Conversion of N-acetylneuraminic acid glycosyl chloride into dibenzyl glycosyl phosphate: O-glycosylation in the absence of a promoter

Readily accessible N-acetylneuraminic acid (Neu5Ac) glycosyl chloride, which was regarded to be a poor glycosyl donor, was shown to react with dibenzyl phosphoric acid salts in the absence of glycosylation promoters to give the corresponding -Neu5Ac dibenzyl glycosyl phosphate in high yield.     

One-pot synthesis of sialo-containing glycosyl amino acids by use of an N-trichloroethoxycarbonyl-beta-thiophenyl sialoside

We describe an efficient synthesis of 2,6- and 2,3-sialyl T antigens linked to serine in a one-pot glycosylation. We first investigated the glycosidation of thiosialosides by varying the N-protecting group. Modification of the C-5 amino group of beta-thiosialosides into the N-9-fluorenylmethoxycarbonyl, N-2,2,2-trichloroethoxycarbonyl (N-Troc), and N-trichloroacetyl derivatives enhanced the reactivity of these compounds towards glycosidation. Addition of a minimum amount of 3 A molecular sieves was also effective in improving the yield of alpha-linked sialosides. Next, we conducted one-pot syntheses of the glycosyl amino acids by using the N-Troc sialyl donor. The N-Troc derivative can be converted into the N-acetyl derivative without racemization of the amino acids. Branched-type one-pot glycosylation, initiated by regioselective glycosylation of the 3,6-dihydroxy galactoside with the N-Troc-beta-thiophenyl sialoside, provided the protected 2,6-sialyl T antigen in good yield. Linear-type one-pot glycosylation, initiated by chemoselective glycosylation of galactosyl fluoride with the N-Troc-beta-thiophenyl sialoside, afforded the protected 2,3-sialyl T antigen in excellent yield. Both protected glycosyl amino acids were converted into the fully deprotected 2,6- and 2,3-sialyl T antigens linked to serine in good yields.     

Synthetic fragments of antigenic lipophosphoglycans from Leishmania major and Leishmania mexicana and their use for characterisation of the Leishmania elongating alpha-D-mannopyranosylphosphate transferase

The phosphorylated branched heptasaccharides 7 and 8, the octasaccharide 9 and the phosphorylated trisaccharides 5 and 6, which are fragments of the phosphoglycan portion of the surface lipophosphoglycans from Leishmania mexicana (5) or L. major (6-9), were synthesised by using the glycosyl hydrogenphosphonate method for the preparation of phosphodiester bridges. The compounds were tested as acceptor substrates/putative inhibitors for the Leishmania elongating alpha-D-mannosylphosphate transferase.     

Improved determination of tributyl phosphate degradation products (mono- and dibutyl phosphates) by ion chromatography

Tributyl phosphate (TBP) is a very important compound in the nuclear industry, particularly in the area of nuclear fuel reprocessing. This compound is used in the PUREX (plutonium and uranium refining extraction) process which consists of the extraction of uranium and plutonium from an aqueous nitric acid phase, for the purpose of recycling. But TBP may be degraded to dibutyl phosphate (DBP) and monobutyl phosphate (MBP) by dealkylation of one or two butoxy groups, respectively. We have compared and evaluated the capacity of two resins manufactured by Dionex (AS11 and AS5A) in the separation and measurement of these two degradation products. AS11 generates two interferences: nitrite/DBP and carbonate/MBP. The first one is the most serious. So, we have developed a method for oxidising nitrite ions to nitrate ions which have no trouble over the measurement. The second resin tested, AS5A, allows a very efficient separation between DBP and NO₂⁻ ions and a good separation between MBP and CO₃²⁻ in comparison with the AS11. The detection limits for the AS5A column are 0.13 μM for MBP and 0.71 μM for DBP (injection LOOP=50 μl).     

Convergent stereoselective and efficient synthesis of furanic-steroid derivatives

The stereoselective synthesis of furanic-steroid derivatives involving ring-closing metathesis and catalytic hydrogenation as key steps is described. The synthetic strategy was first illustrated by the synthesis of the furanic-estrane derivative 1 in seven steps starting from estrone and 2-methylene-propane-1,3-diol. This compound initially targeted as a potential inhibitor of 17β-hydroxysteroid dehydrogenase type 1 by a docking experiment was found to inhibit the enzyme. The scope of this new strategy was also extended to furanic-androstane derivatives by synthesizing compound 20.     

Hydrothermal synthesis and structure of organically templated chain, layered and framework scandium phosphates

Four scandium phosphate-based structures have been prepared hydrothermally in the presence of the primary diamines ethylenediamine and diaminobutane and the primary amine cyclohexylamine and characterised by single crystal and powder X-ray diffraction, ³¹P and ⁴⁵Sc solid-state MAS NMR and chemical analysis. Charge balancing protons in the structures are located using bond valence sum calculations and postulated hydrogen bonding networks. Compound 1, [(H₃NC₂H₄NH₃)₃][Sc₃(OH)₂(PO₄)₂(HPO₄)₃(H₂PO₄)], , a=5.4334(6), b=8.5731(9), , α=79.732(4), β=83.544(4), γ=80.891(5)°, Z=2, is built up of scandium phosphate ribbons, based on trimers of ScO₆ octahedra linked by OH groups. These trimers are joined through phosphate groups bound through three oxygens, and are decorated by phosphate groups linked by a single oxygen atom. The ribbons are arranged parallel to the a-axis and linked one to another by fully protonated ethylenediammonium ions. Compounds 2, [(H₃NC₄H₈NH₃)₃][(Sc(OH₂))₆Sc₂(HPO₄)₁₂(PO₄)₂], , a=13.8724(3), , Z=1, and 3, [(H₃NC₄H₈NH₃)₂(H₃O)][Sc₅F₄(HPO₄)₈], C2/m, a=12.8538(4), b=14.9106(4), , β=101.17(9)°, Z=2, were prepared using diaminobutane as the organic template in the absence and presence, respectively, of fluoride ions in the gel. Compound 2 has a pillared layered structure, in which ScO₆ octahedra are linked by three vertices of hydrogenphosphate groups into sheets and the sheets pillared by ScO₆ octahedra to give a three-dimensionally connected framework isostructural with a previously reported iron(III) hydrogenphosphate. The protonated diaminobutane molecules occupy cavities between the layers. Compound 3 has a layered structure in which isolated ScO₆ octahedra and tetrameric arrangements of ScO₄F₂ octahedra, the latter linked in squares through fluoride ions, are connected by phosphate tetrahedra that share two or three oxygens with scandium atoms. In this structure, the protonated diaminobutane molecules connect the layers, the -NH₃⁺ groups fitting into recesses in the layers. Compound 4, [(C₆H₁₁NH₃)][ScF(HPO₄)(H₂PO₄)], Pbca, a=7.650(3), b=12.867(5), , Z=8, the first scandium phosphate to be prepared with a monoamine, is also a layered solid. In this case, the layers contain single chains of ScO₄F₂ octahedra which share fluoride ions in trans positions. Phosphate tetrahedra bridge across scandiums via two of their four oxygens, both within the same chain and also to neighbouring chains to make up the layer. The protonated amine groups of the cyclohexylamine molecules achieve close contact with phosphates of the layer, while the cyclohexyl moieties, which are in the chair configuration, project into the interlayer space.     

A short and stereoselective synthesis of functionalized pentenomycin derivatives

A short and stereoselective synthesis of 2-hydroxymethyl-4-deoxypentenomycin and 2-hydoxymethylpentenomycin derivatives is accomplished in five and seven steps starting from tetrabromonorbornyl derivatives in overall yields of 41% and 38%, respectively.     

A highly stereoselective construction of 1,2-trans-β-glycosidic linkages capitalizing on 2-azido-2-deoxy-d-glycosyl diphenyl phosphates as glycosyl donors

The scope of TMSOTf-promoted glycosidation of 2-azido-2-deoxyglycopyranosyl diphenyl phosphates is investigated. The 3,4,6-tri-O-benzyl-protected glucosyl and galactosyl donors and the 4,6-O-benzylidene-protected galactosyl donor each react with a range of acceptor alcohols in the presence of a stoichiometric amount of TMSOTf in propionitrile at −78 °C to afford 1,2-trans-β-linked disaccharides in high yields with α:β ratios ranging from 9:91 to 1:>99, regardless of the anomeric composition of the donor used. The use of propionitrile as a solvent at −78 °C has proven to be among the best choice for the highest levels of β-selectivity reported to date for this type of glycosidation. A plausible reaction mechanism, which features a large equilibrium preference for α-glycosyl-nitrilium ions over β-nitrilium ions, is proposed based on byproducts formed through their intermediacy and accounts for the observed excellent β-selectivities.     

1-Fluoropyridinium triflates: versatile reagents for transformation of thioglycoside into O-glycoside, glycosyl azide and sulfoxide

1-Fluoropyridinium triflates are versatile reagents to transform thioglycoside into O-glycoside, glycosyl azide and sulfoxide. The electronic nature of the substituents on the pyridine ring can control their ability to activate thioglycosides.     

2-Deoxy-2-iodo-alpha-mannopyranosyl and -talopyranosyl acetates: highly stereoselective glycosyl donors for the synthesis of 2-deoxy-alpha-glycosides

[formula: see text] TMS-OTf- or TBS-OTf-promoted glycosidation reactions of 2-deoxy-2-iodo-alpha-mannopyranosyl acetates 8-10 and the 2-deoxy-2-iodo-alpha-talopyranosyl acetate 11 provide the corresponding 2-deoxy-2-iodo-alpha-pyranosides, precursors to 2-deoxy-alpha-glycosides, as the only observed reaction products.     

在线样品前处理大体积进样离子色谱法直接测定海水中亚硝酸盐、硝酸盐和磷酸盐

采用戴安公司谱睿(Pre)在线样品除氯技术,结合OnGuard Ba柱去除硫酸盐,建立了离子色谱直接测定海水中亚硝酸盐、硝酸盐和磷酸盐的方法。该方法以IonPac AG23为富集柱,高容量IonPac AS23为分离柱,淋洗液自动发生装置在线产生KOH溶液进行梯度淋洗,抑制电导检测。实验结果表明: 样品稀释5～10倍时,直接进样不会干扰目标物测定。当流速为1 mL/min、进样量为500 μL时,海水中NO~2-N、NO~3-N、PO3~4-P的方法检出限分别为0.3、0.4、0.2 μg/L,线性范围分别为10～500 μg/L、14～680 μg/L、3.4～170 μg/L,线性相关系数r均大于0.9990。测得人工海水样品中目标物的加标回收率为92%～106%,相对标准偏差(RSD, n=6)为1.2%～7.7%。该方法一次进样可在13 min内完成分析,具有操作简单快捷、无污染等优点,能满足近海海水中NO~2、NO~3、PO3~4的定量分析要求。     

Three-step synthesis of chiral and sterically hindered amino alcohols based on cyclic enol phosphates

The new synthesis of chiral and sterically hindered 1,2-amino alcohols derivatives of 2-methyl-indane and 1,2,3,4-tethrahydrophenanthrene based on cyclic enol phosphates were investigated. The desired products were obtained using three step procedure: oxidation of accessible enol phosphates, transformation α-hydroxy ketones into corresponding oximes and finally reduction of the last one to 1,2-amino alcohols. The optimal conditions of all stages to obtain products with high enantioselectivity or diastereomeric ratio were found and elaborated. The structures and absolute configurations of (3R)-2,3-dihydro-3-hydroxy-1H-phenanthren-4-one and corresponding oxime were confirmed by X-ray analysis.     

Highly regio- and stereoselective synthesis of tricyclic frameworks using Baylis-Hillman derivatives

A simple and convenient synthetic route for the synthesis of tricyclic chromeno[4,3-b]pyrrolidine frameworks using Baylis-Hillman bromides involving in situ formation of an imine, decarboxylation and a [3+2] cycloaddition sequence is described.     

Efficient and direct synthesis of saccharidic 1,2-ethylidenes, orthoesters, and glycals from peracetylated sugars via the in situ generation of glycosyl iodides with I2/Et3SiH

Peracetylated sugars can be efficiently converted into the corresponding 1,2-ethylidenes, -orthoesters, and -glycals via the in situ generation of glycosyl iodides promoted by I₂/Et₃SiH. The approach is straightforward and avoids isolation of the sensitive iodinated intermediates.     

A new strategy for the stereoselective synthesis of 2,3-dideoxy-3-fluoro-D-ribofuranose derivatives

The important intermediate for syntheses of various anti-HIV nucleoside analogues, methyl 2,3-dideoxy-3-fluoro-6-O-(p-methylbenzoyl)-a-D-ribofuranoside, was synthesized starting from 2-deoxy-D-ribose in 5 steps with an overall yield of 24%. This strategy can be also used for synthesizing other analogues with various substitutions at 3-C position.     

Preparation and use of enantioenriched allenylsilanes for the stereoselective synthesis of homopropargylic ethers

A convenient procedure for the synthesis of highly enantioenriched allenylsilanes by Johnson orthoester Claisen rearrangement of 1-silyl propargylic alcohols is described. Allenylsilanes are then used as carbon nucleophiles in three-component, Lewis acid mediated additions to in situ generated oxonium ions, resulting in enantioenriched homopropargylic ethers.     

2-Deoxy-2-iodo-beta-glucopyranosyl fluorides: mild and highly stereoselective glycosyl donors for the synthesis of 2-deoxy-beta-glycosides from beta-hydroxy ketones

2-Deoxy-2-iodo-beta-glucopyranosyl fluoride 14 is a highly stereoselective glucopyranosyl donor that may be activated under mild conditions. Application of this new glycosyl donor to the glycosidation reactions of a variety of acceptors including beta-hydroxy ketones affords beta-glycosides with high efficiency and stereoselectivity. [reaction--see text]