Structural and stereochemical studies of a tetralin norsesquiterpenoid from Ligularia kangtingensis

A chiral tetralin norsesquiterpenoid, ligukangtinol, was isolated from the plant Ligularia kangtingensis. Its planar structure was determined by extensive analysis of spectroscopic data (MS, IR, and NMR), and (1S,3R) absolute configuration of the tetralin ring was established by TDDFT-ECD calculations of the solution conformers. Conformational analysis and ECD calculations proved that the semiempirical helicity rules of 6-hydroxytetralins correlating the (1)L(b) Cotton effect and P/M helicity of the fused carbocyclic ring correctly predicts the absolute configuration and thus can be used for the configurational assignment of related substituted tetralin derivatives.