The Experts below are selected from a list of 84 Experts worldwide ranked by ideXlab platform
David Saman - One of the best experts on this subject based on the ideXlab platform.
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koenigs Knorr Synthesis of cycloalkyl glycosides
Molecules, 2004Co-Authors: Zdenek Wimmer, Lucie Pechova, David SamanAbstract:Abstract: Cadmium carbonate was found to be a useful promoter in the Koenigs-Knorr Synthesis of 2-(4-methoxybenzyl)cyclohexyl-β- D -glycopyranosides. Using this promoter model glucoside and galactoside derivatives of cyclic (i.e., secondary) alcohols were synthesized in 50–60 % overall yields. Diastereoisomeric mixtures of products were obtained in these syntheses, which started from racemic isomers of 2-(4-methoxy-benzyl)cyclohexanol. The prepared compounds have been purified and characterized by their 1 H- and 13 C-NMR spectra, as well as by their IR and MS spectra, in order to use them as reference compounds in planned subsequent research. Keywords: Koenigs-Knorr Synthesis; Cycloalkyl-β- D -glucopyranosides; Cycloalkyl-β- D -galactopyranosides; Cadmium carbonate. Introduction The Koenigs-Knorr method for the Synthesis of glycosides and alkyl glycosides probably represents the most widely used procedure in the chemistry of carbohydrate derivatives. Application of the Koenigs-Knorr method confers a strong glycosyl donor character to the activated species by exchange of the anomeric hydroxyl functionality by a bromine or chlorine atom in the activation step [1-3]. The α-halosubstituted carbohydrate generated in the activation step, can be readily further activated in the glycosylation step by halophilic promoters, i.e. heavy metal salts, resulting in an irreversible glycosyl transfer to the acceptor. This method is the basis of a valuable technique for the
Zdenek Wimmer - One of the best experts on this subject based on the ideXlab platform.
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koenigs Knorr Synthesis of cycloalkyl glycosides
Molecules, 2004Co-Authors: Zdenek Wimmer, Lucie Pechova, David SamanAbstract:Abstract: Cadmium carbonate was found to be a useful promoter in the Koenigs-Knorr Synthesis of 2-(4-methoxybenzyl)cyclohexyl-β- D -glycopyranosides. Using this promoter model glucoside and galactoside derivatives of cyclic (i.e., secondary) alcohols were synthesized in 50–60 % overall yields. Diastereoisomeric mixtures of products were obtained in these syntheses, which started from racemic isomers of 2-(4-methoxy-benzyl)cyclohexanol. The prepared compounds have been purified and characterized by their 1 H- and 13 C-NMR spectra, as well as by their IR and MS spectra, in order to use them as reference compounds in planned subsequent research. Keywords: Koenigs-Knorr Synthesis; Cycloalkyl-β- D -glucopyranosides; Cycloalkyl-β- D -galactopyranosides; Cadmium carbonate. Introduction The Koenigs-Knorr method for the Synthesis of glycosides and alkyl glycosides probably represents the most widely used procedure in the chemistry of carbohydrate derivatives. Application of the Koenigs-Knorr method confers a strong glycosyl donor character to the activated species by exchange of the anomeric hydroxyl functionality by a bromine or chlorine atom in the activation step [1-3]. The α-halosubstituted carbohydrate generated in the activation step, can be readily further activated in the glycosylation step by halophilic promoters, i.e. heavy metal salts, resulting in an irreversible glycosyl transfer to the acceptor. This method is the basis of a valuable technique for the
Doyle G Graham - One of the best experts on this subject based on the ideXlab platform.
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intermediates in the paal Knorr Synthesis of pyrroles 4 oxoaldehydes
Chemical Research in Toxicology, 1995Co-Authors: Venkataraman Amarnath, Kalyani Amarnath, William M Valentine, Michael A Eng, Doyle G GrahamAbstract:The mechanism of pyrrole formation between a 4-ketoaldehyde, such as 4-oxohexanal (4), and a primary amine is examined. In organic solvents 4 readily formed the imine 6 that decomposed to pyrrole 9. In phosphate buffer (pH 7.4) the presence of deuteriums in the dideuterio (4-d2) and hexadeuterio (4-d6) analogs retarded the reaction rate by factors of 1.9 and 2.6, which are much less than the isotope effects exhibited by reactions involving cleavage of the carbon-hydrogen bond. Moreover, the deuterium labels from the uncyclized ketoaldehyde remained intact. These results suggest that the hemiaminal 5 rather than the enamine 8 is the intermediate undergoing cyclization. Due to the absence of a methyl substituent at one of the carbonyls the rate of pyrrole formation of 4-oxohexanal was 2 orders of magnitude larger than that of 2,5-hexanedione. The higher rate of pyrrole formation may account for the increased rate of pyrrole-mediated cross-linking of proteins caused by gamma-ketoaldehydes relative to gamma-diketones.
Lucie Pechova - One of the best experts on this subject based on the ideXlab platform.
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koenigs Knorr Synthesis of cycloalkyl glycosides
Molecules, 2004Co-Authors: Zdenek Wimmer, Lucie Pechova, David SamanAbstract:Abstract: Cadmium carbonate was found to be a useful promoter in the Koenigs-Knorr Synthesis of 2-(4-methoxybenzyl)cyclohexyl-β- D -glycopyranosides. Using this promoter model glucoside and galactoside derivatives of cyclic (i.e., secondary) alcohols were synthesized in 50–60 % overall yields. Diastereoisomeric mixtures of products were obtained in these syntheses, which started from racemic isomers of 2-(4-methoxy-benzyl)cyclohexanol. The prepared compounds have been purified and characterized by their 1 H- and 13 C-NMR spectra, as well as by their IR and MS spectra, in order to use them as reference compounds in planned subsequent research. Keywords: Koenigs-Knorr Synthesis; Cycloalkyl-β- D -glucopyranosides; Cycloalkyl-β- D -galactopyranosides; Cadmium carbonate. Introduction The Koenigs-Knorr method for the Synthesis of glycosides and alkyl glycosides probably represents the most widely used procedure in the chemistry of carbohydrate derivatives. Application of the Koenigs-Knorr method confers a strong glycosyl donor character to the activated species by exchange of the anomeric hydroxyl functionality by a bromine or chlorine atom in the activation step [1-3]. The α-halosubstituted carbohydrate generated in the activation step, can be readily further activated in the glycosylation step by halophilic promoters, i.e. heavy metal salts, resulting in an irreversible glycosyl transfer to the acceptor. This method is the basis of a valuable technique for the
Yves Janin - One of the best experts on this subject based on the ideXlab platform.
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On the Knorr Synthesis of 6-bromo-4-methylquinolin-2(1H)-one
SYNTHESIS, 2011Co-Authors: Nicolas Wlodarczyk, Catherine Simenel, Muriel Delepierre, Jean-christophe Barale, Yves JaninAbstract:In the course of our work on infectious diseases, we were led to prepare 6-bromo-2-chloro-4-methylquinoline as a starting material. Since surprisingly little has been reported in the literature, the two synthetic steps to this compound were investigated. The Synthesis involves a condensation between -ketoesters and 4-bromoaniline and the cyclization of the resulting anilides into 6-bromoquinolin-2(1H)-one otherwise known as the Knorr reaction. The 1H NMR monitoring of the first step allowed us to optimize the conditions leading specifically to the anilide without the occurrence of the alternative crotonate. To illustrate the scope of our finding, few additional anilides featuring electron attracting groups were prepared. The study of their cyclization revealed some unsuspected steric effect governing this second step. Aside from rectifying few claims in this chemistry, this study led to a three-step preparation of 6-bromo-2-chloro-4-methylquinoline in a 48 % overall yield from 4-bromoaniline.
