A-D-Ribofuranose

Preparation of 2-fluorofuranoses is also important in relation to the synthesis of biologically active 2 -fluoro derivatives of nucleosides (see Section 111,4). Su and coworkers prepared the 2-triflates 236 and 239 through acid-catalyzed methanolysis of 3,5-di-O-benzyl-1,2-(9-isopropylidene-a-D-ribofuranose [to give 235 (major) and 238] and subsequent triflylation. On treatment with fluoride ion, the anomer 236 afforded exclusively the furan derivative 237, whereas the a anomer 239 gave the 2-fluoro compound 240... 

C19H24BrN09S 5-0-(p-Bromophenylsulfonyl)-3-deoxy-3-C-(R)-(ethox-ycarbonylformamido)methyl-l,2-0-isopropylidene-a-D-ribofuranose (BDEIRF)284... 

Ir(CO)2(aniline-dithiocarbamate) shows a moderate activity against Ehrlich ascites at 50 mg kg 1,704 The synthesis of air-unstable [Ir2(//-L)(cod)2], where H2L = RiSSH2(l,2-0-isopropylidene-2,5-dithio-a-D-ribofuranose, XySSH2(l,2-0-isopropylidene-3,5-dithio-a-Z)-xylofuranose), is described.705... 

A stereochemical dependence has been observed for the 5/f,h-i values observed for a number of 3-deoxy-3-C-(fluoromethylene)-l,2 5,6-di-0-isopropylidene-a-D-ribofuranose derivatives n. =... 

Two ciT-dihydroxylation reactions of alkenes formed steps in the synthesis of the antiviral drug (-)-oseltamvir ( tamiflu ) were carried out with RuO /aq. Na(IO )/ EtOAc-CH3CN/4°C [169]. Terminal alkene groups in nucleosides were oxidised to alcohols by RuClj/aq. Na(lO )/EtOAc-CH3CN/0°C thus 3,5-di-0-benzyl-l,2-di-O-isopropylidene-3-C-vinyl-a-D-ribofuranose (1) gave the diol (2) which, on cleavage with Na(lO ) and reduction with NaBH yielded 3,5-di-0-benzyl-l,2-di-O-isopropylidene-3-C-hydroxy-methyl-a-D-ribofuranose (3) (Fig. 3.4) [170]. 

Vitamin Bi2 is a D-ribofuranose derivative, and the structure of vitamin B12 5 -phosphate, a precursoi 11 of vitamin B12, has been determined. The a-D-glycosidic bond lies 16° (0.51 A) out of the plane of the 5,6-dimethylbenzimidazole ring, because of steric or nonbonded interactions. The D-ribofuranose moiety has that envelope conformation having C-2 exo (0.77 A exoplanar) C-3 and C-5 bear phosphate groups. 

More than 90% yield can be achieved when the reaction is scaled up in a manufacturing facility to 800 kg.398 It is noticeable that the intermediary formed l,3,5-tri-(9-benzoyl-2-0-fluorosulfonyl-a-D-ribofuranose can also be isolated in pure form when the temperature is held at 60 C.398... 

Tribenzoyl-2-0[(3-trifluoromethyl)benzoyl]-a-D-ribofuranose a-D-Ribofuranose, 1,3,5-tribenzoate 2-[3-(trifluoromethyl)benzoate (13) (145828-13-3)... 

A useful modification of the Barton deoxygenation of secondary alcohols involves the use of O-phenylthionocarbonates developed by Robins et al. [15]. Application of this method for the generation and cyclization of a hex-5-ynyI radical is shown is Scheme 5. The precursors are readily prepared from D-ribose by a Grignard addition, followed by selective alcohol derivatizations. The major exo-isomer has been converted into carba-a-D-ribofuranose [16]. 

Figure 6. (a) a-D-Ribofuranose oxyanion (b) 2-deoxy-a-n-ribofuranose oxyanion... 

In a series of excellent studies on DD, Toraya and coworkers [12,28,74] have investigated a number of analogs with systematic variations in the nucleotide loop. This laboratory has synthetically replaced the a-D-ribofuranose ring at the nucleotide loop with a methylene chain, -(CH2),T where n = 2, 3, 4, and 6. 

Debenzylation of the benzyl esters of phosphoric acid has been employed in the synthesis of phosphorylated alcohols. Examples are shown in eqs. 13.2348 and 13.24.49 Tener and Khorana synthesized a-D-ribofuranose 1,5-diphosphate (36) by hydrogenolysis of the benzyl phenyl phosphate 35, first, in the presence of 5% Pd-C, and then in the presence of Adams platinum to remove, respectively, the benzyl and the phenyl groups (eq. 13.25).50... 

An unusual example of solvent-dependent, virtual coupling involving a hydroxyl group has been reported for 1,3,5-tri-O-benzoyl-a-D-ribofuranose (72) which, in acetone solution, showed the signals of... 

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