Diversity of halogenated secondary metabolites in Okinawan Aplysia argus including 12-hydroxypinnaterpene C and their feeding targets.

A new irieane-type diterpene, 12-hydroxypinnaterpene C (1), and 21 known compounds, angasiol acetate (2), angasiol (3), 11-deacetylpinnaterpene C (4), palisadin A (5), 12-acetoxypalisadin B (6), 12-hydroxypalisadin B (7), aplysistatin (8), luzodiol (9), 2-bromo-3-chloro-5-acetoxy-chamigra-7(14)-9-dien-8-one (10), neoirietriol (11), neoirietetraol (12), 3Z-laurenyne (13), cupalaurenol (14), cupalaurenol acetate (15), 3Z-venustinene (16), 10-hydroxykahukuene B (17), aplysiol B (18), (3Z)-13-epipinnatifidenyne (19), 3Z,6R,7R,12S,13S-obtusenyne (20), (3Z,9Z)-7-chloro-6-hydroxy-12-oxo-pentadeca-3,9-dien-1-yne (21), and cholest-7-en-3,5,7-triol (22) were isolated from the digestive diverticula of Aplysia argus from the Ikei Island in Okinawa, Japan. The structures of these compounds were determined using spectroscopic methods such as NMR and HR-ESI-MS. These compounds were tested for their antibacterial activity against the phytopathogen Ralstonia solanacearum. Neoirietriol (11) and (3Z,9Z)-7-chloro-6-hydroxy-12-oxo-pentadeca-3,9-dien-1-yne (21) exhibited antibacterial activity at 30 µg/disc. In this study, we also discuss the types of red algae that A. argus feeds on in the shallow waters of Okinawa Prefecture.