C07K 5/0222

Peptides containing up to four amino acids in a fully defined sequence; Derivatives thereof containing at least one abnormal peptide link {containing the structure -X-C(=O)-(C)n-N-C-C(=O)-Y-; X and Y being heteroatoms; n being 1 or 2 with the first amino acid being heterocyclic, e.g. Pro, Trp}