[C-13]-ENRICHED METHYL ALDOPYRANOSIDES - STRUCTURAL INTERPRETATIONS OF C-13-1H SPIN-COUPLING CONSTANTS AND H-1 CHEMICAL-SHIFTS

A series of methyl D-aldopentopyranosides and D-aldohexopyranosides ha ving different configurations has been synthesized with single sites o f C-13-enrichment at various sites, and one-, two-, and three-bond C-1 3-H-1 spin-coupling constants ((1)J(CH), (2)J(CH), and (3)J(CH)) in th ese compounds have been obtained in (H2O)-H-2 by 1-D and/or 2-D NMR me thods. The effects of ring configuration and conformation on these J(C H) values were assessed with the aim of identifying specific structura l features that affect their magnitudes and signs. H-1 chemical shifts for the same compounds were also measured, and the data were used to derive empirical relationships between chemical shift and aldopyranosy l ring configuration. The correlations obtained on these conformationa lly-stable glycosides have implications for the interpretation of simi lar NMR parameters in biologically-important oligosaccharides and in c onformationally flexible aldofuranosyl rings such as those found in DN A and RNA.