Bioinspired photoenzymatic cascade enabled by a bifunctional arylformamidase for efficient synthesis of L-kynurenine derivatives

Abstract

L-Kynurenine (L-Kyn) serves as a pivotal metabolite and a versatile building block for numerous bioactive natural products and pharmaceuticals. However, conventional synthetic routes are often hampered by poor step economy due to extensive protective-group manipulations, the usage of environmentally detrimental reagents particularly for the required deprotection steps, as well as harsh conditions, which all conflict with green chemistry principles. Herein, we report a bioinspired, one-pot one-step photoenzymatic cascade that integrates metal-free photocatalyst cercosporin (CP) and an engineered bifunctional arylformamidase (AchAF-V170A) to directly convert L-tryptophan or its ester derivatives into L-Kyn under mild and aqueous conditions. Through structure-guided semi-rational mutagenesis, we enhanced the enzymatic activity and elucidated its dual amidase/esterase function, enabling efficient transformation of diverse substrates with excellent functional group tolerance, which was well explained by molecular dynamics simulations. The reaction proceeds via a singlet oxygen-mediated photooxidation followed by enzymatic hydrolysis, offering a protecting group-free strategy that significantly simplifies synthesis. Scale-up experiments and green metrics evaluation (E‑factor = 1.4, EcoScale = 67) underscore the practical and environmental advantages of this method. This work establishes a sustainable and efficient photoenzymatic platform for the synthesis of L-Kyn and its derivatives, bridging photocatalysis and biocatalysis in a synergistic, green synthesis paradigm.