Cyclic peptide, cell scaffold material, cell separating material, and medium

A cyclic peptide comprising:

• a cyclic segment comprising an RGD sequence and having 8 to 14 amino acid residues,
• a thioether bond being formed between an amino acid residue Xa located on a most N-terminal side of the cyclic segment and an amino acid residue Xb located on a most C-terminal side of the cyclic segment,
• wherein one of the amino acid residue Xa and the amino acid residue Xb is a 2-amino-4-acetylamino-butanoic acid residue, an N-δ-acetyl-ornithine residue, or an N-ε-acetyl-lysine residue, and
• the other one of the amino acid residue Xa and the amino acid residue Xb is an L-homocysteine residue or a D-homocysteine residue,
• wherein the α carbon of the 2-amino-4-acetylamino-butanoic acid residue, the N-δ-acetyl-ornithine residue, or the N-ε-acetyl-lysine residue is separated from the sulfur atom of the L-homocysteine residue or the D-homocysteine residue by five or more atoms, and
• wherein the cyclic segment comprises an amino acid sequence having 80% or more sequence identity to the amino acid sequence IPRGDNFR (SEQ ID NO:
• 1), IPRGDSFA (SEQ ID NO:
• 170), VPRGDTFA (SEQ ID NO:
• 171), or TPRGDTFA (SEQ ID NO:
• 172).