Bioactive phloroglucinols from the brown alga Zonaria diesingiana

Three phloroglucinols with a C-20 acyl side chain were isolated from marine brown alga Zonaria diesingiana. The structures were determined on the basis of NMR spectral analyses and comparison with data in the literature. They all showed antibacterial activity against Bacillus subtilis and Staphylococcus aureus and cytotoxic activity by inhibiting cell division in fertilized sea urchin eggs (Echinometra mathaei). These activities suggest their possible for pharmacological purposes. These phloroglucinols also showed toxicity against brine shrimp (Artemia salina), guppy fish (Poecilia reticulata), rice-land shrimp (Macrobrachium lanchesteri) and the diatom Chaetoceros gracilis. They probably act as chemical defenses against herbivores and also reduce surface fouling by epiphytic algae and larvae, suggesting their important roles in the marine ecosystem.