The synthesis of polysaccharides containing oligosaccharide repeating units has been accomplished by polycondensation of suitable monomers, namely, trityl ethers of 1,2-0(1-cyanoethylidene) derivatives of the respective oligosaccharides'-3. These monomers were prepared from 1,2-0-(1-cyanoethylidene) derivatives of oligosaccharides, which, in turn, were obtained by the reaction of acetylated glycosyl bromides with silver cyanide in boiling xylene4 (Coxon-Fletcher procedure') or with sodium (or potassium) cyanide in acetonitrile2'6. As part of our study of the synthesis of heteropolysaccharides, we have examined an alternative approach to 1,20cyanoethylidene derivatives of oligosaccharides, namely, glycosylation of monosaccharide 1,20cyanoethylidene derivatives which are themselves glycosylating agents (cf. ref.
2), and now report the preparation of some disaccharide 1,20cyanoethylidene derivatives by this approach. Two types of monosaccharide cyanoethylidene derivatives were employed, containing free hydroxyl groups or a trityl group. The former were glycosylated by using acylglycosyl bromides under Helferich conditions (acetonitrile, mercuric cyanide), and the latter using sugar 1,2-thio-orthoesters.
Interaction of the diol 1 {m.p. 108-108.5" (from chloroform), [o]; +12.5" (c 2.5, chloroform), obtained by Zemplen deacetylation of the corresponding diacetate'] with 2,3,4-tri-Oacetyl-ol+rhamnopyranosyl bromide (1.4 equiv.) afforded disaccharide derivatives 2 and 3" (Table I) along with a trisaccharide derivative (14%). Identical products were obtained on benzoylation of 3 and rhamnosylation of 4 {m.p. 108.5-109.5" (from ether-hexane),
[a]$ -13" (c 2.6, chloroform), prepared by selective benzoylation of 1). Analogous glycosylation of 1 using 2,3,4,6-tetra-U-acetyl-o-D-glucopyranosyl bromide followed by acetylation gave the disaccharide derivatives 5-7 together with a trisaccharide derivative (4%). Glucosylation of the 4-acetate of 1 afforded 5 and 6 in the ratio -4: 1 (r3C-n.m.r. data; total yield, 36%). Disaccharides 8 and 9 (ratio -2 : 3; total yield, 37%) were obtained from 4.
*All new compounds gave correct C, H, and N analyses, and the 'H-and '%r.m.r. spectra were inaccord with the structures assigned.