Scientists create pyridoxal photoenzymes for asymmetric radical cross-couplings
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An international team of chemists has established pyridoxal 5′-phosphate as a photoenzymatic cofactor, creating a new class of enzymes for asymmetric radical–radical cross-couplings, according to a study published today in Nature. The approach overcomes long-standing challenges in radical chemistry by enabling selective bond formation without the need for radical sorting or persistent radical effects.
Pyridoxal Photoenzymes
Researchers leveraged the excited state quinonoid intermediate of pyridoxal 5′-phosphate as a potent single-electron reductant. By employing non-native benzyl amine substrates and exploiting Förster resonance energy transfer from an exogenous photosensitizer, they overcame the poor photophysical properties of the native quinonoid. This redox neutral strategy enables an asymmetric radical–radical cross-coupling between benzyl amines and reductive radical precursors, generating and localizing a radical pair within the enzyme active site to achieve selectivity.
Overcoming Radical Chemistry Limitations
The method circumvents typical challenges of radical–radical cross-couplings by eliminating the need for radical sorting and the persistent radical effect. Conventional small-molecule catalysts often struggle with selectivity in such reactions. The photoenzymatic system confines the radical pair in a chiral environment, allowing precise control over bond formation. This work opens pyridoxal-dependent enzymes to a range of previously inaccessible bond-forming events.
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