6-Substituted purines containing thienyl or furyl substituents as artificial nucleobases for metal-mediated base pairing.

Sinha I, Kösters J, Hepp A, Müller J

Abstract

The artificial nucleobases 6-(2'-thienyl)-purine () and 6-(2'-furyl)-purine () have been investigated in terms of their applicability in metal-mediated base pairs. In principle, these nucleobases should be capable of providing an S,N- and O,N-coordination environment, respectively. Two metal complexes have been synthesized and structurally characterized, using the N9-methylated derivatives of and as model nucleobases. The silver(i) complex [Ag()(CH3CN)(NO3)]n is of polymeric nature. The thienyl substituent is not involved in metal binding. In contrast, the dinuclear copper(ii) complex [Cu()Cl2(OH2)]2 clearly shows that the furyl substituent can participate in the coordination of the metal ion. Oligonucleotide double helices comprising a : or a : mispair are slightly stabilized in the presence of silver(i). However, a distinction between the formation of a metal-mediated base pair and an unspecific binding event cannot be finally made. Based on these studies, it is proposed that the formation of Hoogsteen-type metal-mediated base pairs should be the more promising alternative compared with the originally anticipated Watson-Crick-type metal-mediated base pairs.

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