The Experts below are selected from a list of 90 Experts worldwide ranked by ideXlab platform
F G West - One of the best experts on this subject based on the ideXlab platform.
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Asymmetric synthesis of (+)-laurencin using a stereoselective Stevens [1,2]-shift of a sulfonium ylide
Strategies and Tactics in Organic Synthesis, 2020Co-Authors: F G WestAbstract:Abstract This chapter describes a novel approach to medium-sized cyclic ethers using a Stevens [1,2]-shift of a sulfonium ylide derived from a readily accessible 1,3-oxathiane (Monothioacetal) precursor with a pendent diazoketoester group. The concise and efficient transformation offered a high degree of chirality transfer and provided sulfur-bridged eight-membered cyclic ethers with retention of configuration at the migrating anomeric center. The resulting sulfur bridge could be conveniently removed by reductive desulfurization to furnish a highly functionalized eight-membered cyclic ether. This transformation has been applied as the key step in an asymmetric formal synthesis of (+)-laurencin by intercepting an advanced intermediate in the total synthesis by Holmes.
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medium sized cyclic ethers via stevens 1 2 shift of mixed Monothioacetal derived sulfonium ylides application to formal synthesis of laurencin
Organic Letters, 2017Co-Authors: F G WestAbstract:A novel approach to medium-sized cyclic ethers was devised using a Stevens [1,2]-shift of a sulfonium ylide derived from a readily accessible six-membered mixed-Monothioacetal precursor. The concise and efficient transformation offers a surprising degree of chirality transfer with observed retention of stereochemical configuration on the anomeric migrating carbon and has been applied as the key step in an enantioselective formal synthesis of (+)-laurencin.
Philippe Retif - One of the best experts on this subject based on the ideXlab platform.
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functional polythiiranes 6 hydrolysis of side chains ester and Monothioacetal functions of comb like polythiiranes
Reactive & Functional Polymers, 1999Co-Authors: Chantal Bonnansplaisance, Philippe RetifAbstract:The hydrolysis of comb-like polymers with polythiirane main chains and PEO side chains linked with Monothioacetal function or ester function was studied in various conditions. The Monothioacetal link exhibited a rather good stability except in very acidic conditions. In a buffered medium, acidic as well as basic, the hydrolysis of the ester link was degenerated first order. In basic stoichiometric conditions the kinetics is second order and a ionic strength effect was evidenced. The energy of activation was also evaluated in these conditions.
Hideya Yuasa - One of the best experts on this subject based on the ideXlab platform.
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synthesis of methyl 5 thio α isomaltoside via an acyclic Monothioacetal and its behavior toward glucoamylase
Chemistry: A European Journal, 1996Co-Authors: Hironobu Hashimoto, Masashi Kawanishi, Hideya YuasaAbstract:: Methyl 5'-thio-α-isomaltoside (1), which contains the ring-sulfur analogue of the nonreducing glucoside of isomaltose, was synthesized from gentiobiose through a novel ring opening-recyclization approach. The nonreducing glucoside of per-O-benzylated phenyl 1-thio-β-gentiobioside underwent O-5'-C-1' bond cleavage with dimethyl-boron bromide and thiolacetic acid to give the acyclic Monothioacetal 4 with the 1-thioglucopyranoside at the reducing end intact. The HO-5' group in 4 was inverted by a standard oxidation-reduction process with good efficiency. Recyclization under Mitsunobu condition allowed C-5'-S-1' bond formation with inversion of configuration at C-5', to give 1 after functional group interconversion. TLC analysis showed that 1, unlike isomaltose, was not hydrolyzed by glucoamylase from Rhizopus niveus. A fluorometric assay confirmed that the dissociation constant (Kd ) for 1 with the enzyme was 39 mM at 20°C, which is comparable with that for isomaltose. A binding assay involving fluorescence titration of the enzyme-1 complex with gluconolactone indicated that the disaccharide 1 was bound to the catalytic and noncatalytic subsites. Since isomaltose is known to bind only to the noncatalytic subsites, this result indicates a relatively high affinity of the 5-thioglucose moiety for the catalytic subsite.
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Novel conversion of aldopyranosides into 5-thioaldopyranosides via acyclic Monothioacetals with inversion and retention of configuration at C-5
Carbohydrate Research, 1996Co-Authors: Hironobu Hashimoto, Masashi Kawanishi, Hideya YuasaAbstract:Abstract A new strategy for synthesis of 5-thioaldopyranosides was developed. This included the ring opening of d-aldopyranosides with dimethylboron bromide and thioacetic acid, giving the acyclic Monothioacetals, followed by the intramolecular cyclization between C-5 and 1-S. Cyclization with inversion of configuration at C-5 was achieved by simultaneous S -deacetylation and intramolecular nucleophilic substitution of the 5-methanesulfonylated Monothioacetal to give 5-thio-1-aldopyranosides. The 5-hydroxyMonothioacetal underwent cyclization with the Mitsunobu reagents to give the same 5-thio-1.-aldopyranosides. Syntheses of 5-thio-d-glucopyranosides were achieved by double inversion of C-5. The glycos-5-ulose derivatives of the Monothioacetals spontaneously cyclized on S -deacetylation to give 5- C -hydroxyl-5-thio- d -glucopyranosides, which were deoxygenated at C-5 to give 5-thio-d-glucopyranosides, with net retention of configuration at C-5 from the Monothioacetal. Stereoselective reduction of glycos-5-ulose followed by intramolecular cyclization with the Mitsunobu reagents also gave 5-thio-d-glucopyranosides. The strategy for l enantiomers was applied to the synthesis of 5-thio-l-galactose. The inhibitory effect of 5-thio-lgalactose toward α-l-fucosidase ( K i 960 μ M) is also reported.
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new and facile synthetic routes to 5 thioaldohexopyranosides via aldose Monothioacetal derivatives
Tetrahedron Letters, 1991Co-Authors: Hironobu Hashimoto, Masashi Kawanishi, Hideya YuasaAbstract:Abstract Two new synthetic routes of 5-thioaldohexopyranosides were developed via aldose S-acetyl O-methyl Monothioacetals obtained by one-pot treatment of methyl hexopyranosides with dimethylboron bromide and then thiolacetic acid.
Chantal Bonnansplaisance - One of the best experts on this subject based on the ideXlab platform.
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functional polythiiranes 6 hydrolysis of side chains ester and Monothioacetal functions of comb like polythiiranes
Reactive & Functional Polymers, 1999Co-Authors: Chantal Bonnansplaisance, Philippe RetifAbstract:The hydrolysis of comb-like polymers with polythiirane main chains and PEO side chains linked with Monothioacetal function or ester function was studied in various conditions. The Monothioacetal link exhibited a rather good stability except in very acidic conditions. In a buffered medium, acidic as well as basic, the hydrolysis of the ester link was degenerated first order. In basic stoichiometric conditions the kinetics is second order and a ionic strength effect was evidenced. The energy of activation was also evaluated in these conditions.
Hironobu Hashimoto - One of the best experts on this subject based on the ideXlab platform.
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synthesis of methyl 5 thio α isomaltoside via an acyclic Monothioacetal and its behavior toward glucoamylase
Chemistry: A European Journal, 1996Co-Authors: Hironobu Hashimoto, Masashi Kawanishi, Hideya YuasaAbstract:: Methyl 5'-thio-α-isomaltoside (1), which contains the ring-sulfur analogue of the nonreducing glucoside of isomaltose, was synthesized from gentiobiose through a novel ring opening-recyclization approach. The nonreducing glucoside of per-O-benzylated phenyl 1-thio-β-gentiobioside underwent O-5'-C-1' bond cleavage with dimethyl-boron bromide and thiolacetic acid to give the acyclic Monothioacetal 4 with the 1-thioglucopyranoside at the reducing end intact. The HO-5' group in 4 was inverted by a standard oxidation-reduction process with good efficiency. Recyclization under Mitsunobu condition allowed C-5'-S-1' bond formation with inversion of configuration at C-5', to give 1 after functional group interconversion. TLC analysis showed that 1, unlike isomaltose, was not hydrolyzed by glucoamylase from Rhizopus niveus. A fluorometric assay confirmed that the dissociation constant (Kd ) for 1 with the enzyme was 39 mM at 20°C, which is comparable with that for isomaltose. A binding assay involving fluorescence titration of the enzyme-1 complex with gluconolactone indicated that the disaccharide 1 was bound to the catalytic and noncatalytic subsites. Since isomaltose is known to bind only to the noncatalytic subsites, this result indicates a relatively high affinity of the 5-thioglucose moiety for the catalytic subsite.
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Novel conversion of aldopyranosides into 5-thioaldopyranosides via acyclic Monothioacetals with inversion and retention of configuration at C-5
Carbohydrate Research, 1996Co-Authors: Hironobu Hashimoto, Masashi Kawanishi, Hideya YuasaAbstract:Abstract A new strategy for synthesis of 5-thioaldopyranosides was developed. This included the ring opening of d-aldopyranosides with dimethylboron bromide and thioacetic acid, giving the acyclic Monothioacetals, followed by the intramolecular cyclization between C-5 and 1-S. Cyclization with inversion of configuration at C-5 was achieved by simultaneous S -deacetylation and intramolecular nucleophilic substitution of the 5-methanesulfonylated Monothioacetal to give 5-thio-1-aldopyranosides. The 5-hydroxyMonothioacetal underwent cyclization with the Mitsunobu reagents to give the same 5-thio-1.-aldopyranosides. Syntheses of 5-thio-d-glucopyranosides were achieved by double inversion of C-5. The glycos-5-ulose derivatives of the Monothioacetals spontaneously cyclized on S -deacetylation to give 5- C -hydroxyl-5-thio- d -glucopyranosides, which were deoxygenated at C-5 to give 5-thio-d-glucopyranosides, with net retention of configuration at C-5 from the Monothioacetal. Stereoselective reduction of glycos-5-ulose followed by intramolecular cyclization with the Mitsunobu reagents also gave 5-thio-d-glucopyranosides. The strategy for l enantiomers was applied to the synthesis of 5-thio-l-galactose. The inhibitory effect of 5-thio-lgalactose toward α-l-fucosidase ( K i 960 μ M) is also reported.
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new and facile synthetic routes to 5 thioaldohexopyranosides via aldose Monothioacetal derivatives
Tetrahedron Letters, 1991Co-Authors: Hironobu Hashimoto, Masashi Kawanishi, Hideya YuasaAbstract:Abstract Two new synthetic routes of 5-thioaldohexopyranosides were developed via aldose S-acetyl O-methyl Monothioacetals obtained by one-pot treatment of methyl hexopyranosides with dimethylboron bromide and then thiolacetic acid.