One new phenylalanine derivative 4′-OMe-asperphenamate (1), along with one known phenylalanine derivative (2) and two new cytochalasins, aspochalasin A1 (3) and cytochalasin Z24 (4), as well as eight known cytochalasin analogues (5–12) were isolated from the fermentation broth of Aspergillus elegans ZJ-2008010, a fungus obtained from a soft coral Sarcophyton sp. collected from the South China Sea. Their structures and the relative configurations were elucidated using comprehensive spectroscopic methods. The absolute configuration of 1 was determined by chemical synthesis and Marfey’s method. All isolated metabolites (1–12) were evaluated for their antifouling and antibacterial activities. Cytochalasins 5, 6, 8 and 9 showed strong antifouling activity against the larval settlement of the barnacle Balanus amphitrite, with the EC₅₀ values ranging from 6.2 to 37 μM. This is the first report of antifouling activity for this class of metabolites. Additionally, 8 exhibited a broad spectrum of antibacterial activity, especially against four pathogenic bacteria Staphylococcus albus, S. aureus, Escherichia coli and Bacillus cereus.

A new prenylated indole alkaloid, named paraherquamide J (1), together with four known compounds (2–5), were isolated from the mangrove rhizosphere soil-derived fungus Penicillium janthinellum HK1-6. The planar structure and relative configuration of 1 were determined by detailed analysis of the spectroscopic data especially the NOESY spectrum. The absolute configuration of 1 was determined by ECD spectra. Compound 2 was first isolated as a natural product and named as paraherquamide K. All isolated metabolites were evaluated for their antibacterial, topoisomerase I (topo I) inhibitory activities and lethality towards brine shrimp Artemia salina.

Marine organism-derived secondary metabolites are promising potential sources for discovering environmentally safe antifouling agents. In present study, 55 marine secondary metabolites and their synthesized derivatives were tested and evaluated for their antifouling activities and security. These compounds include 44 natural products isolated from marine invertebrates and their symbiotic microorganisms collected from the South China Sea and 11 structural modified products derived from the isolated compounds. The natural secondary metabolites, covering phenyl ether derivatives, terpenoids, 9, 11-secosteroids, anthraquinones, alkaloids, nucleoside derivatives and peptides, were isolated from two corals, one sponge and five symbiotic fungi. All of the isolated and synthesized compounds were tested for their antifouling activities against the cyprids of barnacle Balanus (Amphibalanus) amphitrite Darwin. Noticeably, five phenyl ether derivatives (9, 11, 13–15) exhibited potent anti-larval settlement activity with the EC50 values lower than 3.05 μM and the LC50/EC50 ratios higher than 15. The study of structure–activity relationship (SAR) revealed that the introduction of acetoxy groups and bromine atoms to phenyl ether derivatives could significantly improve their antifouling activities. This is the first report on the SAR of phenyl ether derivatives on antifouling activity against barnacle B. amphitrite. The polybrominated diphenyl ether derivative, 2, 4, 6, 2′, 4′, 6′-hexabromo-diorcinol (13), which displayed excellent antifouling activity, was considered as a promising candidate of environmentally friendly antifouling agents.