A new tigliane-type diterpene from Euphorbia dracunculoides Lam

Abstract One new tigliane-type diterpene, 4-deoxy-4(β)H-8-hydroperoxyphorbol-12-benzoate-13-isobutyrate (1), together with two known diterpenoids, 3-acetyl-5,8-dibenzoyl-14α-propanoyl-13,17-epoxy-7-myrsinaone diterpene with C9–C10 cyclised to form an additional lactone ring (2), Euphodendriane A (3) have been isolated from the whole plants of Euphorbia dracunculoides Lam. Their structures were elucidated by means of extensive spectroscopic analysis (NMR and HR-ESI-MS) and comparison with data reported in the literature. This is the first isolation of 8-hydroperoxy tigliane diterpene (1) from the genus of Euphorbia. All compounds were evaluated for their antifungal activities.


Introduction
Euphorbia is the largest genus of the plant family Euphorbiaceae, with approximately 2160 species. Many plants from the genus Euphorbia are used as a folk medicine for the treatment of skin diseases, diarrhoea, oedemas, etc. The major characteristic constituents of the genus are diterpenoids with many different core skeletons, including jatrophanes, lathyranes, tiglianes, daphnane, ingenanes, myrsinols, etc. (Shi et al. 2008;Ferreira et al. 2013;Ghanadian et al. 2013;Rehman et al. 2014;Vasas & Hohmann 2014). Euphorbia dracunculoides Lam is a perennial herb mainly distributed in Tropical African, South Europe and South-west Asia. The plant has been used ethnobotanically for its purgative and diuretic purposes in India.
Previous phytochemical studies on E. dracunculoides Lam led to the isolation of a number of structurally diverse diterpenoids, triterpenoids, etc. . In this study, one new tigliane-type diterpene (1), together with two known diterpenoids (2 and 3) (Figure 1) has been isolated from E. dracunculoides Lam. All isolated metabolites (1-3) were evaluated for their antifungal activities against Candida albicans. Herein, we report the isolation, structure elucidation and antifungal activities of isolated compounds.
All isolated metabolites (1-3) were found to be inactive at the highest test concentration of 128 μg/mL used against the pathogenic fungi C. albicans.

Plant material
The whole plants of E. dracunculoides Lam were collected in Lijiang, Yunnan Province, China, in July, 2012, and identified by Prof Fan Du. A voucher specimen (No. 120701) is deposited in the Key Laboratory for Forest Resources Conservation and utilization in the Southwest Mountains of China, Southwest Forestry university, Kunming City, Yunnan Province, China.

Antifungal assays
Antifungal activity was determined against the pathogenic fungi C. albicans, using the microplate assay methods described in the previous publication (Shi et al. 2015). Amphotericin B was used as the positive control.

Supplementary material
Supplementary material relating to this article are available online, alongside Figures S1-S15 and  Table S1.