2-DIMENSIONAL PROTON CHEMICAL-SHIFT CORRELATED NMR-SPECTROSCOPY OF DIGITOXOSE

The hydroxyl proton coupled 1H NMR spectra of solutions of .beta.-D-digitoxopyranose and of an equilibrated mixture of the 4 ring forms of D-digitoxose in dimethylsulfoxide-d6 were assigned completely by 2-dimensional, proton chemical shift correlated NMR spectroscopy and spin decoupling at 400 MHz. Analysis of resolution enhanced, 1-dimensional 1H NMR spectra yielded an almost complete set of CH and OH proton-proton coupling constants for the 4 ring forms. The free aldehydo form of D-digitoxose in dimethylsulfoxide-d6 solution was detected by means of its characteristic H-1 quartet at .delta. 9.687. Quantitative analysis of the equilibrated mixture of the five forms of D-digitoxose gave the composition: .alpha.-pyranose, .beta.-pyranose, .alpha.-furanose, .beta.-furanose, aldehydo form, 11.2, 67.3, 8.4, 13.0 and 0.1%, respectively. The 4C1 chain conformations were assigned to the .alpha.- and .beta.-pyranose forms by analysis of the coupling constants and are discussed qualitatively in terms of their relative stabilities.