N-Fmoc-N '- triphenylmethyl-L-histidine belongs to the L-histidine class of derivatives and is an essential amino acid for humans. Compared with other amino acids, except for some common chemical reactions, L-histidine can form a brownish red compound with diazobenzenesulfonic acid due to its right-hand chain imidazole group, known as the Pauly reaction.