Methyl-a-D-arabinopyranoside

Two sites of periodic acid cleavage in methyl a D arabinopyranoside C 3 lost as formic acid... 

Similar reactions of 2-methanesulfonic esters with sodiiun methoxide have been described by Fletcher and coworkers 1,3,5-tri-0-benzoyl-2-0-(methylsulfonyl)-a-D-ribose afforded methyl a-D-arabinopyranoside. From l,3,5-tri-0-benzoyl-2-0-(methylsul-fonyl)-/8-D-arabinose, a mixture of methyl /3-D-ribofuranoside and methyl /3-D-ribopyranoside was obtained, whereas only the latter glycoside was isolated when 2-0-(methylsulfonyl)-l,3,5-tri-0-(p-nitrobenzoyl)-)8-D-arabinose was the starting material. 

C16H20O5S2 Methyl 4,6-0-benzylidene-2-deoxy-3-0-[(methylthio)thio-carbonyl]-a-D-arabinopyranoside (MBDARP)88... 

Many other glycosides have been subjected to selective chlorination with sulfuryl chloride. Methyl /3-L-arabinopyranoside afforded methyl 4-chloro-4-deoxy-a-D-xylopyranoside 2,3-di(chlorosulfate) in 29% yield, whereas the a-L anomer gave357 methyl 3,4-dichloro-3,4-dideoxy-/3-i)-ribopyranoside 2-(chlorosulfate) (30%). Methyl /3-d-ribopyranoside was converted into methyl 3,4-dichloro-3,4-dideoxy-a-L-arabinopyranoside through the action of pyridine hydrochloride on its 2,3,4-tri(chlorosulfate).358 Methyl a-D-lyxopyranoside gave only the 2,3,4-tri(chlorosulfate),353 as would be expected from the disposition of its hydroxyl groups, similar to that in the rhamno- and manno-pyranosides. Methyl a-D-altropyranoside was transformed into the 6-chloro-6-deoxy 2,3,4-tri(chlorosulfate) derivative in 80% yield.353... 

In 1934, Hudson and his group observed that treatment of a number of methyl D-aldohexopyranoside tetraacetates gave the a-D-aldohexopyranose pentaacetates on acetolysis with sulfuric acid as catalyst. Three years later, they observed that methyl jS-D-arabinopyranoside 2,3,4-triacetate gives 56% of alde%do-D-arabinose hexaacetate and 11% of /3-D-arabino-pyranose 1,2,3,4-tetraacetate the optical rotation of the mixture decreased steadily during the reaction. However, for the a-D-arabinoside, the rotation rose very sharply during the first minute and then fell more slowly. At the end of the reaction, the products were essentially those from the jS-D-glycoside at the point of maximum rotation, a 14% yield of methyl jS-D-arabinopyranoside was isolated, showing that anomerization can occur under these conditions, followed by subsequent acetolysis to the peracetate. 

Of the two chair conformations of an alkyl /S-D-arabinopyranoside (81), the IC form is the more stable. In this conformation, the hydroxyl group on C-4 is axial, and catalytic oxidation (in the presence of Adams catalyst, in neutral solution at 45°) proceeds smoothly to afford " the alkyl /8-D-starting material, because the oxidation product is obtained as an unstable sirup which isomerizes " and decomposes to give acids. A better starting material is benzyl /3-d-arabinopyranoside, which yields a relatively stable, crystalline mono-hydrate of a benzyl pentosidulose (82) this is obtained pure by recrystallization or by column chromatography. The structure of the product was determined by reduction with sodium amalgam to a mixture of D-arabinose and L-xylose. 

Fig. 2.—Separation of Fully Methylated Methyl Glycopyranosides. (Peaks in order of appearance (1) methyl 2,3,4-tri-0-methyl-/3-D-xylopyranoside (2) methyl 2,3,4-trl-O-methyl- 8-L-arabinopyranoside (3) quinoline (standard) (4) methyl 2,3,4,6-tetra-O-methyl-a-D-mannopyranoside (5) methyl 2,3,4,6-tetra-O-methyl-a-D-glucopyranoside (6) methyl 2,3,4,6-tetra-O-methyl-a-D-galactopyranoside. Conditions column (8 ft. x 7 mm.) of Apiezon M on Celite 645 (1 4 w/w) 170° 130 ml. of helium/min. thermal conductivity detector.)...

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