Identification of chirality of phenylthiohydantoin-D-amino acid residue of[D-Ala(2)]-methionine enkephalin by capillary electrophoresis: Suppressionand control of racemization ratio in the Edman sequencing method

This paper describes the suppression and control of the racemization ratio (D or L/D+L) of phenylthiohydantoin (PTH) amino acids in the Edman sequenci ng method. Most of the racemization occurs in the cyclization/cleavage step . Although optimization of partial racemization using a mixture of TFA and boron trifluoride (BF3)-ethyl ether complex, which is effective in suppress ing racemization in the cyclization/cleavage reaction. The partial racemiza tion in PTH derivatization is often useful for DL differentiation, because a minor L- or D-peak produced by racemization can be used as an internal st andard in CE. Using the partial racemization method with mixed acids as a c yclization/cleavage reagent, the sequence determination of [D-Ala(2)]-methi onine enkephalin, with DL differentiation, was achieved on a sequencer.