Tricyclic Diterpenes from Halimium viscosum.

Abstract Several tricyclic diterpenes with a valparane skeleton have been isolated from the aerial parts of Halimium viscosum collected at Celorico da Beira, Portugal. Two new compounds have been identified as valpara-2,15-diene-1,4-dione and 3α,4α-epoxyvalpar-15-en-2-one, besides the previously known compounds: valpara-2,13-diene; valpara-2,15-diene; valpara-3,15-dien-2-one; 2β,3β-epoxyvalpar-14-ene and 1β-metoxy-valpara-2,15-diene. Their structures have been established by means of 2D NMR experiments ( 1 H 13 C, and HMQC) and X-ray studies. This plant sample may represent a new chemotype.