Labdane and Abietane Diterpenoids from <i>Juniperus oblonga</i> and Their Cytotoxic Activity

A phytochemical investigation of the whole plant of Juniperus oblonga led to the isolation of one previously undescribed labdane diterpenoid, (4R,5S,9S,10R)-13-des-ethyl-13-oxolabda-8(17),11E-dien-19-oic acid (1), together with nine known diterpenoids (2&#8211;3, 6&#8211;12), two lignans (4, 5), and a coumarin (13). The structures of all the compounds were elucidated on the basis of spectrometric data, primarily one-dimensional (1D)- and two-dimensional (2D)-NMR and mass spectrometry. Electronic circular dichroism (ECD) calculations determined the absolute configuration of 1. In addition, the isolated compounds were evaluated for their cytotoxic activity against three human tumor cell lines (HepG2, MCF-7, and HeLa). 6,12-Dihydroxyabieta-5,8,11,13-tetraen-7-one (6) showed moderate cytotoxicity against all three cell lines with IC50 values ranging from 24.41 &#956;M to 58.39 &#956;M and trilobinone (10) showed weaker activity with IC50 values ranging from 56.93 &#956;M to 79.98 &#956;M. None of the isolated diterpenoids have been previously reported from Juniperus oblonga, and five compounds are here reported from the genus Juniperus for the first time