Synthesis and Evaluation of MGB Polyamide-Oligonucleotide Conjugates as Gene Expression Control Compounds

MGB polyamide-oligonucleotide conjugates ON 1-4 with linked MGB polyamides at the 2-exocyclic amino group of a guanine base using aminoalkyl linkers were synthesized and evaluated in terms of binding affinity for complementary DNA containing the MGB polyamide binding sequence using T(m) and CD analyses. The MGB polyamides comprised pyrrole polyamides (Py(4)- and Py(3)-), which possess binding affinity for A-T base pairs, and imidazole (Im(3)-) and pyrrole-γ-imidazole (Py(3)-γ-Im(3)-) polyamide hairpin motifs, which possess binding affinity for C-G base pairs. It was found that the stability of modified dsDNA was greatly influenced by the linker length. Py(4)- and Py(3)-oligonucleotide conjugates (ON 1 (n = 4) and ON 2 (n = 4)) containing the 4-aminobutyl linker formed stable dsDNA with complementary DNA. Although Im(3)-oligonucleotide conjugate ON 3 (n = 4) containing the 4-aminobutyl linker formed stable dsDNA with complementary DNA, stabilization of dsDNA by the imidazole amide moiety of ON 3 (n = 4) was lower compared with the pyrrole amide moiety of ON 2 (n = 4). The Py(3)-γ-Im(3)-oligonucleotide conjugate ON 4 (n = 2), which possesses binding affinity for C-G base pairs via a pyrrole/imidazole combination and contains a 2-aminoethyl linker, showed high binding ability for complementary DNA. Furthermore, the DNA sequence recognition of MGB polyamide-oligonucleotide conjugates was investigated using single-base mismatch DNAs, which possess a mismatch base in the MGB polyamide binding sequence. The Py(3)-γ-Im(3)-oligonucleotide conjugate ON 4 (n = 2) showed high sequence recognition ability for complementary DNA.