Synthesis and application of N^α-Fmoc-N^π-4-methoxybenzyloxymethylhistidine in solid phase peptide synthesis

The 4-methoxybenzyloxymethyl (MBom) group was introduced at the N^π-position of the histidine (His) residue by using a regioselective procedure, and its utility was examined under standard conditions used for the conventional and the microwave (MW)-assisted solid phase peptide synthesis (SPPS) with 9-fluorenylmethyoxycarbonyl (Fmoc) chemistry. The N^π-MBom group fulfilling the requirements for the Fmoc strategy was found to prevent side-chain-induced racemization during incorporation of the His residue even in the case of MW-assisted SPPS performed at a high temperature. In particular, the MBom group proved to be a suitable protecting group for the convergent synthesis because it remains attached to the imidazole ring during detachment of the protected His-containing peptide segments from acid-sensitive linkers by treatment with a weak acid such as 1% trifluoroacetic acid in dichloromethane. We also demonstrated the facile synthesis of Fmoc-His(π-MBom)-OH with the aid of purification procedure by crystallization to effectively remove the undesired τ-isomer without resorting to silica gel column chromatography. This means that the present synthetic procedure can be used for large-scale production without any obstacles. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.