Laccase-induced derivatization of unprotected amino acid L-tryptophan by coupling with p-hydroquinone 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide

We have studied the enzymatic derivatization of amino acids by use of the polyphenol oxidase laccase. Derivatization of L-tryptophan was achieved by enzymatic crosslinking with the laccase substrate 2,5-dihydroxy-N-(2-hydroxyethyl)-benzamide. The main product (yield up to 70%) was identified as the quinoid compound 2-[2-(2-hydroxy-ethylcarbamoyl)-3,6-dioxo-cyclohexa-1,4-dienylamino]-3-(1H-indol-3-yl)- propionic acid and demonstrates that laccase-catalyzed C-N-coupling occurred on the amino group of the aliphatic side chain. These enzyme based reactions provide a simple and fast method for the derivatization of unprotected amino acids.