Chemistry Of Ferrocene Conjugates Showing DNA Cleavage And Photocytotoxic Activity
Ferrocene is an important molecule in the field of chemical biology due to its stability, unique redox property and significant lipophilicity for better cellular delivery. The medicinal importance of ferrocene is well recognized after its successful incorporation into breast cancer drug tamoxifen and antimalarial drug chloroquin. Designing ferrocene conjugated transition metal complexes is an interesting area of research in the field of photodynamic therapy, a new modality of light activated cancer treatment. The objective of the present thesis work is to develop photoactive ferrocene conjugates showing DNA photocleavage and photocytotoxic activity. We have synthesized the ferrocene conjugated imidazophenanthroline derivative which exhibits visible light induced DNA photocleavage activity and photocytotoxicity in HeLa cell line. The corresponding phenyl analogue is found to be inactive. Polypyridyl platinum(II) complexes of ferrocenyl as well as phenyl moiety are prepared and studied their interactions with calf thymus DNA. The cytotoxicity of the complexes enhance significantly upon irradiation of UV-A light of 365 nm. To enhance the photodynamic potential and to understand the role of organometallic ferrocenyl moiety, ferrocene conjugated terpyridyl copper(II) complexes having planar phenanthroline bases are prepared. The interaction of these complexes with duplex DNA and their photo-induced DNA cleavage and anticancer activity in HeLa cancer cells are studied. The complexes are able to generate ROS in the presence of visible light which causes DNA damage as well as cell death. The importance of ferrocenyl moiety is evidenced from the less activity of the corresponding phenyl analogues complex. We have prepared copper(II) complexes of ferrocenyl methyl dipicolylamine ligand to understand the role of terpyridyl moiety. These complexes lacking any conjugation between the copper(II) and the ferrocenyl moiety are found to be less active compared to the terpyridyl conjugated system. The copper(II) complexes are found to show undesirable dark cytotoxicity in the presence of cellular thiols like GSH. To overcome the dark toxicity problem and to understand the mechanistic aspects of DNA photocleavage and photocytotoxicity, a series of binary ferrocene conjugated terpyridyl complexes of Fe(II), Co(II), Cu(II) and Zn(II) are prepared and their DNA photocleavage and anticancer activity studied. The zinc(II) complex having redox-active ferrocenyl moiety and redox-inactive zinc(II) center exhibits significant PDT effect with low dark toxicity compared to its copper(II) analogue. The ferrocenyl moiety plays an important role towards showing photocytotoxic activity since its phenyl analogue is inactive in nature. Finally, the present thesis work opens up a new strategy for designing and developing new ferrocene based metal complexes as novel photosensitizers for PDT applications.
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