Peptide with Safer Secondary Structure, Peptide Library, and Production Methods for Same

A process of preparing a peptide having a secondary structure stabilized with a crosslinked structure, comprising:

• (i) translationally synthesizing a special peptide having, in the molecule thereof, at least one combination of an amino acid having, in the side chain thereof, a sulfanyl group and a special amino acid represented by the following formula (I):
• wherein (A) represents a single bond or a linking group having, in the main chain thereof, from 1 to 10 atoms, (B) represents a group containing at least one carbon-carbon double bond, a group containing at least an aromatic ring, or a ketone group, (C) represents a hydrogen atom or an alkyl group which may be substituted with a substituent, and X represents a group substitutable by a substitution reaction with a sulfanyl group;
• and
• (ii) forming a thioether bond between the sulfanyl group and the side chain of the special amino acid of the formula (I) in each combination to form a crosslinked structure.