A green enzymatic route for the biotransformation of naphthalene to phthalic acid.

Abstract

Naphthalene, an abundant polycyclic aromatic hydrocarbon (PAH) often emitted as an industrial byproduct, represents a significant yet underutilized carbon feedstock for chemical synthesis. Due to its high chemical stability and hydrophobicity, conventional physicochemical treatment methods are often energy-intensive, condition-dependent, and prone to causing secondary pollution. Biocatalysis offers a green strategy for the selective activation and cleavage of aromatic rings under mild conditions. In this study, we constructed a multi-enzyme cascade reaction for the continuous biocatalytic conversion of naphthalene to phthalic acid. The cascade begins with the oxyfunctionalization of naphthalene into 1-naphthol by using the unspecific peroxygenase AaeUPO, followed by a carboxylation-oxygenation coupling reaction to yield 2'-carboxybenzyl-pyruvic acid, and ultimately an NAD⁺-dependent oxidation to transform 2-carboxybenzaldehyde into phthalic acid. This work demonstrates a promising multi-enzyme strategy for the mild conversion of naphthalene and provides a methodological and conceptual basis for developing green and sustainable biotransformation routes for PAHs.