Patent GB-714834-A (GB)
Title: Improvements in or relating to the manufacture of peptides, polypeptides and derivatives thereof
Inventor: KENNER GEORGE WALLACE
Filed: 1950-11-28
Abstract: A mixed anhydride of an N-substituted aminocarboxylic acid and sulphuric acid is made by reacting a salt of the N-substituted amino-carboxylic acid with sulphur trioxide under anhydrous conditions.  The anhydride contains the group -CO.O.SO3H. On reacting the anhydride with the salt of a peptide, polypeptide or an aminocarboxylic acid having an unsubstituted amino group peptides, polypeptides or derivatives thereof are obtained. Sulphur trioxide may be used in the form of a complex with dimethylformamide, a tertiary amine, e.g. pyridine, or ether, e.g. dioxane.  Complicated or simple polypeptides may be obtained by utilizing as the N-substituted amino-acid, a peptide or polypeptide whose terminal amino-group is protected by a hydrolysable substituent or by using as the salt of the amino-carboxylic acid, a salt of a peptide or polypeptide. Preferably the salt of the amino-carboxylic acid is the salt of an alpha-amino carboxylic acid, e.g. an alkali metal or quaternary ammonium salt.  The second reaction is preferably effected under non-acidic conditions with a molar excess of salt.  In an illustration of the process a solution of an amino-acid, e.g. a peptide or polypeptide, the amino group of which is protected by a carbobenzyloxy or p-toluenesulphonyl group, in dimethylformamide is neutralized with a methanol solution of potassium methoxide or trimethylphenyl ammonium methoxide and on distillation of a portion of the solvent at 50-55 DEG  C. an anhydrous solution of the salt of the amino-acid is obtained.  The anhydride is then prepared by the addition of one molecular proportion of sulphur trioxide in dimethylformamide.  The addition of an aqueous alkaline solution of an amino-acid, peptide or polypeptide now leads to coupling and the production of the required amino-acid or peptide derivative.  The product may be isolated by means of counter current distribution between ethyl acetate and an aqueous solution of a phosphate buffer. The product may be converted into a mixed anhydride and reacted with salts by the process of the invention to produce complex polypeptides.  In examples (1) the mixed anhydride of p-toluenesulphonyl - dl - alanine and sulphuric acid is obtained as its potassium salt by neutralizing the amino-acid dissolved in dimethyl-formamide with a methanol solution of potassium methoxide and reacting with sulphur trioxide in dimethylformamide; (2) the anhydride of carbobenzyloxyglycine is made as in (1) and reacted with dl-phenylalanine in aqueous sodium hydroxide to yield carbobenzyloxy-glycyl-dl-phenyl alanine; and in (3) and (4) methanol containing phenyltrimethylammonium methoxide is added respectively to carbobenzyloxyglycyl-dl- or l-phenylalanine in dimethylformamide, some solvent removed, sulphur trioxide in dimethylformamide added and then glycine in aqueous sodium hydroxide to yield the corresponding carbobenzyloxyglycyl - phenylalanylglycine.  It is stated that the following compounds have been made: p-toluenesulphonyl-dl - alanylglycine, carbobenzyloxy - dl - alanylglycine, carbobenzyloxyglycyl-dl-phenylalanine, carbobenzyloxyglycyl - l - phenylalanine, carbobenzyloxy - l - phenylalanylglycine and p-toluenesulphonyl - glycyl - dl - phenylalanine.