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41.
The short and efficient asymmetric synthesis of (-)-1-hydroxyquinolizidinone was achieved in seven steps and 25.2% overall yield from readily available 5-chloropentanal. It is a key intermediate in the formal syntheses of (-)-homopumilotoxin 223G and (-)-epiquinamide. 相似文献
42.
Prof. Dr. Yolanda Arroyo Prof. Dr. M. Ascensión Sanz‐Tejedor Dr. Alejandro Parra Prof. Dr. José Luis García Ruano 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(17):5314-5318
Asymmetric nucleophilic monofluoroalkylation of a broad range of aldehydes with an α‐fluoro‐γ‐sulfinylbenzyl carbanion takes place with complete control of the facial selectivity at the carbanion and good to high anti‐diastereoselectivity to give easily separable mixtures of two optically pure 1,2‐fluorohydrin derivatives (up to 24:1 anti/syn). Separation and removal of the p‐tolylsulfinyl group with tBuLi provides enantiomerically pure anti‐1,2‐disubstituted‐1,2‐fluorohydrins, whereas α‐fluorobenzylketones can be obtained by desulfinylation of the mixture followed by pyridinium chlorochromate oxidation (one‐pot process). 相似文献
43.
José Alejandro Sánchez-Gutiérrez Monserrat Vázquez-Sánchez Dioselina Álvarez-Bernal María Daniela Mares-Quiñones Juan Ignacio Valiente-Banuet 《Analytical letters》2018,51(13):1986-1998
The total phenolic and flavonoid content, phenolic composition, and in vitro antioxidant capacity of ethanolic extracts of Ximenia parviflora Benth. var. parviflora fruits collected at Zinaparo, Michoacan (in central Mexico) were determined. Fruit extracts present a high scavenging activity of 2,2-diphenyl-1-picrylhydrazyl and 2,2′-azino-bis[3-ethylbenzothiazoline-6-sulfonic acid] radicals (71.49?±?0.11% and 85.00?±?1.29% inhibition, respectively). The four phenolic compounds identified in fruit extracts by high-performance liquid chromatography with diode array detection were gallic acid, chlorogenic acid, caffeic acid, and quercetin. X. parviflora fruits may be used as a starting material for the extraction of high value antioxidant phenolic compounds with potential applications in the pharmaceutical and dietary supplement industries. 相似文献
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The reactivity of 2,3-dehydroproline and 2,3-dehydropipecolic acid methyl ester derivatives with S-nucleophiles in the thio-Michael addition reaction has been explored. The addition of triphenylmethanethiol and subsequent trityl cleavage led to the corresponding cis- and trans-(±)-3-mercaptoproline and pipecolic acid derivatives in good yields. 相似文献
48.
Gustavo Hernández-Vargas César Alejandro Ponce-Ponce de León José González-Valdez Hafiz M. N. Iqbal 《Separation & Purification Reviews》2018,47(3):199-213
In recent years, smart polymers (SPs), which are also referred to as bio-responsive polymers, have gained considerable attention as a unique class of polymers and their applications have been increasing significantly. These so-called “smart” polymers, either synthetic or biological, have been defined as “polymers designed to respond or undergo physical and structural conformational changes/rearrangement in response to slight changes in their surrounding environment”. They are categorized as thermo-, pH-, electro- and magneto-responsive polymers. The advances in upstream bio-production stages and the high cost associated with downstream chromatographic techniques have pushed the development of new alternatives. In this context, the use of SPs, in combination with non-chromatographic technologies, represents a useful approach to the development of new downstream operation units. With the key scientific advancements, SPs have become the “next generation” of the bio-separation tool for eco-friendlier and cost-effective purification. This review describes the different characteristics and classifications of various “smart” polymers available for use in bio-separation strategy. Focus is also given to the recent advances in SP inclusion in the improvement of alternative non-chromatographic methods in downstream bioprocessings. 相似文献
49.
Alejandro R. Engelmann Mario A. Natiello Mikael Hghede Erik Engdahl Erkki Brndas 《International journal of quantum chemistry》1987,31(5):841-845
In the present article we show how the bound states of the Coulomb potential may be associated with resonances that occur when this potential is perturbed by a barrier potential. The main idea is to trace the bound states on successive switching on of the barrier perturbation. It is found that those bound states that are localized inside the barrier are highly sensitive to variation with respect to the barrier height, whereas those that are localized outside are less sensitive. However, there are certain intervals for the barrier height when the role of being “a state localized inside the barrier” is shifted from one bound state to another. The result can be pictured as a “relay race,” where the “deliveries of the baton” are carried out over corresponding avoided crossings. The baton is ultimately handed over to a shape-type resonance state. 相似文献
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