Phonerilins A–K, cytotoxic ingenane and ingol diterpenoids from Euphorbia neriifolia

A phytochemical study of the aerial parts of Euphorbia neriifolia led to the isolation of six new ingenane-type diterpenoids, phonerilins A–F (1–6), five new ingol-type diterpenoids, phonerilins G–K (7–11), and five known analogues (12–16). Their structures with absolute configurations were elucidated by a combined method. Phonerilin A (1) is the second rearranged ingenane diterpenoid with a unique 6/6/7/3-fused ring system. Based on single-crystal X-ray diffraction and NOESY data, the structure of 20-deoxy-16-hydroxyingenol was revised as 20-deoxy-17-hydroxyingenol (12) that is likely the biogenetic precursor of 1. Biological evaluation revealed some isolates exhibited cytotoxic effects against two human tumor cell lines, A549 and HL-60.