Parallel-Stranded Duplex DNA and Self-Assembled Quartet Structures Formed by Isoguanine and Related Bases

Abstract
Parallel-stranded (ps) oligonucleotide duplexes are described containing isoguanine-cytosine and/or 5-methylisocytosine-guanine base pairs. A parallel hybrid is also formed when 5-aza-7-deazaguanine base pairs with guanine while the base pair with isoguanine results in an antiparallel duplex. Oligomers such as d(T4isoG4T4) form selfassembled tetraplexes which show a cation selectivity different from that of the G-quartet.