13C NMR Studies of [l-13C]Aldoses: Empirical Rules Correlating Pyranose Ring Configuration and Conformation with 13C Chemical Shifts and 13C-13C Spin Couplings

Abstract

Glycolaldehyde, DL-glyceraldehyde, D-erythrose, D-threose, D-arabinose, D-lyxose, D-ribose, D-xylose, D-allose, D-altrose, D-galactose, D-glucose, D-gulose, D-mannose, and D-talose have been synthesized and purified with [13C]-enrichment (99 atom %) at the anomeric carbon. 13C NMR spectra (75 MHz) of the natural and enriched compounds have been obtained in 2H2O, from which 13C-13C couplings to the enriched sites were measured. On the basis of 13C-13C coupling patterns, 13C chemical shifts for the aldoses were confirmed and some signals (e.g., talose) were reassigned. Complex spectra of enriched compounds were simplified by employing the INADEQUATE method of data collection (spectral editing), and signal assignments to specific tautomers were made in several cases with the aid of selective13C-decoupling An empirical method has been developed that predicts 13C chemical shifts in aldopyranose rings and has been used to examine the effect of pyranose structure on13C chemical shifts. The dependence of 13C-13C couplings involving Cl on furanose and pyranose ring configuration and conformation has been reexamined, and previous correlations have been modified to accommodate new data. © 1987, American Chemical Society. All rights reserved.