Nouveau polypeptide et sa préparation

The polypeptide I (Ser4-Lys8-Vasoprossin) and its acid addition salts is prepared by oxidizing the nonapeptide V in an aqueous solution at a pH value from about 4 to about 9, and when it is desired to produce an acid addition salt reacting the peptide I with an organic or inorganic acid. The linear nonapeptide V is in turn prepared by condensing N-trityl-L-serine with L-asparaginyl - S - benzyl - L - cysteinyl - L - prolyl - N - e - p - toluenesulphonyl - L - lysyl glycinamide and after removing the N-trityl group from the hexapeptide condensing it with N-carbo-benzoxy - S - benzyl - L - cysteinyl - L - tyrosyl-L-phenylalanine p-nitrophenyl ester to form the protected nonapeptide and removing the blocking groups. Pharmaceutical compositions comprise the peptides of Formula I or salts thereof and a pharmaceutical carrier or diluent. The compositions which may be administered either enterally or parenterally possess antidiuretic properties.