Improved synthesis of daunomycin conjugates with triplex-forming oligonucleotides. The polypurine tract of HIV-1 as a target.

Triple helix-forming oligonucleotides (TFOs) are promising agents for the control of gene expression, as they can selectively bind to a chosen oligopyrimidine-oligopurine region of a gene of interest thus interfering with its expression. The stability of the triplex formed by the TFO and the duplex is often too poor for successful applications of TFOs in vivo and the conjugation of a DNA intercalating moiety to the TFO is a common way to enhance the TFO affinity for its target. In a previous work, we investigated the properties of daunomycin conjugated TFO (dauno-TFO) and found that this class of compounds showed a higher degree of affinity than native oligonucleotides for an oligopyrimidine-oligopurine duplex target and that the presence of the amino sugar increases such stability. Here, we report a significantly improved synthetic procedure for the preparation of the conjugates, based on the protection of the daunosamine moiety by N-trifluoroacetylation. This protecting group is removed as a final step from the conjugation product by mild basic hydrolysis to give the desired dauno-TFO. Compared to the previous synthetic procedure, the improvement is important. The synthesis is now more reproducible and no side products are formed. Moreover, the thus protected daunomycin derivative is very stable, up to at least one year. Two dauno-TFOs, differing by the length of the oligonucleotide moiety, were prepared to target the polypurine tract (PPT) of HIV-1. Triplex formation by these compounds with model duplexes was studied by UV spectroscopy, thermal gradient gel electrophoresis (TGGE) and gel electrophoretic mobility shift. The experimental results demonstrate that dauno-TFOs bind to the PPT of HIV-1 more strongly than the unconjugated TFOs. (c) 2005 Elsevier Ltd. All rights reserved.