Dihydrocystodytine G, a new tetracyclic aromatic alkaloid isolated from a specimen of the marine tunicate Cystodytes sp. collected off Rufisque - Senegal

Our recent research on the brown tunic of Cystodytes sp. has led to the isolation of four tetracyclic aromatic alkaloids. Among these compounds, cystodytin B (1) and cystodytin G (2) have already been well characterized. Cystodytin L (3) was also found, a compound we had previously identified and published. Above all, the study highlighted the discovery of a new alkaloid: Dihydrocystodytine G (4). The chemical structures of these compounds were elucidated by combining the determination of specific rotatory power ([α]D), various spectroscopic techniques (1D and 2D NMR), mass spectrometry and comparison with literature data. In addition, the absolute C-12 configuration of compounds 2 to 4 was established as R using electron circular dichroism (ECD) spectroscopy and time-dependent DFT (Density Functional Theory) calculations. In this article, we describe the isolation and structural elucidation of this new compound.