Histidine (His) racemizes with relative ease during peptide synthesis. One strategy to suppress this racemization is to protect the nitrogen atom of the imidazole moiety in His with a suitable protecting group. Among the numerous protecting groups that have already been tested, the p-methoxybenzyloxymethyl (PMBOM) group on the Ï-nitrogen atom effectively suppresses the racemization. However, a large-scale synthesis of N(Ï)-PMBOM-protected derivatives has hitherto been hampered by the requirement of a freshly prepared unstable reagent. Herein we report the synthesis of N(Ï)-2-naphthylmethoxymethyl (NAPOM)-protected His derivatives, which can be prepared on a gram scale and do not suffer from the aforementioned instability problems. Furthermore, these NAPOM-protected His derivatives suppress the racemization in Boc- A nd Fmoc-based peptide synthesis.
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