Marmaricines A-C: Antimicrobial Brominated Pyrrole Alkaloids from the Red Sea Marine Sponge Agelas sp. Aff. Marmarica

The Red Sea is the home of a rich diversity of sponge species, with unique ecological adaptations that thrive in its saline, warm, and nutrient-poor waters. Red Sea sponges offer potential as sources of novel drugs and bioactive compounds. The organic extract of the Red Sea sponge Agelas sp. aff. marmarica was investigated for its antimicrobial constituents. Through bioassay-guided fractionation of the antimicrobial fraction of the extract on SiO₂, Sephadex LH-20, and HPLC purification, three bioactive compounds, marmaricines A-C (1-3), were isolated. Structural elucidation of the compounds was performed using 1D (1H and 13C) and 2D (COSY, HSQC, HMBC and NOESY) NMR, as well as (+)-high-resolution electron spray ionization mass spectroscopy, leading to the identification of the compounds. Marmaricines A-C exhibited significant antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA), with inhibition zones of 14, 15, and 12 mm, respectively. Further, marmaricines B and C showed activity against Candida albicans, with inhibition zones of 15 and 14 mm, while compound 1 displayed no activity. The results indicate that compounds 1-3 are selectively active against MRSA, and compounds 2 and 3 demonstrate potential against C. albicans, making them promising candidates for the development of novel antimicrobial agents targeting resistant pathogens.