Solid-Phase Synthesis of Oligonucleotides Containing a Bipyridine Ligand at the 3 0 -3 0 Inversion of Polarity Site Aldo Galeone, Luciano Mayol,* Giorgia Oliviero, Daniela Rigano and Michela Varra Dip. di Chimica delle Sostanze Naturali, Univ. di Napoli ``Federico II'', Via D. Montesano, 49 I-80131 Napoli, Italy Received 28 July 2000; revised 20 November 2000; accepted 23 November 2000 AbstractÐThe preparation of a solid support useful for the synthesis of oligonucleotides with a 3 0 -3 0 inversion of polarity, via a linker containing a chelating molecule, namely 2,2 0 -bipyridine, is described. # 2001 Elsevier Science Ltd. All rights reserved. Introduction There is a growing interest in design and synthesis of newly modi®ed oligonucleotides (ODNs) as potential drugs in anticancer or antiviral therapy. 1,2 Such mole- cules, indeed, may be very ecient tools in the selective inhibition of gene expression, both in the antisense approach, where the target is an mRNA, and in the antigene strategy, through the formation of a triple helix complex (triplex) with a selected double-stranded DNA sequence. 2 6 In the latter strategy, one of the major restrictions is that a stable triplex, via Hoogsteen triads formation, can be envisaged under physiological condi- tions only for relatively long (15±17 bases) homopurine tracts within the same strand of a double helical DNA fragment and such a requirement is rarely met in biolo- gically important regions of DNA. To recognize a wider number of DNA sequences, a possible solution is the use of ODNs containing a 3 0 -3 0 inversion of polarity, able to target (purine) m (pyrimidine) n sequences by hybridization of the adjacent purine blocks on alternate strands and by switching strand at the junction between the oligopurine and the oligopyrimidine domains. 7 9 From a chemical point of view, the 3 0 -3 0 inversion can be ful®lled by a suitable linker capable of crossing the major groove and whose properties can be, in addition, exploited to supply the oligonucleotide with useful characteristics. For example, the 3 0 -3 0 linker may incor- porate an intercalating agent or a major groove ligand in order to improve the hybridization between the probe ODN and the target duplex. In this frame, we have designed and prepared a solid- phase support useful for the synthesis of oligonucleo- tides with 3 0 -3 0 inversion containing a chelating agent, namely a bipyridine moiety. Transition metal com- plexesÐcontaining oligonucleotides (ODNs) 10,11 Ð represent a topic in constant growth. Such conjugates are involved in the study of electron transfer processes 12 14 as well as in the development of arti®cial nucleases characterized by a high sequence-speci®city and eciency. 15,16 In fact, a metal centre tethered to a particular sequence could enable the complex to oxida- tively modify or cleave a nucleic acid target. Chemistry The synthetic route (see Scheme 1) used for the pre- paration of oligomers with a 3 0 -3 0 inversion containing a bipyridine moiety is based on a three-functionalized molecule (2-amino-1,3-propandiol) that allows: (i) anchorage to the polymeric support (Tentagel-NH 2 ); (ii) linkage to the metal complexing unit (2,2 0 -dipyridine); (iii) oligonucleotide chain assembly. 2-Amino-1,3-propandiol (1) is protected at the amino function and at one of the two hydroxyls by 9-¯uor- enylmethoxy-carbonyl (Fmoc) and 4,4 0 -dimethoxytrityl protecting groups, respectively (derivatives 2 and 3). 17,18 Subsequently, the Fmoc group is removed by piperidine thus giving derivative 4 19 which, in turn, is reacted with the penta¯uorophenolic ester of 2,2 0 -bipyridine-4,4 0 -dicar- boxylic acid (6) 20 aording derivative 7. 21 Compound 6 represents the activated chelating molecule and is obtained by reaction of commercially available 2,2 0 -bipyridine-4,4 0 - dicarboxylic acid (5) with the penta¯uorophenolic ester of 0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0960-894X(00)00673-9 Bioorganic & Medicinal Chemistry Letters 11 (2001) 383±386 *Corresponding author. Fax: +39-81-678552; e-mail: mayoll@unina.it