Excolide C, Unusual 2,3‐seco <i>ent</i> ‐Isopimaranoid from the Stems of <i>Excoecaria agallocha</i>

ABSTRACT Excolide C ( 1 ), possessing an unusual 2,3‐seco ent‐ isopimarane diterpenoid with a rearranged bilactone derivative was isolated from the acetone extract of the stems of Excoecaria agallocha , collected from the Nizampatnam sea coast. The structure of excolide C ( 1 ) was unambiguously established by means of extensive one‐dimensional and two‐dimensional NMR, IR, HR‐ESIMS spectroscopic data analysis, chemical transformations, and biogenetic considerations. It represents the first member of the tetracyclic 2,3‐seco ent‐ isopimarane carbocyclic framework.