Availability of phenylisothiocyanate for the amino acid sequence/configuration determination of peptides containing D/L-amino acids.

A potential use for phenylisothiocyanate (PITC), the most popular Edman reagent, is presented for analysis of the amino acid sequence and configuration in peptides containing D/L-amino acids. After derivatization with PITC of the N-terminal amino acid (L-Tyr) of an enkephalin analogue, [D-Ala2, D-Leu5]-enkephalin, followed by cleavage/cyclization with trifluoroacetic acid at 50 degrees C for 5 min, the liberated 2-anilino-5-thiazolinone-L-Tyr (ATZ-L-Tyr) was further treated with 20% aqueous trifluoroacetic acid at 50 degrees C for 10 min. The resultant phenylthiohydantoin (PTH)-L-Tyr was then separated on a chiral stationary phase (a penylcarbamoylated cyclodextrin column), retaining its configuration. The residual sequence and configurations of the peptide (D-Ala-Gly-L-Phe-D-Leu) were also determined by separating the corresponding PTH-D- or L-amino acids on chiral columns. This method may be applicable to an automatic Edman sequence analyzer for the configuration determination of peptides containing D/L-amino acids.