3-D-Ribofuranose

The most important derivatives of pyrimidines and purines are nucleosides Nucleosides are N glycosides m which a pyrimidine or purine nitrogen is bonded to the anomeric carbon of a carbohydrate The nucleosides listed m Table 28 2 are the mam building blocks of nucleic acids In RNA the carbohydrate component is d ribofuranose m DNA It IS 2 deoxy d ribofuranose... 

Of the four possible 5-deoxy-pent-4-enofuranoses, the D-erythro-isomer was of interest as a potential source of derivatives of L-lyxofuranose. For this purpose, a vinyl ether having the D-en/ hro-configuration has been prepared from derivatives of D-ribose. Condensation of D-ribose with acetone in the presence of methanol, cupric sulfate and sulfuric acid at 30°C., as described by Levene and Stiller(30) afforded a sirupy product consisting mainly of methyl 2,3-O-isopropylidene-D-ribofuranose (40). Treatment of a pyridine solution of the sirup with tosyl chloride... 

Because activated 4-0-trimethylsilylated-2, 3, 5 -0-acyluridines such as 3 are also obtained as reactive intermediates in the Friedel-Crafts-catalyzed silyl-Hilbert-Johnson reaction [59, 59 a] of persilylated uracils or 6-azauracils such as 227 with sugars such as l-0-acetyl-2,3,5-tri-0-benzoyl-/9-D-ribofuranose 228 in the presence of SnCl4, treatment of the reactive intermediate 229 with a large excess of pyrrolidine neutralizes the SnCLi. used and aminates 229 to afford the protected 6-aza-cytidine 230, although in 57% yield only [49, 59] (Scheme 4.20). 

The preparation of glycosyl fluorides is described next. Aiming to have a convenient glycosyl donor convertible into 1,2-CM-furanosides, Mukaiyama and coworkers prepared 2,3,5-tri-O-benzyl-yS-D-ribofuranosyl fluoride (36y3) by treatment of a protected D-ribofuranose (35) with 2-fluoro-1 -meth-ylpyridinium tosylate (FMPTs) the total yield was raised by anomerizing the simultaneously produced a-1-fluoride (36a, 7, p 66, 72.f 24 Hz) to 36 (7, F 63.5 Hz, 72,F very small ) by treatment with BF3-OEt2. 

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... 

Deoxy-5 -fluoroadenosine (911) and the analogs 910, 912, 913 were prepared by coupling of 5-deoxy-5-fluoro-D-ribofuranose and 6-chloro-purine. 2, 5 -Dideoxy-5 -fluoroadenosine (914) was prepared through a displacement reaction of the corresponding 5 -0-tosyl precursor with fluoride (BU4NF in DMF). The carbocyclic nucleosides 915 and 916 have been prepared and their antiviral activities evaluated. 

C13H26N205P2S2 jS-D-Ribofuranose l,5 2,3-di-[(diethylamido)thiono-phosphate] (ETRBFN)79... 

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... 

Such enzymes catalyse the condensation of specific compounds, accompanied by the breakdown of a pyrophosphate bond in adenosine triphosphate (10.64). Adenosine is the condensation product of a pentose (D-ribofuranose) and a purine (adenine). Scheme 10.15 shows the action of glutamine synthetase on a mixture of L-glutamic acid (10.65) and... 

The unusual formation of an anhydro sugar by the hydrolysis of a trityl derivative has been described.76 The treatment of 5-trityl-D-ribofuranose triacetate with hydrogen bromide in acetic acid gives a ribosan diacetate which is presumed to be 1,5-anhydro-D-ribofuranose diacetate. 

Reumycin 311 was silylated with F3CC( = A-SiMe3)-OSiMe3 to give 411, which was glycosylated with tetra-0-acetyl-/3-D-ribofuranose 412 to... 

Esterification of 5 -nucleoside derivatives with N-(aminoacyl)-imidazoles yields 2 - and 3 -(aminoacyl) derivatives and proceeds with apparently little selectivity169,170 this is not surprising in view of the facile, base-catalyzed, ester migration that may occur in 2 (3 )-esters of the D-ribofuranose system (see Section VII,1). 

Buchanan and co workers71 found that treatment of the 7 3 mixture of the D-altro (68) and D-alio (69) hept-l-ynitol derivatives obtained from 2,3,5-tri-O-benzyl-D-ribofuranose and ethynylmagnesium bromide with 2.2 equivalents of p-toluenesulfonyl chloride at 60° gives the 1-D-ribofuranosylethyne derivatives (70 and 71) in 52 and 13%... 

Cyclization72 of the D-allo-hept-l-ynitol derivative 72, obtained from 2,3-O-isopropylidene-D-ribofuranose and ethynylmagnesium bromide, leads in very high yield to the amorphous a-D-ribosylethyne derivative 73, which gave crystalline 1-a-D-ribofuranosylethyne (74) after acid hydrolysis. 

Alkylidene derivatives corresponding to 85 have not yet been reported in the D-ribofuranose series, as evidenced by the formation of the nitrile 82 in high yield. 

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