N7-Guanine as a C+ Mimic in Hairpin aeg/aepPNA-DNA Triplex:  Probing Binding Selectivity by UV-Tm and Kinetics by Fluorescence-Based Strand-Invasion Assay

N7-substituted guanine (N7G) has been introduced into aminoethylglycyl bisPNA (7) as a C(+) mimic to achieve pH-independent triplex formation with complementary DNA sequences. The introduction of chiral, cationic aminoethylprolyl units with C(+) and C(+) mimic N7G in the backbone of bisPNAs (8, 9) influenced the recognition of complementary DNA in an orientation-selective manner. A simple fluorescence assay is developed to examine the process of strand invasion of target DNA duplex by these modified bisPNAs and comparative results of the study employing triplex forming polypyrimidine (C/T) (6, 8) and purine-pyrimidine (N7G/T) mixmer-bisPNAs (7, 9) are presented.