Selectively recognizing extrahelical conformations of DNA trinucleotide repeats by a hydroxylated porphyrin ligand.

Trinucleotide repeats (TRs) with abnormal lengths and atypical folding are implicated in various neurodegenerative diseases. The least stable cytosine-cytosine (C-C) mismatches in TRs when structuring into homoduplexes/hairpins have more chance in certain sequence contexts to preferentially adopt an extrahelical (E-motif) conformation with respect to those in polarity-inverted intrahelical counterparts. Herein, we designed a trihydroxyphenyl porphyrin ligand (POH3) to meet the challenge towards resolving the E-motif conformation. POH3 exhibited a specific 2:1 binding with DNAs adopting the E-motif cytosine conformation, independent of the TRs length. The trihydroxyl pattern was very crucial to gain the E-motif selectivity over the polarity-inverted counterparts via the complementary hydrogen bonding that occurred in the minor groove. Our work first elucidates the rationale in designing ligands to selectively resolve the E-motif nucleotides within TRs.