A highly diastereoselective synthesis of dl-oleandrose

Racemic oleandrose (2,6-dideoxy-3-O-methyl-arabino-hexone) has been obtained starting from the Diels-Alder adduct between 4-methoxy-3-buten-2-one and isobutyl vinyl ether, which was converted into a mixture of the isobutyl β- and α-oleandrosides through hydroboration-oxidation. The latter reaction is highly diastereoselective since attack by borane takes place exclusively anti to the OMe group: none of the diasteroisomeric cymarosides are formed. The only side-products are small amounts of the isobutyl β- and α-amicetodies formed by a demthoxylation occuring during the hydroboration step.     

Reaction of 1-[2-(vinyloxy)ethyl]-1<Emphasis Type="Italic">H</Emphasis>-pyrroles with trifluoroacetic anhydride

Chemo- and stereoselectivity of the reaction of 1-[2-(vinyloxy)ethyl]-1H-pyrroles with trifluoroacetic anhydride have been studied. The reaction with an equimolar amount of trifluoroacetic anhydride chemoselectively involves the free α-position of the pyrrole ring with formation of the corresponding α-trifluoroacetylpyrroles. In the reaction with 2 equiv of trifluoroacetic anhydride, acylation of both α-position of the pyrrole ring and β-position of the vinyloxy group leads to the formation of 1-(2-{[(1E)-4,4,4-trifluoro-3-oxobut-1-en-1-yl]oxy}ethyl)-2-trifluoroacetyl derivatives with high stereoselectivity.     

Anion recognition by d-ribose-based receptors

Anion recognition properties of d-ribose-based receptors α- and β-1 were measured by ¹H NMR in CDCl₃ and MeCN-d₃. Receptor β-1 showed effective binding with anions by cooperative hydrogen bonds of cis-diol. The anomeric isomer α-1 is a less effective anion receptor which has similar cis-diol as a recognition site, indicating that the stereo configuration of the anomeric position is of significant influence on the anion recognition ability.     

Asymmetric synthesis of potent glycosidase and very potent α-mannosidase inhibitors: 4-amino-4-deoxy-l-erythrose and 4-amino-4,5-dideoxy-l-ribose

Pyrrolidine amino-sugars, cyclic iminoalditols as well as linear aminoalditols in 4-amino-l-erythrose and 4-amino-5-deoxy-l-ribose series were synthesised by asymmetric hetero-Diels-Alder reaction followed by chemical transformations. 4-Amino-4-deoxy-l-erythrose and 4-amino-4,5-dideoxy-l-ribose were potent β-d-glucosidase, α-d-mannosidase, α- and β-d-galactosidase inhibitors. We have shown that the ribose derivative was a very potent inhibitor of α-d-mannosidase.     

Role of the key mutation in the selective binding of avian and human influenza hemagglutinin to sialosides revealed by quantum-mechanical calculations

The selective binding between avian and human influenza A viral hemagglutinins (HA) subtype H3 and Neu5Acα2-3 and α2-6Gal (avian α2-3, human α2-6) is qualitatively rationalized by the fragment molecular orbital (FMO) method. We suggest a general model of analyzing protein-ligand interactions based on the electrostatic, polarization, dispersion, and desolvation components obtained from quantum-mechanical calculations at the MP2/6-31G(d) level with the polarizable continuum model of solvation. The favorable avian H3 (A/duck/Ukraine/1963)-avian α2-3 binding arises from the hydrophilic interaction between Gal-4 OH and side-chain NH(2)CO on Gln226, which is supported by the intermolecular hydrogen-bond network to the 1-COO group on Neu5Ac moiety. A substitution of Gln226Leu in the avian H3 HA1 domain increases the binding affinity to human α2-6 due to the Leu226···human α2-6 dispersion with a small entropic penalty during the complex formation. The remarkable human H3 (A/Aichi/2/1968)-human α2-6 binding is not governed by the Ser228-OH···OH-9 Neu5Ac hydrogen bond. These fragment-based chemical aspects can help design monovalent inhibitors of the influenza viral HA-sialoside binding and the simulation studies on the viral HAs-human α2-6 binding.     

3-(4,5-Dihydro-1<Emphasis Type="Italic">H</Emphasis>-pyrazol-1-ylmethyl)oxazolidines and 3-(4,5-dihydro-1<Emphasis Type="Italic">H</Emphasis>-pyrazol-1-ylmethyl)perhydro-1,3-oxazines

3-(4,5-Dihydro-1H-pyrazol-1-ylmethyl)oxazolidines and 3-(4,5-dihydro-1H-pyrazol-1-ylmethyl)perhydro-1,3-oxazines were synthesized in 54–85% yield by reactions of α-amino alcohols and 3-aminopropan-1-ol, respectively, with formaldehyde and 4,5-dihydro-1H-pyrazoles.     

一维SEMDY和旋转坐标NOE差谱NMR新技术用于天然化合物中寡糖的结构研究

报告从日本续断根部的乙醇提取物中分得二个新的五糖三萜皂甙,应用一维SEMDY和旋转坐标NOE差谱等NMR新技术互相配合的方法对它们的结构进行了研究,确定为：3-O-α-L-吡喃鼠李糖（1→3）-β-D-吡喃葡萄糖（1→3）-α-L-吡喃鼠李糖（1→2）-α-L-吡喃阿拉伯糖-常春藤甙元-28-O-β-吡喃葡萄糖酯甙（1）,和3-O-[β-D-吡喃葡萄糖（1→4）] [α-L-吡喃鼠李糖（1→3）]-β-D-吡喃葡萄糖（1→3）-α-L-吡喃鼠李糖（1→2）-α-L-吡喃阿拉伯糖-齐墩果酸（2）·结果表明,一维SEMDY和旋转坐标NOE差谱技术互相配合的方法测定寡糖链结构十分有效,高度重叠的糖基1H-NMR信号可按一定规律分离,容易鉴别,糖基之间的连接顺序和连接位置可以准确测定,不需要对化合物进行化学降解或衍生化。     

Asymmetric synthesis of d-fagomine and its diastereoisomers

A divergent strategy for the asymmetric syntheses of d-fagomine and three of its diastereoisomers has been developed. The diastereoselective conjugate addition of an enantiopure lithium amide to an α,β-unsaturated ester was used as the key step to install the correct configuration required for the C(5)-stereogenic centre within the targets. In situ enolate oxidation generated the corresponding anti-α-hydroxy-β-amino ester, which possessed the correct configuration required for the C(4)-stereogenic centre within both d-fagomine and d-3-epi-fagomine. Subsequent epimerisation of this key anti-α-hydroxy-β-amino ester upon oxidation and diastereoselective reduction gave the corresponding syn-α-hydroxy-β-amino ester, which possessed the correct configuration required for the C(4)-stereogenic centre within both d-4-epi-fagomine and d-5-epi-fagomine. Elaboration of both α-hydroxy-β-amino esters upon reduction to the corresponding aldehydes followed by aldol reaction generated the requisite C(3)-stereogenic centres within the target compounds, then cyclisation and deprotection gave the enantiopure iminosugars in good overall yields, as single diastereoisomers (>99:1 dr).     

Synthesis of the 3-methyl and 4-methyl derivatives of 3-amino-3,4-dihydro-1-hydroxycarbostyril and related compounds

The 3-methyl and 4-methyl derivatives of 3-amino-3,4-dihydro-1-hydroxycarbostyril were synthesized by the reductive cyclization of α-methyl-β-(o-nitrophenyl)alanine and α-amino-β-(o-nitrophenyl)butyric acid hydrohalides, respectively, under conditions of catalytic hydrogenation in acidic solution. The free bases of the latter two o-nitroaromatic amino acids were also catalytically hydrogenated under neutral conditions to yield the respective α-methyl-β-(o-aminophenyl)alanine and α-amino-β-(o-aminophenyl)butyric acid which were converted to the corresponding lactams, 3-methyl- and 4-methyl-3-amino-3,4-dihydrocarbostyrils. α-Methyl-β-(o-nitrophenyl)alanine was obtained by acid hydrolysis of 5-methy)-5-(o-nitrobenzyl)hydantoin which was prepared by treatment of o-nitrophenylacetone with potassium cyanide and ammonium carbonate. α-Amino-β-(o-nitrophenyl)butyric acid was synthesized by condensation of α-bromo-o-nitroethylbenzene with diethyl acetamidomalonate, followed by acid hydrolysis of the condensation product. The 4-methylated compounds were obtained as synthetic mixtures of two diasteromeric racemates in nearly the same amounts as shown by nmr spectral analysis. Unlike the demethylated parent compound, 3-amino-3,4-dihydro-1-hydroxycarbostyril, neither the 3-methyl nor 4-methyl analog was found to possess any antibacterial activity.     

Synthesis of carbazoles via 2-vinylindoles.

2-Vinylindoles are obtained from the Fischer indolization of α,β-unsaturated ketones. Heating 2-(2-methylpropenyl)indole (4) with the Vilsmeier reagent (DMF/POCl₃) gave 2-methylcarbazole in good yield, presumably $\text{via}$ an electrocyclic ring closure of a hexatrienic intermediate.     

A highly effective asymmetric synthesis of α-hydroxy acids by alkylation of chiral n-(benzyloxyacetyl)-trans-2,5-bis(methoxymethoxymethyl)pyrrolidine

Alkylation of lithiated $\text{N}$-(benzyloxyacetyl)-$\text{trans}$-2,5-bis(mehtoxyymethoxymethyl)- pyrrolidine proceeded with high stereoselectivity (≥96% de) and subsequent transformations of the alkylated products gave synthetically useful α-benzyloxy acids or α-hydroxy acids of high enantiomeric purity.     

α,ω-Bis(4-substituted-3-quinolinylthio)alkanes from reactions of thioquinanthrene with alkoxides

The reaction of thioquinanthrene 1 with sodium alkoxides and α,ω-dihaloalkanes leads to the formation of α,ω-bis[4-(4-methoxy-3-quinolinylthio)-3-quinolinylthio]alkanes 4 . The yield depends on the nature of α,ω-dihalo-alkanes. The effect of α,ω-dihaloalkanes of the following types: XCH₂X (X = Cl,Br,I), X(CH₂)₂X (X = Cl,Br,I), Br(CH₂)₃Br and Br(CH₂)₆Br were studied. The preparation of 4-alkoxy-3′-(ω-bromoalkylthio)-3,4′-diquinolinyl sulfide 3 and their transformation to α,ω-bis(4-alkoxy-3-quinolinylthio)alkanes 6 were studied as well.     

Synthesis of mono- and di-α-l-fucosylated 2-acetamido-2-deoxy-N-glycyl-β-d-glucopyranosylamines,spacered fragments of glycans of N-glycoproteins

Russian Chemical Bulletin - α-l-Fucp-(1→3)-d-GlcNAc, α-l-Fucp-(1→6)-[α-l-Fucp-(1→3)]-d-GlcNAc, and β-d-Galp-(1→3)-[α-l-Fucp-(1→4)]-d-GlcNAc...     

Synthesis of substituted 2-(thiophen-2-yl)-1<Emphasis Type="Italic">H</Emphasis>-imidazol-1-ols

Substituted 2-(thiophen-2-yl)-1H-imidazol-1-ols were synthesized by cyclization of the corresponding α-thienyl nitrones in alkaline medium. α-Thienyl nitrones were obtained by reaction of N-(1-hydroxyimine-1-R-propan-2-yl)hydroxylamines with thiophene-2-carbaldehyde in methanol. At boiling α-thienyl nitrones in methanol in the presence of sodium methylate 5-aryl(hetaryl)-2-(thiophen-2-yl)-1H-imidazol-1-ols are formed chemoselectively.     

The synthesis of peptides containing purine and pyrimidine derivatives of DL-alanine

The incorporation of the “base-bearing amino acids”, DL - β - (uracil - 1 - yl)alanine 1 (Uala), DL - β - (thymin - 1 - yl)alanine 2 (Tala), DL - β - (cytosin - 1 - yl)alanine 3 (Cala) and DL - β - (adenin - 9 - yl 4 (Aala) into peptides has been studied. The carboxyl group of each of these compounds was protected by the formation of the ethyl ester. The t - butoxycarbonyl (t-BOC) group was suitable for the protection of the α-amino group of 1 but not that of 2, 3 and 4 because of the formation of ring substituted compounds. Peptides containing the amino acids 1–4 and L-serine were synthesised, however, by the mixed anhydride method; uracil, thymine and adenine residues needed no protection, neither did the cytosine residue provided that it was not present in the intermediate which was treated with ethyl chloroformate to produce the mixed anhydride. In this case reaction with the cytosine residue occurred. By these procedures, four protected dipeptides, namely α - N - t - BOC - L - seryl derivatives of 1–4 and three protected tetrapeptides, namely α - N - t - BOC - L - seryl - DL - β - (thymin - 1 - yl)alanyl - L - ethyl ester (t - BOC - Ser - Tala - Ser - Tala - OEt), t - BOC - Ser - Aala - Ser - Aala - OEt and t - BOC - Ser - Uala - Ser - Uala - OEt were obtained. For the protection of the α-amino group of 2 or 3 the formyl group was found to be satisfactory.     

Reaction of 2-(2-Oxo-1,2-dihydro-3<Emphasis Type="Italic">H</Emphasis>-indol-3-ylidene)acetic acids esters with phenylhydrazine

2-(2-Oxo-1,2-dihydro-3H-indol-3-ylidene)acetic acids esters reacted with phenylhydrazine yielding products of the regioselective addition of the latter in the α-(C²)-position of the exo ethylene bond, (2-oxo-2,3-dihydro-1H-indol-3-yl)(2-phenylhydrazino)acetic acids esters.     

Ring-opening of oxazolines derived from l-serine: a short and efficient stereoselective synthesis of all four diastereomers of 3-mercaptoaspartic acid derivatives

Facile methods are described for accessing four diastereomerically pure 3-mercaptoaspartic acid derivative from l-aspartic acid. In our synthesis, ring-opening reactions of oxazoline-4,5-dicarboxylate with thiolacetic acid as well as the stereochemical interconversion of both α- and β-configuration via oxazoline chemistry were utilized as key steps.     

三缺位杂多阴离子XW9O34^1^0^-(X=Si,Ge)的稀土衍生物的合成与表征

三缺位杂多阴离子A, α-和A, β-SiW9, A, α-和A, β-GeW9与稀土硝酸盐反应生成A, α-和A, -β[Ln3O3.(X2W9O34)2]^1^7^-(Ln=La, Ce, Pr, Nd, Sm, Eu, Gd,Er)型杂多阴离子。183W NMR结果表明, 配体XW9O34^1^0^-的结构在反应前后并没有发生明显的变化, 本文还对合成化合物的磁性质及氧化还原性质等进行了研究。     

Synthesis of functionalized α-CF3-α-aminophosphonates via Cu(I)-catalyzed 1,3-dipolar cycloaddition

A convenient method for the preparation of α-CF₃-α-aminophosphonates bearing alkynyl group at the α-carbon atom has been described. New alkynylphosphonates have been further utilized in the synthesis of functionalized triazole-containing α-CF₃-α-aminophosphonates via copper-catalyzed (3+2)-cycloaddition to different organic azides.     

Quantum chemical research on structures, linear and nonlinear optical properties of the Li@n-acenes salt (n = 1, 2, 3, and 4)

On the basis of the n-acenes (n = 1, 2, 3 and 4), the α-Li@n-acenes and β-Li@n-acenes salts were selected to investigate how increasing the number n of conjugated benzenoid rings affects the linear and nonlinear optical responses. The α-Li@n-acenes and β-Li@n-acenes salts are obtained by a lithium atom substituting the α-H and β-H, respectively. In the present work, both ab initio (HF and MP2) and DFT (B3LYP, BhandHLYP, M05-2X, and CAM-B3LYP) methods are adopted to calculate the polarizability (α(0)) and first hyperpolarizability (β(tot)) of the α-Li@n-acenes and β-Li@n-acenes salts. MP2 results show that the α(0) values of both classes of lithium salts increase with increasing number n of conjugated benzenoid rings. Interestingly, we found that the β(tot) values of α-Li@n-acenes and β-Li@n-acenes salts take on opposite trends: the β(tot) values of α-Li@n-acenes are decreasing slowly (2187 for α-Li@benzene > 1978 for α-Li@naphthalene > 1898 for α-Li@anthrecene > 1830 au for α-Li@tetracene) and inceasing remarkably (2738 for β-Li@naphthalene < 3186 for β-Li@anthrecene < 3314 au for β-Li@tetracene) for β-Li@n-acenes. Furthermore, we found that the β(tot) values (2738-3314 au) of the β-Li@n-acenes are larger than those of the α-Li@n-acenes (1830-2187 au). On the other hand, comparing the results of different methods, the β(tot) values obtained by the M05-2X and CAM-B3LYP methods reproduce the polarizability and first hyperpolarizability of the α-Li@n-acenes and β-Li@n-acenes salts well, which test and verify the results of the MP2 method. Our present work may be beneficial to development of high-performance organic NLO optical materials.