Arginine-modified DNA aptamers that show enantioselective recognition of the dicarboxylic acid moiety of glutamic acid

We have screened glutamic acid-binding aptamers from a modified DNA pool containing arginine residues using the method of systematic evolution of ligands by exponential enrichment (SELEX). Thirty-one modified DNA molecules were obtained from the enriched pool after the 17th round of selection, and their binding affinities for the target were evaluated by binding assays using affinity gels. Three modified DNA molecules having higher affinity were sequenced and we determined their affinity and specificity for the target by surface plasmon resonance (SPR) measurements. The SPR studies indicated that two of these three aptamers distinguished the dicarboxylic acid moiety of the D-isomer from that of the L-isomer; however, the third aptamer did not show enantioselectivity.     

Highly enantioselective fluorescent recognition of α-amino acid derivatives

Bisbinaphthyl-based macrocycles are found to carry out enantioselective fluorescent recognition of α-amino acid derivatives. It is observed that one enantiomer of a N-protected phenyl glycine can increase the fluorescence intensity of the binaphthyl fluorophores by over 4-fold but the other enantiomer does not cause much fluorescence enhancement. This highly enantioselective fluorescent response makes the binaphthyl macrocycles practically useful for the enantioselective fluorescent recognition of the amino acid substrate.     

Highly enantioselective fluorescent recognition of mandelic acid derivatives by chiral salen macrocycles

Calixarene-like chiral salen macrocycles can be used for the enantioselective fluorescent recognition of mandelic acid derivatives. It was observed that one enantiomer of mandelic acid causes a 28-fold increase in the fluorescence intensity of a chiral salen macrocycle, whereas the other enantiomer causes only a 14-fold fluorescence enhancement. This highly enantioselective fluorescent response makes chiral salen macrocycles useful for the enantioselective fluorescent recognition of some mandelic acid derivatives.     

Highly enantioselective fluorescent recognition of amino acid derivatives by unsymmetrical salan sensors

Novel unsymmetrical salan fluorescent sensors 2a and 2b have been designed and synthesized. The chiral recognition of N-Boc-protected amino acids by 2a and 2b has been investigated. Sensor 2a possesses higher sensitivity and enantioselectivity than sensor 2b does. Job analysis and nonlinear regression results show that 2a can form a 1:1 stoichiometric complex with a N-Boc-protected amino acid. The obtained response selectivities and the association constants indicate that 2a is a highly enantioselective and sensitive fluorescent sensor toward N-Boc-protected amino acids.     

Highly enantioselective fluorescent sensor for chiral recognition of amino acid derivatives

A highly enantioselective fluorescent sensor, containing benzylaminomethyl groups at 3,3′-position of 1,1′-bi-2-naphthol (BINOL), has been used to conduct the chiral recognition of α-amino acid derivatives. It is observed that one enantiomer of N-Boc-proline can increase the fluorescence intensity of the binaphthyl fluorophores by over 57-fold, while the other enantiomer can cause only sixfold fluorescence enhancement. Such unusually highly enantioselective response demonstrates that this sensor is potentially useful in the enantioselective recognition of amino acid derivatives.     

Highly enantioselective organocatalysis of the Hajos-Parrish-Eder-Sauer-Wiechert reaction by the beta-amino acid cispentacin

The beta-amino acid cispentacin promotes the Hajos-Parrish-Eder-Sauer-Wiechert reaction with levels of enantioselectivity comparable to or higher than proline.     

Troger's base molecular scaffolds in dicarboxylic acid recognition

Artificial receptors (1-5) have been designed and synthesized from simple precursors. The chain length selectivity studies of dicarboxylic acids within the cavities of new fluorescent Troger's base molecular frameworks (1-3) have been carried out with a critical examination of their role of rigidity as well as flexibility in selective binding in comparison to receptor 5. The chiral resolution of the racemic Troger's base receptors (1 and 2) by chiral recognition with (+)- camphoric acid using hydrogen-bonding interactions has been studied.     

Highly enantioselective synthesis of a fluorescent amino acid

A high enantiomeric excess (>99.5%) synthesis of 2-amino-3-(7-methoxy-4-coumaryl) propionic acid ( Amp) is described. The two step synthesis route of this non-proteinogenic amino acid includes an oxazinone derivative as glycine enolate, which is alkylated with the fluorogenic group.     

胆甾类分子钳对氨基酸衍生物的对映选择性识别

用差紫外光谱滴定法考察了以脱氧胆酸作spacer的手性分子钳1～3对一系列α-氨基酸甲酯的对映选择性识别性能。结果表明,分子钳1和2与客体氨基酸甲酯形成1:1型超分子配合物,并显示较好的手性识别能力。分钳3对所考察的氨基酸甲酯均没有明显的识别作用。讨论了主-客体间尺寸/形状匹配、几何互补等因素对形成超分子配合物的影响,并利用计算机模拟作辅助手段对实验结果和现象进行了解释。     

Highly enantioselective Michael-cyclization cascade promoted by synergistic asymmetric aminocatalysis and Lewis acid catalysis

The novel dual cooperative asymmetric aminocatalysis and Lewis acid catalysis has been successfully developed for promoting cascade Michael-cyclization reaction with high enantio-, regio- and chemo-selectivity. The simple and practical process affords a one-pot approach to synthetically useful cyclopentenes.     

Fluorescent sensors for the enantioselective recognition of mandelic acid: signal amplification by dendritic branching

Novel chiral bisbinaphthyl compounds have been synthesized for the enantioselective fluorescent recognition of mandelic acid. By introducing dendritic branches to the chiral receptor unit, the fluorescence signals of the receptors are significantly amplified because of the light-harvesting effect of the dendritic structure. This has greatly increased the sensitivity of the sensors in the fluorescent recognition. Study of the three generation sensors demonstrates that the generation zero sensor is the best choice for the recognition of mandelic acid because of its greatly increased fluorescence signal over the core and its high enantioselectivity. This sensor is potentially useful for the high throughput screening of chiral catalysts for the asymmetric synthesis of alpha-hydroxycarboxylic acids.     

Highly enantioselective rhodium-catalyzed hydrogenation of beta-dehydroamino acid derivatives using monodentate phosphoramidites

New and very easily accessible monodentate phosphoramidite ligands have been developed that lead to excellent ee's and full conversions in the hydrogenation of (E)- and (Z)-beta-dehydroamino acid derivatives with both aliphatic and aromatic side chains. Particularly, two different catalytic systems were established for (E)-beta-(acylamino)acrylates (98-99% ee) and (Z)-beta-(acylamino)acrylates (92-95% ee) based on phosphoramidites 2 and 3, respectively.     

Highly enantioselective Biginelli reaction catalyzed by SPINOL-phosphoric acids

A highly enantioselective Biginelli reaction promoted by chiral spirocyclic SPINOL-phosphoric acids has been developed. Under the optimized conditions with 5 mol% catalyst loading, a wide range of optically active dihydropyrimidinethiones (DHPMs) were obtained in high yields (up to 98%) with good to excellent enantioselectivities (up to 99% ee). The synthetic utility of this method was demonstrated by the synthesis of chiral precursors of three drugs, including (S)-Monastrol, (S)-L-771688 and (S)-SQ 32926.