Dityrosine (DY) can be used as a biomarker to detect oxidative protein damage and selective proteolysis. It is generally prepared by horseradish peroxidase (HRP)-catalyzed oxidation of L-tyrosine (Y) followed by multistep chromatographic separations. In this study, we present an alternative method for the preparation of DY by HRP-catalyzed synthesis of N,N'-diBoc-dityrosine (DBDY) from N-Boc-L-tyrosine (BY). The presence of the tert-butoxycarbonyl (Boc) group ensured that the fraction of further oxidized by-products (e.g., trimers and pulcherosine) was quite low. The yield of DBDY (37.5%) was comparable to that reported for DY (> 26%). DBDY could be purified by a simple one-step silica column chromatography procedure that resulted in a purity of 89.7%. DBDY is considered to be better than DY for subsequent chemical reactions (for binding to polymers, amino acids, drugs, antibodies, etc.) because such reactions can be selectively performed by using the carboxylic acid and amine groups in the following sequence: first, the carboxylic acid groups are used; next, the Boc groups are removed; and finally, the amino groups are used. To prepare DY, the Boc groups in DBDY were simply and completely removed by treatment with trifluoroacetic acid. (C) 2010 Elsevier Ltd. All rights reserved.