LC-MS/MS Profiling and Antimicrobial Evaluation of Marine Alkaloids from Pseudoceratina purpurea

<b>Background and Objective:</b> Alkaloids are a group of naturally occurring compounds with diverse pharmacological properties, including their use as antibacterial and antifungal agents such as chloramphenicol and nystatin (CY and NY). This study aimed to investigate the alkaloid profile and antimicrobial potential of the marine sponge <i>Pseudoceratina purpurea</i> collected from Southeast Sulawesi. <b>Materials and Methods:</b> Methanol extraction was performed to obtain the methanol extract (ME), which was then fractionated using n-hexane to yield the n-hexane extract and methanol extract residue (MER). Alkaloid isolation was conducted on the MER to obtain the alkaloid isolate (AI). The AI was partially analyzed using UPLC-HRMS for compound identification, while the remaining portion was tested for antimicrobial activity against <i>Escherichia coli</i>, <i>Staphylococcus aureus</i> and <i>Candida albicans</i>. <b>Results:</b> A total of 117 alkaloid compounds were identified and classified into seven subclasses: Indole (1.8%), isoquinoline (4.14%), lipid (32.66%), proto (52.90%), purine (2.02%), pyridine (6.39%) and steroidal alkaloids (0.1%). The AI demonstrated strong antimicrobial activity, with minimum inhibitory concentration (MIC) values of 4±0.064 ppm against <i>E. coli</i>, 8±0.09 ppm against <i>S. aureus</i> and 4±0.05 ppm against <i>C. albicans</i>. <b>Conclusion:</b> These findings suggest that the alkaloid isolate from <i>P. purpurea</i> possesses promising broad-spectrum antimicrobial properties and may serve as a potential candidate for the development of novel antimicrobial agents.