Methyl a-L-rhamnopyranoside

Our initial studies were directed towards the synthesis and characterization of phenylboronate esters derived from methyl 6-deoxy-/ -D-allopyranoside, methyl a-L-rhamnopyranoside, methyl -L-fucopyranoside, and methyl 6-deoxy-/ -D-glucopyranoside. Previous work (14) in this laboratory indicated that the reaction of triphenylboroxole and methyl... 

Reaction of methyl a-L-rhamnopyranoside with triphenylboroxole gave a syrupy boronate ester which was characterized as a crystalline phenyl-carbamate. Removal of the phenylboronic acid residue gave a product identified as methyl a-L-rhamnopyranoside 4-N-phenylcarbamate, since it was identical with that resulting from removal of the ketal group from methyl 2,3-O-isopr opylidene-a-L-rhamnopyranoside 4-N-phenylcarbamate (12). This establishes the structure of the original ester as methyl a-L-rhamnopyranoside 2,3-phenylboronate (24). 

Fig. 21.—Partial 13C-N.m.r. Spectrum of the Rhamnomannan (16) of Sporothrix schenckii, with Shift Comparisons with Signals of Methyl a-D-Mannopyranoside (Lower Inset Lines) and Methyl a-L-Rhamnopyranoside (Upper Inset Lines). (Solvent, D20 temperature, 33° chemical shifts expressed as 8C, relative to external tetramethyl-silane.)...

The reaction of nitroethane/sodium ethoxide with the dialdehyde (31), obtained by periodate oxidation of methyl a-L-rhamnopyranoside (30), leads after deionization to a sirupy mixture (32), which was shown by thin-layer chromatography to contain five main components together with traces of other substances. After acetylation one di-O-acetate (33) crystallized from the mixture and was isolated in 12.5% 5deld, based on the rhamnoside (30). Reduction ot (33) with lithium aluminiumhydride gave methyl 3-C-methyl-3-amino-3,6-dideoxy-a-L-glucopyranoside (34), which was additionally characterized as the triacetate (35)... 

SCHEME 5. Richardson s application of the Fischer nitromethane cyclization to the sugar dialdehyde derived from periodate cleavage methyl a-L-rhamnopyranoside (1961). 

Excess benzyl bromide and triethylamine in the presence of tin(II)chloride catalyst were used [91] for partial benzylation of methyl a-L-rhamnopyranoside and its 4-O-benzyl ether. Complexation of tin(II)chloride with vicinal m-disposed hydroxyl groups permitted selective benzylation at the 3- and 2-positions. Methyl 3-O-benzyl-or 3,4-di-O-benzyl-a-L-rhamnopyranoside, respectively, could be prepared in good yield by this method. No benzylation took place when benzyl chloride was used instead of benzyl bromide, or when other solvents than ethyl acetate or acetonitrile were tested. 

N. E. Nifantiev, A. S. Shashkov, G. M. Lipkind, and N. K. Kochetkov, Synthesis, NMR, and conformational studies of branched oligosaccharides. 7. Synthesis and l3C NMR spectra of 2,3-di-O-glycosyl derivatives of methyl a-L-rhamnopyranoside and methyl a-D-mannopyrano-side, Carbohydr. Res., 237 (1992)95-113. 

Ascarylose (94) and the (35) deuterium-labeled ascarylose were prepared starting from methyl a-L-rhamnopyranoside via the 2,3-anhydro sugar 120 (Scheme 34).204 Opening of the epoxide ring with lithium aluminum hydride in THF led selectively to the 3-deoxy derivative. If reduction was performed with lithium aluminum deuteride, the methyl (3S)-[32H]ascaryloside (3S)-[32H]119 was obtained. 

Although the 2,3-dimethyl and 3,4-dimethyl ethers of L-rhamnose were known, the 2,4-dimethyl ether had not been synthesized prior to its preparation through a trifluoroacetyl intermediate. - The synthesis started from methyl 2,3-0-isopropylidene-a-L-rhamnopyranoside this was methylated and the acetal group removed, to give methyl 4-0-methyl-a-L-rhamnopyranoside (6). Conversion to the 2,3-bis(trifluoroacetate) (7) was readily achieved with trifluoroacetic anhydride in the presence of sodium trifluoroacetate. As expected, the trifluoroacetate (7) was completely de-acylated by treatment with alcohol, regenerating (6) this process was complete after 25 min. at room temperature. The procedure for selective de-esterification was based on the observation that, if excess carbon tetrachloride (6 vol.) is present, very little methanolysis occurs. By use of a mixed methanol-carbon tetrachloride solvent (65 35 vol./vol.), the meth-... 

Fig. 9 Construction and screening of a single-mutant library of amylosucrase from N. polysac-charea for their ability to glucosylate methyl a-L-rhamnopyranoside (a) and allyl 2-/V-acetyl-2-deoxy-a-D-glucopyranoside (b) WT wild-type amylosucrase [139]...

Preparation. 6-Deoxy-L-talose was prepared by a method described by Collins and Overend.187 The yield has been improved by a method which involves inversion of configuration at C-4 of a derivative of methyl a-L-rhamnopyranoside.188 Other similar strategies have been described.189... 

A synthesis of L-fucose starting from methyl a-L-rhamnopyranoside has been described.188... 

Relatively few dialdehydes are thus far known in crystalline form. The first reported example is that obtained from methyl a-L-rhamnopyranoside and related 6-deoxyglycosides its elemental composition is that of a dialdehyde monohydrate, but it has been found to possess a hemialdal structure, as it... 

AUyl 2-0-methyl-a-L-fucopyranoside, A-92 AUyl 4-0-methyl-a-L-rhamnopyranoside, A-95 AUyl rhamnopyranoside, A-95 AUyl ribofuranoside, A-96... 

Methyl 2,3-0-isopropylidene-4-O-methyl-a-D-lyxopyranoside, M-202 Methyl 2,3-0-isopropylidene-6-O-methyl-a-D-mannopyranoside, M-200 Methyl 2,3-0-isopropylidene-5-0-methyl-a-L-rhamnofuranoside, M-206 Methyl 2,3-0-isopropylidene-5-0-methyl-p-L-rhamnofuranoside, M-206 Methyl 2,3-0-isopropylidene-4-O-methyl-a-L-rhamnopyranoside, M-207 Methyl 3,4-0-isopropylidene-2-0-methyl-p-D-ribopyranoside, M-209 Methyl 3,4-0 -isopropylidene-2- O -methyl-1 -thio- p-L-fucopyranoside, T-63 Methyl 2,3-0-isopropylidene-5-5-methyl-5-thio-p-D-ribofuranoside, T-91 Methyl 2,3-0 -isopropylidene-6-O-methyl-5-O-tosyl-p-L-allofuranoside, M-148... 

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