Natural-abundance carbon-I 3 n.m.r. spectra of all the glucobioses and of four selected glucotrioses in aqueous solution have been measured and are discussed. Peak assignments were made on the basis of comparison with the spectra of methyl glucopyranosides, four mono-0-methylglucoses and five methyl glucobiosides. Carbon-I 3 n.m.r. spectroscopy proved to be a useful tool for stereochemical characterisation of these oligosaccharides. In addition, carbon-I 3 n.m.r. spectra of the a-limit dextrins from glycogen and amylopectin have been measured and the differences between them are discussed.SPECTROMETRIC methods (i.r.,l o.r.d.,2 and lH n.m.r.3~4) have been used for establishing the configuration of glycosidic linkages of oligosaccharides and polysaccharides. The Karplus equation in lH n.m.r. has been applied extensively in the structural studies of monosaccharide pyranose and furanose derivatives.5 Positions of linkage in oligosaccharides have been determined by chemical methods and by biochemical degradation.+lO Recently, the 13C n.m.r. spectra of monosaccharides 11,12 and some common oligosaccharides 13*14 have been published and interpreted. These reports show that 13C chemical shift differences in sugars could be explained in terms of steric hindrance and proximity effectsWe have already reported that 13C n.m.r. spectroscopy can be used for the determination of the anomeric configurations of glucobi~ses.~~ We now describe the application of 13C n.m.r. to the configurational and conformational analysis of glucose oligomers and polymers, as well as to the determination of their linkage positions. Some tentative assignments l5 arc corrected on the basis of further data reported here. RESULTS AND DISCUSSIONIn 13C n.m.r. spectroscopy, it is difficult and laborious t o give a full peak assignment of sugar carbon atoms, although information from previous work has made it considerably ~imp1er.ll-l~ Roberts and his co-workers l1 showed that (a) methylation of a hydroxy-group effects

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New Syntheses of Nucleosides 149 with water. Evaporation of the ether solutions gave 114 mg. and 179 mg., respectively, of an amorphous light brown powder which would not crystallize from methanol. Acidification of the basic extracts in both cases, yielded reddish tar.Acknowledgment.-We wish to thank W. D. Ollis of the University of Bristol and Gideon Fraenkel of this department for enlightening discussions.

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