. LI* National Laboratory of Applied Organic Chemistry & Institute of Organic Chemistry Lanzhou University Lanzhou 《中国化学快报》2003,(8)
In our previous letter1, we have reported the unique catalytic reactivity of MgI2 etherate 1 in the chemoselective Mukaiyama-type aldol reactions of aryl or vinyl aldehyde and aldehyde acetals with silyl enolates. Aryl or alkyl a, b-unsaturated aldehydes (and their acetals) are particularly reactive in this catalytic addition reaction due to possibly the effective activation of the electron-rich carbonyl by highly oxyphilic Lewis acidic species, i.e. IMg+, in non-coordinative media (i.e. CH… 相似文献
9.
An efficient one-pot synthesis of functionalized thiazol-2(3H)-imines by a three-component reaction between aroylisothiocyanates, a-amino acids, and a-bromoketones in an ionic liquid is described. 相似文献
10.
S.Z. Abbas S. Sugiyama J. Diakur R.A. Pon R. Roy 《Journal of carbohydrate chemistry》2013,32(6):891-901
ABSTRACT Acid hydrolysis of colominic acid, an α-(2→8)-linked oligomer of sialic acid, yielded Neu5Ac α-(2→8) Neu5Ac (di-Neu5Ac) 2 as one of the products. Starting from this disaccharide, it was possible to prepare two potential di-Neu5Ac donors, 5 and 8, as their corresponding 2-chloro derivatives. Subsequent reaction of the donor 8 with methanol as a simple acceptor led to the α- and β-methyl Neu5Ac α-(2→8) Neu5Ac glycosides. 相似文献
11.
M. M. Krayushkin V. Z. Shirinian D. M. Nikalin A. A. Shimkin 《Russian Chemical Bulletin》2004,53(3):631-634
Regioselective C- or O-alkylation of alkyl 4-hydroxy-2-methylthiophene-3-carboxylates with -halo ketones is possible, depending on the solvent nature. A convenient preparative method of C-alkylation was proposed and previously not easily accessible -hydroxythiophene derivatives were synthesized. 相似文献
12.
13.
《Tetrahedron: Asymmetry》2000,11(1):319-335
Reaction of 2,3:5,6-di-O-isopropylidene-d-mannofuranose 1 with C-2 lithio derivatives of glyoxylate mercaptal in the presence of MgBr2 afforded d-glycero-d-galacto-2-octulosonates 2 and 3, respectively. Their 3-O-deoxygenation led to Kdo. N-Iodosuccinimide treatment of 3 gave thioglycoside 11 directly, which was transformed into Ko derivative 12 via epimerisation of the 3-hydroxy group. 3-O-Benzoylation of 12 and then transformation into phosphite furnished 15, an efficient glycosyl donor. Reaction of 15 with 6-O-unprotected glucosamine derivative 22 as acceptor gave α-glycoside 23, which was successfully transformed either into Kdo-disaccharide 27 or into Ko-disaccharide 29. 相似文献
14.
XingXianZHANG WeiDongZ.LI 《中国化学快报》2003,14(8):800-803
Regioselective addition reactions of silyl enolates to α,β-unsaturated aldehyde and its acetal catalyzed by MgI2 etherate give aldol adducts (1, 2-addition) preferentially over Michael adducts (1, 4-addition). This unique regioselectivity is distinctly different with other Lewis acidic promoters and may be attributed to the high oxyphilicity of IMg^ . 相似文献
15.
An efficient catalytic method for the synthesis of α, β-diamino acid derivatives has been developed via regioselective ring opening of aziridines by amines in the presence of indium(III) salt under very mild reaction conditions. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献
16.
Trichodiene (1), a sesquiterpene hydrocarbon, was isolated and characterized by Nozoe and Machida in 1970.1 Trichodiene (1) has been shown to be the biogenetic precursor of the trichothecane family of sesquiterpenoids characterized by the cytotoxic fungal metabolite (–)-trichodermin (2).2,3 We recently reported a total synthesis of (±)-trichodiene (1) via lactone 3.4 Now, we wish to report another stereoselective total synthesis of (±)-trichodiene (1) via lactone 3 which is highly regioselective. 相似文献
17.
Gupta Kalyan K. Sen Bhattacharjee Nandini Pal Biswajit Ghosh Saktiprosad 《Transition Metal Chemistry》1999,24(3):268-273
The kinetics of oxidation of the neutralized -hydroxy acids: lactic, -hydroxyisobutyric, mandelic, benzilic and atrolactic acids by tris(pyridine-2-carboxylato)manganese(III) have been studied. The reactions were carried out in a Na(pic)-picH [Na(pic) = sodium salt of pyridine-2-carboxylic acid and picH = pyridine-2-carboxylic acid] buffer medium in the 4.89–6.10pH range. The oxidation rate was found to be independent of pH, and rate follows the order: benzilate > mandelate >atrolactate>lactate > -hydroxy isobutyrate. The oxidation products are MeCHO, Me2CO, PhCHO, Ph2CO and PhCOMe for the respective reactions. A mechanism is proposed involving intermediate formation of hepta-coordinated MnIII complexes in a fast step. The complexes then decompose to give free radicals and MnII in the rate determining step. The free radicals subsequently react with another molecule of the MnIII species to give the respective carbonyl compounds in a fast step. 相似文献
18.
《Tetrahedron letters》1986,27(12):1411-1414
(±)-Gabaculine has been synthesized via an intramolecular reaction of an N-acyliminium intermediate with a propargyl silane, followed by allene ozonolysis and a Shapiro reaction. 相似文献
19.
Diphasic boehmite derived unseeded and seeded (by either -Al2O3, -Fe2O3, or Fe(NO3)3) alumina gel planar monoliths were examined by DTA, XRD and photoluminescence spectroscopy. Luminescence spectra enable sensitive monitoring of the - and -Al2O3 crystallization in heat-treated gels due to Cr3+ impurity traces. Fe(NO3)3 unlike other seeds effectively influences crystallization of both - and -Al2O3. The present results are interpreted as prevailing solution or Fe3+ ion effect on the crystallization process. 相似文献
20.
Pseudomonas Cepacia lipase supported on ceramic particles (lipase PS-C) and on diatomite (lipase PS-D) regioselectively acylated 2′-deoxynucleosides and ribonucleosides to 3′-O-acetyl-2′-deoxynucleosides and 3′-O-acetyl-ribonucleosides with oxime esters in organic solvents at room temperature. This enzymatic reaction was significant because the regioselectivity was total; as any other regioisomer nor the N-acylated product were observed. 相似文献