Diterpenes from the Far-eastern brown alga Dictyota dichotoma

Two diterpenes, ent-erogorgiaene (1) and (+)-1,5-cyclo-5,8,9,10-tetrahydroerogorgiaene (2), have been isolated from the brown alga Dictyota dichotoma. Their structures were elucidated by analysis of 1D and 2D NMR, mass spectra and optical rotation data.