D-Ribofuranosides, methyl

This general method has been employed for the preparation of methyl 5-chloro-5-deoxy-oc-D-ribofuranoside, methyl 5-chloro-5-deoxy-p-D-ribofuranoside, methyl 5-chloro-5-deoxy-a-D-xylofuranoside, and methyl 5-chloro-5-deoxy-p-D-xylofuranoside. 

Draw a structural formula for methyl /3-D-ribofuranoside (methyl /3-D-riboside). Label the anomeric carbon and the glycosidic bond. 

Methyl 5-deoxy-2,3-0-isopropylidene l3-T>-erythro-pent-4-enofurano-side (43). A solution of methyl 5-deoxy-5-iodo-2,3-0-isopropylidene-/ -D-ribofuranoside (42) (30) (1.0 grams) in pyridine (10 ml.) was shaken for 7 hours at room temperature with anhydrous silver fluoride (1.5 grams). Isolation of the product as described previously afforded the 4-ene (43) as a sirup (414 mg., 70%) which distilled at 40°C. (bath) at 0.1 mm. G.l.c. showed the presence of a major component (95%) together with 5% of another component which was not investigated. [ ]D21 + 26.3° (c, 2.3). Anal Calcd. for C9H1404 C, 58.05 H, 7.6. Found C, 57.9 H, 7.7. 

Unlike the 4,6-O-benzylidene derivatives, methyl 2,3-O-benzylidene-5-0-methyl-/ -D-ribofuranoside (99) (9) in which the acetal spans two secondary hydroxyl groups, reacts with NBS to give (48) the isomeric bromobenzoates 100 and 101. These are formed in a ratio of 2 1, and,... 

Methyl p-D-ribofuranoside 5-(hydrogen phosphonate) or methyl 5-deoxy-p-D-ribofuranosid-5-yl hydrogen phosphonate... 

Difluoro compounds have been prepared by treatment of carbonyl compounds with DAST. These are methyl 5-deoxy-5,5-difluoro-2,3,-0-isopropylidene-)S-D-ribofuranoside, 6-deoxy-6,6-difluoro-1,2 3,4-di-0-isopropylidene-a-D-galactopyranose, methyl 2-deoxy-2,2-difluoro-... 

Methyl aldofuranosides are reluctant to complex Ca2+. In aqueous solution, at 298.2 K, K1 values range from 0.1 for methyl a-D-xylofuranoside to 1.4 for methyl a-D-ribofuranoside (46), though in methanol KA — 120 for the latter (655). 

Boron trichloride appears to form with methyl /3-D-ribofuranoside a complex which, after treatment with appropriate nucleophiles, such as sodium methoxide, or the carbanion derived from diethyl 2-(ethox-ycarbonylmethyl)malonate, gives the corresponding a-glycosyl compound.147... 

Mlotkowska, B., Tropp, B.E., and Engel, R., The preparation of methyl 5-deoxy-5-(dihydroxyphosphinoyl)hydroxymethyl-2,3-0-isopropylidene-fS-D-ribofuranoside, a precursor to a hydroxymethylene analog of D-ribose 5-phosphate, Carbohydr. Res., 117, 95, 1985. 

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). 

Potassium fluoride in 1,2-ethanediol has further been used, as, for example, in the preparation of 5-deoxy-5-fluoro-D-ribose from methyl 2,3-0-isopropylidene-5-0-(methylsulfonyl)-a-D-ribofuranoside,87 and of 6-deoxy-6-fluoro-D-glucose from methyl 6-O-p-tolylsulfoiiyl-a-D-glucopyranoside.77 In one study of primary fluorinations with potas-... 

The Koenigs—Knorr reaction109,130 of the halide 112 with methyl 2,3-di-O-acetyl-jS-D-ribofuranoside (123) in 3 1 (v/v) benzene—1,4-dioxane in the presence of silver carbonate gave a low yield of the disaccharide 124 (see Scheme 34). Compound 124 and its deacetylation and deesterification products, 125 and 126, were used as model compounds for 1H- and 13C-n.m.r. studies47,107 of the KDO-containing exopolysaccharides from Escherichia coli strains LP 1092 and 06 K13 H1 (refs. 84 and 86). 

Primary alcohol groups in several protected ribo-, fructo- and glucofuranoses including 2,3,4-tri-O-benzoyl-D-glucose, 1,2-isopropylidene-D-xylo-furanose, 2,3 4,5-di-0-isopropylid-ene-D-fructopyranose, methyl 2,3-O-isopropylidene-P-D-ribofuranoside, l,2-0-isopropylidene-3,5-0-benzylidene-D-glucofuranose and... 

If the benzylidene acetal ring spans the oxygen atoms of two erstwhile secondary hydroxyl groups, the reaction with N-bromosuc-cinimide usually affords isomeric, bromodeoxy sugar benzoates. Thus, for example, the reaction with methyl 2,3-0-benzylidene-5-0-methyl-/3-D-ribofuranoside (106) afforded145 an approximately 1 1 mixture of the bromides 109 and 108, presumably by way of attack on C-2 and C-3 of the benzoxonium intermediate 107 by bromide ion. 

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. 

C-3 (or C-4) from a 1,3-dioxolane actually, this reaction (see Section HI, 14) was observed for 2,2-disubstituted 1,3-dioxolanes, and it may be assumed that, if there is any competition between removal of a proton from C-2 and from C-3 (or C-4), the rate of the first reaction is far greater than that of the second. The possibility of dioxolanylium ions reacting with nucleophilic reagents was first demonstrated by Hanes-sian and Staub,152 and the scope of these reactions was independently investigated by Pedersen and coworkers.153-157 Hanessian and Staub152 treated methyl 5-0-benzoyl-2,3-0-benzylidene-j3-D-ribofuranoside (125) with triphenylmethyl fluoroborate in acetonitrile, and obtained, after hydrolysis, a 1 1 mixture of the two benzoates 127 and 128 (yield 83%), probably through the benzoxonium ion 126. The same reaction... 

Studies have revealed that the deamination of 2-amino-2-deoxy-D-glucosides is more complicated than previously supposed. It has been reported that methyl 2-amino-2-deoxy-a- and -/3-d-glucopyranoside give, in addition to 2,5-anhydro-D-mannose, methyl 2-deoxy-2-C-formyl-a- and -/S-D-ribofuranoside (for example, 97 to 98) in yields of 25 and 19%, respectively, under the experi-... 

H. Yamamoto, H. Sasaki, and S. Inokawa, Reaction of lithium dimethyl cuprate with methyl 2,3-anhydro-5-deoxy-a-D-ribofuranoside. A new, convenient route for the preparation of 2,5-dideoxy-2-C-methyl-D-arabinofuranose derivatives, Carbohydr. Res. 100 C44 (1982). 

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