DOI: 10.1002/chem.200601058 DNA-Based Phosphane Ligands Mihaela Caprioara, [a] Roberto Fiammengo, [a] Marianne Engeser, [b] and Andres Jäschke* [a] Introduction The incorporation of transition-metal complexes into DNA and RNA is an important objective for the development of functional biomolecules with potential applications as thera- peutics, [1] artificial nucleases, [2–4] and as nanotechnology con- struction material. [5,6] Inspired by the pioneering work of Whitesides, [7] who showed that asymmetric catalytic hydro- genations could be performed by anchoring an achiral Rh I complex in a chiral cavity of the protein avidin, [8,9] we aim at embedding transition-metal complexes in nucleic acids folds in order to generate metalloribozymes and metallo- deoxyribozymes. The potential of nucleic acids in asymmetric catalysis is thus far practically unexplored. To date, there are only two documented examples of nucleic acid-based asymmetric cat- alysis. Our lab has discovered RNA enzymes that catalyze Diels–Alder cycloadditions of anthracene and maleimide de- rivatives with fast multiple turnover and high enantioselec- tivity. [10,11] Structural and mechanistic data, however, indi- cate that in this system, metal ions play no catalytic role. [12,13] Feringa and co-workers recently demonstrated that double-helical DNA could be employed as chirality source in Lewis acid catalyzed Diels–Alder reactions using Cu II complexes tethered to an intercalator [14] or able to interact directly with double stranded DNA. [15] In these systems, however, the exact position of the metal complexes within the DNA is not defined, making a thorough understanding of DNA)s role difficult. Towards this end, a well-defined po- sitioning of the metal complex and a precise control of the coordination environment are essential. The most common approach to introduce metal com- plexes into DNA is the post-synthetic derivatization of oli- gonucleotides that contain tethered primary amino groups with activated esters, affording nucleic acids that carry metal-based cleavage reagents, luminescent probes, photo- oxidants and redox-active species. [16–22] Alternatively, solid- phase strategies have utilized ligand-tethered [2–4] or metallat- ed [23–25] nucleoside analogues or metal-coordinating nucleo- side mimics (ligandosides). [26–30] However, the major draw- back of these solid-phase strategies is the requirement for stable ligands that can survive the conditions used in DNA automated synthesis (capping, oxidation), deprotection and isolation. Therefore the known repertoire of metal-binding Abstract: In order to expand the reper- toire of DNA sequences specifically in- teracting with transition metals, we report here the first examples of DNA sequences carrying mono- and biden- tate phosphane ligands as well as P,N- ligands. Aminoalkyl-modified oligonu- cleotides have been reacted at prede- termined internal sites with carboxylate derivatives of pyrphos, BINAP and phosphinooxazoline (PHOX) 2b–d. Carbodiimide coupling in the presence of N-hydroxysuccinimide provided the DNA–ligand conjugates in 38–78% yield. Phosphane-containing oligonu- cleotides and their phosphane sulfide analogues were characterized by mass spectrometry (MALDI-TOF and FT- ICR-ESI) and their stability after pu- rification and isolation was systemati- cally investigated. While DNA-append- ed pyrphos ligand was quickly oxidized, BINAP and PHOX conjugates showed high stabilities, making them useful precursors for incorporation of transi- tion metals into DNA. Keywords: DNA · nucleic acids · oxazoline · phosphane ligands [a] Dipl.-Chem. M. Caprioara, Dr. R. Fiammengo, Prof. Dr. A. Jäschke Institute of Pharmacy and Molecular Biotechnology Ruprecht-Karls University Heidelberg 69120 Heidelberg (Germany) Fax: (+ 49)6221-54-6430 E-mail: jaeschke@uni-hd.de [b] Dr. M. Engeser KekulØ-Institute of Organic Chemistry and Biochemistry University of Bonn, 53121 Bonn (Germany) Supporting information for this article is available on the WWW under http://www.chemeurj.org/ or from the author: Experimental procedure for the synthesis of amino-modified oligonucleotides ODN1–3, MALDI TOF analysis, reversed-phase HPLC gradients and retention times for all DNA conjugates ODN1–6, and original elec- trospray mass spectrum of ODN4 b. Chem.Eur.J. 2007, 13, 2089–2095 # 2007 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 2089 FULL PAPER