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. Show more