Published online 2 February 2004
Nucleic Acids Research, 2004, Vol. 32, No. 2 710-718
© 2004 Oxford University Press
A novel concept for ligand attachment to oligonucleotides via a 2'-succinyl linker
Institute for Pharmaceutical Chemistry, Universität Wien, Pharmaziezentrum, Althanstraße 14, 1090 Wien, Austria 1 Department of Clinical Pharmacology, Section of Experimental Oncology and 2 Department of Dermatology, Universität Wien, Währinger Gürtel 18–20, 1090 Wien, Austria
*To whom correspondence should be addressed. Tel: +431 4277 55103; Fax: +431 4277 9551; Email: christian.noe{at}univie.ac.at
Conjugation of ligands to antisense oligonucleotides is a promising approach for enhancing their effects. In this report, a new method for synthesizing oligonucleotide conjugates is described. 2'-Amino-2'-deoxy-5'-dimethoxytrityl-uridine was select ively acylated with a succinic acid linker at the 2' position. This compound was incorporated at the 3' end of an oligonucleotide corresponding to the sequence of Oblimersen. The carboxyl group was protected for oligonucleotide synthesis as a benzyl ester, which could be selectively cleaved at the solid phase by a catalytic phase transfer reaction using palladium nanoparticles as catalyst. An oligonucleotide–fluorescein conjugate was prepared by condensation of aminofluorescein. Circular dichroism spectroscopic experiments showed a B-DNA type structure. The melting temperature of the duplex was only slightly lower than that of Oblimersen. Biological activity measured by western blotting resulted in a Bcl-2 target downregulation nearly identical to that of control Oblimersen on human melanoma cells, proving that this method is attractive for the binding of ligands located in the minor groove.