Polynucleotides interaction with purines

Polynucleotides were reported to form triple helices as early as 1957. Triple strands can form by non-Watson-Crick hydrogen bonds between the third strand and purines involved in Watson-Crick hydrogen bonding with the complementary strand of the duplex (for review, see Ref 34). Thus, triple-stranded structures can be formed between a third strand composed of pyrimidines or purines that interact with a homopurine strand in a homopurine-homopyrimidine strand in a duplex DNA. With the demonstration that homopyrimidine oligonucleotides could indeed form triplex structures (35-37), interest in triple-strand approaches to inhibit transcription heightened. 

In a monumental piece of research, Roques and co-workers 235-239) have employed exceedingly sophisticated and difficult high-field H- and P-NMR experiments to examine the interaction of nonlinear bispyridocarbazoles, such as ditercalinium (212), with small polynucleotides. As in their earlier work on monomers 233), the self-complementary tetra- and hexanucleotides were used. It was found that ditercalinium is a bis-intercalator with a preference for alternating sequences, pyrimidine-purine or purine-pyrimidine, and, in agreement with the classic pyrimidine-purine model 240,241), it was found that the linking chain lies in the major groove of the helix. 

Interaction of Polynucleotides with Nucleosides, Nucleotides, and Purines... 

The identification of DNA as a primary target for metal-based drugs, especially cisplatin, has focused attention on the interactions of metal complexes with nucleic acid constituents, which include the simple purine and pyrimidine bases and their nucleoside and nucleotide derivatives. The structures, with abbreviations, are represented in Appendix 1. Simple complexes can represent models for cross links in DNA, which can be studied in more detail with small polynucleotides, from the simpler dinucleotides to oligonucleotides and this topic is covered in Section 4.4. There has been extensive use of substituted purines and pyrimidines as models for the DNA bases and in the examination of steric and electronic effects. The structures of many of these analogues are also collected in Appendix 1. 

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