Discovery of Quassinoids and Indole Alkaloids With Antifouling Activity Against Barnacle Settlement From the Seeds of Brucea javanica

From the ethanol extract of Brucea javanica seeds, an undescribed C19‐type quassinoid, javanicolide I (1) and its epimer, javanicolide J (2), a new indole alkaloid, bruceolline O (3), a new‐to‐nature 1H‐Indole‐3‐butanoic acid, α‐methyl‐γ‐oxobutanoic acid (4), together with 13 known compounds (5–17) were isolated and structurally characterized by spectroscopic analysis. All compounds were evaluated for antifouling activity against Balanus amphitrite cyprid larval settlement. Aglycone of yadanzioside D (6) not only exhibits potent anti‐settlement activity but also demonstrates low toxicity, with an EC50 of 1.06 µg/mL and an LC50/EC50 ratio of 20.68 (>15, indicating low toxicity), outperforming the positive control SeaNine 211. Further resuscitation and zebrafish embryo assays also confirmed its low toxicity, highlighting its potential as a promising antifouling candidate.