Structure Investigation and Proton and Carbon-13 Assignments of Digitonin and Cholesterol using Multidimensional NMR Techniques

Digitonin, a spirostanolglycoside from the seeds of Digitalis purpurea L., is a highly haemolytically active saponin. This effect is considered to be based on complex formation between cholesterin and digitonin. Against the background of investigations concerning the interaction between glycosides and membrane components, and the determination of the structure of the digitonin–cholesterol complex, a detailed NMR spectroscopic investigation of thecomplex-forming compounds was carried out. Assignment of the 1H and 13C spectra of digitonin was made by using one- and two-dimensional NMR techniques (1D TOCSY, 2D TOCSY, HMQC and HMBC); 3D TOCSY–ROESY, 1D ROESY and HMBC experiments provided information about the sequence of the oligosaccharide chain and the position of glycosidations. The precise analysis of the COSY, HMQC und HMBC spectra made the assignment of all proton resonance signals of cholesterol possible for the first time.