Artificial Copper Enzymes for Asymmetric Diels–Alder Reactions



The development of artificial copper enzymes from sterol carrier protein type 2 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-2L V83C 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.