Synthesis, X-ray crystal structures, and phosphate ester cleavage properties of bis(2-pyridylmethyl)amine copper(II) complexes with guanidinium pendant groups

Three new derivatives of bis(2-pyridylmethyl)amine (DPA) featuring ethylguanidinium (L(1)), propylguanidinium (L(2)), or butylguanidinium (L(3)) pendant groups have been prepared by the reaction of N,N-bis(2-pyridylmethyl)alkane-alpha,omega)-diamines with 1H-pyrazole-1-carboxamidine hydrochloride. The corresponding mononuclear copper(II) complexes were prepared by reacting the ligands with copper(II) nitrate and were isolated as [Cu(LH(+))(OH(2))](ClO(4))(3)center dot xNaClO(4)center dot yH(2)O (C1: L = L(1), x = 2, y = 3; C2: L = L(2), x = 2, y = 4; C3: L = L(3), x = 1, y = 0) following cation exchange purification. Recrystallization yielded crystals of composition [Cu(LH(+))(X)](ClO(4))(3)center dot X (C1': L = L(1), X = MeOH; C2': L = L(2), X = H(2)O; C3' L = L(3), X = H(2)O), which were suitable for X-ray crystallography, The crystal structures of C1', C2', and C3' indicate that the DPA moieties of the ligands coordinate to the copper(II) centers in a meridional fashion, with a water or methanol molecule occupying the fourth basal position. Weakly bound perchlorate anions located in the axial positions complete the distorted octahedral coordination spheres. The noncoordinating, monoprotonated guanidinium groups project away from the Cu(II)-DPA units and are involved in extensive charge-assisted hydrogen-bonding interactions with cocrystallized water/methanol molecules and perchlorate anions within the crystal lattices. The copper(II) complexes were tested for their ability to promote the cleavage of two model phosphodiesters, bis(p-nitrophenyl) phosphate (BNPP) and uridine-3'-p-nitrophenylphosphate (UpNP), as well as supercoiled plasmid DNA (pBR 322). While the presence of the guanidine pendants was found to be detrimental to BNPP cleavage efficiency, the functionalized complexes were found to cleave plasmid DNA and, in some cases, the model ribose phosphate diester, UpNP, at a faster rate than the parent copper(II) complex of DPA.