Fungal metabolites. Part IV. Solvent and transition metal effects on proton chemical shifts in multifunctional molecules

Abstract

During attempts to define the stereochemistry of secalonic acids isolated from fungi, we made use of a europium shift reagent and were able to define the major complexing sites in these multifunctional compounds. However, we also observed changes in the chemical shifts of protons near hydroxy-groups in the secalonic acids simply on change of solvent. From an examination of the ¹H n.m.r. spectra of sterols, terpenols, other alcohols, and phenols, we have been able to propose a relationship between the amount by which the chemical shift of a proton moves on change of solvent and the distance of the proton from a hydroxy-group. The relationship can be used to determine the torsional angle between a methyl and a hydroxy-group situated in a 1,2-relationship. In multifunctional compounds, these solvent-induced changes can be influenced by other groups close to the proton considered.