Bioactive Natural Product Discovery from Two Annonaceae Plants: Uvaria rufa and Marsypopetalum modestum

Plants are a valuable source of bioactive natural products with a potential to use in drug discovery. Annonaceae family contains many species of plants used in traditional medicine and known to possess a variety of bioactive secondary metabolites, such as cytotoxic Annonaceous acetogenins with anticancer potential. The overall objective of this project was to isolate and identify new and bioactive natural products from two Annonaceae plant species, Uvaria rufa and Marsypopetalum modestum. Extraction and chromatographic separation led to the isolation of forty-three compounds, including eleven new structures. Structure elucidation was accomplished by interpretation of spectroscopic data, including 1D and 2D NMR, HRESIMS and MALDI-MS/MS. Absolute configurations were assigned using ECD data and Mosher ester analysis. The isolated compounds represent the classes of acetogenins, polyoxygenated cyclohexene derivatives, flavonoids, lignans, alkaloids, glycosides and others. Among the acetogenins isolated from U. rufa, the new structure of uvarirufin constitutes a unique C-39 skeleton. The isolated compounds were evaluated for biological activities in several disease models. Most tested acetogenins exhibited cytotoxicity against cancer cells, with IC50 values in the low micromolar range, as assessed by the MTT assay in a panel of cell lines (HCT 116, 22Rv1, MDA-MB-435, OVCAR3). Uvarirufin was among the most potent acetogenins (IC50 = 1.23 μM in HCT 116). The inhibitory activity against Mycobacterium tuberculosis was measured with MABA assay, and the antitubercular effects of dipyrithione from M. modestum were confirmed. Inhibition of LPS-induced NO production in RAW 264.7 cells served to estimate the anti-inflammatory potential of phytoconstituents of U. rufa. Cherrevenaphthalene D and 8-hydroxy-5,7-dimethoxyflavanone exhibited NO inhibition with EC50 values of 8.54 µM and 43.62 µM, respectively. Additionally, new application of Dragendorff reagent and the use of the Feature-Based Molecular Networking and MS2LDA analysis are proposed herein for early detection and dereplication of acetogenins. Overall, this project on the isolation, structure elucidation and bioactivity study of U. rufa and M. modestum has enriched the available knowledge about the chemical profile and biological potential of these Annonaceae plants and contributed to the growing evidence of anticancer potential of acetogenins.