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 beta-ol [1] and olean-12,15-diene-3 beta-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 1st 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.