Solid phase process for synthesizing peptides

In a solid phase peptide synthesis process for producing a peptide of a desired amino acid sequence by the steps of (a) temporarily chemically protecting the reactive amino group and any other reactive groups, other than the carboxylic acid group at the alpha-position, on the C-terminal amino acid of the peptide;

• (b) chemically binding the protected C-terminal amino acid via the carboxylic acid (--COOH) group thereof to a resin support;
• (c) chemically deprotecting the reactive amino group of the resin-bound protected amino acid;
• (d) chemically coupling via a peptide bond the next amino acid in the desired sequence by contacting the resin-bound amino acid from step (c) with the next amino acid in the desired sequence with all of the reactive groups thereof, other than the carboxylic acid group at the alpha-position, chemically protected, in the presence of a coupling agent;
• (e) chemically deprotecting the reactive amino group of the coupled amino acid from step (d);
• (f) continuing the synthesis by repeating steps (d) and (e) with successive amino acids in the desired sequence being added one at a time until the total desired sequence of the protected peptide is built up on the resin;
• and (g) cleaving the protected peptide from the resin support and deprotecting protected reaction groups;
• the improvement comprising
• in step (g) contacting the resin bound protected peptide with a mixture of hydrogen bromide, anisole and thioanisole to simultaneously cleave the protected peptide from the resin support and remove the protecting groups.