Provided is a method for producing an exendin derivative, in which a labeling target site is radioactively labeled, with high yield. The present invention relates to a method for producing a polypeptide, which comprises a process wherein a molecular probe precursor represented by the amino acid sequence set forth in formula (1) is labeled using a labeling compound that is capable of labeling lysine or a lysine derivative. Y1-Leu-Ser-Xaa12-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Xaa27-Asn-Gly-Y2 (1) (SEQ ID NO: 1) In formula (1), Y1 represents the amino acid sequence set forth in SEQ ID NO: 2 or an amino acid sequence which is produced by deleting 1-8 amino acids from the N-terminus in the amino acid sequence set forth in SEQ ID NO: 2 Xaa12 represents lysine or a lysine derivative Xaa27 represents a basic amino acid that does not have a functional group, which is reactive with the labeling compound, in a side chain, methyl lysine or acetylated lysine and Y2 represents the amino acid sequence set forth in SEQ ID NO: 3 or an amino acid sequence which is produced by deleting 1-9 amino acids from the C-terminus in the amino acid sequence set forth in SEQ ID NO: 3. His-Gly-Glu-Gly-Thr-Phe-Thr-Ser-Asp (2) (SEQ ID NO: 2) Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser (3) (SEQ ID NO: 3)Cette invention concerne un procédé de production dun dérivé de lexendine au rendement élevé et dans lequel un site cible de marquage est marqué radioactivement. Linvention concerne un procédé de production dun polypeptide comprenant un procédé dans lequel un précurseur de sonde moléculaire représenté par la séquence dacides aminés de formule (1) est marqué en utilisant un composé capable de marquer la lysine ou un dérivé de la lysine. Y1-Leu-Ser-Xaa12-Gln-Met-Glu-Glu-Glu-Ala-Val-Arg-Leu-Phe-Ile-Glu-Trp-Leu-Xaa27-Asn-Gly-Y2 (1) (SEQ ID NO : 1) Dans la formule (1), Y1 représente la séquence dacides aminés exposée en SEQ ID NO : 2 ou une séquence dacides aminés qui est produite en suppr
