Caesalactones A-I, rare 8,15-seco-ent-kaurane diterpenoids from the leaves and stems of Caesalpinia enneaphylla with cytotoxic activities

Natural products, especially diterpenoids, are widely used for clinical treatments with commercially available drugs. For the purpose of finding much more bioactive diterpenoids, twelve 8,15- seco - ent -kaurane-type diterpenoids including 9 new ones, caesalactones A-I ( 1–9 ), along with 3 new natural products ( 10–12 ) were obtained from the leaves and stems of Caesalpinia enneaphylla . Their planar structures were established based on the comprehensive investigations of one dimensional nuclear magnetic resonance (1D NMR), 2D NMR and high resolution electrospray ionization mass spectrometry (HR-ESI-MS) data. The absolute configurations of compounds 1 and 2 were established by single-crystal X-ray diffraction, whereas those for the others were established by circular dichroism (CD) data analysis. Compounds 1–12 were identified as a group of rare 8,15- seco - ent -kaur-16-en-8,15-olides. Hitherto, only five representative structures of this type have been found among ent -kaurane derivatives. Cytotoxic activities evaluation revealed that compound 8 exhibited significant cytotoxicity superior to the positive control cisplatin against MDA-MB-231, MCF-7 and HCT-116 cell lines with IC 50 values of 7.03, 26.8 and 7.76 μ M, respectively. This study suggested the isolation of 8,15- seco - ent -kaurane diterpenoids from C. enneaphylla had new potential applications in pharmaceutical industry. • Twelve 8,15- seco - ent -kaurane-type diterpenoids, including 9 new ones, were isolated from Caesalpinia enneaphylla . • The absolute configurations were established by single-crystal X-ray diffraction and circular dichroism (CD) analysis. • Compound 8 exhibited significant cytotoxicity superior to the positive control cisplatin against MDA-MB-231, MCF-7 and HCT-116 cell lines .