¹³C NMR signal assignment of friedelin and 3α‐hydroxyfriedelan‐2‐one

Abstract

Abstract The 13 C NMR spectrum of the pentacyclic triterpene friedelin was fully assigned, taking into account signal multiplicities, correlations of the carbon lines with known proton resonances and Eu‐induced shifts. This work clarifies the situation prevalent in the literature, in which three separate groups have published contradictory information. In addition, the carbon and proton spectra of the naturally occurring 3α‐hydroxyfriedelan‐2‐one and its synthetic acetate were analysed. The different preferred conformations of the D/E rings for friedelin (boat‐boat) and polpunonic acid (chair‐chair) are rationalized.