Two New Eremophilane Sesquiterpenes and One New Resorcinol from Ligularia knorringiana

Two new eremophilane sesquiterpenes, 12-oxa-1β, 5β,8,9aβ-tetramethyl-4α,5-ethano-4aβ-hydroxy-7β,10aβ-epoxy-9β-angeloyloxy-1,2,3,4,4a,5,6,7,9,9a,10,10a- dodecahydro-anthracen-13-on (knorringianalarin A, 1) and 6,9-dien-8-oxoeremophil-12-nor-11-ketone (knorringianalarin B, 2), and a new resorcinol, 4-acetyl- 6-(2-methylpropionyl)-1,3-resorcinol (knorringianalarin C, 3) were isolated from the roots and rhizomes of Ligularia knorringiana, together with three known eremophilane sesquiterpenes (4-6). The structures of the new compounds were identified by spectroscopic methods including 2D-NMR techniques.