BI- and Tricyclic Diterpenoids from Halimium viscosum

Abstract The study of the acid and neutral parts of the n-hexane extract of Halimium viscosum (S. Joao da Pesqueira, Portugal) has led to the isolation of various known diterpenoids with the ent-halimane skeleton. Five new compounds have now been isolated, one with the ent-halimane skeleton, and four with the valparane skeleton, two of them with the valparane skeleton degraded. The structures of these compounds, determined by spectroscopic methods using 2D experiments (1H-13C, HMQC and HMBC), were dimethyl 1(10)-halimen-15,18-dioate, dimethyl 3,19-dinor-15-valparen-2,4-dioate, methyl 16-nor-2,3-secovalpara-3,15-dioxo-2-oate, 1,3,5,15-valparatetraene and 3R-4α-methoxy-15-valparen-2-one.