Labdane diterpenes from Cistus symphytifolius

4 pages.
The investigation of the aerial part of Cistus symphytifolius afforded, in addition to sitosterol, trimethoxykaempferol, cativic acid, labdenic acid, labdanolic acid and labdan-8α,15-diol, three new bicyclic diterpenes: cistadienic acid, cistenolic acid and labd-13(E)- ene-8α,15-diol. The structures of these were determined by spectral studies and correlations. CD spectral studies showed that cistenolic acid and salvic acid are enantiomeric compounds, so the stereochemistry of salvic acid (7α-hydroxy-labd-8(17)-ene-15-oic acid) should be changed to 7β-hydroxy-eperu-8(17)-ene-15-oic acid (7β-hydroxy-ent-labd-8(17)-ene-15-oic acid).
Part of this work was subsidized by the Comisión Asesora de Investigación Científica y Técnica. M.C. wishes to thank the Centro Iberoamericano de Cooperación of Spain for a fellowship.