Two novel diterpenes from the stems and leaves of tropical seagrass Enhalus acoroides in the South China sea

Two novel diterpenes Enhoidin A (1) and Enhoidin B (2) featuring an unusual gibberellane skeleton were isolated from the stems and leaves of Enhalus acoroides. Their structures were elucidated on the basis of spectroscopic analysis including 1D and 2D NMR techniques and HR-ESI-MS. This is the first time that this type of lactone ring between C-18 and C-20 has been found among gibberellanes from the tropical seagrasses. Evaluation of the all compounds for cytotoxicity against four human cancer cell lines (MCF-7, HCT-116, HepG-2 and HeLa), and showed moderate cytotoxic activities.