Phyllanfranins A-F, anti-inflammatory ent-cleistanthane diterpenoids from Phyllanthus franchetianus

A comprehensive chemical investigation of the EtOAc extract derived from the dried branches and leaves of Phyllanthus franchetianus H. Lév had successfully resulted to the isolation of six undescribed cleistanthane diterpenoids phyllanfranins A-F (1-6), along with three known compounds phyllarheophol C (7), phyacioid C (8), and spruceanol (9). The chemical structures of these compounds were elucidated by combined means of HRESIMS, 1D and 2D NMR spectra, together with ECD calculations. The absolute configuration of phyllanfranin A (1) was established by single crystal X-ray diffraction analysis. Notably, phyllanfranin F (6) represents the first ent-cleistanthane diterpenoid with the unique 6/6/6/6 tetracyclic system occurring in nature. Additionally, all the isolates were evaluated for anti-inflammatory activities. As a result, compounds 4 and 8 showed notable inhibitory activity against NO production in LPS-stimulated macrophages RAW264.7 cells, with IC₅₀ values of 19.03 and 18.14 μM, respectively.