Fabaceae family is recognized as a prolific flavonoid producer, including some unusual flavonoid skeletons. Although classic flavonoids have well-established biological properties in the literature, these unusual compounds remain underinvestigated. Based on that, the current study sought to explore the chemistry and biological activity of rare flavonoids in Fabaceae with a review comprising their occurrence, extraction, isolation and pharmacological potential. Additionally, the use of LC-MS applied to the study of seven subclasses (aurones, biflavonoids, coumestans, homoisoflavonoids, neoflavonoids, pterocarpans, and rotenoids) is also discussed. The review was carried out by searching for specified uniterms on SciFinder and Web of Science, covering the last ten years. In addition, to assess ADMET and drug-like properties by in silico predictions, all the substances considered in this work were compiled and organized into a curated dataset. As a result, a total of 170 flavonoid structures were included, most of which were found in the roots and leaves. In addition, a wide range of biological activities were observed, such as cytotoxic, antiviral and anti-inflammatory. Despite advancements in the use of LC-MS for bioprospection, just a few reports dedicated to the study of these compounds were found. Regarding ADMET profiles, most subclasses showed favorable bioavailability characteristics, with biflavonoids being the main exception. Together, this review highlights the significance of unusual flavonoids from the Fabaceae family, demonstrating their remarkable chemical diversity and largely, but still, unexplored pharmacological potential. These findings encourage further investigations, particularly in the fields of natural products chemistry, medicinal chemistry, and pharmacology.

This is the report of the HPLC-MSn-guided isolation of new anti-inflammatory prenylated isoflavonoids and pterocarpans from the stems of Acosmium diffusissimum using GNPS molecular networking as the main tool. Cluster analysis guided the isolation of five new prenylated isoflavonoids, diffusiflavone A-E (1-4 and 9), two prenylated pterocarpans, diffusicarpan A and B (5 and 6), and two known compounds 6-prenylorobol (7) and 3-O-methylquercetin (8). The in vitro anti-inflammatory potential of compounds 1-6 and 9 was assessed in macrophages induced with lipopolysaccharide (LPS). Compounds 2, 3, 5, and 9 were observed to have a reduction in NO levels in at least one of the concentrations tested (1.25, 2.5, 5, 10, and 20 μg/mL) and also reduced IL-1β and IL-6 cytokines, especially diffusicarpan A which reduced cytokine levels in all the concentrations tested.