MAGNETIC PROTON RESONANCE SPECTROSCOPY OF BUFADIENOLIDES (STEROIDAL TOAD POISONS)

The NMR. spectra of nearly all bufadienolides (steroidal toad poisons) of known structure (aglycones and acetyl derivatives) were measured (some in various solvents) and evaluated. The results obtained allow the application of the principle of the self‐consistent chemical shift values (‘rule of additivity’) for the calculation of the chemical shifts of the 18‐ and 19‐ methyl groups. The frequencies of resonance and the coupling of the protons of the 17β‐pentadienolide ring and of the α‐protons of the functional groups were analysed. For the determination of the NMR. spectra of polyhydroxylated bufadienolides and cardenolides d6‐dimethylsulfoxide proved to be the most suitable solvent. In this solvent not only the nature but also the relative positions of several hydroxyl groups can be recognized, the rule of additivity being also applicable. On the basis of the data recorded the position and stereochemistry of functional groups in steroidal toad poisons of unknown structure can be determined with a high degree of probability. Copyright © 1969 Verlag GmbH & Co. KGaA, Weinheim