Incorporation of modified nucleosides with a flexible universal linker is of great value for post-synthetic modification of nucleic acids. Thus, C8-alkynyl- and alkylamino substituted 2'-deoxyguanosines were synthesized for the first time and incorporated into short oligonucleotide sequences. The preference for syn conformation of these C8-substituted 2'-deoxyguanosines and the stability of the duplexes were discussed. The stabilizing effect of Z-DNA has also been examined. (c) 2008 Elsevier Ltd. All rights reserved.