Ribofuranoside benzyl

D-Ribofuranoside Benzyl 2,3-O-isopropylidene-5-O-benzyl- Methyl 2,3-O-isopropyIidene-5-ehloro-5-deoxy- ... 

Transformation of chiral nitrones into enantiomer enriched a-chiral N -hydroxylamines and their derivatives, has been successfully employed in the enantioselective synthesis of (+ )-(R)- and (—)-(S)-zileuton (216). An expeditious synthesis of thymine polyoxin C (347), based on the stereocontrolled addition of 2-lithiofuran (a masked carboxylate group) to the A-benzyl nitrone derived from methyl 2,3-O-isopropylidene-dialdo-D-ribofuranoside, is described (Scheme 2.151) (194). 

A base-catalyzed, elimination reaction was a key step in a synthesis of D-ribose from L-glutamic acid.188 In that work, L-glutamic acid was converted, by a series of reactions, into 5-0-benzyl-2,3-dideoxy-D-glycero-pentofuranose (157) from compound 157, a mixture of glycosides was obtained which, on treatment with bromine and calcium carbonate, gave the monobromo derivative 158 as a mixture of diastereoisomers. Base-catalyzed dehydrobromination of 158 afforded the unsaturated derivative 159. Hydroxylation of 159 with potassium permanganate or with osmium tetraoxide gave a mixture of methyl 5-0-benzyl-/3-D-ribofuranoside and methyl 5-O-benzyl-a-D-lyxofuranoside. 

Benzyl 2-amino-2-deoxy-6-0-a-D-mannopyranosyl-a-D-glucopyran-oside yielded 2,5-anhydro-6-0-a-D-mannopyranosyl-D-mannose,48a and was characterized as already described. Also formed was a byproduct which, in the light of the results just discussed, may be benzyl 2-deoxy-2-C-formyl-5-0-a-D-mannopyranosyl-D-ribofuranoside. 

The methyl, propyl, and benzyl 1-thio-a-D-glucofuranosides were prepared" by the original method (with neutralization by sodium hydroxide). Use of the method of Pacsu and Wilson" gave the methyl, ethyl, propyl, and isopropyl 1-thio-a-D-ribofuranosides in yields ranging from 65 to 80%. Sodium (methyl l-thio-a-D-glucofuranosid)uronate and the ethyl and propyl analogs were obtained 7 similarly from the sodium salt of the... 

Five-membered stannylene derivatives of furanosides exhibit almost no regio-selectivity. A 1 1 mixture of 2 - and 3 -0-benzyl derivatives has been obtained from uridine [128]. Similarly, methyl 5-0-benzoyl-P-D-ribofuranoside gave a 2 3 mixture of 2-benzyl and 3-benzyl ethers in 70 % yield [147], a slightly better result (ratio of 1 3) was obtained-for the parent methyl P-D-ribofuranoside [147a], The reversed ratio (4 1) was found for the a-anomer, methyl 2-0-benzyl-oc-D-ribofuranoside being the major product [147a]. 

A 5-benzyl-D-ribose has been prepared by Kenner, Taylor and Todd,90 who etherified the methyl 2,3-isopropylidene-D-ribofuranoside (XXI) of Levene and Stiller91 with benzyl chloride to obtain methyl 2,3-iso-propylidene-5-benzyl-D-ribofuranoside (XXII), which was subsequently hydrolyzed to give amorphous 5-benzyl-D-ribose (XXIII). The structure of this ether was confirmed through acetylation to its triacetate (XXIV), hydrogenolysis to 1,2,3-triacetyl-D-ribofuranose (XXV) and further acetylation to the known, crystalline tetraacetyl-D-ribofuranose (XXVI). 

Selective activation of the phenyl selenoribofuranoside 195 in the presence of 1-thioribofuranoside acceptors was also studied.87 Surprisingly, reaction of 195 with benzylated ethyl 1 -thio-/3-D-ribofuranoside (202) afforded the product of trans glycosidation, 203 (Table VI). The same phenomenon... 

A sugar derivative related to the purine nucleosides, namely methyl 5-(adenin-l-yl)-5-deoxy-2,3-0-isopropylidene-j8-D-ribofurano-side, is formed by the reaction of methyl 5-amino-5-deoxy-2,3-0-iso-propylidene-jS-D-ribofuranoside with l-benzyl-5-cyano-4[(ethoxy-methylene)amino]imidazole, followed by removal of the benzyl group. On fusion, this compound rearranges to methyl 5-deoxy-2,3-0-isopropylidene-5-[(purin-6-yl)amino]-/8-D-ribofuranoside, which can also be obtained from the reaction of methyl 5-amino-5-deoxy-2,3-0-isopropylidene-/8-D-ribofuranoside with 6-chloro-9-(tetrahydropyran-2-yl)purine. In the same manner, methyl 5-amino-5-deoxy-2,3-di-0-p-tolylsulfonyl-/3-D-ribofuranoside reacts with 6-chloro-9-(tetrahydro-pyran-2-yl)purine to give methyl 5-deoxy-5-[9-(tetrahydropyran-2-yl)-purin-6-yl]amino-2,3-di-0-p-tolylsulfonyl-j8-D-ribofuranoside. With liquid ammonia, 5 -0-p-tolylsulfonyladenosine gives 5 -amino-5 -deoxyadenosine. On heating in p-dioxane, ring closure to 3,5 -an-hydroadenosine is observed. ... 

Acetamido-5-deoxy-D-ribose has been synthesized from benzyl 2,3-O-isopropylidene-)3-0-ribofuranoside through the sequence of the 5-0-p-tolylsulfonyl, 5-azido, and 5-acetamido derivatives. Hydrolysis of benzyl 5-acetamido-5-deoxy-2,3-0-isopropylidene-j8-D-... 

Mukaiyama and co-workers revealed that Li salts play a significant role in controlling the novel stereochemical preference that is involved in the glycosidation with ribofur-anose derivatives (Sch. 52). In particular, LiC104 [101-105] and LiNTf2 [105] were found to be effective additives in the stereocontrolled synthesis of a-o-ribofuranosides from 2,3,5-tri-O-benzyl-D-ribofuranose and several alcohols, whereas p anomers were formed in the absence of the lithium salts. Sch. 52 shows several examples that emphasize general characteristics with or without the addition of lithium salts. In the most recently advanced system (Sch. 53), a hypothetical mechanism of this reverse stereocontrol to yield 110 with the influence of lithium salt is also discussed. In the presence of 10 mol % TrC104, both pure a anomer 110 (a /3 = >99 <1) and P anomer 111 a-.p = <1 >99) isomerized to afford a P anomer-rich mixture (a p = 6 94). 

Illustrative of the fusion method, 6-methylthio-8-azapurine and 1-0-ace-tyl-2,3,5-tri-0-benzoyl-a-D-arabinofuranose, when fused at 200 C, gave the 7-, 8-, and 9-arabinosides in 5,24, and 37% yields, respectively. A similar reaction to make the ribofuranoside benefited from the catalytic action of bis-p-nitrophenyl phosphate. In an attempt to obtain the anomer, 6-methylthio-8-azapurine and 2,3,5-tri-O-benzyl- D-arabinofuranosyl chloride were fused (120 C, 45 min). Even under these mUder conditions, much anomerization to the unwanted a isomer occurred. In a modificaction of the fusion reaction, tetra-O-acetyl-D-ribofuranose was heated with 6-nonan-oylamino-8-azapurine to give azaadenosine in 14% yield. ... 

For conducting acetal condensations under very mild conditions, anhydrous copper(II) sulfate alone, or with the addition of a low concentration (0.1-0.25%) of sulfuric acid, has been used. At room temperature, in the absence of acid, the reaction is allowed to proceed for 3 to 10 days. This procedure is most suitable for furanoid derivatives. It should be mentioned that benzyl 8-D-ribofuranoside was acetonated by refluxing with copper(II) sulfate in acetone for 5 hours. Other catalysts that have been employed include phosphorus pentaoxide, anhydrous... 

Alkaline hydrolysis of methyl 2,3-anhydro-p-D-ribofuranoside (400) and -a-D-/yxofuranoside (401) led to methyl furanosides of D-xylose and D-arabinose. Reaction of 400 with sodium benzyl mercaptide gave, after acetylation, methyl... 

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