A TRISPYRAZOLYLBORATO IRON CYSTEINATO COMPLEX AS A FUNCTIONAL MODEL FOR THE CYSTEINE DIOXYGENASE

The cysteine dioxygenase (CDO) is a non-heme mononuclear iron enzyme that catalyzes the irreversible oxidation of cysteine by dioxygen to yield cysteine sulfinic acid, which is the first major step in cysteine catabolism in mammalian tissues.^[1] While the function of many oxygenating non-heme iron enzymes could be successfully imitated within the last decades using molecular model compounds,^[2] to date there are hardly any reports in the literature on biomimetic models for the CDO.

Unlike other mononuclear non-heme iron dioxygenases, the active sites of which typically contain a 2-histidine-1-carboxylate coordination motive, the iron ion of CDO is bound by three histidine ligands.^[1] To this unit, the substrate cysteine coordinates through the sulfur atom and the nitrogen atom as a chelating ligand.

Here we present the successful coordination and dioxygenation of a protected cysteinato ligand to a (His)₃Fe^II analogue (see Scheme):^[3] In complex [Tp^Me,PhFeCysOEt], the Tp^Me,Ph ligand excellently mimics the (His)₃-coordination sphere and also the function is simulated, as treatment with dioxygen mainly leads to cysteine sulfinic acid. 1 is thus the hitherto most realistic model for the active site of the CDO.