Antibiotic Isoflavonoids, Anthraquinones, and Pterocarpanoids from Pigeon Pea ( L.) Seeds against Multidrug-Resistant .

L. (pigeon pea, locally known in the Philippines as kadios) seed is a functional food with health benefits that extend beyond their nutritional value. seeds contain highly diverse secondary metabolites with enriched beneficial properties, such as antibacterial, anticancer, and antioxidant activities. However, the antibacterial activities of secondary metabolites from Philippine-grown , against multidrug-resistant have not been thoroughly described. Here, we investigated the in vitro antibacterial properties of seed against multidrug-resistant ATCC BAA-44 (MDRSA) and three other strains ( ATCC 25923, ATCC 6538, and coagulase-negative ) and, subsequently, identified the antibiotic markers against strains using mass spectrometry. Secondary metabolites from seeds were extracted using acetone, methanol, or 95% ethanol. Antibacterial screening revealed antibiotic activity for the acetone extract. Bioassay-guided purification of the acetone extract afforded three semi-pure high-performance liquid chromatography (HPLC) fractions exhibiting 32-64 µg/mL minimum inhibitory concentration (MIC) against MDRSA. Chemical profiling of these fractions using liquid chromatography mass spectrometry (LCMS) identified six compounds that are antibacterial against MDRSA. High-resolution mass spectrometry (HRMS), MS/MS, and dereplication using Global Natural Products Social Molecular Networking (GNPS)™, and National Institute of Standards and Technology (NIST) Library identified the metabolites as rhein, formononetin, laccaic acid D, crotafuran E, ayamenin A, and biochanin A. These isoflavonoids, anthraquinones, and pterocarpanoids from seeds are potential bioactive compounds against , including the multidrug-resistant strains.