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

New bromoditerpenes having an α-methylene carbonyl structure, azuriaplysins A ( 1 ) and B ( 2 ), were isolated from the sea hare Aplysia kurodai . 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 ( 1 ) and B ( 2 ), the key points of which were bromocyclization of farnesol and optical resolution of a key intermediate. Azuriaplysin B ( 2 ) and its enantiomer exhibited moderate cytotoxicity against HeLa S3 cells.