Highly diastereoselective addition of nitromethane anion to chiral alpha-amidoalkylphenyl sulfones. Synthesis of optically active alpha-amino acid derivatives

Optically active syn-alpha-amidoalkylphenyl sulfones can be prepared from chiral aldehydes in anhydrous conditions using benzenesulfinic acid. These sulfones in basic conditions give N-acylimines that react with sodium methanenitronate to afford the corresponding nitro adducts with high anti diastereoselectivity. PM3 semiempirical calculations provide a rationale for the observed opposite stereoselectivity. The obtained nitro derivatives undergo a Nef reaction followed by a methylation giving optically active beta-hydroxy-alpha-amino acid and alpha,beta-diamino acid esters in good yield. These amino acid derivatives are important building blocks for the preparation of biologically active compounds.     

Synthesis of beta-amino-alpha-hydroxy esters and beta-amino-alpha-azido ester by Sharpless asymmetric aminohydroxylation, byproducts analysis

[reaction: see text] Synthesis of enantiomerically pure beta-amino-alpha-hydroxy esters (1, 2) and beta-amino-alpha-azido ester (3) using Sharpless AA as a key step is described. A hitherto unreported side reaction, the oxidation of the beta-hydroxy-alpha-amino ester (5) into the alpha,alpha-di-tert-butyloxycarbamoyl-beta-ketoester (8) under AA conditions, is documented.     

Lobocyclamide B from Lyngbya confervoides. Configuration and asymmetric synthesis of beta-hydroxy-alpha-amino acids by (-)-sparteine-mediated aldol addition

[reaction: see text] Lobocyclamide B, a cyclododecapeptide containing five beta-hydroxy-alpha-amino acid residues, was isolated from Lyngbya confervoides. This is the first reported occurrence of gamma-hydroxythreonine in a natural peptide. Optically active beta-hydroxy-alpha-amino acids required for configurational analysis of the title compound were prepared using a novel (-)-sparteine-mediated asymmetric aldol addition of N-(diphenylmethylene)glycine tert-butyl ester to aldehydes. The method is general for aliphatic and aryl aldehydes and notable for operational simplicity.     

Studies on Ester Exchange Reaction

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新型鹅去氧胆酸分子裂缝的设计合成

分子识别是生物体系的基本特征,并在生命活动中起中心作用。生物酶高效专一地催化生化反应,抗体与抗原的结合,蛋白质分子与DNA序列的相互作用等都源于精确的分子识别[1,2]。利用合成的人工受体与适当底物之间的分子识别以建立仿生仿酶模型的研究,已成为生物有机化学前沿富有挑战性的领域。分子裂缝作为一类新型的人工受体,以其灵活的结构以及易于将功能团聚集在受体与底物结合的活性部位上等优点,引起了人们的广泛关注[3-5]。胆甾因其具有刚性的凹面结构和天然的手性,是构筑分子裂缝人工受体的理想结构单元。我们曾报道3α-OH和7α-OH同…     

Direct organocatalytic asymmetric aldol reactions of alpha-amino aldehydes: expedient syntheses of highly enantiomerically enriched anti-beta-hydroxy-alpha-amino acids

[reaction: see text] A simple and efficient method for the synthesis of highly enantiomerically enriched beta-hydroxy-alpha-amino acid derivatives has been developed. Direct asymmetric aldol reactions of a glycine aldehyde (aminoacetaldehyde) derivative have been performed under organocatalysis using l-proline or (S)-5-pyrrolidine-2-yl-1H-tetrazole. The reactions afforded anti-beta-hydroxy-alpha-amino aldehydes in good yield with high diastereoselectivity (dr up to >100:1) and high enantioselectivity (up to >99.5% ee), which were easily transformed into beta-hydroxy-alpha-amino acid derivatives.     

α-猪去氧胆酸类分子钳的设计合成

以α-猪去氧胆酸为隔离基，芳香族化合物为手臂设计合成了一类新型的酯键 型分子钳，结构均经^1H NMR，IR,MS及元素分析所确证，并且考察了其对芳香胺类 化合物和D／L-氨基酸甲酯的识别性能．初步研究结果表明，这类分子钳受体不但 对中性小分子具有识别性能，而且对D／L-氨基酸甲酯具有对映选择性识别性能．     

新型鹅去氧胆酸分子钳的设计合成和分子识别性质研究

以鹅去氧胆酸为隔离基, 芳香族化合物为手臂设计合成了一类新型的分子钳, 其结构经¹H NMR, IR, MS及元素分析确证. 利用紫外光谱滴定法考察了其与D/L氨基酸甲酯的对映选择性识别性能. 结果表明, 分子钳3a～3e对所考察的氨基酸甲酯均具有识别能力, 其对L-氨基酸甲酯的识别优于对D-氨基酸甲酯的识别. 从主客体的大小形状匹配及几何互补关系等方面对这些受体的识别能力及对映选择性进行了讨论.     

Highly diastereoselective cyanation of methyl ketimines obtained from (R)-glyceraldehyde

[reaction: see text] Addition of trimethylsilyl cyanide to ketimines derived from (R)-2,2-dimethyl-1,3-dioxolan-4-yl methyl ketone to generate a quaternary stereocenter has been achieved with high yields and excellent diastereoselectivity. The stereoselectivity was found to be temperature and solvent dependent. The beta-hydroxy-alpha-amino nitrile of syn configuration was the major compound in kinetically controlled reactions, whereas the anti stereoisomer was obtained in excess in thermodynamically controlled reactions. Double stereodifferentiation under kinetic control conditions was successful, and the cyanation reaction occurred with complete syn diastereoselectivity using the matched pair. The versatility of the resulting amino nitrile as a synthetic intermediate was tested by performing the synthesis of orthogonally protected (R)-(2-aminomethyl)alanine.     

The first ammonium aromatic diselenoates: stable heavy congeners of aromatic carboxylic acid salts

Ammonium aromatic diselenoates were synthesized by reacting aromatic diselenoic acid 2-(trimethylsilyl)ethyl esters derived from aluminum 2-(trimethylsilyl)ethyl selenolate with aromatic selenoic acid O-methyl esters with ammonium fluorides. The results of molecular structure analysis and NMR studies of ammonium salts supported the double-bond character between the carbon atom and selenium atoms.     

Modification of catalysts for propylene polymerization: Alcohols and lewis bases

A series of compounds were examined as modifiers for the high activity supported catalyst TiCl₄/MgCl₂–AlEt₃ for isospecific propylene polymerization. The list included two aromatic acid esters, 21 various Lewis bases, and 12 alcohols. A convenient graphic method is described for comparing the performance of different modifiers by plotting experimental results in coordinates “relative activity-isotactic index” and a kinetic rationale for this evaluation is presented. Aromatic acid esters exhibit much better performance than the bulk of Lewis bases but some sterically demanding aromatic alcohols show behavior show similar to that of the esters.     

氨基甲酸酯型脱氧胆酸分子钳对氨基酸甲酯的手性识别 研究

以脱氧胆酸为spacer,通过三光气桥连各种芳胺,合成了新的氨基甲酸酯型分子钳受体1～4,这些化合物的结构经IR,^1HNMR和元素分析所证实。利用差光谱滴定法考察了其与D/L氨基酸甲酯的对映选择性识别性能。结果表明,分子钳1～4对所考察的氨基酸甲酯均具有识别能力,其对D-氨基酸甲酯的识别优于对L-氨基酸甲酯的识别。从主客体间的大小形状匹配及几何互补关系等方面对这些受体的识别能力及对映选择性进行了讨论。     

新型酯键型鹅去氧胆酸分子钳的设计合成

以鹅去氧胆酸为隔离基、芳香族化合物为手臂设计合成了一类新型的分子钳, 其结构经¹H NMR, IR, MS和元素分析确证, 并且考察了其对D/L-氨基酸甲酯的对映选择性识别性能. 初步的结果表明, 这类手性分子钳对D-氨基酸甲酯有较好的识别性能.     

手性芳酰胺类分子钳的设计与微波合成

以间苯二甲酸为隔离基, 酰胺键桥联L-氨基酸甲酯构成手臂, 在微波辐射下合成了具有不同手性中心和裂穴的新型手性芳酰胺类分子钳. 结构均经¹H NMR, IR及元素分析确证, 并考察了其对芳香胺类化合物和D/L-氨基酸甲酯的识别性能. 初步研究表明, 这类分子钳受体不仅对中性小分子具有优良的识别性能, 其结合常数(K_a)可达2.66×10³ L•mol^－1, 而且对D/L-氨基酸甲酯亦具有良好的手性识别能力.     

Two-step synthesis of ferrocenyl esters of vanillic acid

Successive reactions of vanillin with aromatic aldehydes at the phenol group and ferroceneboronic acid at the carbonyl group catalyzed with various N-heterocyclic carbenes afforded the corresponding ferrocenyl esters. In these reactions copper(II) sulfate, cinnamic aldehyde, and air oxygen act as oxidants. The resulting ferrocenyl esters of vanillic acid were tested for cytotoxicity.     

Natural product propolis: chemical composition

The chemical composition of propolis from East Mediterranean (Hatay, Adana and Mersin) was studied in order to determine the major compounds by using GC-MS. In this study, the ethanolic extract of propolis prepared by mixing 1900mL 70% ethanol and 100g propolis was used. Chemical analysis of propolis extracts indicated that the propolis samples had high concentrations of the aromatic acids, esters and other derivatives which are responsible for the anti-bacterial, anti-fungal, anti-viral, anti-inflammatory and anti-cancer properties of propolis such as benzyl cinnamate, methyl cinnamate, caffeic acid, cinnamyl cinnamate and cinnamoylglcine besides the most common compounds as fatty acid, terpenoids, esters, alcohols hydrocarbons and aromatic acids.     

Recognition of enantiomers with chiral molecular tweezers derived from (+)- or (−)-usnic acid

The synthesis of four stereoisomers of a chiral molecular tweezer using trans-1,2-diaminocyclohexane as spacer and two molecules of usnic acid as pincers is reported. The behavior of these chiral tweezers as chiral complexing agents was evaluated in NMR with various chiral esters containing an electron-poor aromatic ring to allow non-covalent aromatic–aromatic interactions.     

Use of Some Silver Salts of Aromatic Sulfonic Acids in Thin-Layer Chromatography

Abstract

Some silver salts of aromatic sulfonic acids were used for thin-layer impregnation. The chromatographic properties of these salts were examined by separation of fatty acid methyl esters with different degrees of saturation as well as of their cis- and trans-isomers. Benzene sulfonic acid silver salt was more thoroughly investigated. An attempt was made to prove the effect of the anion of the different silver salts on the R_f values of a model mixture of fatty acid methyl esters.     

微波促进一锅法合成氨基甲酸酯型α-猪去氧胆酸分子钳

在微波辐射条件下, 以α-猪去氧胆酸为隔离基, 通过三光气桥连各种芳香胺, 以很好的产率合成了一系列新的手性分子钳, 其结构经¹H NMR, IR, MS和元素分析确证, 并且考察了其对中性分子和D/L-氨基酸甲酯的识别性能. 实验结果表明, 这类分子钳人工受体不仅对中性有机小分子具有优良的识别性能, 而且对D/L-氨基酸甲酯亦具有良好的对映选择性识别能力.     

Catalytic enantioselective aldol additions of alpha-isothiocyanato imides to aldehydes

Highly enantioselective organocatalytic aldol additions of alpha-isothiocyanato imides to aldehydes are reported. These reactions provide convenient access to enantiomerically enriched and protected beta-hydroxy-alpha-amino acids with catalyst loadings as low as 1 mol%.