Bioassay-guided isolation, identification, and evaluation of anti-inflammatory activity of β-boswellic alcohol and 3-o-acetyl-11-hydroxy-β-boswellic acid from the leaves of Boswellia serrata

Background: There are no in-depth studies on the extracts of the leaves of Boswellia serrata (BS), which contain many bioactive phytoconstituents and responsible for their anti-inflammatory effects. Objectives: The goal of this research plan was the isolation and purification of most active compounds from the leaves of BS via bioassay-guided fractionation based on anti-inflammatory activity. Materials and Methods: The silica gel column chromatographic techniques with different solvent systems were used for the separation of the constituents of the ethyl acetate-soluble fraction of BS leaves. The structures of the isolated compounds were assigned based on various spectroscopic analysis (high-resolution mass spectrometry,[1]H NMR, and[13]C NMR) and comparison with literature data. The anti-inflammatory activity of all crude extracts, subfractions of ethyl acetate extract, and two isolated new compounds were evaluated in cell-free (cyclooxygenase and 5-lipoxygenase) and cell-based assays (nitrite and tumor necrosis factor-alpha) in RAW264.7. Results: Bioassay-guided fractionation of the extracts of the leaves of BS afforded two ursane-type triterpenoids (compound 5, β-boswellic alcohol, and compound 6, 3-O-acetyl-11-hydroxy-β-boswellic acid) and other ten known triterpene acids. Compound 5 and 6 exhibited strong anti-inflammatory activity with an IC50value of a range 26.5–34.2 μM and 18.3–21.1 μM, respectively, in cell-free and cell-based assays. Conclusion: This is the first report on isolation and identification of β-boswellic alcohol and 3-O-acetyl-11-hydroxy-β-boswellic acid from the leaves of BS, which showed strong anti-inflammatory activity and holds great promise for the treatment of numerous inflammatory diseases.