Dictyotadimer A, a new dissymmetric bis-diterpene from a brown alga of the genus Dictyota

A phytochemical investigation of a Mediterranean brown alga (Dictyota sp.) led to the isolation of a novel C₄₀bis-diterpene, named dictyotadimer A. The chemical structure of this unusual dissymmetric dimer, characterized by a C-C linkage between two different xenicane units, was elucidated by 1D and 2D NMR analyses together with HR-ESI mass spectrometry. The relative configuration of the two diterpenoid components was determined by NOESY NMR correlations and molecular modeling. A plausible biogenetic pathway of dictyotadimer A was also proposed.