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- Aplander, Karolina, et al.
(författare)
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Asymmetric Lewis Acid Catalysis in Water: alpha-Amino Acids as Effective Ligands in Aqueous Biphasic Catalytic Michael Additions
- 2009
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Ingår i: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; :6, s. 810-821
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Tidskriftsartikel (refereegranskat)abstract
- This article explores the potential of native a-amino acids as chiral ligands in aqueous asymmetric Lewis acid catalysis, employing the C-C bond forming Michael addition as a model reaction. Some insights are provided regarding the details of Yb(OTf)(3)/alpha-amino acid-catalyzed Michael additions in water through new kinetic data as well as studies on how both yield and selectivity are influenced by variations in metal/ligand ratio, pH, temperature, and structure of the a-amino acid, Through this investigation it was found that reaction conditions that require only 5 mol-% of the Lewis acid, provides enantiomeric excesses of up to 79 % and is applicable to a wider range of donors and acceptors than previously demonstrated. Importantly, it was also demonstrated that the a-amino acid complexed ytterbium. catalyst might have potential for large-scale applications as it displays not only large ligand accelerations, but also good solubility and stability in water. It can be recycled multiple times without appreciable loss of activity. The result is a promising example of a water-compatible chiral Lewis acid. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
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- Aplander, Karolina, et al.
(författare)
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Entropy-Controlled and Enantiodivergent Lewis Acid Catalysis in Water
- 2012
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Ingår i: Synthesis. - : Georg Thieme Verlag KG. - 0039-7881 .- 1437-210X. ; 44:6, s. 848-856
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Tidskriftsartikel (refereegranskat)abstract
- Developing new and useful methods in asymmetric catalysis is of continuous importance. A current challenge is to address the imperatives of green chemistry, such that processes maximize resource-efficiency and minimize the generation of waste. To this end, this article discloses the potential of alpha-amino acids in the development of entropy-controlled and enantiodivergent Lewis acid catalysis. In an ytterbium-catalyzed aqueous Michael addition reaction, natural alpha-amino acids induced not only a large rate acceleration, but also an unusual and remarkable reversed temperature effect on enantioselectivity. As demonstrated with 17 alpha-amino acids, the enantioselectivity of the reaction can be significantly altered, and even reversed, simply by modifying the reaction temperature. After determining differential thermodynamic activation parameters, it was revealed that an unusually large entropy contribution was responsible for the observed effects. By further correlation to the influence of the aqueous medium, we put forward the concept of stereospecific aqueous solvation (SAS), which describes the bearing of aqueous solvation on the equilibrium of diastereomeric transition states, and thus on the R/S ratio of the product.
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- Aplander, Karolina, et al.
(författare)
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Molecular wipes : application to epidemic keratoconjuctivitis
- 2011
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Ingår i: Journal of Medicinal Chemistry. - Easton, Pa. : American Chemical Society. - 0022-2623 .- 1520-4804. ; 54:19, s. 6670-6675
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Tidskriftsartikel (refereegranskat)abstract
- Epidemic keratoconjunctivitis (EKC) is a severe disease of the eye, caused by members of the Adenoviridae (Ad) family, with symptoms such as keratitis, conjunctivitis, pain, edema, and reduced vision that may last for months or years. There are no vaccines or antiviral drugs available to prevent or treat EKC. It was found previously that EKC-causing Ads use sialic acid as a cellular receptor and demonstrated that soluble, sialic acid-containing molecules can prevent infection. In this study, multivalent sialic acid constructs based on 10,12-pentacosadiynoic acid (PDA) have been synthesized, and these constructs are shown to be efficient inhibitors of Ad binding (IC(50) = 0.9 mu M) and Ad infectivity (IC(50) = 0.7 mu M). The mechanism of action is to aggregate virus particles and thereby prevent them from binding to ocular cells. Such formulations may be used for topical treatment of adenovirus-caused EKC.
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- Aplander, Karolina
(författare)
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Organic synthesis in water - Investigations of Lewis acid catalysis and chiral hydrophobic auxiliaries in aqueous Michael additions
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Asymmetrisk katalys har under de senaste decennierna utvecklats kraftigt. År 2001 delade Knowles, Noyori och Sharpless Nobelpriset i kemi för sina banbrytande bidrag inom just detta område. Utmaningen idag är att utveckla nya metoder inom asymmetrisk katalys som även tar hänsyn till vår växande miljöpåfrestning. Nästan alla av dagens kirala katalysatorer är utvecklade för syntes i organiska lösningsmedel, vilket innebär en negativ effekt på både miljö och hälsa In recent years, the improvement of new and practical strategies in asymmetric catalysis has been in the forefront of organic chemistry. The challenge for organic chemists in the 21st century is to apply these strategies to Green Chemistry, such as being resource-efficient and to minimize the production of waste. When the interest in water as a solvent was rejuvenated in the 1990's the concept ?Green Chemistry? was first introduced. Water as a nontoxic, cheap and environmentally benign reaction medium has called for the development of new and practical methods of asymmetric catalysis in aqueous media. The Michael addition is one of the most important C-C bond-forming reactions and since the reaction often leads to a stereogenic center, efforts have been devoted to making the reaction enantioselective. The primary intention with the work presented in this thesis, was to investigate the potential of natural ?-amino acids as chiral ligands in asymmetric Yb(OTf)3-catalyzed Michael additions in aqueous media. We have tried to clarify the details of this reaction through kinetic data as well as studies on how yield and selectivity were influenced by variations in metal/ligand ratio, pH, temperature and ?-amino acids. We found large ligand acceleration for the ?-amino acid complexed Yb(OTf)3-catalysts as well as reversed temperature effects on selectivity for almost all ?-amino acids tested. Various chiral hydrophobic auxiliaries were also synthesized and stereoselectivity in aqueous Michael reactions was observed for some of them.
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