Isolation and Synthesis of Azuriaplysins A and B, Bromoditerpenes with an α-Methylene Carbonyl from the Sea Hare .

New bromoditerpenes having an α-methylene carbonyl structure, azuriaplysins A () and B (), were isolated from the sea hare . Their relative stereostructures were determined based on one- and two-dimensional NMR spectroscopic analysis. In addition, the absolute stereostructures were determined by the total synthesis of both enantiomers of azuriaplysins A () and B (), the key points of which were bromocyclization of farnesol and optical resolution of a key intermediate. Azuriaplysin B () and its enantiomer exhibited moderate cytotoxicity against HeLa S3 cells.