New cassane- and norcassane-type diterpenoids from the seed kernels of Caesalpinia sinensis and their anti-inflammatory activity in vitro

The first investigation of phytochemistry on the seed kernels of Caesalpinia sinensis led to the isolation and characterization of six new compounds including three tricyclic-type cassane diterpenoids ( 1 ‐– 3 ) and three norcassane-type diterpenoids ( 4 – 6 ), together with three know compounds ( 7 – 9 ). Compounds 1 – 9 represented the first discovery of cassane-type diterpenoids from C. sinensis. Their structures were elucidated by a combination of spectroscopic analysis, single-crystal X-ray diffraction experiment and ECD calculation. The characters for compounds 4 and 5 possessing the 15,16-degradative cassane skeleton were observed, which was extremely rare structural type in the genus Caesalpinia . The anti-inflammatory activities of all isolates were evaluated via examining their inhibitory effects against NO production in LPS-simulated RAW 264.7 cells. The results demonstrated that compound 1 exhibited the most significantly inhibitory efficacy with inhibition rate 67.3% at 10 μM. The iNOS enzyme activity assay further revealed that compound 1 showed potent NO inhibitory effect by reducing the enzymatic activity of iNOS. • Six undescribed cassane diterpenoids were isolated from the seed kernels of Caesalpinia sinensis . • Cassane derivatives were firstly found in this plant, which enriched the chemical constituents of C. sinensis . • Compounds 1-9 exhibited different levels of anti-inflammatory activities in LPS-simulated RAW 264.7 cells. • 1 significantly inhibited the production of NO through suppressing the iNOS enzymatic activity.