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From the whole plant of Euphorbia peplus L., a new diterpene based on a rare pepluane skeleton, named pepluanone (1), was isolated together with a known pepluane diterpene (2). The stereostructure of pepluanone was determined on the basis of an extensive NMR study, MS data, and chemical reaction. The ability of these compounds to act as antiinflammatory agents has been evaluated for the first time by in vivo tests on carrageenin-induced rat paw edema, an experimental model of acute inflammation. Comparison of the bioactivity of pepluanone and compound 2 in terms of chemical structure, evidenced the high efficiency of pepluanone and the absence of appreciable activity for compound 2, thus giving a first insight into the structure-activity relationship. Further in vitro experiments performed on pepluanone let us hypothesize that its activity could be explained in reducing the production of nitric oxide, prostaglandin E(2), and TNF-alpha by inhibiting the expression of inducible nitric oxide synthase, cyclooxygenase-2, and TNF-alpha mRNA through the down-regulation of NF-kappaB binding activity.

The Mediterranean spurge Euphorbia characias L. afforded twelve new diterpenes based on a jatrophane skeleton named euphocharacins A-L. Their chemical structures were elucidated by extensive nuclear magnetic resonance and mass spectrometry methods. Euphocharacins A-L were tested as inhibitors of the daunomycin-efflux activity of P-glycoprotein from cancer cells. The results were used to extend the structure-activity relationship established for this class of compounds, highlighting the positive effects of propyl and benzoyl groups at positions 3 and 9, respectively, and evidencing the negative effect of a free hydroxyl group at position 2. Among the tested compounds, euphocharacins C and I showed an activity higher than cyclosporin to inhibit Pgp-mediated daunomycin transport.

From the whole plant of Euphorbia peplus L., five new diterpenes based on a jatrophane skeleton (pepluanins A-E, 1-5) were isolated, together with two known analogues (6 and 7), which served to divulge in detail the structure-activity relationships within this class of P-glycoprotein inhibitors. The results revealed the importance of substitutions on the medium-sized ring (carbons 8, 9, 14, and 15). In particular, the activity is collapsed by the presence of a free hydroxyl at C-8, while it increases with a carbonyl at C-14, an acetoxyl at C-9, and a free hydroxyl at C-15. The most potent compound of the series, pepluanin A, showed a very high activity for a jatrophane diterpene, outperforming cyclosporin A by a factor of at least 2 in the inhibition of Pgp-mediated daunomycin transport.

The new diterpenoids terracinolides J-L (1-3), 13alpha-OH terracinolide F (8), abeodendroidin F (11) and epiabeodendroidin F (12) have been identified from Euphorbia dendroides L. The new compounds and six co-occurring known terracinolides were tested as inhibitors of the drug-efflux activity of P-glycoprotein from cancer cells. The results were used to extend the structure-activity relationships established for this class of compounds highlighting the relevance of substitution at positions 2, 3, 6, and 15 and disclosing a remarkable tolerance toward connectivity changes in the terpenoid core.

The Mediterranean spurge Euphorbia dendroides L. afforded a series of 10 closely related jatrophane polyesters, nine of which are new, which served as a base for the establishment of structure-activity relationships within this class of P-glycoprotein inhibitors. The results, while pointing to the general role of lipophilicity for activity, also highlighted the relevance of the substitution pattern at the positions 2, 3, and 5, suggesting the involvement of this fragment in binding. The most powerful compound of the series, euphodendroidin D (4), outperformed cyclosporin by a factor of 2 to inhibit Pgp-mediated daunomycin transport.