Design and synthesis of marine natural product-based 1H-indole-2,3-dione scaffold as a new antifouling/antibacterial agent against fouling bacteria

• Isatin is antifungal and ecologically defensive marine natural product tested for SAR study.
• An efficient synthesis was achieved using simple synthetic manipulations.
• 3-Acetonylidene oxindole 5a is identified as the most potent antibacterial agent.
• Report represents the first studies towards the inhibitory activity of isatin & its derivatives.
• The screening of natural products analogues is a promising way to find novel antimicrobial agents.

Marine organisms such as seaweeds, sponges and corals protect their own surfaces from fouling by their high anesthetic, repellant, and settlement inhibition properties. Within the marine ecosystem, evolution has allowed for the development of certain antifouling properties. Isatin is a biologically active chemical produced by an Alteromonas sp. strain inhibiting the surface of embryos of the cardiean shrimp Palaemon macrodectylus, which protect them from the pathogenic fungus Lagenidium callinectes. In present study, an antibacterial activity of isatin and its synthetic analogues were evaluated against different fouling bacteria in order to explore the structure activity relationships for the first time. The synthesized compounds along with parent isatin were tested against different ecologically relevant marine microorganisms by using the Kirby–Bauer disc diffusion method. Few synthetically modified isatin exhibited potent inhibitory activity at concentration of 2 μg/disc against Planococcus donghaensis, Erythrobacter litoralis, Alivibrio salmonicida, Vibrio furnisii. Overall, the modified analogues showed stronger activity than the parent marine natural product (isatin) and hence 1H-indole-2,3-dione scaffold has immense potential as future antibacterial/antifouling candidate.

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