Ethylcarbamoyl protection for cysteine in the preparation of peptide-conjugate immunogens.

During the solid-phase synthesis of over 100 peptides, we have observed that the ethylcarbamoyl group is useful for the side chain protection of cysteine in peptides containing a single cysteine residue. The ethylcarbamoyl group is stable to the conditions of acidolytic cleavage, purification and long term storage. Brief treatment of peptides containing an S-ethylcarbamoyl-cysteine residue with aqueous sodium hydroxide gives the deprotected cysteine peptide that can be coupled to carrier molecules such as proteins to give immunogen conjugates.