Isolation of 6-hydroxy-L-tryptophan from the fruiting body of for use as a tyrosinase inhibitor.

Tyrosinase is the key enzyme that controls melanin formation. We found that a hot water extract of the lyophilized fruiting body of the fungus inhibited tyrosinase from . The extract was fractionated by ODS column chromatography, and an active compound was obtained by purification through successive preparative HPLC using an ODS and a HILIC column. Using spectroscopic data, the compound was identified to be an uncommon amino acid, 6-hydroxytryptophan. 6-Hydroxy-L-tryptophan and 6-hydroxy-D-tryptophan were prepared through a Fenton reaction from L-tryptophan and D-tryptophan, respectively. The active compound was determined to be 6-hydroxy-L-tryptophan by comparison of their circular dichroism spectra and retention time on HPLC analysis of the -(5-fluoro-2,4-dinitrophenyl)-L-leuciamide derivative with those of 6-hydroxy-L-tryptophan and 6-hydroxy-D-tryptophan. A Lineweaver-Burk plot of the enzyme reaction in the presence of 6-hydroxy-L-tryptophan indicated that this compound was a competitive inhibitor. The IC values of 6-hydroxy-L-tryptophan was 0.23 mM.