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Oligo-2'-deoxyribonucleotides containing uracil modified at the 5-position with linkers ending with guanidinium groups.

We report here the synthesis and binding studies of oligo-2'-deoxyribonucleotides (ODNs) containing 2'-deoxyuridines, modified at the 5-position by linkers ending with either one or two guanidinium groups. Comparison was made with ODNs containing 2'-deoxyuridines modified at the 5-position with linkers ending with either two or one amino groups. One or two modified 2'-deoxyuridines were incorporated into pyrimidine strands, and their influence on the stability of duplex (with both DNA and RNA targets) and triplex structures was studied. The strongest stabilization was obtained with modified ODNs containing guanidinium groups. This result confirms that the reduction of the global negative charge number on one strand is an important parameter in the stability of duplex and triplex structures.