We report the synthesis of new NHC gold(I) and NHC gold(III) halide, amino acid and dipeptide complexes. Transmetallation of the N-phenylalanine-substituted NHC silver complex 3 with Me2SAuCl yields the phenylalanine-NHC gold(I) conjugate 4a. Halide exchange with LiBr and oxidation of 4a with Br2 in CH2Cl2 yields the phenylalanine-NHC Au(I) and Au(III) bromides 4b and 4c, respectively. Reaction of N-Boc protected cysteine methyl ester (Boc-Cys-OMe) or the dipeptide N-Boc-Leu-Cys-OMe with the NHC gold chloride 6a yields the (NHC)Au-S complexed amino acid and dipeptide derivatives 8 and 9. The NHC gold(III) complexes 4c and 6c were characterised by single crystal X-ray analysis. All of the tested gold carbene complexes showed significant anti-tumor activity on the HeLa, HepG2 and HT-29 cancer cell lines. The best compounds show activity comparable to the well-known anti-cancer drug cisplatin. There seems to be no clear cut structure-activity relationship in the compounds tested, nor did we observe a dependence on the metal oxidation state or the different halide substituents. Given the ease of preparation, stability and high activity of the compounds described herein, it may be possible to design tumor-specific anti-cancer agents based on NHC gold amino acid conjugates in the future.

While N-heterocyclic carbenes (NHCs) are ubiquitous ligands in catalysts for organic or industrial synthesis, their potential to form stable transition metal complexes has hardly been exploited in metal bioconjugates. In this work, we describe a straightforward synthesis of carboxylato-functionalized imidazolium salts for covalent binding to peptides. Carbene complexes of Ru and Rh were prepared from these imidazolium salts using Ag 2 O, followed by transmetallation. The neuropeptide [Leu 5 ]-enkephalin (Tyr-Gly-Gly-Phe-Leu) was chosen as a model peptide. Exploratory NMR experiments identified the Ru(p-cymene)Cl 2 complex of the asymmetrically substituted imidazol-2-ylidene 3b as the most suitable metal carbene precursor for solid phase peptide synthe-

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Mono-and bis(trifluoromethylthio)-substituted and perfluorooctanesulfonylferrocene derivatives were prepared by nucleophilic substitution reactions on the ferrocene core. Thus, Hg(SCF 3 ) 2 was activated in situ by Cu and used for nucleophilic displacement reactions of bromide. Trifluoromethylsulfonylferrocene was not accessible by this method. The reaction of lithioferrocene with trifluoromethylsulfonyl chloride gave chloroferrocene in small yield, presumably due to the high lattice energy of solid LiF. On the other hand, the known trifluoromethylferrocene was obtained as the only isolable compound from the photochemical reaction of CF 3 SSCF 3 with ferrocene. The same product was detected in small amounts in the reaction of chloromercuryferrocene with trifluoromethylsulfonyl chloride. It thus appears that most established methods for trifluoromethylation of purely organic compounds fail for ferrocene due to concurring redox reactions. The new compounds have been comprehensively characterized by elemental analyses, NMR and IR spectroscopy, mass spectrometry, and electrochemistry. The SCF 3 group appears to be almost as electronwithdrawing as a trifluoromethyl group on the ferrocene core.

Das International Symposium on Bioorganometallic Chemistry (ISBOMC) ist ein Forum der Biorganometallchemie. Zum ISBOMC '06, der dritten Veranstaltung dieser Art (nach Paris 2002 und Zürich 2004), fanden sich Anfang Juli ca. 150 Chemiker aus Hochschule und Industrie an der Universität Mailand ein. Mehr als 30 Referenten, darunter eingeladene Professoren und viele Nachwuchswissenschaftler, nutzten die Gelegenheit zur Präsentation ihrer Arbeiten. Diskussionen in den Kaffeepausen und an mehr als 50 Postern lieferten die Grundlage für Erfahrungsaustausch und mögliche Kooperationen.