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  • Author: Michael Schmittel x
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The oxidative coupling of various symmetric (5 -7) as well as unsymmetric silicon bisnaphtholates (11, 12), initiated by different oxidants (iron(III), cerium(IV), copper(II) or hypervalent iodine), furnishes the corresponding symmetric and unsymmetric binaphthols 13 - 17. The coupling reaction of the substrates follows strictly an intramolecular pathway.

Several new 4.7-donor substituted 1.10-phenanthrolines were synthesized and the corre­sponding tris(1,10-phenanthroline)iron(II) complexes were studied by cyclic voltammetry. All iron(II) complexes showed fully reversible waves at scan rates between 50 and 500 mV/s. For some redox systems the kinetics in their reaction with chlorine was studied. Complexes 7k and 71 significantly extent the potential range of tris(1,10-phenanthroline)iron(II) complexes.

A synthetic route to 6,6′-dimesityl-2,2′-bipyridine is presented that involves a Suzuki coupling of 6,6′-dibromo-2,2′-bipyridine with mesityl boronic acid. The new sterically crowded ligand is investigated by X-ray analysis and its coordination behavior in the presence of copper(I) is examined.

Abstract

Ribonucleotide reductases (RNRs) catalyze the production of deoxyribonucleotides, which are essential for DNA synthesis and repair in all organisms. The three currently known classes of RNRs are postulated to utilize a similar mechanism for ribonucleotide reduction via a transient thiyl radical, but they differ in the way this radical is generated. Class I RNR, found in all eukaryotic organisms and in some eubacteria and viruses, employs a diferric iron center and a stable tyrosyl radical in a second protein subunit, R2, to drive thiyl radical generation near the substrate binding site in subunit R1. From extensive experimental and theoretical research during the last decades, a general mechanistic model for class I RNR has emerged, showing three major mechanistic steps: generation of the tyrosyl radical by the diiron center in subunit R2, radical transfer to generate the proposed thiyl radical near the substrate bound in subunit R1, and finally catalytic reduction of the bound ribonucleotide. Amino acid- or substrate-derived radicals are involved in all three major reactions. This article summarizes the present mechanistic picture of class I RNR and highlights experimental and theoretical approaches that have contributed to our current understanding of this important class of radical enzymes.

Four novel stable enols (one characterized by X-ray crystal structure analysis) were synthesized and investigated under oxidative conditions to yield benzofurans. Depending on the donor qualities of the heteroaryl substituent the reaction following the one-electron oxidation could be stopped on the stage of the cyclohexadienyl cation whose lifetime was measured. Oxidation potentials were determined for the enols, the enolates and the α-carbonyl radicals. Oxidation of benzofurans yielded dimeric species or intramolecular cyclization products.

A three-step preparation of the benzofluorene core is presented. The last step involves thermal cyclization of 3 -ene-1,6 -diyne (7) leading to the formation of four benzofluorene derivatives, one of which has been investigated by X-ray analysis. The harsh thermal conditions indicate that the cyclization of 7 might not proceed via a biradical intermediate as would be anticipated by a mechanistic proposal from Ueda.