Advancing the Chemical Characterization of Eperua oleifera Duke Oleoresin: A UHPLC-HRMS-Based Approach

<i>Eperua oleifera</i> Ducke (Fabaceae), commonly known as <i>copaíba-jacaré</i>, is traditionally used for therapeutic purposes, like <i>Copaifera</i> oleoresins. Previous GC-MS studies reported its chemical composition as mainly composed of diterpenic acids, consistent with species of the same genus. Although GC-MS remains widely used for comparing compound retention times and fragmentation patterns, its application to diterpenic acids requires a derivatization step to form methyl esters due to the poor chromatographic performance of carboxylic acids on methyl silicone stationary phases. This step may lead to misinterpretations, especially considering recent findings of naturally occurring methyl esters in oleoresins that may co-elute with derivatized acids. This study aimed to apply more sensitive analytical techniques to identify both target and untargeted compounds. The resin of <i>E. oleifera</i> was analyzed by GC-MS to assess the presence of volatile components. Additionally, UHPLC-HRMS was employed using full-scan MS, data-dependent acquisition (DDA), and parallel reaction monitoring (PRM) in both positive and negative ESI modes. GC-MS confirmed the absence of volatile sesquiterpenes, classifying <i>E. oleifera</i> as a resin. Targeted UHPLC-HRMS detected natural methyl esters of diterpenic acids, while untargeted analysis using Compound Discoverer 3.3 software revealed flavonoids and phenolic compounds not previously reported. These findings support the application of UHPLC-HRMS as a powerful tool in phytochemical studies.