Halitunal, an unusual diterpene aldehyde from the marine alga .

Halituna(1), a novel diterpene aldehyde possessing a unique cyclopentadieno[c]pyran ring system, has been isolated from the marine alga . The structure of 1 was elucidated by spectroscopic techniques. Halitunal shows antiviral activity against murine coronavirus A59 in-vitro.