Ribopyranosides, methyl 2,3-anhydro

In an attempt to synthesize 2-desoxy-L-ribose, Mukherjee and Todd68 treated methyl 2,3-anhydro-jS-L-ribopyranoside (LXXII) with sodium thiomethoxide and then reduced the amorphous product. The sulfur-free sirup thus obtained was inert to the action of periodate and is therefore methyl 3-desoxy-/3-L-riboside (ayn., methyl 3-desoxy-/3-L-xyloside) (LXXIV) rather than the desired 2-desoxy derivative. The methylthio intermediate (LXXIII) was consequently a 3-methylthio-L-xylose derivative rather than a 2-methylthio-L-arabinose compound. The presence of a trace of the latter, however, is not wholly excluded since the sirupy desoxypentoside (LXXIV) gave a feeble green coloration in the Keller-Kiliani test, a reaction generally accepted as being specific for 2-desoxy-sugars. 

Honeyman147 reported the synthesis of methyl 2,3-anhydro-/3-L-lyxopyranoside, and claimed that, on alkaline hydrolysis, this gives a 2 1 ratio of L-xyloside L-arabinoside, but these results could not be substantiated by Buchanan and R. Fletcher,68 who recorded different constants for the epoxide and for the disulfonic ester claimed147 to be the starting material for its synthesis. The same epoxide has been synthesized by Reist and coworkers,160 and its properties are in agreement with Buchanan and Fletcher s results. Ethyl or methyl 3,4-anhydro-/3-L-ribopyranoside undergoes substitution at C-4 in all the reactions thus far studied. Neither half-chair conformation would seem to be clearly favored, but the specificity observed can be rationalized by considering the steric and polar interactions that may arise in the transition state substitution at C-3 in conformation 58 would involve marked interactions between the nucleophile and... 

Methyl 2,3-anhydro-/3-L-ribopyranoside (LVII) was caused to react with sodium methylmercaptide and thereafter the product was boiled under reflux with Raney nickel. The main desoxypentoside obtained was methyl 3-desoxy- 3-L-riboside (LVIII) and only traces of methyl 2-desoxy-/3-L-riboside were detected. 1 173 That the structure assigned to LVIII was correct was demonstrated by hydrolysis to the desoxy-... 

Independent proof of the structure of B was furnished by the fact that it could be obtained from methyl 2,3-anhydro-/3-D-ribopyranoside by a series of transformations which did not affect the lactol ring structure of the initial material or intermediates in the conversion.179... 

Honeyman oi has reported, on the other hand, that iMlditi in of water to methyl 2,3-anhydro-jS-D-ribopyranoside (Eq. 545) takes place at C(8), rather than Cia>, giving methyl /5 D-xyloside. 

Besides anionic nucleophiles (e. g. NJ), poor nucleophiles such as F can also be used in the ring-opening reactions in the presence of acids or Lewis acids as catalysts. For example, the reaction of methyl 2,3-anhydro-/3-D-ribopyranoside 26 with F does not proceed except when acidic KF HF is used to provide the nucleophile, yielding 3-deoxy-3-fluoroxylopyranoside 27 (O Scheme 13) [18]. 

Methyl 2,3-anhydro-4-0-benzyl-,8-L-ribopyranoside Mglj 3-substituted l-xylose — e 56... 

Other instances of a low hydroxyl-stretching frequency arising from the hydroxyl group (s) on a pair of 1,3-m-diaxial C—0 bonds have been reported in the spectra of methyl 2-C-methyl- 3-L-ribopyranoside (at 3512 cm. ) and methyl 3,6-anhydro-a-D-glucopyranoside (at 3500 cm. 0-The latter compound is constrained in the 1C conformation, and the band at 3512 cm. shows that the former compound is in the 1C conformation also. The occurrence of this characteristically low frequency in the spectra of some branched-chain sugars enabled their configuration to be determined by indicating the presence of such diaxial C—0 bonds. ... 

The anomeric effect was also found to play a significant role in determining the conformation of methyl 2,3-anhydro-a- and -/3-L-ribopyranosides and the corresponding 2,3-unsaturated derivatives. Both anomers adopt that half-chair conformation having the bond to the 1-methoxyl group quasi-a.xia.1. 

For further apphcation of this methodology to the synthesis of a specific target, an alkyl group at C-6 needs to be introduced, since the entire class of polyether antibiotics contains at least one methyl moiety on a tetrahydrofu-ran ring. Alkylation of the enolate of the o ,/ -imsaturated ester was expected to yield an Q -alkyl-/ ,y-imsaturated ester. Indeed, the dianion of methyl pro-pionyl acetate (7) reacted with benzyl 2,3-anhydro-jS-L-ribopyranoside (1) in THF at - 78 °C to afford a 1 1 mixture of the diastereoisomers 8 and 9 in 90% combined yield (Scheme 2). Due to the formation of a mixture, 50% of the desired product got lost. Treatment of the mixture of 8 and 9 with 1% TFA in CH2CI2 caused epimerization and afforded a 9 1 mixture of (6S)-8 and (6i )-10 (Scheme 2) [33]. 

The stepwise synthesis of methyl 4-(9-[3,4-di-0-( 3-D-xylopyranosyl)-j3-D-xylopyranosyl]-/3-D-xylopyranoside (17), a methyl xylotetraoside related to branched xylans, has been achieved by stereoselective condensation of 2,4-di-(9-acetyl-2-O-benzyl-a-D-xylopyranosyl bromide with methyl 2,3-anhydro- -D-ribopyranoside and reaction of the deacetylated product with 2,3,4-tri-C>-acetyl-a-D-xylopyranosyl bromide. 

Me glycoside, 4-tosyl Methyl 2,3-anhydro-4A)-tosyl-a-D-ribopyranoside [58394-21-1]... 

Anhydro, Me glycoside, 2 -benzyl Methyl 2,3-anhydro-4-0-(2-0-benzyl-p-D-xylopyranosyl) - -D-ribopyranoside,... 

Benzyl 2,3-anhydro-4-0-a-L-arabinopyranosyl-p-D-ribopyranoside, A-848 Benzyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside, A-484 Benzyl 2,3-anhydro-4,6-0-benzylidene-p-D-gulopyranoside, A-639 Benzyl 2,3-anhydro-4,6-0-benzylidene-a-D-mannopyranoside, A-676 Benzyl 3,4-anhydro-2,6-dideoxy-a-L-r -hexopyranoside, A-591 Benzyl 2,3-anhydro-4- O - p-D-galactopyranosyl- p-D-ribopyranoside, G-173 Benzyl 2,3-anhydro-a-D-mannopyranoside, A-676 Benzyl 2,3-anhydro-p-D-mannopyranoside, A-676 Benzyl 3,4-anhydro-2-0-mesyl-6-0-trityl-a-D-altropyranoside, A-495 Benzyl 2,3-anhydro-4-0-methyl-p-D-ribopyranoside, A-693 Benzyl 2,3-anhydro-p-D-ery /iro-pentopyranosid-4-ulose, A-682 Benzyl 2,3-anhydro-p-L-eyy /iro-pentopyranosid-4-ulose, A-682 Benzyl 2,3-anhydro-a-D-ribopyranoside, A-693 Benzyl 2,3-anhydro-p-D-ribopyranoside, A-693 Benzyl 2,3-anhydro-p-L-ribopyranoside, A-693... 

Methyl 2-0-acetyl-3,4-anhydro-a-D-arabinopyranoside, A-504 Methyl 2-0-acetyl-3,4-anhydro-p-L-arabinopyranoside, A-504 Methyl 4-0-acetyl-2,3-anhydro-6-deoxy-a-D-gulopyranoside, A-527 Methyl 4-0-acetyl-2,3-anhydro-6-deoxy-p-D-gulopyranoside, A-527 Methyl 4-0-acetyl-2,3-anhydro-6-deoxy-a-D-mannopyranoside, A-687 Methyl 4-0-acetyl-3,6-anhydro-a-D-galactopyranoside, A-620 Methyl 5-0-acetyl-2,3-anhydro-a-D-lyxofuranoside, A-664 Methyl 5-0-acetyl-2,3-anhydro-p-D-lyxofuranoside, A-664 Methyl 3-0-acetyl-2,6-anhydro-4-0-methyl-p-D-mannopyranoside, A-678 Methyl 4-0-acetyl-2,3-anhydro-a-D-rhamnopyranoside, A-687 Methyl 5-0-acetyl-2,3-anhydro-a-D-ribofuranoside, A-690 Methyl 5-0-acetyl-2,3-anhydro-p-D-ribofuranoside, A-690 Methyl 4-0-acetyl-2,3-anhydro-p-D-ribopyranoside, A-693 Methyl 4-0-acetyl-2,3-anhydro-6-0-trityl-a-D-mannopyranoside, A-676 Methyl 2-0-acetyl-p-L-arabinopyranoside, M-153 Methyl 3-0 -acetyl-2-azido-4,6-0 -benzylidene-2-deoxy-a-D-mannopyranoside, A-912... 

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