A One- and Two-Dimensional ¹H and ¹³C N.M.R. Study of Some Lichen Triterpenoids of the Pyxinol Group

Abstract

A complete assignment of the ¹³C and ¹H n.m.r. resonances of the lichen triterpenoids, pyxinol, 3,25-di-O-acetylpyxinol and 3,12,25-tri-O-acetylpyxinol has been achieved by using a combination of one- and two-dimensional n.m.r. data and T₁ values. Hydrogen bonding between the 12β- hydroxy group and the carbonyl oxygen of the 25-acetoxy group of 3,25- di-O-acetylpyxinol leads to the furan ring system adopting a  conformation different from that adopted by 25-hydroxy analogues, hence differing chemical shifts are observed for some of the carbons of rings C and D and the furan ring.