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Relevant academic research and scientific papers

Studies of the series of cellooligosaccharide peracetates as a model for cellulose triacetate by 13C CP/MAS NMR spectroscopy and X-ray analyses

The series of crystalline oligomers from α-cellobiose octaacetate through α-cellohexaose eicosaacetate, listed as below, was prepared from homogeneous acetylation of the corresponding cellooligosaccharides and characterized by 13C CP/MAS NMR spectroscopy and X-ray analysis in order to obtain the structural models of cellulose triacetate (CTA) in solid state. Progressing toward the hexamer, the NMR spectral feature of the oligomers, in comparison with two allomorphs of CTA I and CTA II, gradually approached that of CTA I. Specifically, chemical shifts of both the hexamer and the pentamer were in considerable respective agreement with those of CTA I. In addition, X-ray diffraction patterns of the oligomers established that the crystalline pentamer and hexamer have a CTA I lattice in spite of recrystallization from ethylacetate-hexane. We therefore concluded that the pentamer and hexamer would be useful models for the CTA I structure. Copyright (C) 1999 Elsevier Science Ltd.

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]

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.

First synthesis of cellooctaose by a convergent synthetic method

The first chemical synthesis of cellooctaose by a convergent synthetic method is described. A challenging glycosylation between cellotetraosyl donor 5 and acceptor 7 proceeded in a one-step reaction using a high-vacuum system for anhydrous glycosylation a