Enzyme‐Catalyzed Complex‐Formation of Amino Acid Esters and Phenolic Humus Constituents

• Published in: Soil Science Society of America journal Vol. 49; no. 2; pp. 337 - 342
• Main Authors: Liu, Shu‐Yen, Freyer, Alan J., Minard, Robert D., Bollag, Jean‐Marc
• Format: Journal Article
• Language: English
• Published: Madison, WI Soil Science Society of America 01-03-1985
• Subjects: Agronomy. Soil science and plant productions; Applied sciences; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Organic matter; Other techniques and industries; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Soil science; Complexation; Ester; Organic matter; Humus; Enzyme; Nitrogen heterocycle; Aminoacid; Humification; Phenols; Soil; Catalysis; Laccase
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj1985.03615995004900020013x

The cross‐coupling reaction between amino acid esters and phenolic humus constituents was investigated using a fungal laccase as a catalyst. A number of hybrid products were isolated and characterized by spectrometric analysis. When phenylalanine ethyl ester was combined with protocatechuic acid, the latter was oxidized to a quinone, which in turn coupled with the amino acid ester to form a quinonoid dimer. Two phenylalanine ethyl ester molecules coupled with a protocatechuic acid derivative through a single C‐N bond (N‐phenyl linkage), or through an imine linkage to form hybrid trimers. Similarly, the binding of phenylalanine ethyl ester to a syringic acid product took place at a carbonyl group via an imine linkage or at an aromatic C through a single C‐N bond. The amino acid moiety and the phenolic compound in all trimers had a molecular ratio of 2:1. Our results provided clear evidence that enzymes can cause the linkage of amino acids to a lignin derivative by a covalent binding between amino N and an aromatic C. The chemical structures of some hybrid trimers also showed ring formation through a N atom to form a heterocyclic compound.