A double-headed nucleotide with two cytosines: DNA with condensed information and improved duplex stability.

Double-headed nucleotide monomers are capable of condensing the genetic information of DNA. Herein, a double-headed nucleotide with two cytosine bases (CC) is constructed. The additional cytosine is connected through a methylene linker to the 2'-position of arabinocytidine. The nucleotide is incorporated into oligonucleotides and its effect on duplex stability is studied. For single incorporations, a thermal stabilization of 4.0 °C is found as compared to the unmodified duplex and it is shown that both nucleobases of CC participate in Watson-Crick base pairing. In combination with the previously published UT monomer, it is also shown that multiple incorporations are tolerated. For instance, a 16-mer sequence is targeted by a 13-mer oligonucleotide by using one CC and two UT monomers without compromising the overall duplex stability. Finally, the potential of double-headed nucleotides in triplex-forming oligonucleotides is studied, however, with the conclusion that the present design is not well-suited for this function.