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... 

Hydantocidin. Hydantocidin (182), C2H2QN2O3, is elaborated by S. hygroscopicus (278). It is unique in that the anomeric carbon of the ribosyl moiety forms the spHo bond of hydantoin (279). The ribofuranose moiety which has been reported to be in a Q -endo conformation (279) has been synthesized (280,281). Hydantocidin is a herbicidal nucleoside with activity against monocotyledenous and dicotyledenous plants. 

Methoxyurldlne-2,3,S-trl-0 benzoate (4).3 To 5-methoxy-2,4-bis(tnmethylsiiyloxy)uracil 1(11 mmol, 34 mL of 0 356 N solution In 1,2-dichioroethane) and 1-0-acetyl-2,3,5-lrl-0-benzoyl-p 0-ribofuranose 2 (5 04 g, 10 mmol) in dichioroethane (75 mL) was added trimethyisllyl inflate 3(12 mmol, 22 8 mL of 0 522 N solution in dichioroethane) and the mixture was stirred lor 4 h at 2S C The clear yellow solution was diluted with CH2CI2 (50 mL) extracted with an ice cooled solution of NaHCOa (50 mL) and after washing with water (2x20 mL), the organic phase was dned (Na2S04), the solvent evaporated and the residue recrystallized from EtOAc-hexane to afford 5 24 g of 4 (89%), mp 205-207°C... 

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... 

Problem 25.16 I Draw the products you would obtain by reaction of /3-n-ribofuranose with (a) CH3I, Ag2C) (b) (CH3C0)20, pyridine... 

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. 

Any discussion of the prebiotic phosphorylation of nucleosides must take into account the probably neutral or alkaline conditions in a prebiotic environment. Some model phosphorylating systems have been studied, for example, the synthesis of /S-o-ribofuranose 1-phosphate from ribose and inorganic phosphate in the presence of cyanogen. Sodium trimetaphosphate will phosphorylate cw-glycols in good yield under alkaline... 

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

P2j Z = 2 Dx = 1.33 R = 0.09 for 792 intensities. The molecule is tricyclic, with a five-membered and a seven-membered ring fused to the ribofuranose ring. Both five-membered rings have an envelope conformation. The seven-membered ring has the same conformation as is found in 2,5-arabinosylcytidine monophosphate.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. 

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