18464-08-9Relevant articles and documents
Oligosaccharide analogues of polysaccharides. Part 19. Synthesis of 2- (naphthalen-1-yl)ethyl cellooligoglycosides and [(naphthalene-1,8- diyl)di(ethane-2,1-diyl)] bis[cellooligoglycosides]
Xu, Jinwang,Vasella, Andrea
, p. 1728 - 1752 (2007/10/03)
Glucosyl, cellobiosyl, cellotriosyl, cellotetraosyl, and cellooctaosyl residues were attached to naphthalene-1,8-diethanol (3) with the goal of preparing mimics of cellulose I. Among the templates that were considered, 1,8-diethynylnaphthalene (1) led to unstable products, and glycosidation of naphthalene-1,8-dimethanol (2) gave orthoesters that could not be rearranged to glycosides (Scheme 1). The conformation of 3 in the crystal and of its dimethyl ether 14 in solution was studied by X-ray analysis and force-field calculation (Figs. 1-3). Rotation around the Ar-CH2 and CH2-CH2 bonds of 14 is only weakly hindered and the O···O distance of crystalline 3 (6.01 A) corresponds to the mean distance of the parallel chains of cellulose I(β). The acetylated glycosyl bromides 18 and 19 were prepared by a new convergent synthesis (Scheme 2). Glycosylation of 3 by the glycosyl bromides 15-19 under established conditions of the Koenigs-Knorr reaction proved problematic, particularly on account of an acetyl transfer blocking one of the hydroxyethyl groups. Basic zinc carbonate, however, promoted glycosylation of 12 and 3 by the glycosyl bromides 15-19 and did not lead to transacetylation (Scheme 3). The mono- to tetrasaccharides 32-35 and 42-45 were isolated in yields of 5682%, and the octasaccharides 36 and 46 in 32 and 16%, respectively. The mono- and disaccharides 32, 33, 42, and 43 were deacetylated with NaOMe in MeOH. Aqueous NaOH was used for the tri-, tetra-, and octasaccharides 34-36 and 44-46, as their partially deacetylated derivatives proved insoluble in MeOH. The fully deprotected saccharides 37-41 and 47-50 were isolated in over 90%, while the yield of the dioctaoside 51 was lower on account of its poor water solubility.
