Chemical syntheses of six a-linked disaccharides are described, namely, 6-0-(a- [Traduit par le journal]DCan J Cheili 51 J? (1973) This paper presents syntheses of the six a-linked disaccharides (I to 6) from previously reported (1) oximino-disaccharide structures; namely, the tri-0-acetyl-2-oxin7ino-a-D-arabiko-hexopyranosyl and tri-0-acetyl-2-oxirnino-a-D-/jlxo-hexopyranosyl derivatives of 1,2;5,6-di-0-isopropyiidene-a-D-glucofuranose and of 1,2;3,4-di-0-isopropylidene-a-D-galaclopyranose. The latter compounds were deoximated (2) and the resulting ketonic substances were reduced with sodium borohydride (3) without prior purification. In the preparation of compounds 4, 5, and 6, the use of acetaldehyde in acetonitrilehydrochloric acid reagent (2) for deoximation caused substantial loss of the acid labile 5,6-0-isopropylidene protecting group. However, in the preparation of compounds 1, 2, and 3, deoxirnation under similar conditions caused only small losses of the 0-In view of the high degree of stereoselectivity observed in the reductions to a-D-glucopyranosides (3), the preparations of compounds B and 4 proceeded with little difficulty in 54 and 67% yields, respectively. Although both the interme-propylidene-a-u-galactopyranose and its tetraacetate failed to crystallize, both 3-0-(a-D-glucopyranosyl) -1,2 i5.6-di-0-isopropylidene-a-D-glucofuranose and its tetraacetate were obtained in crystalline condition.As previously reported (3), the reduction of a tri-0-acetyl-a-D-lyxo-hexosuloside with sodium borohydride leads to a mixture of galactosides and talosides. 6-0-(Tetra-0-acetyl-x-D-galactopyranosyl) -1,2:3,4-di-0-isopropylidene-a -D-galactopyranose was obtained crystalline in 51%yield and was readily separated from 6-0-(tetraisopropylidene groups. Treatment of the crude 0-acetyl-a-D-talopyranosy1)-1 ,2:3,4-di-0-isoproketones in these cases with 2,2-dirnethoxypropane pylidene-a-D-galactopyranose (30$/: yield as a andp-to!uenesulfonic acid monohydrate re-intro-syrup) by column chromatography on silicic acid. duced these groups in near quantitative yields. This was not the case in the preparation of compounds 4, 5, and 6. Therefore, lor the syl~tllesis of these compounds deoximation under neutral conditions with titanium trichloride (3, 4) was used. Reduction followed by 0-acetylation enabled compounds 1 to 4 to be isolated as the O-(tetra-8-acetyl-31-~-P1exopyranosy~)-di-0-isopropylidene-D-hexoses. 'Presented at the ihlst National American Chemical Society Meeting, Eos Angeles, California, March 28,1971. 'University of Alberta Postdoctoral Fellow, 1970. 3Professional Research Associate, 1970 Column chromatography on a resin in the hydroxide fornu (5) was used to separate 3-0-(a-Dgalactopyranosyl) -1,2:5,6-di -0 -isopropylidener-D-glucofuranose from the talo-isomer. Both compou~lds were obtained crystalline. The disaccharides (I to 6) were prepared from the di-0-isopropylider?e derivatives by hydrolysis of the isopropylidene groups using aqueous triAuoroacetic acid (6) followed by chromatographic purificat...

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The oxidation of authentic 1.2: 4.5-di-O-cyclohexylidene-D-fructopyranose and of 1.2: 4.5-di-O-isopropylidene-D-fructopyranose with dimethyl sulphoxide-acetic anhydride yields 1.2: 4.5-di-O-cyclohexylidene-D-eryfhrohex-3-ulopyranose and 1,2:4,5-di-O-isopropylidene-D-eryfhro-hex-3-ulopyranose, respectively. Reduction of the latter to 1.2: 4.5-di-O-isopropylidene-D-psicopyranose was achieved with sodium borohydride (9842% stereoselective) and with lithium aluminium hydride (90% stereoselective) ; this psicose derivative underwent rearrangement to the known di-O-isopropylidene-D-psicose. The formation of 1,2:4,5-di-O-cyclohexylidene-D-psicopyranose by the reduction of the appropriate 3-oxo-compound was found to be more highly stereoselective.1.2: 5.6-Di-O-cyclohexylidene-a-D-glucofuranose was oxidised to 1,2: 5.6-di-O-cyclohexylidene-a-D-ribohex-3-ulofuranose which was then reduced completely stereoselectively to 1.2: 5.6-di-O-cyclohexylidene-a-Dallofuranose. All the 3-oxo-compounds were accompanied by substantial amounts (23-27%) of the corresponding 3-O-methylthiomethyl derivatives ; in the case of 1.2: 5.6-di-O-cyclohexylidene-3-O-methylthiomethyla-D-glucofuranose the configuration a t C-3 was established from its n.m.r. spectrum.

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