Antifouling Brominated Diterpenoids from Japanese Marine Red Alga Laurencia venusta Yamada.

The marine red algal genus Laurencia has abundant halogenated secondary metabolites, which exhibit novel structural types and possess various unique biological potentials, including antifouling activity. In this study, we report the isolation, structure elucidation, and antifouling activities of two novel brominated diterpenoids, aplysin-20 aldehyde (1), 13-dehydroxyisoaplysin-20 (2), and its congeners. We screened marine red alga Laurencia venusta Yamada for their antifouling activity against the mussel Mytilus galloprovincialis. Ethyl acetate extracts of L. venusta from Hiroshima and Chiba, Japan, were isolated and purified, and the compound structures were identified using 1D and 2D NMR, HR-APCI-MS, IR, and chemical synthesis. Seven secondary metabolites were identified, and their antifouling activities were evaluated. Compounds 1, 2, and aplysin-20 (3) exhibited strong activities against M. galloprovincialis. Therefore, these compounds can be explored as natural antifouling drugs.

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), 5-acetoxy-2-bromo-3-chloro-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. Compounds 11 and 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.

Furanocembranoid from the Okinawan soft coral Sinularia sp.

One new furanocembranoid diterpene, 11-hydroxy-Δ12(13)-pukalide (1), along with six known secondary metabolites, 11-acetoxy-Δ12(13)-pukalide (2), 13α-acetoxypukalide (3), pukalide (4), 3α-methoxyfuranocembranoid (5), Δ9(15)-africanene (6), and methyl (5'E)-5-(2',6'-dimethylocta-5',7'-dienyl)furan-3-carboxylate (7) were isolated from the Okinawan soft coral Sinularia sp. Their chemical structures were elucidated based on spectroscopic analysis (FTIR, NMR, and HRESIMS), and the relative stereochemistry of 1 was determined by NOESY experiments and acetylation, which yielded derivative 2. In addition, compounds 1 and 7 exhibited toxicity in the brine shrimp lethality test.