A bottom up approach towards artificial oxygenases by combining iron coordination complexes and peptides

Abstract

Supramolecular systems resulting from the combination of peptides and a chiral iron coordination complex catalyze asymmetric epoxidation with aqueous hydrogen peroxide, providing good to excellent yields and high enantioselectivities in short reaction times. The peptide is shown to play a dual role; the terminal carboxylic acid assists the iron center in the efficient H2O2 activation step, while its β-turn structure is crucial to induce high enantioselectivity in the oxygen delivering step. The high levels of stereoselection (84–92% ee) obtained by these supramolecular catalysts in the epoxidation of 1,1′-alkyl orthosubstituted styrenes, a notoriously challenging class of substrates for asymmetric catalysis, are not attainable with any other epoxidation methodology described so far. The current work combining an iron center ligated to N and O based ligands, and a peptide scaffold that shapes the second coordination sphere may be seen as a bottom up approach towards the design of artificial oxygenases.

Recent developments in enantioselective iron-catalyzed transformations

“…In the same area, chiral peptide 39 was combined with the same iron catalyst 35 to promote comparable asymmetric epoxidations of a-alkyl-substituted styrenes 37 [52]. As shown in Scheme 20, the corresponding chiral epoxides 38 were achieved in moderate to quantitative yields (66-99%) and moderate to high enantioselectivities (64-92% ee).…”

“…Scheme 20. Epoxidations of a-alkyl-substituted styrenes and cis-aromatic alkenes catalyzed by a chiral bipyrrolidine-derived aminopyridine iron complex in the presence of a chiral peptide as a co-ligand [52]. ric epoxidation of various aromatic a,b-unsaturated ketones 44 performed at À30°C in acetonitrile led to the corresponding epoxides 45 in both moderate to high yields (34-93%) and enantioselectivities (54->99% ee).…”

Biologically inspired oxidation catalysis using metallopeptides

“…33 A synergistic combination of one of these catalysts with peptides has been recently described to create a highly enantioselective epoxidation catalytic system. 34 In this work, peptides were employed with the aim to shape the second coordination sphere of the metal and also to establish noncovalent interactions with the substrates. 4b,6b These features were envisioned to play an important role in defining the reactivity of the metal center and the chemo-and regioselectivity of the reactions.…”

Iron(III) Complexes with Cross‐Bridged Cyclams: Synthesis and Use in Alcohol and Water Oxidation Catalysis

“…Considering non‐heme catalysts, iron complexes bearing robust N‐macrocyclic donor have been widely investigated for oxidation of organic substrates, using peroxides, peracids and molecular oxygen as external oxidant . Costas, Lanzalunga, and their co‐workers developed various catalytic systems based on iron tetradentate complexes for the oxidation of alcohols and alkanes, the epoxidation and the dihydroxylation of olefins.…”