The Experts below are selected from a list of 3267 Experts worldwide ranked by ideXlab platform
Eiji Yashima - One of the best experts on this subject based on the ideXlab platform.
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remarkable enhancement of the enantioselectivity of an organocatalyzed asymmetric henry reaction assisted by helical poly phenylacetylene s bearing cinchona alkaloid pendants via an Amide Linkage
ACS Macro Letters, 2012Co-Authors: Zhenglin Tang, Hiroki Iida, Eiji YashimaAbstract:A series of novel helical poly(phenylacetylene)s bearing amino-functionalized cinchona alkaloid pendant groups connecting to the phenyl rings through an Amide Linkage were prepared by the polymerization of the corresponding phenylacetylenes using a rhodium catalyst. All of the polymers formed a preferred-handed helical conformation biased by the optically active pendants, resulting in the induced circular dichroism in their π-conjugated polymer backbone regions. The optically active helical polymers efficiently catalyzed the asymmetric Henry reaction of benzaldehydes with nitromethane, giving optically active products up to 94% enantiomeric excess (ee) when the poly(phenylacetylene) bearing an amino-functionalized quinine pendant group was used as the polymeric organocatalyst; the enantioselectivity was remarkably higher than those catalyzed by the corresponding nonhelical poly(phenylacetylene) (18% ee) and the monomer (28% ee).
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stimuli responsive helical poly phenylacetylene s bearing cyclodextrin pendants that exhibit enantioselective gelation in response to chirality of a chiral amine and hierarchical super structured helix formation
Macromolecules, 2011Co-Authors: Katsuhiro Maeda, Hiroaki Mochizuki, Keiko Osato, Eiji YashimaAbstract:Novel poly(phenylacetylene)s bearing a β-cyclodextrin (CyD) residue connected to the phenyl ring through an ester (poly-2β) and an ether Linkage (poly-3β) as well as an Amide Linkage (poly-1β) were synthesized and their chiroptical properties were investigated with circular dichroism (CD) and absorption spectroscopies. The chiroptical studies demonstrated that the Linkage groups play an important role in the conformational change induced by external chiral and achiral stimuli, such as temperature, solvent, and interactions with a chiral amine. Poly-1β and poly-2β showed a unique enantioselective gelation in response to the chirality of a chiral amine, and the polymers further formed hierarchical superstructured helical assemblies on a micrometer scale with a controlled helix sense, as evidenced by the scanning electron microscopy observations.
Gaetano Giammona - One of the best experts on this subject based on the ideXlab platform.
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synthesis mechanical and thermal rheological properties of new gellan gum derivatives
International Journal of Biological Macromolecules, 2017Co-Authors: Stefano Agnello, Luca Gasperini, Joao F Mano, Giovanna Pitarresi, Fabio Salvatore Palumbo, Rui L Reis, Gaetano GiammonaAbstract:New derivatives of gellan gum (GG) were prepared by covalent attachment of octadecylamine (C18-NH2) to polysaccharide backbone via Amide Linkage by using bis(4-nitrophenyl) carbonate (4-NPBC) as a coupling agent. The effect of the alkyl chain grafted onto hydrophilic backbone of high molecular weight GG was investigated in terms of physicochemical properties and ability of new derivatives to form hydrogels. A series of hydrogels was obtained in solutions with different kind and concentration of ions and their stability and mechanical properties were evaluated. The obtained derivatives resulted soluble at temperature lower than starting GG and physicochemical properties of obtained hydrogels suggested their potential use in biomedical field.
Norbert Sewald - One of the best experts on this subject based on the ideXlab platform.
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"Clicktophycin-52": a bioactive cryptophycin-52 triazole analogue.
Organic letters, 2010Co-Authors: Markus Nahrwold, Tobias Bogner, Stefan Eissler, Spart Verma, Norbert SewaldAbstract:An endocyclic trans-Amide Linkage within the macrocyclic antitumor agent cryptophycin-52 was replaced by a 1,4-disubstituted 1H-1,2,3-triazole ring. Macrocyclisation of the triazole analogue was accomplished by macrolactamization as well as by Cu(I)-mediated “click”-cyclization. Compared to cryptophycin-52, in vitro cytotoxicity of “clicktophycin-52” against the multidrug resistant human cancer cell line KB-V1 is only slightly reduced.
Squire J Booker - One of the best experts on this subject based on the ideXlab platform.
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mechanistic investigations of lipoic acid biosynthesis in escherichia coli both sulfur atoms in lipoic acid are contributed by the same lipoyl synthase polypeptide
Journal of the American Chemical Society, 2005Co-Authors: Robert M Cicchillo, Squire J BookerAbstract:Lipoyl synthase catalyzes the final step in the de novo biosynthesis of the lipoyl cofactor, which is the insertion of two sulfur atoms into an octanoyl chain that is bound in an Amide Linkage to a conserved lysine on a lipoyl-accepting protein. We show herein that the sulfur atoms in the lipoyl cofactor are derived from lipoyl synthase itself, and that each lipoyl synthase polypeptide contributes both of the sulfur atoms to the intact cofactor.
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lipoyl synthase requires two equivalents of s adenosyl l methionine to synthesize one equivalent of lipoic acid
Biochemistry, 2004Co-Authors: Robert M Cicchillo, David F Iwig, Daniel A Jones, Natasha M Nesbitt, Camelia Baleanugogonea, Matthew G Souder, Squire J BookerAbstract:Lipoyl synthase (LipA) catalyzes the formation of the lipoyl cofactor, which is employed by several multienzyme complexes for the oxidative decarboxylation of various α-keto acids, as well as the cleavage of glycine into CO2 and NH3, with concomitant transfer of its α-carbon to tetrahydrofolate, generating N5,N10-methylenetetrahydrofolate. In each case, the lipoyl cofactor is tethered covalently in an Amide Linkage to a conserved lysine residue located on a designated lipoyl-bearing subunit of the complex. Genetic and biochemical studies suggest that lipoyl synthase is a member of a newly established class of metalloenzymes that use S-adenosyl-l-methionine (AdoMet) as a source of a 5‘-deoxyadenosyl radical (5‘-dA•), which is an obligate intermediate in each reaction. These enzymes contain iron−sulfur clusters, which provide an electron during the cleavage of AdoMet, forming l-methionine in addition to the primary radical. Recently, one substrate for lipoyl synthase has been shown to be the octanoylated de...
Markus Nahrwold - One of the best experts on this subject based on the ideXlab platform.
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"Clicktophycin-52": a bioactive cryptophycin-52 triazole analogue.
Organic letters, 2010Co-Authors: Markus Nahrwold, Tobias Bogner, Stefan Eissler, Spart Verma, Norbert SewaldAbstract:An endocyclic trans-Amide Linkage within the macrocyclic antitumor agent cryptophycin-52 was replaced by a 1,4-disubstituted 1H-1,2,3-triazole ring. Macrocyclisation of the triazole analogue was accomplished by macrolactamization as well as by Cu(I)-mediated “click”-cyclization. Compared to cryptophycin-52, in vitro cytotoxicity of “clicktophycin-52” against the multidrug resistant human cancer cell line KB-V1 is only slightly reduced.