Younosuke Araki

A comparison of bis(tributyltin) oxide, potassium cyanide, and potassium hydroxide as reagents for the regioselective 1-O-deacetylation of fully acetylated sugars

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.

Stereoselective radical cyclization for the synthesis of bicyclic higher-carbon sugars. Synthesis of the sugar moiety of octosyl acids

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.

Synthesis of C-glycosyl compounds by the addition of glycosyl radicals to olefins☆

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.

Highly stereoselective C-α-d-ribofuranosylation. Reactions of d-ribofuranosyl fluoride derivatives with enol trimethylsilyl ethers and with allyltrimethylsilane

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.

Additions of a ribofuranosyl radical to olefins. A formal synthesis of showdomycin

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.

Synthesis of Glycosyl Cyanides and C-Allyl Glycosides by the use of Glycosyl Fluoride Derivatives

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...

Bis(tributyltin) oxide-phenyl isocyanate system for regioselective (phenylcarbamoyl)ation of purine and pyrimidine ribonucleosides☆

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.

Structural elucidation and a novel reductive cleavage of ribofuranosyl ring C-1 - O bond of the intramolecular C-arylation product of tri-O-benzyl-β-D-ribofuranosyl fluoride

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.

Solvent effects on the photochemical addition of acetone to 3,4,6-tri-O-acetyl-D-glucal☆

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.

Synthesis of higher-carbon sugars by tributyltin hydride-azobisisobutyronitrile induced radical additions

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.