Conformational analysis of lappaconitine and heteratisine

The conformation of the carbon skeleton in diterpenoid alkaloids of the lappaconitine, heteratisine, and lycoctonine types was analyzed as a function of the nature of the substituents and intramolecular H-bonds and their states in the crystal based on x-ray structure analyses of lappaconitine and heteratisine and data in the Cambridge Crystallographic Data Centre. Ring A in these diterpenoid alkaloids adopted the boat or chair conformation depending on the presence or absence of an intramolecular H-bond between atoms of the skeleton N and O in the C1 position, respectively. The other rings C, D, and F of the framework did not undergo substantial conformational changes whereas rings B and E showed slight distortion that converted them to other similar canonical forms.