Nucleic Acids Research, 2002, Vol. 30, No. 24 5485-5496
© 2002 Oxford University Press
Propynyl groups in duplex DNA: stability of base pairs incorporating 7-substituted 8-aza-7-deazapurines or 5-substituted pyrimidines
Laboratorium für Organische und Bioorganische Chemie, Institut für Chemie, Universität Osnabrück, Barbarastraße 7, D-49069 Osnabrück, Germany
*To whom correspondence should be addressed. Tel: +49 541 969 2791; Fax: +49 541 969 2370; Email: frank.seela{at}uni-osnabrueck.de
Oligonucleotides incorporating the 7-propynyl derivatives of 8-aza-7-deaza-2'-deoxyguanosine (3b) and 8-aza-7-deaza-2'-deoxyadenosine (4b) were synthesized and their duplex stability was compared with those containing the 5-propynyl derivatives of 2'-deoxycytidine (1) and 2'-deoxyuridine (2). For this purpose phosphoramidites of the 8-aza- 7-deazapurine (pyrazolo[3,4-d]pyrimidine) nucleosides were prepared and employed in solid-phase synthesis. All propynyl nucleosides exert a positive effect on the DNA duplex stability because of the increased polarizability of the nucleobase and the hydrophobic character of the propynyl group. The propynyl residues introduced into the 7-position of the 8-aza-7-deazapurines are generally more stabilizing than those at the 5-position of the pyrimidine bases. The duplex stabilization of the propynyl derivative 4b was higher than for the bromo nucleoside 4c. The extraordinary stability of duplexes containing the 7-propynyl derivative of 8-aza-7- deazapurin-2,6-diamine (5b) is attributed to the formation of a third hydrogen bond, which is apparently not present in the base pair of the purin-2,6-diamine 2'-deoxyribonucleoside with dT.