Synthesis and properties of a new oligonucleotide analogue containing an internucleotide squaryl amide linkage.

We report here the synthesis and properties of a new oligonucleotide analogue (5'-CGCATsqTAGCC-3') containing a squaryl group in place of the fifth phosphate group from the 5'-terminus. The modified thymidine dimer building unit was synthesized by use of 5'-amino-5'-deoxythymidine and a 3'-amino-3'-deoxythymidine derivative. This building unit was phosphitylated and incorporated into the oligonucleotide by the phosphoramidite method. The hybridization ability of this modified oligomer with the complementary oligonucleotide was studied in detail by using Tm experiments and CD spectroscopy as well as computer simulations. These results suggest that this modified duplex has a unique bend conformation.