Labdane diterpenoids from Leonotis leonurus.

Abstract Three known (leoleorins A–C) and eight hitherto unknown (leoleorins D-J and 16- epi -leoleorin F) labdane diterpenoids, were isolated from leaves of Leonotis leonurus . The absolute configurations of leoleorins A and D were established by X-ray crystallographic analyses. In a competitive binding assay, all isolated compounds showed inhibition in excess of 50% at various CNS receptors. Leoleorin C showed moderate binding affinity ( K i  = 2.9 μM) for the Sigma 1 receptor.