Conformation analysis of three germacranolides by the PM3 semi-empirical method

Abstract

The conformations of the C-6 lactonized germacranolides 1–3 were calculated by applying the PM3 semi-empirical method. The low-temperature 1H-NMR spectra of parthenolide (1) were also measured. The relations between the calculated and the experimentally determined geometries were established using a modified Karplus equation. The applied quantum-chemical calculations proved to be an efficient and easy-to-use tool for the elucidation and prediction of the properties of germacranolide-type sesquiterpene lactones.

Konformacije germakranolida 1–3, laktonizovanih u položaju (6), izračunate su primenom PM3 semi-empirijske MO metode. Takođe su snimljeni protonski NMR spektri partenolida (1) na niskim temperaturama. Pomoću modifikovane Karplusove jednačine je uspostavljena korelacija između eksperimentalno utvrđenih i izračunatih najstabilnijih konformacija. Zaključeno je da primenjena kvantno-hemijska izračunavanja brzo i pouzdano mogu predvideti i objasniti osobine seskviterpenskih laktona tipa germakranolida.