Physicochemical and biological properties of nucleosides modified with an imidazole ring and their copper complexes

摘要

Copper(II) complexes with novel chelator-type nucleosides: histidine modified 2′-deoxyriboadenosine (N-[(9-β-D-2′-deoxyribofuranosylpurin-6-yl)-carbamoyl]histidine) and histamine modified 2′-deoxyriboadenosine (N-[(9-beta-D-2′-deoxyribofuranosylpurin-6-yl)-carbamoyl]histamine) were studied by potentiometric and spectroscopic (UV–VIS, CD, EPR) techniques. A histidine or histamine residue was inserted in the purine part of a nucleoside. The ligands can act as bidentate or tridentate, depending on the pH range. The Cu(II) ions bind specifically to the modified deoxynucleosides forming very stable chelates. In acidic pH, a very stable dimeric complex Cu2L2 predominates, with coordination spheres of both metal ions composed of oxygen atoms from carboxylic groups, one oxygen atom from ureido group and two nitrogen atoms derived from a purine base and histidine ring. Above pH 5, deprotonation of carbamoyl nitrogens leads to the formation of CuL2, Cu2L2H-1 and Cu2L2H-2 species. The CuL2H-1 and CuL2H-2 complexes, with three or four nitrogens in Cu(II) coordination sphere, have been detected in alkaline medium. The cleavage of double stranded pEGFP-C1 in 5 mM Tris–HCl/5 mM NaCl buffer (pH, 7.5) by ligands and Cu(II) complexes, in the absence of any reducing agent has been studied by gel electrophoresis. The ligands and their copper complexes have introduced single-strand nicks into pEGFP-C1 plasmid DNA at micromolar concentrations, converting the supercoiled into open circular forms. The chelates have been found to be more active as DNA cleavers than the free ligands.