Bioorganometallic Chemistry: B12-Cofactors and B12-Enzyme Models

12-Bioorganometallic Chemistry Vitamin B12 and the B12-coenzymes are unique but still ubiquitous cobalt- containing biological catalysts (enzymatic cofactors) if basic relevance in the fields of medicine, biology and chemistry. The present project is planned to center around questions concering the synthesis and the chemical reactivity of organometallic B12-derivatives and, in this way, to contribute on important chemical aspects of these unique metal containing biocatalysts. Specifically, it is proposed to prepare and structurally characterize (in solution and in the solid state) some novel organometallic B12-derivatives, which may function as structural and functional models for enzyme-bound B12- cofactors an of whole B12-enzymes. Of particular concern will be the biologically central problem, oh how the molecular and supramolecular environment of the organometallic and corrinoid cobalt complex influences the reactivity of the metal bound organic group. For this purpose, (i) covalent conjugates between coenzyme B12- derivatives and cyclodextrins will be prepared and characterized, (ii) dimeric organometallic B12-derivatives will be prepared and examined. In a separate section, the new finding will be taken up, that organometallic B12- derivatives may be intermediates in bioremediation as well as in the natural biological dechlorination of chlorohydrocarbons: it is proposed to prepare a set of chloroalkyl-corrinoids, which are potentially the searched-for organometallic intermediates in the natural reductive dechlorination processes, and to study their chemical reactivity. The project is planned to unravel new structure-based aspects of the biologically important chemical reactivity of organometallic B12-derivatives and to contribute in this way to the understanding of the newly developing filed of bioorganometallic chemistry.