Selective Separation of Tryptophan-Containing Peptides via Hydrophobic Modification with 2-Nitro-4-Carboxy-phenylsulfenyl Chloride

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Abstract
Selective separation of tryptophan-containing peptides has been attempted using 2-nitro-4-carboxyphenylsulfenyl chloride (NCps)-C1 as a reagent for hydrophobic modification of tryptophan. S-Carboxymethylated proteins were modified with NCps-C1 in 70% acetic acid and digested with TPCK-trypsin, and the digests were fractionated, directly or after partial fractionation on a Sephadex G-25 column, by high performance liquid chromatography using a reverse phase column. The tryptophan-containing peptides from the tryptic digests of S-carboxymethylated hen-egg white lysozyme and Trimeresurus flavoviridis phospholipase A2 were thus selectively separated and the amino acid sequences were determined, showing the validity of the method. The phenylthiohydantoin derivative of 2-(2'-nitro-4'-carboxyphenyl-thio)-L-tryptophan was synthesized and its spectroscopic and chromatographic properties determined, enabling us to identify the derivative on Edman sequencing.