13C NMR spectra of a number of penta- and hexacyclic triterpenoids derived from glycyrrhetic acid
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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.
KeywordsCarboxy Group Upfield Shift Singlet Signal Shift Reagent Boron Trifluoride Etherate
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