Characterisation of flavonoids from methanolic extract of <i>Brucea javanica</i> leaves using feature-based molecular networking, SIRIUS5, and NMR spectroscopy

<i>Brucea javanica</i> (L.) Merr. (Simaroubaceae) is a traditional medicinal plant widely used in Southeast Asia to treat ailments such as cancer, diabetes, and fever. While previous phytochemical studies focused on its fruits, stems, and roots, identifying quassinoids as the major chemical class, limited information exists on its leaf composition. This study aimed to profile the leaf metabolome of <i>B. javanica</i>, emphasising flavonoid constituents. Methanolic leaf extract was analysed using UHPLC-PDA-ESI-ORBITRAP-MS/MS, followed by feature-based molecular networking (FBMN). Flavonoid annotation was enhanced through <i>in-silico</i> fragmentation <i>via</i> SIRIUS5, and key compounds were isolated and characterised using 1D and 2D NMR spectroscopy. Fourteen flavonoids were annotated, including flavone-7-<i>O</i>-glycosides, flavonolignans, flavone monomers, and isoflavones. Ten are reported for the first time in the <i>Brucea</i> genus. Additionally, two new hydnocarpin-type flavonolignan isomers, (+)-bruceacarpin (<b>8</b>) and (+)-hydnocarpin (<b>9</b>), were isolated and structurally confirmed. These findings enrich the chemotaxonomic and phytochemical understanding of <i>B. javanica</i> and highlight the potential of its leaves.