4-Sulfobenzyl ester – its use in peptide synthesis

Amino acid 4-sulfobenzyl esters were employed for the synthesis of peptides in solution. They significantly increase the hydrophilicity of protected intermediates as shown by analytical reversed-phase high performance liquid chromatography and counter-current distribution. General methods for working up are described which permit simple and standardized isolations of products. The use of several coupling methods was demonstrated in the synthesis of Z-Val-Gly-OBzl-SO₃NH₄. Ion-exchange chromatography was introduced as a selective purification procedure for protected peptide 4-sulfobenzyl esters. A step-wise synthesis of [Leu⁵]-enkephalin was performed, starting from leucine 4-sulfobenzyl ester. Removal of N-terminal protecting groups produced zwitterionic peptide 4-sulfobenzyl esters. These were readily purified by crystallization from slightly acidic media; no further purification was necessary. The biologically fully active pentapeptide Tyr-Gly-Gly-Phe-Leu was obtained in an overall yield of 30.2%.