A phytochemical investigation of the whole plant of Juniperus oblonga led to the isolationof 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 (2–3, 6–12), two lignans (4, 5),and a coumarin (13). The structures of all the compounds were elucidated on the basis ofspectrometric data, primarily one‐dimensional (1D)‐ and two‐dimensional (2D)‐NMR and massspectrometry. Electronic circular

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... ism (ECD) calculations determined the absoluteconfiguration of 1. In addition, the isolated compounds were evaluated for their cytotoxic activityagainst 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 rangingfrom 24.41 μM to 58.39 μM and trilobinone (10) showed weaker activity with IC50 values rangingfrom 56.93 μM to 79.98 μM. None of the isolated diterpenoids have been previously reported fromJuniperus oblonga, and five compounds are here reported from the genus Juniperus for the first time.