Semi-synthesis of indole-fused taraxerone derivatives from Rhizophora stylosa Griff.: anti-bacterial study and docking insights.

A series of novel semisynthetic indole-fused taraxerone derivatives (2a-2f) were synthesised from taraxerone isolated from Rhizophora stylosa Griff. and characterised by 1H NMR,13C NMR, and HRMS analyses. Incorporation of the pharmacologically important indole moiety was aimed at enhancing protein-ligand interactions and antibacterial activity. The synthesised compounds, 2a-2f, were evaluated against Gram-positive bacteria (Lysinibacillus sp. and Bacillus circulans) and Gram-negative bacteria (Pseudomonas putida and Salmonella paratyphi). All derivatives exhibited notable antibacterial activity, with minimum inhibitory concentration (MIC) values ranging from 3.12 to 25 µg mL-1. Among them, compound 2e showed the highest potency, with an MIC of 3.12 µg mL-1, approximately two-fold more active than streptomycin sulphate (MIC = 6.25 µg mL-1). Molecular docking studies against the bacterial target protein (PDB ID: 5JZX) revealed favourable binding affinities for compounds 2d-2f. These results identify indole-fused taraxerone derivatives as promising leads for antibacterial drug development.