Guanine-rich DNA sequences can adopt stable non-classical four-stranded guanine quadruplex structures in-vitro under near physiological conditions. It has been shown that a ligand stabilizing such quadruplex could inhibit the extension of telomeric DNA by the human telomerase. Therefore, ligands stabilizing and/or inducing the formation of human telomeric quadruplex have potential as anti-cancer therapeutic agents. Since quadruplex structures differ considerably from double-stranded B-DNA helices, there has been considerable interest in the design and development of ligands that selectively stabilize G-quadruplex over duplex DNA.
Further, sequences in the promoter region of certain oncogenes can potentially form quadruplex structures and it is believed that such structures can interfere with the expression level of these genes. However, it also raises the important need to ultimately generate ligands that show discrimination not only between quadruplex and duplex DNA but also between quadruplexes themselves. We propose here the design and synthesis of several heterocycle-based planar macrocycles where heterocycles (e.g. pyridine, oxazole and thiazole) are either directly linked through C-C bond or through amides. Such structures are inspired from the natural p roduct telomestatin, a flat poly-oxazole macrocycle, which is the most potent telomerase inhibitors identified so far.
Those planar macrocycles should offer the advantage of better solubility when compared to telomestatin and represent an original platform for appending side-chains capable of interacting with specific loops and grooves of a particular quadruplex. These new ligands will then be screened against three biologically relevant quadruplexes located within the promoter regions of oncogenes c-kit, N-ras and H-ras, which have recently been identified in the Balasubramanian's group.
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