Stereospecific interactions of chiral cobalt(III)-amine complexes with guanosine 5′-monophosphate

Abstract

The interactions of two chiral cobalt(III)-amine complex cations, [Co(sep)] 3+ where sep = sepulchrate (1, 3, 6, 8,10,13,16,19-octaazabicyclo[6.6.6]eicosane), and [Co(tetren)(OH)] 2+ where tetren = tetraethylene-pentaamine (1,4,7,10,13-pentaazatridecane), with guanosine 5′-monophospbate (5′-GMP) were characterized in the solid state and in aqueous solution. 1H nuclear magnetic resonance (AMR,) studies show that interactions persist even in dilute solutions of this compound. The 1H NMR spectrum of the products formed when racemic [Co(sep)] 3+ reacts with β- d-5′-GMP reveals a splitting o the AB multiplet of the methylene bridge protons of [CO(sep)] 3+ into two AB multiplets of equal intensity. This is shown to be the result of the formation of the diastereomers [Λ-(+)-Co(sep)] 2(β- d-GMP) 3 and [δ-(−)-Co(sep)] 2(β- d-5′-GMP) 3. The phosphate is not involved in covalent bonding, but could be participating in hydrogen bonding. Fourier transform infrared data of solid [Co(sep)] 2(5′-GMP) 3 · 12H 20 suggest the possibility of hydrogen bonding of N-H sites on the cobalt ligands with N7 and 06 of the guanine base. The compound {[Co(tetren)] 2(5′-GMP)}(ClO 4) 4 · 6H 20 was synthesized and it was found that the phosphate was covalently bonded to the Co(III). The solid decomposes into [Co(tetren) (5′-GMP)] + in aqueous solution. Di-astereomer formation is observed in the 31P NMR when [Co(tetren)(5′-GMP)] + is formed in solution from racemic [Co(tetren)(OH)] 2+ and β- d-5′-GMP 2−, and 1H NMR reveals interactions between the etbylenic protons and guanine moiety. The K′ assoc for [Co(tetren (5′-GMP)] + is 0.17 ± 0.05. Molecular modeling was done and the structures determined correlated well with the experimental data. These Co(III)-amine complex ions illustrate the variety of highly specific interactions which can occur with biomolecules.