TRICYCLIC DITERPENES FROM HALIMIUM-VISCOSUM

Several tricyclic diterpenes with a valparane skeleton have been isola ted from the aerial parts of Halimium viscosum collected at Celorico d a Beira, Portugal. Two new compounds have been identified as valpara-2 ,15-diene-1,4-dione and 3 alpha,4 alpha-epoxyvalpar-15-en-2-one, besid es the previously known compounds: valpara-2,13-diene; valpara-2,15-di ene; valpara-3,15-dien-2-one; 2 beta,3 beta-epoxyvalpar-14-ene and 1 b eta-metoxyvalpara-2,15-diene. Their structures have been established b y means of 2D NMR experiments (H-1-C-13, and HMQC) and X-ray studies. This plant sample may represent a new chemotype. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.