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Yasufumi Ohfune - One of the best experts on this subject based on the ideXlab platform.
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Asymmetric Synthesis of α-Substituted α-Amino Acids: Strecker and Claisen Approaches
2009Co-Authors: Yasufumi Ohfune, Kazuhiko Sakaguchi, Tetsuro ShinadaAbstract:Two efficient methods for the Synthesis of a class of optically active α-substituted α-amino acids developed in our laboratories are disclosed. An asymmetric version of the Strecker Synthesis of α-acyloxy ketones possessing an optically acitive amino acid as a chirality transferring acyl group produced acyclic and cyclic α-substituted serine analogs. Novel vinylsilane-containing α- or α,β-substinited α-amino acids were synthesized by the Claisen rearrangement of a-acyloxy-a-alkenylsilanes. These methods were used for the Synthesis of biologically active amino acids and natural products.
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on the stereoselectivity of asymmetric Strecker Synthesis in a cyclohexane system Synthesis of optically active cis and trans 1 amino 2 hydroxycyclohexane 1 carboxylic acids
Bulletin of the Chemical Society of Japan, 2006Co-Authors: Tetsuro Shinada, Kosuke Namba, Tadashi Kawakami, Hiroshi Sakai, Hiromi Matsuda, Taiki Umezawa, Masaki Kawasaki, Yasufumi OhfuneAbstract:Stereoselective Synthesis of both optically active cis- and fra/M-1-amino-2-hydroxycyclohexane-l-carboxylic acids (Ahhs) la and 1b was accomplished by an asymmetric version of the Strecker Synthesis. Stereochemical aspects of their chiral induction processes are investigated.
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asymmetric Strecker route toward the Synthesis of biologically active α α disubstituted α amino acids
Bulletin of the Chemical Society of Japan, 2003Co-Authors: Yasufumi Ohfune, Tetsuro ShinadaAbstract:A series of optically active α,α-disubstituted α-amino acids have been synthesized starting with an achiral or a racemic α-hydroxy or α-diazo ketone. In the present Synthesis, the key transformation is an asymmetric version of the Strecker Synthesis. An α-acyloxy ketone having a chiral amino acid as the acyloxy group afforded cyclic α-amino nitrile in a highly stereoselective manner; in this reaction the amino group and the chirality were diastereoselectively transplanted into the internal ketone group via an imine-enamine equilibrium of the cyclic ketimine intermediate. Oxidation of the amino group followed by removal of the resulting imino group and hydrolysis of the nitrile group afforded α-hydroxymethyl α-amino acid. The use of L-amino acid as the acyloxy group gave R enantiomer, and its S enantiomer was obtained when D-amino acid was employed. Some problematic processes that remained in the Strecker Synthesis, i.e., preparation of the starting α-acyloxy ketone and oxidative conversion of α-amino nitr...
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Efficient Synthesis of optically active α-substituted glutamate analogs possessing α-hydroxymethyl and α-alkoxymethyl groups
Tetrahedron Letters, 2003Co-Authors: Masanori Kawasaki, Kosuke Namba, Tetsuro Shinada, Hidekazu Tsujishima, Yasufumi OhfuneAbstract:Highly enantioselective Synthesis of (2R)-α-(hydroxymethyl)glutamate (1), a selective agonist of mGluR2 and 3, was achieved in short steps using an asymmetric version of the Strecker Synthesis. This was converted into its α-methoxymethyl- and α-benzyloxymethyl derivatives 2 and 3, possible ligands as tools to investigate glutamate receptors, via protection of the sterically hindered amino group by means of phase transfer catalyst.
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Novel and efficient transformation of α-amino nitrile to α-imino and α-amide nitriles in asymmetric Strecker Synthesis
Tetrahedron Letters, 2001Co-Authors: Kosuke Namba, Masanori Kawasaki, Ichinori Takada, Seiji Iwama, Masashi Izumida, Tetsuro Shinada, Yasufumi OhfuneAbstract:Abstract Oxidation of α-amino nitrile 4 with ozone gave rise to a mixture of α-imino nitrile 5 and a novel fragmentation product of 6 in one-step. The mixture was converted to a variety of α-substituted α-amino acids 7 in high yields, which enabled the asymmetric transferring Strecker Synthesis to be a widely useful method.
Tetsuro Shinada - One of the best experts on this subject based on the ideXlab platform.
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Asymmetric Synthesis of α-Substituted α-Amino Acids: Strecker and Claisen Approaches
2009Co-Authors: Yasufumi Ohfune, Kazuhiko Sakaguchi, Tetsuro ShinadaAbstract:Two efficient methods for the Synthesis of a class of optically active α-substituted α-amino acids developed in our laboratories are disclosed. An asymmetric version of the Strecker Synthesis of α-acyloxy ketones possessing an optically acitive amino acid as a chirality transferring acyl group produced acyclic and cyclic α-substituted serine analogs. Novel vinylsilane-containing α- or α,β-substinited α-amino acids were synthesized by the Claisen rearrangement of a-acyloxy-a-alkenylsilanes. These methods were used for the Synthesis of biologically active amino acids and natural products.
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Total Synthesis of (−)-5,6,11-Trideoxytetrodotoxin and Its 4-Epimer
Organic Letters, 2006Co-Authors: Taiki Umezawa, Masashi Izumida, Hiroshi Sakai, Toshihiro Hayashi, Hidetoshi Teramoto, Takeshi Yoshikawa, Yoshinori Tamatani, Tadashi Hirose, And Yasufumi Ohfune, Tetsuro ShinadaAbstract:The first total Synthesis of 5,6,11-trideoxytetrodotoxin (1) and its 4-epimer were achieved. The Synthesis is characterized by the stereoselective construction of the quaternary amino carbon center at C8a by an asymmetric transferring Strecker Synthesis and the highly efficient conversion of cyanohydrin 4 to 1 via intramolecular cyclization reactions.
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on the stereoselectivity of asymmetric Strecker Synthesis in a cyclohexane system Synthesis of optically active cis and trans 1 amino 2 hydroxycyclohexane 1 carboxylic acids
Bulletin of the Chemical Society of Japan, 2006Co-Authors: Tetsuro Shinada, Kosuke Namba, Tadashi Kawakami, Hiroshi Sakai, Hiromi Matsuda, Taiki Umezawa, Masaki Kawasaki, Yasufumi OhfuneAbstract:Stereoselective Synthesis of both optically active cis- and fra/M-1-amino-2-hydroxycyclohexane-l-carboxylic acids (Ahhs) la and 1b was accomplished by an asymmetric version of the Strecker Synthesis. Stereochemical aspects of their chiral induction processes are investigated.
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asymmetric Strecker route toward the Synthesis of biologically active α α disubstituted α amino acids
Bulletin of the Chemical Society of Japan, 2003Co-Authors: Yasufumi Ohfune, Tetsuro ShinadaAbstract:A series of optically active α,α-disubstituted α-amino acids have been synthesized starting with an achiral or a racemic α-hydroxy or α-diazo ketone. In the present Synthesis, the key transformation is an asymmetric version of the Strecker Synthesis. An α-acyloxy ketone having a chiral amino acid as the acyloxy group afforded cyclic α-amino nitrile in a highly stereoselective manner; in this reaction the amino group and the chirality were diastereoselectively transplanted into the internal ketone group via an imine-enamine equilibrium of the cyclic ketimine intermediate. Oxidation of the amino group followed by removal of the resulting imino group and hydrolysis of the nitrile group afforded α-hydroxymethyl α-amino acid. The use of L-amino acid as the acyloxy group gave R enantiomer, and its S enantiomer was obtained when D-amino acid was employed. Some problematic processes that remained in the Strecker Synthesis, i.e., preparation of the starting α-acyloxy ketone and oxidative conversion of α-amino nitr...
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Efficient Synthesis of optically active α-substituted glutamate analogs possessing α-hydroxymethyl and α-alkoxymethyl groups
Tetrahedron Letters, 2003Co-Authors: Masanori Kawasaki, Kosuke Namba, Tetsuro Shinada, Hidekazu Tsujishima, Yasufumi OhfuneAbstract:Highly enantioselective Synthesis of (2R)-α-(hydroxymethyl)glutamate (1), a selective agonist of mGluR2 and 3, was achieved in short steps using an asymmetric version of the Strecker Synthesis. This was converted into its α-methoxymethyl- and α-benzyloxymethyl derivatives 2 and 3, possible ligands as tools to investigate glutamate receptors, via protection of the sterically hindered amino group by means of phase transfer catalyst.
August W. Frahm - One of the best experts on this subject based on the ideXlab platform.
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Asymmetric Strecker Synthesis of enantiopure 2,4-ethanothreonines
Tetrahedron-asymmetry, 2004Co-Authors: Udo Meyer, E. Breitling, Philippe Bisel, August W. FrahmAbstract:Abstract The second generation asymmetric Synthesis reported herein proceeds via a Strecker reaction of chiral ketimines, obtained from the condensation of racemic 2-methoxycyclopentanone and (S)- and (R)-1-phenylethylamine. In the key stereodifferentiating step, the cyanide addition leads to mixtures of diastereomeric nitriles, the composition of which dramatically changes under the influence of protic and aprotic solvents. Hydrolysis of the nitriles to carboxamides with concd H2SO4 yielded diastereomeric mixtures of carboxamides each of which was hydrogenolysed and hydrolysed after separation to the four stereoisomers of the 1-amino-2-methoxy- and 1-amino-2-hydroxy-cyclopentanecarboxylic acid. Their stereochemistry was established by NMR methods and by X-ray analyses of the trans as well as the cis configured compounds.
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Cyclobutane amino acids (CBAAs): asymmetric Strecker Synthesis of enantiopure cis- and trans-2,4-methanovalines
Tetrahedron-asymmetry, 2003Co-Authors: Franz-j. Volk, Marita Wagner, August W. FrahmAbstract:Synthesis of enantiopure 2,4-methanovalines has been achieved by means of asymmetric Strecker Synthesis starting from racemic 2-methylcyclobutanone. The trans-configured α-amino acids were obtained from cyanide additions carried out in methanol, whereas the cis-configured 2,4-methanovalines were accessible via reactions in hexane. Relative stereochemistry was elucidated from NOESY experiments, while absolute configurations were assigned from X-ray crystallographic analysis.
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Asymmetric Synthesis and chromatographic resolution of all four stereomers of the alpha,beta-propanoleucine.
Die Pharmazie, 2001Co-Authors: Philippe Bisel, E. Breitling, M. Schlauch, August W. FrahmAbstract:The paper describes the first Synthesis of the enantiomerically pure cis-alpha,beta-propanoleucines 6c and 6d by means of asymmetric Strecker Synthesis. Furthermore, an improved procedure for the preparation of the stereomeric trans compounds 6a and 6b is proposed. Finally, the four feasible stereomeric alpha,alpha-quaternary-alpha-amino acids are resolved on a penicillamine based chiral stationary phase allowing the determination of ee values ranging from 92.9% to > 98%.
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Carbocyclic α-amino acids: asymmetric Strecker Synthesis of a series of 2-alkylated 1-aminocyclopentanecarboxylic acids
Tetrahedron-asymmetry, 2000Co-Authors: Judith Wede, Franz-j. Volk, August W. FrahmAbstract:Abstract A series of 12 carbocyclic α-amino acids has been prepared from four different racemic 2-alkylated cyclopentanones and ( R )-1-phenylethylamine as the chiral auxiliary by means of an asymmetric Strecker Synthesis. The stereoselectivity was influenced by solvent, temperature and size of the substituent at the 2-position of the cyclopentanones. For the methyl and ethyl substituted amino acids all four possible stereoisomers could be obtained, whereas for the isopropyl and tertiary butyl compounds an unexpected side reaction prohibited the isolation of the cis configured amino acids. The 1,3-induction mechanism observed for the kinetically controlled α-amino nitrile formation in the 2-methyl and 2-ethyl series was overlayed by a 1,2-induction in the respective 2-isopropyl and 2-tertiary butyl series.
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Carbocyclic α-amino acids: asymmetric Synthesis of all four 1-amino-2-hydroxycyclohexanecarboxylic acids
Tetrahedron-asymmetry, 1999Co-Authors: Kamalesh P. Fondekar, Franz-j. Volk, August W. FrahmAbstract:Abstract Starting from racemic 2-methoxycyclohexanone and ( S )- or ( R )-1-phenylethylamine, respectively, the four stereoisomers of 1-amino-2-hydroxycyclohexanecarboxylic acid are obtained via an asymmetric Strecker Synthesis with ee values ranging from 87 to 98%. Their stereochemistry is established by NMR methods and by X-ray analyses. Hydrogenolysis of a benzylic C–N bond by conc. sulphuric acid as well as cleavage of a methoxy ether by conc. HCl are two intriguing reactions which are observed within the five-step procedure described herein.
Ombretta Porta - One of the best experts on this subject based on the ideXlab platform.
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Free-radical version of the Strecker Synthesis of alpha-aminoamides promoted by aqueous H2O2/TiCl3/HCONH2 system.
Journal of the American Chemical Society, 2006Co-Authors: Rosalba Cannella, Angelo Clerici, Walter Panzeri, Nadia Pastori, Carlo Punta, Ombretta PortaAbstract:A new reaction of general synthetic interest representing the free-radical version of the Strecker Synthesis to α-aminoamides is reported. A hydroxy radical, generated by Ti(III) one-electron reduction of H2O2, abstracts a H atom from the C−H bond of formamide, and the resulting carbamoyl radical adds to the C atom of aldimines formed in situ, leading to a one-pot Synthesis of α-aminoamides. Several types of aldehydes can participate in this process.
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free radical version of the Strecker Synthesis of alpha aminoamides promoted by aqueous h2o2 ticl3 hconh2 system
Journal of the American Chemical Society, 2006Co-Authors: Rosalba Cannella, Angelo Clerici, Walter Panzeri, Nadia Pastori, Carlo Punta, Ombretta PortaAbstract:A new reaction of general synthetic interest representing the free-radical version of the Strecker Synthesis to α-aminoamides is reported. A hydroxy radical, generated by Ti(III) one-electron reduction of H2O2, abstracts a H atom from the C−H bond of formamide, and the resulting carbamoyl radical adds to the C atom of aldimines formed in situ, leading to a one-pot Synthesis of α-aminoamides. Several types of aldehydes can participate in this process.
Muhammad Afzal Subhani - One of the best experts on this subject based on the ideXlab platform.
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a new one pot hydroformylation Strecker Synthesis as a versatile synthetic tool for polyfunctional compounds and functionalization of dendrimers
Organic and Biomolecular Chemistry, 2009Co-Authors: Muhammad Afzal Subhani, Kai-sven Müller, Fikret Koc, Peter EilbrachtAbstract:A versatile and high yielding one-pot hydroformylation/Strecker Synthesis is reported for the Synthesis of various α-aminonitriles. This methodology allows functionalization of dendrimers (e.g.polyamines 4–7) and hyper branched polymers (e.g. polyallyl glycerol 12) to give corresponding dendritic structures with α-aminonitriles and/or amino acids in the outer shell in good to excellent yields.
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A new one-pot hydroformylation/Strecker Synthesis as a versatile synthetic tool for polyfunctional compounds and functionalization of dendrimers.
Organic and Biomolecular Chemistry, 2009Co-Authors: Muhammad Afzal Subhani, Kai-sven Müller, Fikret Koc, Peter EilbrachtAbstract:A versatile and high yielding one-pot hydroformylation/Strecker Synthesis is reported for the Synthesis of various α-aminonitriles. This methodology allows functionalization of dendrimers (e.g.polyamines 4–7) and hyper branched polymers (e.g. polyallyl glycerol 12) to give corresponding dendritic structures with α-aminonitriles and/or amino acids in the outer shell in good to excellent yields.
