- CHIRAL BINUCLEAR METAL COMPLEXES FOR STEREOSELECTIVE GLYCOSIDE HYDROLYSIS OF SACCHARIDES
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Disclosed herein is a class of chiral binuclear metal complexes for stereoselective glycoside hydrolysis of saccharides, and more particular chiral binuclear transition metal complex catalysts that discriminate epimeric glycosides and α- and β-glycosidic bonds of saccharides in aqueous solutions at near physiological pHs. The chiral binuclear metal complexes include a Schiff-base-type ligand derived from a chiral diamino building block, and a binuclear transition metal core, each which can be varied for selectivity. The metal core is a Lewis-acidic metal ion, such as copper, zinc, lanthanum, iron and nickel. The Schiff-base may be a reduced or non-reduced Schiff-base derived from aliphatic linear, aliphatic cyclic diamino alcohols or aromatic aldehydes. The ligand can be a penta- or heptadentate ligand derived from pyridinecarbaldehydes, benzaldehydes, linear or cyclic diamines or diamino alcohols.
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Paragraph 0044; 0047
(2017/10/13)
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- Binuclear copper(II) complexes discriminating epimeric glycosides and α- And β-glycosidic bonds in aqueous solution
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Two chiral binuclear copper(II) complexes were synthesized and characterized for the first time as efficient chemoselective catalysts for the hydrolysis of aryl glycosides and disaccharides in aqueous solution at near neutral pH. Under these conditions, discrimination of epimeric aryl α-glycopyranosides was observed by both 29-fold different reaction rates and 3-fold different proficiency of the catalyst. Additionally, large differentiation of the nature of α- and β-glycosidic bond in aryl glycosides as model compounds is apparent, but also noted in selected disaccharides. The influence of the chirality of the complexes and the role of the configuration of the carbohydrate upon interaction with the catalyst is discussed in detail. Lastly, a putative mechanism for the metal complex-catalyzed hydrolysis is derived from the experimental evidence pointing at deprotonation of the hydroxyl group at C-2 as a pre-requisite for glycoside hydrolysis.
- Striegler, Susanne,Fan, Qiu-Hua,Rath, Nigam P.
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p. 349 - 364
(2016/05/24)
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- Versatile Synthesis of Stereospecifically Labelled D-Amino Acids via Labelled Aziridines - Preparation of (2R,3S)-- and (2R,3R)--Serine; (2S,2'S,3S,3'S)-- and (2S,2'S,3R,3'R)--Cystine; and (2S,3S)- and (2S,3R)--β-Chloroalanine
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Stereospecifically β-labelled protected 2-carboxyaziridines 2, with the stereochemistry of a D-amino acid at C-2, have been prepared by a chemicoenzymic synthesis.Preparation of the labelled malates 5, by hydration of fumaric acid using the enzyme fumarase or by amination with aspartase followed by nitrosation, was followed by conversion into the isoserines 3, by a process involving Curtius rearrangement with retention of stereochemistry at the chirally labelled primary centre.Protection and ring closure gave the aziridines 2, which, on ring opening with the appropriate nucleophiles and deprotection, gave stereospecifically labelled samples of D-serine 16, D-cystine 20 and β-chloro-D-alanine 22.
- Axelsson, B. Svante,O'Toole, Kevin J.,Spencer, Philip A.,Young, Douglas W.
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p. 807 - 816
(2007/10/02)
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