Ribo-furanoside

As confirmation of the structure of D-ribofuranose tetraacetate, may be mentioned its use in the synthesis of the naturally occurring D-ribo-furanoside xanthosine.100... 

While various authors29-96-107,108 have hydrolyzed arylamine D-ribo-furanoside triacetates to 2,3,5-triacetyl-D-ribose, the latter has thus far been obtained only in crude amorphous form. 

In subsequent work Levene and Stiller91 showed that condensation of D-ribose with methanol and acetone in the presence of anhydrous copper sulfate and sulfuric acid gave methyl 2,3-isopropylidene-D-ribo-furanoside (Cl) which was identified by conversion to XCVIII, then to XCIX and, finally, to the crystalline p-bromophenylosazone of XCIX, identical with the derivative previously prepared from XCVII. When these authors166 attempted to acetonate methyl D-ribopyranoside (CIV),... 

Peroxy acids normally form anhydrides when reacted with 1,2-dicarbonyl compounds in inert solvents or acids in alkaline or acidic media. An exception to this generality is the oxidation of the keto ester (74 Scheme 24), in which the ring oxygen facilitates tetrahydrofiiran ring migration. Ohno and coworkers have exploited this reaction to develop a chemicoenzymatic approach from furan to the protected L-ribo-furanoside (75). 

It has been emphasized that care must be taken in the use of the t-butyl-dimethylsilyl group as a partial blocking group in nucleosides, because intramolecular migration between the l - and 3 -hydroxy-groups occurs in ribo-furanoside and is very rapid ( i/2 = 0.5 min) in the presence of triethylamine. ... 

Structures of a range of base and/or sugar-modified nucleoside analogues have been described. The 6-azacytosine 71, pyrazolo[3,4-/>]quinoline P-ribo-furanoside 72 5 -0-benzoyl-3 -deoxy-2 -keto-a-uridine, 3 -deoxy-3 -5-(2-nitrophenyldisulfanyl)thymidine, ° anhydronucleoside 73, 5-adamantyl-2 -deoxy-4 -thio-a-uridine, the bicyclic nucleoside analogue 74, and bicyclic analogues 75 (both epimers) and 76. ... 

Methyl D-ribofuranoside-boron chloride complex, prepared from methyl D-ribo-furanoside and BCI3 according to T. G. Bonner, E. J. Bourne, and S. McNally, Soc. 1962, 761, and 6-benzylthiopurine refluxed 2 hrs. in chloroform in the presence of pyridine -> 9-a-D-ribofuranosyl-6-benzylthiopurine. Y 52%. - Protection of the hydroxyl group is not necessary. a-Anomers can be obtained in fairly good yield by this method. F. e. s. Y. Furukawa, K. Imai, and M. Honjo, Tetrah. Let. 1968, 4655. 

It has been shown that tetrahydrouridine (77), and other ribo-furanosides of fully reduced cyclic ureas, undergo a rapid acid-catalysed isomerization to the -D-ribopyranosyl isomers, which predominate at equilibrium. In the case of tetrahydrouridine, the pyranose isomer was synthesized by the Vorbruggen procedure,... 

Me glycoside, H,2,5-tri-Ac Methyl 3-acet-amido-2,5-di-0-acetyl-3-deoxy-a-D-ribo-furanoside... 

Et glycoside Ethyl 2,3-anhydro-a-D-ribo-furanoside C7H12O4 160.169... 

Allyl-5-O-ethylfumaroyl-2,3-0-isopropylidene-d-ribo furanoside 2,3-0-isopropylidene-d-ribo furanoside... 

The conformational analysis of a range of 1,2-O-isopropylidene-cx-D-gluco-and -allo-furanose derivatives (6) has been reported, using n.m.r., and the 3,S-phenylboronate of the giuco isomer was also examined. Rotamers about the C-5-C-6 bond were distinguished. The n.m.r. spectra of a- and /S-anomers of phenyl, thiophenyl, and 1-naphthyl 2,3,5-tri-O-acetyl-D-ribo-furanosides have shown that the preferred conformation is Cz-endo. Changing... 

Other differences which have been observed are the following. Ribo-furanoside 3-phosphate is more labile than ribofuranoside 2-phosphate . A methylene group at position 2 labilizes the phosphorus at positions 3 or 6 of galactose . Ribose 5-phosphate is considerably more stable than... 

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