Isolation, characterisation and some biological activities of xanthones and its metal complexes from Garcinia mangostana

The investigation of metal complexes has been predominantly centered on coumarin and flavonoid families, successfully producing compounds with diverse biological activities. Xanthones possess electron-rich functional groups and modifiable macrostructure, making them promising starting materials for synthesizing novel compounds. This study explores the under researched potential of naturally occurring xanthones from Garcinia mangostana and synthesized metal complexes using these ligands. Coordination complexes were formed with manganese (Mn), iron (Fe), copper (Cu), and palladium (Pd) via a one-pot reaction with a 2:1 molar ratio of ligand to metal. The isolated xanthones were elucidated using Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR) and Ultra-Violet-Visible Spectroscopy (UV-Vis). The structure of the metal complexes was deduced using CUN elemental analysis, FTIR, MS spectroscopy and UV-Vis spectroscopy, thermogravimetry (TGA) and differential scanning calorimetry (DSC). The isolated xanthones and synthesized metal complexes were tested for their antibacterial properties using Minimum Inhibitory Concentrations (MICs) and Minimum Bactericidal Concentration (MBCs) method. While, the cytotoxicity was tested using Sulforhodamine B (SRB) assay against NCI-H460 (human lung cancer cell lines) and MCF-7 (human breast cancer cell lines). Six pure compounds namely a-mangostin (GM1), /?-mangostin (GM2), l-hydroxy-7-methoxyxanthone (GM3) and euxanthone (GM4), stigmasterol (GM5) and friedelin (GM6) were successfully isolated and elucidated from stem barks of Garcinia mangostana. A total of eight metal complexes (Cu-10), (Cu-11), (Cu-20), (Cu-21), (Fe-10), (Fe-11), (Mn-20) and (Pd-20) were synthesized and elucidated. The findings have highlighted that metal complexes exhibit enhanced antibacterial properties compared to their parent ligands. Additionally, the results indicate that these metal complexes show increased cytotoxicity against MCF-7 and NCI-H460 cell lines relative to their ligands. The structure-activity relationship (SAR) analysis has revealed the structural features that are responsible for favourable interactions with specific protein receptors, providing further insight into their biological activities. Overall, the biological studies suggest that metal complexes of xanthone hold promising potential as antibacterial agents and anticancer agents.