Artificial Copper Enzymes for Asymmetric Diels-Alder Reactions

The development of artificial copper enzymes from sterol carrier protein type2 like domain (SCP-2L) for the use in asymmetric catalysis was explored. For this purpose, proteins were modified with various nitrogen donor ligands. Maleimide-containing ligands were found most suitable for selective cysteine bio-conjugation. Fluorescence spectroscopy was used to confirm copper binding to an introduced phenanthroline ligand, which was introduced in two unique cysteine containing SCP-2L mutants. Copper adducts of several modified SCP-2L templates were applied in asymmetric Diels-Alder reactions. A clear influence of both the protein environment and the introduced ligand was found in the asymmetric Diels-Alder reaction between azachalcone and cyclopentadiene. A promising enantioselectivity of 25% ee was obtained by using SCP-2LV83C modified with phenanthroline-maleimide ligand. Good endo selectivity was observed for SCP-2L modified with the dipicolylamine-based nitrogen donor ligand. These artificial metalloenzymes provide a suitable starting point for the implementation of various available techniques to optimise the performance of this system.