Terpenes from the gum resin of Boswellia carterii and their NO inhibitory activies

Three new terpenes, classified as one cembrane-type diterpenoid (rel)-(1S,5R,7E,11E)-1-isopropyl-8,12-dimethyl-4-methylenecyclotetradeca-7,11-diene-1,5-diol (1), one dinortirucallane-type triterpene 20,21-dinortirucalla-8,24-diene-3β-ol-7-one (2) and one ursane-type triterpene 21β-hydroxy-3-O-acetyl-11-keto-boswellic acid (3), respectively, along with four known triterpenes, were isolated from the gum resin of Boswellia carterii. Their structure elucidations were achieved by in-depth spectroscopic examination, mainly including experiments and analyses of multiple 1D- and 2D-NMR and HR-ESI-MS. The effects on nitric oxide (NO) production in lipopolysaccharide (LPS)-activated RAW264.7 cells of all the isolated compounds were evaluated in vitro. Compound 1, 4, 5 and 7 exhibited potent inhibitory effects on NO production with IC50 values of 1.32, 3.04, 1.42, and 3.25 μM.