Facile synthesis of a dimeric dipyrrole-polyamide and synergetic DNA-cleaving activity of its Cu(II) complex

Inspired by the potent DNA-cleaving activity of the Cu(II) complex of monopyrrole-polyamide dimer 1 (i.e., 1@Cu(2+)), we designed a new dimeric dipyrrole-polyamide analog 2 with the aim to optimize the catalytic activities of the metal complexes of this type of polypyrrole-polyamides. Compound 2 was prepared in 50% yield from the reaction of 1-methyl-4-[(1-methyl-4-nitro-1H-pyrrole-2-carbonyl)-amino]-1H-pyrrole-2-carboxylic acid with 2,2'-(ethane-1,2-diylbis(oxy))diethanamine, and fully characterized on the basis of NMR ((1)H and (13)C), MS (ESI and HR) and IR. Spectrophotometric titration, ESI-MS and conductivity measurements indicated that compound 2 formed a 1:1 complex with Cu(2+) ion (i.e., 2@Cu(2+)). Agarose gel electrophoresis studies indicated that 2@Cu(2+) was capable of efficiently converting pBR322 DNA into open circular and linear forms under physiological conditions, most probably via an oxidative mechanism. Its overall catalytic activity was estimated to be at least 30-fold higher than that of 1@Cu(2+). The fact that the cleaving activities of these Cu(II) complexes parallel, exactly, their binding affinities, raises the possibility that the cleaving activities of polypyrrole-polyamide derivatives of the type can be regulated by the binding affinities.