Younosuke Araki
Tokyo Institute of Technology
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Featured researches published by Younosuke Araki.
Carbohydrate Research | 1986
Kazuko Watanabe; Kiyotaka Itoh; Younosuke Araki; Yoshiharu Ishido
Abstract Treatments of fully acetylated sugars with bis(tributyltin) oxide in toluene at reflux, and with potassium cyanide or potassium hydroxide, or both, in mixtures of tetrahydrofuran and 2-propanol were found to be effective for regioselective 1- O -deacetylation of fully acetylated sugars.
Tetrahedron Letters | 1989
Younosuke Araki; Tadatoshi Endo; Yoshifusa Arai; Masaki Tanji; Yoshiharu Ishido
The Bu3SnH - AIBN induced radical cyclization of 6-bromo-6-deoxy-3-O-[(E)-2-ethoxycarbonylethenyl]-1,2-O-isopropylidene-α-???-allofuranose (1) gave ethyl 3,7-anhydro-6,8-dideoxy-1,2-O-isopropylidene-α-???-glycero-???-allo-nonofuranuronate (2) in 80% yield. Similar cyclizations of furanose derivatives and a synthesis of the sugar moiety of octosyl acids were described.
Tetrahedron Letters | 1987
Younosuke Araki; Tadatoshi Endo; Masaki Tanji; Jun'ichi Nagasawa; Yoshiharu Ishido
The Bu3SnH - AIBN induced radical additions of 2,3,4,6-tetra-O-acetyl-D-glucopyranosyl derivatives, bearing α-Br (1), α-I (5) β-OCSSMe (7), and β-SePh (8) groups on the anomeric carbon, with olefins such as dimethyl maleate, methyl vinyl ketone, dimethyl acetylenedicarboxylate, butyl vinyl ether, and N-ethylmaleimide were examined for a synthesis of C-glycosyl compounds.
Carbohydrate Research | 1987
Younosuke Araki; Naoki Kobayashi; Yoshiharu Ishido; Jun'ichi Nagasawa
Abstract 2,3,5-Tri-O-methyl- d -ribofuranosyl flouride (6), 2,3-di-O-benzyl-5-O-methyl- d -ribofuranosyl fluoride (7), and 5-O-benzyl-2,3-di-O-methyl- d -ribofuranosyl fluoride (8) were obtained in 57 (6α, 15; and 6β, 42), 87 (7α, 22; and 7β, 65), and 85.5 (8α, 35.5; and 8β, 50%) yields, respectively, from the corresponding OH-1 derivatives by the reaction with N,N-diethyl-1,1,2,3,3,3-hexafluoropropylamine, adduct of hexafluoropropene with diethylamine. These fluorides and 2,3,5-tri-O-benzyl- d -ribofuranosyl fluoride (5) reacted with isopropenyl trimethylsilyl ether, (Z)-1-ethyl-1-propenyl trimethylsilyl ether, and allyltrimethylsilane, in the presence of boron trifluoride·diethyl etherate to give the corresponding 1- d -ribofuranosyl-2-propanones, 2- d -ribofuranosyl-3-pentanones, and 3- d -ribofuranosyl-1-propenes in good yields. C-Acetonylation was confirmed to afford the α- d anomer as the initial product, and the α- d anomer was isomerized into the corresponding β- d anomer to give a mixture. The C-allylation reaction gave only the α- d anomer. C-Pentanonylation, however, gave a mixture of diastereoisomers that could not be isolated. All reactions afforded almost the same results starting with either α- or β- d -ribofuranosyl fluoride. No reaction of the β anomer of 5 with 1-isopropyl-2-methyl-1-propenyl trimethylsilyl ether took place.
Tetrahedron Letters | 1988
Younosuke Araki; Tadatoshi Endo; Masaki Tanji; Jun'ichi Nagasawa; Yoshiharu Ishido
Abstract The Bu3SnH - AIBN induced radical additions of 5- 0 -benzoyl-2,3- 0 -isopropylidene-1- 0 -methylthiothiocarbonyl-β-D-ribofuranose (1) to olefins such as dimethyl maleate, methyl vinyl ketone, methyl acrylate etc. gave corresponding C-ribofuranosyl compounds. And one of the adducts was converted to the key intermediate of a showdomycin synthesis.
Journal of Carbohydrate Chemistry | 1985
Younosuke Araki; Naoki Kobayashi; Kazuko Watanabe; Yoshiharu Ishido
Abstract A treatment of 2,3,5-tri-O-benzyl-B-D-ribofuranosyl fluoride (1) with cyanotrimethylsilane in the presence of boron trifluoride diethyl etherate gave 2,3,5-tri-O-benzyl-α- (2α) and -β-D-ribofuranosyl (2β) cyanide in 46.2% and 46.6% yields, respectively. Confirmation of the corresponding isocyano isomer (3) formation and its conversion into 2 under boron trifluoride catalysis at -78°C made it possible to deduce that both 2α and 2β were produced by way of 3 which was formed preponderantly in the initial stage of the reaction. On the other hand, the reaction of 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl fluoride (4) with cyanotrimethylsilane in diethyl ether by the use of boron trifluoride diethyl etherate (0.05 mol. equiv.) gave 2,3,4,6-tetra-O-benzyl-α -D-glucopyranosyl cyanide (5α), 2,3,4,6-tetra-O-benzyl-α- (6α), and -β-D-glucopyranosyl isocyanide (6β) as a 30:61:9 mixture (94% yield) but that in dichloromethane by the use of the catalyst (1.0 mol. equiv.) gave 5α (85% yield) as a sole product. T...
Carbohydrate Research | 1982
Ichiro Hirao; Kiyotaka Itoh; Nobuo Sakairi; Younosuke Araki; Yoshiharu Ishido
Abstract On benzylaminolysis, 5′- O -benzoyl- N 6 -benzyladenosine 2′,3′-carbonate gave a 3:1 mixture of the corresponding 3′- and 2′-benzylcarbamate (67% total yield); hydrazinolysis and hydroxaminolysis were, however, unsuccessful. An alternative approach to regioselective carbamoylation of ribonucleosides, by use of bis(tributyltin) oxide-phenyl isocyanate, was examined, because it is a much simpler procedure. Procedure A, involving two-stage treatment of ribonucleosides, first with bis(tributyltin) oxide in toluene under reflux, and then with phenyl isocyanate, was found to give the corresponding 5′-phenylcarbamate, but was, however, feasible only for N 6 -benzyladenosine. Procedure B , involving a one-stage treatment of ribonucleosides with bis(tributyltin) oxide-phenyl isocyanate in a solvent, was found to give the corresponding 3′- or 2′-phenylcarbamate regioselectively on suitably changing the polarity (or composition) of the solvent system used, and was useful for a variety of ribonucleosides. The reaction of 2′-deoxyribonucleosides by Procedure B was of interest, as it gave the corresponding 5′-phenylcarbamates regiospecifically. The factors possibly involved in the regioselectivity of these reactions are discussed.
Tetrahedron Letters | 1989
Younosuke Araki; Eiji Mokubo; Naoki Kobayashi; Jun'ichi Nagasawa; Yoshiharu Ishido
Abstract Treatment of 2,3,5-tri- O -benzyl-β- D -ribofuranosyl fluoride ( 1 ) with BF 3 ·OEt 2 in CH 2 Cl 2 gave the intramolecular C -arylation product ( 2 ) formed from the reaction with the 2- O -benzyl group in a 83% yield. Catalytic transfer hydrogenolysis of 2 using HCOOH as a hydrogen donor and the following acetylation of the product gave (3 S ,1′ S ,2′ R )-3-(1,2,3-triacetoxypropyl)isochroman ( 9 ) in a 68% total yield.
Carbohydrate Research | 1973
Kazuo Matsuura; Younosuke Araki; Yoshiharu Ishido; Asao Murai; Katsuhiko Kushida
Abstract Irradiation of a solution of 3,4,6-tri- O -acetyl- D -glucal ( 1 ) in various mixtures of acetone ( 2 ) and isopropyl alcohol was investigated to elucidate solvent effects on the photochemical addition of 2 to 1 . At high concentrations of acetone ( 2 ), 5,6,8-tri- O -acetyl-2,4:3,7-dianhydro-1-deoxy-2- C -methyl- D - glycero - D - ido -octitol ( 3 ) was obtained selectively. In mixtures containing less than 50% (v/v) of 2 , irradiation gave mainly 5,6,8-tri- O -acetyl-3,7-anhydro-1,4-dideoxy-2- C -methyl- D - gluco -octitol ( 4 ). The effects of ethanol and other solvents were examined and the mechanism of the reaction is discussed.
Tetrahedron Letters | 1988
Younosuke Araki; Tadatoshi Endo; Masaki Tanji; Yoshifusa Arai; Yoshiharu Ishido
Abstract The Bu 3 SnH - AIBN induced radical additions of 3,5-di- O -acetyl-6-deoxy-6-iodo-1,2- O -isopropylidene-α- D -gluco- and -allofuranose ( 1 and 10 ), and methyl 5-deoxy-5-iodo-2,3- O -isopropylidene-β- D -ribofuranoside ( 19 ) to dimethyl maleate, methyl acrylate, acrylonitrile, methyl vinyl ketone, and vinylene carbonate gave various types of higher-carbon sugars.