Synthesis of oligonucleotides bearing the non-standard bases iso-C and iso-G. Comparison of iso-C-iso-G, C-G and U-A base-pair stabilities in RNA/DNA duplexes

2′-Deoxy-5-methylisocytidine

“…Transposition of the amino and oxo groups in the canonical nucleic acid base cytosine results in isocytosine. This nucleobase can form a Watson±Crick base pair with isoguanine, forming a DNA with antiparallel (aps) chain orientation (Switzer et al, 1989(Switzer et al, , 1993Tor & Dervan, 1993;Roberts et al, 1995;Horn et al, 1995). More interestingly, isocytosine or 5methylisocytosine can form a reverse Watson±Crick base pair with the canonical DNA base guanine, which then results in parallel (ps) DNA (Sugiyama et al, 1996;Seela et al, 1998;Seela, He & Wei, 1999;Seela, Wei et al, 1999).…”

Stacking Effects on Local Structure in RNA: Changes in the Structure of Tandem GA Pairs when Flanking GC Pairs Are Replaced by isoG−isoC Pairs

“…[13][14][15][17][18][19] The Watson-Crick like iGiC pair, with the amino and carbonyl groups transposed relative to the Watson-Crick GC pair, provides an expanded alphabet [20][21][22][23][24][25][26] for further understanding interactions that shape nucleic acid structure (Figure 1). 7,[25][26][27][28][29][30][31][32] Here, thermodynamic studies of tandem GA pairs flanked by iGiC pairs are reported along with NMR structures of the RNA duplexes (GCiGGAiCGCA) 2 and (GGiCGAiGCCA) 2 . NMR restrained molecular dynamics and energy minimization of (GCiGGAiCGCA) 2 reveal a conformation of tandem sheared GA pairs closed by Watson-Crick like iGiC pairs.…”

The development of isoguanosine: from discovery, synthesis, and modification to supramolecular structures and potential applications

“…Subsequently, in 1990, Benner 93 et al conrmed the existence of the isoG-isoC base pair, as well as a second pair, isoG-T, in vitro polymerase experiments. Aerwards, evidence for isoG-isoC pair without enzymes was obtained by Horn 94 et al and Switzer 95 et al in 1995. The base pairing of isoG in the enol form is stronger than that in the ketone form, which is the rst experimental evidence that tautomerism can lead to base pairing differences.…”