A novel series of DNA triple helix-binding ligands

We have examined the effect of a series of substituted imidazothioxanthones on tire stability of an intermolecular DNA triple helix by DNase I footprinting. We find that, several of these compounds promote the formation of a complex between T5C5 and the target site A(6)G(6) . C6T6, suggesting that they bind specifically to tripler DNA. The only inactive derivative lacked a protonatable function in the side chain, suggesting that this is an essential feature for tripler stabilization. These compounds, which are amongst the first tripler-binding ligands which possess an uncharged chromophore, are selective for the T AT rather than the C+. GC triplet. (C) 1996 Academic Press, Inc.