关键词： energy methods  

摘要： An energy-based approach has been used to investigate the seismic behavior of code-designed asymmetric-plan systems. The systems considered in this investigation had large eccentricities in both directions, were designed for bidirectional earthquake loading, and their responses were computed with both components of ground motion acting simultaneously. The presented results demonstrate that the total input energy is about the same whether the system plan is symmetric or asymmetric. Furthermore, flexible-side elements in asymmetric-plan systems may be more vulnerable to earthquakes than the same elements in symmetric-plan systems if they are not designed to accommodate the higher hysteretic-energy demands. This observation correlates well with the damage observed in street corner buildings during several earthquakes. Stiff-side elements, on the other hand, are expected to suffer no more damage in asymmetric-plan systems than in symmetric-plan systems.

关键词： Isomerization   Organic compounds   Biotechnology   Reaction products   Enantioselective synthesis  

摘要： In recent years, β-amino acids have received a great deal ofattention due to a wide range of their potential biomedicinal andsynthetic applications. In this context, considering the excitingbenefits of fluorine substitution for hydrogen disclosed for thefamily of α-amino acids, the development of new syntheticmethodology for pre- paring fluorine-containing and enantiomericallypure β-amino acids is of particular interest.

关键词： Chromium   Carbene complexes   Peptides and proteins   Monomers   Organic compounds  

摘要： Optically active chromium aminocarbene complexes were alpha-alkylated and then photolyzed in the presence of 2,4,5-trichlorophenol to produce a number of optically active activated alpha-amino esters. These underwent coupling with amino acid esters or a soluble PEG-supported dipeptide to introduce the chromium-carbene-complex-derived amino acid residue into the peptide.

关键词： Reagents   Enolates   Aldehydes   Oxidation   Molecular structure  

摘要： A well-known method for enhancing the biological andpharmacological activity of a molecule is the site-specificintroduction of a fluorine atom. Coupled with the importance ofchirality in bioactive compounds, the development of new and improvedmethods for the enantioselective introduction of fluorine is ofsignificance.

关键词： Redox reactions   Cyclization   Diols   Ethers   Molecular structure  

摘要： Tandem peicyclic reactions have become extremely useful for therapid and efficient construction of highly functionalized *** these laboratories, the tandem {4+2}/[3+2] cycloaddition ofnitroalkenes and nitronates have been developed as a general approachfor the synthesis of a diverse array of cyclic, nitrogen- containingstructures.

关键词： Alcohols   Anions   Organic compounds   Vinyl   Pharmaceuticals  

摘要： A concise asymmetric synthesis of(-)-septicine (1) and (-)-tylophorine (2) was accomplished with a high degree of stereocontrol in eight and nine steps, respectively. Addition of 4-(1-butenyl)magnesium bromide to 1-acylpyridinium salt 3, prepared in situ from 4-methoxy-3-(triisopropylsilyl)pyridine and the chloroformate of (-)-trans-2-(alpha-cumyl)cyclohexanol, gave a 91% yield of diastereomerically pure dihydropyridone 7. Oxidative cleavage of 7 and subsequent reduction provided alcohol 6 in 81% yield. Conversion of 6 to the chloride followed by treatment with sodium methoxide gave indolizidinone 9 in high yield. Bromination and conjugate reduction of 9 with L-Selectride, and trapping the intermediate enolate with N-(5-chloro-2-pyridyl)triflimide, provided bromovinyl triflate 11. Palladium-catalyzed cross-coupling of excess (3,4-dimethoxyphenyl)zinc bromide and 11 gave (-)-septicine (1). On the basis of this synthesis, (-)-1 was assigned the R configuration. Reaction of 1 with vanadium(V) trifluoride oxide in TFA/CH2Cl2 effected oxidative coupling to give a 68% yield of(-)-tylophorine (2).

关键词： Ketones   Mixtures   Ethers   Tetrahydrofurans   Molecular structure  

摘要： An asymmetric synthesis of the naturally occurring antipode of the tetrahydrofuran lignan sesaminone ((-)-1) has been achieved. An X-ray crystal structure of the synthetic material validated the structure proposed in the literature for this lignan. Additionally, the absolute configuration of the natural product was established by correlation of the synthetic tetrahydrofuran with the known absolute configuration of L-Phe. The opening of the synthesis was a diastereoselective Evans aldol reaction between N-4-pentenoyloxazolidinone 6 and piperonal. Reduction of the major diastereomer of the aldol product provided enantiomerically pure diol 4. The primary and secondary hydroxyl groups of 4 were protected in tandem to generate silyl ether-MOM ether 9. The vinyl group contained in 9 was then elaborated, via a series of four steps, to aryl ketone 10. This aryl ketone was transformed to a mixture of silyl enol ether stereoisomers (11a,b);TiCl4-mediated activation of the MOM ethers contained in this mixture of enol ethers yielded tetrahydrofuran 12 as the major product. Treatment of 12 with fluoride provided synthetic (-)-1.

关键词： 高分子   手性   催化剂   不对称合成   环氧化反应  

摘要： 介绍了一种新型高分子手性催化剂及不对称合成反应，催化剂在不对称合成反应中的应用以及初步验证实验。

关键词： .building blocks   isosteres   asymmetric synthesis   dipeptide   CO2But   Stony Brook   peptides and peptidomimetics   lactam synthon method   non-protein amino   isoserines   polyamines poly   enantiopure lactams  

摘要： Recent advances in the syntheses of enantiopure synthetic building blocks useful for non-protein amino acids, dipeptides, oligopeptides using solid state peptide synthesis, isoserines (norstatines), dipeptide isosteres [hydroxy(keto)ethylene, hydroxyethylamine, hydroxyethylene and dihydroxyethylene isosteres], taxoids, polyamines, poly(amino alcohol)s and poly(amino ether)s, and other biologically active compounds through applications of the beta-lactam synthon method is reviewed.

关键词： 蒎烯   手性   硼氢化试剂   不对称合成   还原  

摘要： 对近年来以α－蒎烯类手性硼作还原剂的不对称还原反应作一综述，包括五大类共１１种α－蒎烯类手性还原剂．