Chemical Syntheses of α-Linked Disaccharides

Abstract

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...

The Reaction of Dimeric Tri-O-acetyl-2-deoxy-2-nitroso-α-D-hexopyranosyl Chlorides with Alcohols

“…The compositions and n.m.r. spectra (see Table 2) were in agreement with the assinned structures and the anomeric u configurations of the oximinoglycosyl units were firmly established by conversion of compounds 8, 9,11, and 12 to a-glycosides (10). A consideration of the n.m.r.…”

“…In each case, the desired a-oximinoglycoside was obtained in crystalline condition in good to excellent 5The authors are indebted to Dr. R. E. D. McClung of this Department for his generous offer to provide the analog computer simulations shown in Fig. 1, which enabled us to obtain the calculated values listed in Table 1. yield (see 8,9,11,12, and 13). The compositions and n.m.r.…”

Results and Problems of O‐Glycoside Synthesis

“…The yields obtained on glucosylation of four alcohols by various methods are listed in Table 3"l. The tabulated data cholesterol (39), 1,2,3,4 [55] [a] Yield with protecting groups.…”

“…The yields are based on the amount of diisopropylideneglucose (54) in the startmg materials. (55) is formed in 59% yield, (58) in 52% yield (f <5% E-D-mannOSamine derivative), (57) in 43% yield (+ca. 1.5% a-o-mannose derivative).…”

Reduction of Isopropyl Tri-O-acetyl-2-oximino-α-D-hexopyranosides

“…This high ma~zno to gluco ratio (about 3 :2) for a borane reduction indicates that the stereochemical route of reduction can be influenced by groups neighboring to the oximino group. The catalytic hydrogenation of 2-(2-ox- (26). The g.c.…”