Three unreported ent-abietane-type norditerpene lactones, euphohelides A−C (1−3), and 11 known analogs (4− 14) were isolated from the whole plants of Euphorbia helioscopia L. Euphohelide A (1) is an unprecedented 2-nor-ent-abietane lactone bearing a unique 5/6/6/5 tetracyclic system. Euphohelides B (2) and C (3) possess 2-nor-6/6/6/5 and 2,3-dinor-5/6/6/5 dilactone tetracyclic moieties, respectively. Their structures were established by spectroscopic methods, computational ECD, and X-ray crystallographic analyses. A biomimetic synthesis of 1 was achieved from precursor 4 based on the speculative biogenetic pathway. Compounds 1 and 5 significantly alleviated the release of LPS-induced NO with IC 50 values of 32.98 ± 1.13 and 33.82 ± 3.25 μM, which might be related to the regulation of the NF-κB signaling pathway.

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