Bromopyrrole Alkaloid Stevensines as Potent, Dual-Mechanism Antifouling Agents Targeting GSK-3β and Acetylcholinesterase

Bromopyrrole alkaloids such as hymenialdisine (1) and debromohymenialdisine (2) are recognized as potent protein kinase inhibitors and antifoulants. Despite the urgent need for novel, eco-friendly antifoulants, research on these alkaloids remains narrow, with limited understanding of their environmental fate. This study aimed to investigate the antifouling potential of a hymenialdisine analogue, stevensine, dereplicated from the Indonesian sponge Stylissa carteri. Preliminary antimicrobial activity of the sponge extract was evaluated using disc diffusion assay.  Inspired by initial antimicrobial findings, a comprehensive in-silico investigation was conducted on stevensine and its derivatives, generated via MetaTox analysis. This involved molecular docking against multiple targets: the quorum sensing receptor (QSR), glycogen synthase kinase-3β (GSK-3β), and acetylcholinesterase (AChE). Preliminary antimicrobial activity assessment demonstrated that S. carteri extract inhibited the growth of the biofilm-forming bacteria Acinetobacter baumannii and Staphylococcus aureus, suggesting broad-spectrum antifouling activity. Molecular docking of stevensine and its derivatives revealed tunable scaffolds that exhibit selective inhibition towards either GSK-3β or AChE, potent quorum sensing, and dual- or triple-target inhibition. Statistical analysis showed significant differences in interaction energies among target groups (ANOVA, p = 0.00000832), particularly between AChE and the QSR (p = 0.0000004964) and between GSK-3β and the QSR (p = 0.004177242). Most importantly, predicted ecotoxicity profiles indicated that the stevensine scaffold possesses more favorable Log Koc, BCF, and Log Kow values than commercial antifoulants, suggesting a lower bioaccumulation potential. This study provides first evidence supporting stevensine derivatives as a versatile, multi-stage antifouling agents, positioning them as promising leads for the design of ecofriendly antifoulants.