New Abietane Diterpenes from Euphorbia Pseudocactus Berger (Euphorbiaceae) and Their Antimicrobial Activity

BACKGROUND: Euphorbia is the largest genus in Euphorbiaceae. Terpenoids were isolated from most species of this genus. OBJECTIVE: Since no previous study was reported about Euphorbia pseudocactus Berger, we started here a phytochemical investigation on this species to isolate and identify its terpenoid constituents and to estimate the antimicrobial activity of the isolated compounds. MATERIALS AND METHODS: The n-hexane fraction of the ethanolic extract of E. pseudocactus Berger was chromatographed on silica gel columns, the structures of the isolated compounds (1–5) were identified based on their MS, 1 D, and 2 D NMR spectral data. The antimicrobial activity of the n-hexane fraction and the isolated compounds (1–4) was investigated using diffusion plate method against Gram-positive (Staphylococcus aureus [12600] and Bacillus subtilis [6051]) and Gram-negative (Pseudomonas aeruginosa [10145] and Escherichia coli [11775]) bacteria, yeast (Candida albicans [7102]), and fungi (Aspergillus flavus). RESULTS: Two triterpenes (glut-5-en-3 β-ol [1] and olean-12,15-diene-3 β-ol [2]) and three abietane diterpene (3-hydoxy-19-cyclopropenoyloxy-abietane [3], ent-abieta-9,12,14-triene-12,16-olide [4], and 12,19-dihydroxy-abieta-5-ene [5]) were isolated. Compound 1 exhibited no antibacterial activity against the tested bacteria, compound 2 and n-hexane fraction exhibited weak activity, whereas compounds 3 and 4 showed moderate activity. All samples showed no activity against the tested yeast and fungi. DISCUSSION AND CONCLUSION: Five compounds were isolated for the 1(st) time from E. pseudocactus Berger, three of them (3–5) are new natural compounds. As the major isolated compound (1) exhibited no antimicrobial activity, the observed activity of the n-hexane fraction is mainly due to its diterpenoid constituents. SUMMARY: Two known triterpenes and three new diterpenes were isolated from n-hexane fraction of Euphorbia pseudocactus. The abietane diterpenoids showed higher antimicrobial activity than n-hexane fraction. Abbreviations used: EtOAc: Ethyl acetate, TLC: Thin layer chromatography.