- Alkoxyl Migration in Displacement of a 5-Trifluoromethanesulfonyloxy Group from Ribofuranosides
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Methyl 2,3-O-isopropylidene-5-O-triflyl-β-D-ribofuranoside (2) reacts at room temperature with primary aralkanols such as benzyl alcohol and the steroid alcohols 3a,b in dichloromethane and in the presence of sodium sulfate to give the corresponding aralkyl 2,3-O-isopropylidene-5-O-methyl-β-D-ribofuranosides 5a,b and 11 in 40-45percent yields.Migration of the methoxyl group from C-1 to C-5, via a tricyclic oxonium ion (7a), is suggested as the basis of formation of the new β-glycoside.Anchimeric assistance by a benzyloxy group in the displacement of the sulfonate is observed in the reaction of benzyl 2,3-O-isopropylidene-5-O-triflyl-β-D-ribofuranoside (14) with methanol, which affords methyl 5-O-benzyl-2,3-O-isopropylidene-β-D-ribofuranoside (15) in 40percent yield on treatment with Na2SO4 in CH2Cl2.The elements of anomeric control in these facile transformations remain to be elaborated.
- Iyer, Vaidyanathan K.,Horwitz, Jerome P.
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- A novel pentose synthesis via palladium(II)-catalyzed cyclization of an unstable hemiacetal
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PdCl2(PhCN)2 (5 mol%)-catalyzed cyclization of a hemiacetal derived from (E,2S,3R)-2,3-isopropylidenedioxy-6-(tetrahydro-2H- pyran-2-yl)-4-hexenal and methanol gave substituted furanoside in moderate yield, exclusively via 5-exo-mode cyclization, without the need for a reoxidant. New stereogenic centers at C1 and C4 on the tetrahydrofuran ring showed preferential 1R and 4R stereochemistry due to anomeric effect (n oσ*c-o) and A1,2 strain, respectively. This methodology was applied to stereocontrolled synthesis of pentoses: D-ribose and L-lyxose. The Japan Institute of Heterocyclic Chemistry.
- Awasaguchi, Ken-Ichiro,Miyazawa, Masahiro,Uoya, Ikuyo,Inoue, Koichi,Nakamura, Koji,Yokoyama, Hajime,Hirai, Yoshiro
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p. 2105 - 2121
(2011/04/24)
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- Adhesin-oligosaccharide conjugate vaccine for Haemophilus influenzae
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Disclosed herein are immunogenic polysaccharide-H. influenzae adhesin protein conjugates, a purified H. influenzae adhesin protein and related proteins and polypeptides, DNA useful for producing the proteins, synthetic polyribosylribotol phosphate (PRP) o
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- Synthesis of methyl 2-O-allyl-(and 3-O-allyl-)5-O-benzyl-β-D-ribofuranoside
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D-Ribose was converted into methyl 5-O-benzyl-β-D-ribofuranoside and this, on tin-mediated allylation, gave a mixture of the 2-O-allyl and 3-O-allyl derivatives which were separated by chromatography. The more polar isomer was characterised as the 3-O-allyl derivative after conversion via 3-O-allyl-5-O-benzyl-1,2-O-isopropylidene-α-D-ribofuranose (which was also synthesised from 3-O-allyl-1,2:5,6-di-O-isopropylidene-α-D-allofuranose) into the known 5-O-benzyl-1,2-O-isopropylidene-α-D-ribofuranose. Methyl 3-O-allyl-5-O-benzyl-β-D-ribofuranoside was converted into methyl 2-O-allyl-5-O-benzyl-β-D-ribofuranoside via methyl 2-O-allyl-5-O-benzyl-3-O(prop-1-enyl)-β-D-ribofuranoside.
- Desai,Gigg,Gigg
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p. 209 - 221
(2007/10/03)
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- A NEW APPROACH TO THE SYNTHESIS OF A DIMERIC FRAGMENT OF THE CAPSULAR POLYSACCHARIDE OF HAEMOPHILUS INFLUENZAE type b
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The synthesis of the monomeric fragment of the Haemophilus influenzae type b (HIb) polysaccharide starting from orthoacetate 7 is described.The construction of the dimer is also reported.
- Chan, Laval,Just, George
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p. 4049 - 4052
(2007/10/02)
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- HIGHLY STEREOSELECTIVE C-α-D-RIBOFURANOSYLATION. REACTIONS OF D-RIBOFURANOSYL FLUORIDE DERIVATIVES WITH ENOL TRIMETHYLSILYL ETHERS AND ALLYLTRIMETHYLSILANE
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2,3,5-Tri-O-methyl-D-ribofuranosyl fluoride (6), 2,3-di-O-benzyl-5-O-methyl-D-ribofuranosyl fluoride (7), and 5-O-benzyl-2,3-di-O-methyl-D-ribo-furanosyl fluoride (8) were obtained in 57 (6α, 15; and 6β, 42), 87 (7α, 22; and 7β, 65) and 85.5 (8α, 35.5; an
- Araki, Younosuke,Kobayashi, Naoki,Ishido, Yoshiharu,Nagasawa, Jun'ichi
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p. 125 - 140
(2007/10/02)
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