13C NMR spectra of a number of penta- and hexacyclic triterpenoids derived from glycyrrhetic acid

The¹³C NMR spectra of 22 derivatives of 18α- and 18β-glycyrrhetic acids that have been investigated and an assignment of the signals has been made. It has been shown that a modification of the carboxy group of glycyrrhetic acid leads mainly to a change in the chemical shifts of the α-, β-, and γ-carbon atoms of ring E. The assignment of a number of signals has been confirmed by the use of the shift reagent Eu(fod)_s. It has been established that the C₂₈ and C₁₆ signals are the most sensitive to a change in the C₁₈ configuration in the spectra of glycyrrhetic acid derivatives.