Synthesis and triplex-forming properties of oligonucleotides capable of recognizing corresponding DNA duplexes containing four base pairs

摘要

A triplex-forming oligonucleotide (TFO) could be a useful molecular tool for gene therapy and specific gene modification. However, unmodified TFOs have two serious drawbacks: low binding affinities and high sequence-dependencies. In this paper, we propose a new strategy that uses a new set of modified nucleobases for four-base recognition of TFOs, and thereby overcome these two drawbacks. TFOs containing a 2'-deoxy-4N-(2-guanidoethyl)-5-methylcytidine (d(g)C) residue for a C-G base pair have higher binding and base recognition abilities than those containing 2'-OMe-4N-(2-guanidoethyl)-5-methylcytidine (C-g(2'-OMe)), 2'-OMe-4N-(2-guanidoethyl)-5-methyl-2-thiocytidine (C-g(2'-OMe)s), d(g)C and 4S-(2-guanidoethyl)-4-thiothymidine (T-gs). Further, we observed that N-acetyl-2,7-diamino-1,8-naphtyridine (N-DA(ac)) has a higher binding and base recognition abilities for a T-A base pair compared with that of dG and the other DNA derivatives. On the basis of this knowledge, we successfully synthesized a fully modified TFO containing N-DA(ac), d(g)C, 2'-OMe-2-thiothymidine (T-s(2'-OMe)) and 2'-OMe-8-thioxoadenosine ((s)(2'-OMe)A) with high binding and base recognition abilities. To the best of our knowledge, this is the first report in which a fully modified TFO accurately recognizes a complementary DNA duplex having a mixed sequence under neutral conditions.