Synthesis, crystal structure, Hirshfeld surface analysis and DFT calculations of novel clusianone analogues as anticancer agents that downregulate β-tubulin and Cdk1/Cyclin B1

Clusianone is a natural product that has been shown to possess anticancer activity, however, studies on its potential anticancer activity remain limited and few. In this study, we further investigated the anticancer potential of clusianone by initially isolating clusianone from Garcinia parvifolia leaves and then using it to synthesise a total of 8 analogues, of which 5 are novel and being reported for the first time. Clusianone and its analogues’ reactivity and chemistry were thoroughly investigated, while the crystal structure of methylated clusianone, compound 1, was obtained and discussed. The crystal structure for 1 was used to conduct Hirshfeld surface analysis whereby it was found that H···H interactions contributed the most to the crystal packing. Moreover, DFT calculations showed that the calculated theoretical parameters for the optimised structure of 1 were in good agreement with the experimental x-ray diffraction measurements. The analogues that were obtained in good yields were further screened against A549 (lung) and HK1 (nasopharyngeal) cancer cells via the MTT assay. Results showed that introduction of an imine (C=N) group to clusianone resulted in bioactive compounds, with the methylamine derivative (compound 4) demonstrating the highest cytotoxic activity followed by clusianone. Further studies on clusianone and 4 showed that they caused apoptosis-related morphological changes in the cancer cells. Furthermore, the compounds were found to inhibit cancer cell division via decreasing the protein expression levels of β-tubulin and Cdk1/Cyclin B1 with 4 demonstrating a more pronounced effect against the proteins than clusianone. DFT calculations on 4 suggested that its high bioactivity could be attributed to its high chemical reactivity due to its lower HOMO-LUMO gap and lower chemical hardness. This study demonstrates the potential of 4 as an effective natural product derived anticancer agent.