Published online 23 March 2005
Article |
Post-synthetic and site-specific modification of endocyclic nitrogen atoms of purines in DNA and its potential for biological and structural studies
Department of Chemistry, The Open University Walton Hall, Milton Keynes, MK7 6AA, UK
*To whom correspondence should be addressed. Tel: +44 1980 654064; Fax: +44 1980 858327; Email: y.z.xu{at}open.ac.uk
Received January 25, 2005. Revised March 2, 2005. Accepted March 2, 2005.
Site-specific modification of the N1-position of purine was explored at the nucleoside and oligomer levels. 2'-Deoxyinosine was converted into an N1-2,4-dinitrophenyl derivative 2 that was readily transformed to the desired N1-substituted 2'-deoxyinosine analogues. This approach was used to develop a post-synthetic method for the modification of the endocyclic N1-position of purine at the oligomer level. The phosphoramidite monomer of N1-(2,4-dinitrophenyl)-2'-deoxyinosine 9 was prepared from 2'-deoxyinosine in four steps and incorporated into oligomers using an automated DNA synthesizer. The modified base, N1-(2,4-dinitrophenyl)-hypoxanthine, in synthesized oligomers, upon treatment with respective agents, was converted into corresponding N1-substituted hypoxanthines, including N1-15N-hypoxanthine, N1-methylhypoxanthine and N1-(2-aminoethyl)-hypoxanthine. These modified oligomers can be easily separated and high purity oligomers obtained. Melting curve studies show the oligomer containing N1-methylhypoxanthine or N1-(2-aminoethyl)-hypoxanthine has a reduced thermostability with no particular pairing preference to either cytosine or thymine. The developed method could be adapted for the preparation of oligomers containing mutagenic N1-ß-hydroxyalkyl-hypoxanthines and the availability of the rare base-modified oligomers should offer novel tools for biological and structural studies.