New tirucallane-type triterpenoids from the resin of Boswellia carterii and their NO inhibitory activities

Six new tirucallane-type triterpenoids ( 1 − 6 ), along with ten known triterpenoids, were isolated from methylene chloride extract of the resin of Boswellia carterii Birdw. By the application of the comprehensive spectroscopic data, the structures of the compounds were clarified. The experimental electronic circular dichroism spectra were compared with those calculated, which allowed to assign the absolute configurations. Compounds 5 and 6 possesed a 2, 3-seco tirucallane-type triterpenoid skeleton, which were first reported. Their inhibitory activity against NO formation in LPS-activated BV-2 cells were evaluated. Compound 9 showed appreciable inhibitory effect, with an IC₅₀ value of 7.58 ± 0.87 μmol·L⁻¹.