Catalytic Light-induced Deracemization

Molecules are chiral if they exist in two forms, called enantiomers, which behave like image and mirror image.

In many applications, e.g. in medicine, nutrition, and crop protection, chiral molecules are required as a single enantiomer (enantiomerically pure compound) but not as a mixture (racemate). The market for enantiomerically pure compounds exceeds 100 billion annually and continues to grow rapidly.

Despite significant recent advances in asymmetric catalysis, many chiral compounds are for cost reasons prepared as racemates and separated thereafter. If only one enantiomer is required, the other enantiomer remains as waste.

The aim of the CALIDE project is to provide for the first time a comprehensive set of methods for the quantitative conversion of racemates into single enantiomers employing exclusively light and a photocatalyst.

The process includes the light-induced formation of short-lived achiral intermediates which decay to the starting materials on a thermal reaction channel.

By employing two intrinsically different channels for formation and decay, the transformation overcomes issues of microscopic reversibility which render related thermal deracemization reactions impossible.

The photocatalyst interacts with the racemic substrates and enables the destruction and reformation of the stereogenic element.

A first objective (work package I) is to identify suitable binding motifs to achieve the required proximity in the energy transfer step for compounds displaying an axis or plane of chirality.

The second objective (work package II) aims at a deracemization of compounds with a stereogenic carbon center via a reversible cleavage of carbon-carbon or carbon-heteroatom bonds. The bond cleavage can be initiated by energy or electron transfer. The third objective (work package III) tackles substrates with a carbon-hydrogen bond at the stereogenic carbon atom.

Bond fission by hydrogen abstraction from the catalyst is proposed as the key feature of this method.