Triterpenes from Euphorbia hirta and their cytotoxicity

AIM:To investigate the chemical constituents of the stems,leaves and roots of Euphorbia hirta,and to test for the cytotoxic and antimicrobial potentials of the major constituents of the plant.METHODS:The compounds were isolated by silica gel chromatography and their structures were elucidated by NMR spectroscopy.The cytotoxicity tests were conducted using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT) assay,while the antimicrobial tests employed the agar well method.RESULTS:The air-dried stems of E.hirta afforded taraxerone 1,a mixture of 25-hydroperoxycycloart-23-en-3β-ol(2a) and 24-hydroperoxycycloart-25-en-3β-ol(2b)(sample 2) in a 2:1 ratio,and another mixture of cycloartenol(3a),lupeol(3b),α-amyrin(3c) and β-amyrin(3d)(sample 3) in a 0.5:4:1:1 ratio.The air-dried leaves of E.hirta yielded sample 2 in a 3:2 ratio,sample 3 in a 2:3:1:1 ratio,phytol and phytyl fatty acid ester,while the roots afforded sample 2 in a 2:1 ratio,sample 3 in a 2:1:1:1 ratio,a mixture of cycloartenyl fatty acid ester 4a,lupeol fatty acid ester 4b,α-amyrin fatty acid ester 4c and β-amyrin fatty acid ester 4d(sample 4) in a 3:2:1:1 ratio,linoleic acid,β-sitosterol and squalene.Compound 1 from the stems,sample 2 from the leaves,and sample 3 from the stems were assessed for cytotoxicity against a human cancer cell line,colon carcinoma(HCT 116).Sample 2 showed good activity with an IC50 value of 4.8 μg·mL-1,while 1 and sample 3 were inactive against HCT 116.Sample 2 was further tested for cytotoxicity against non-small cell lung adenocarcinoma(A549).It showed good activity against this cell line with an IC50 value of 4.5 μg·mL-1.Antimicrobial assays were conducted on 1 and sample 2.Results of the study indicated that 1 was active against the bacteria:Pseudomonas aeruginosa and Staphylococcus aureus,but was inactive against Escherichia coli and Bacillus subtilis.Sample 2 was active against the bacteria:Pseudomonas aeruginosa,Staphylococcus aureus and Escherichia coli and fungi:Candida albicans and Trichophyton mentagrophytes.It was inactive against Bacillus subtilis and Aspergillus niger.CONCLUSIONS:The triterpenes:2a,2b,3a,3b,3c and 3d were obtained from the stems,roots and leaves of E.hirta.Taraxerol(1) was only isolated from the stems,the leaves yielded phytol and phytyl fatty acid esters,while the roots afforded 4a-4d,linoleic acid,β-sitosterol,and squalene.Triterpene 1 and sample 2 were found to exhibit antimicrobial activities.Thus,these compounds are some of the active principles of E.hirta which is used in wound healing and the treatment of boils.The cytotoxic properties of sample 2 imply that triterpenes 2a and 2b contribute to the anticancer activity of E.hirta.