Abstract: When the initiation suppression method was used for translation of a peptide having at its N terminus an amino acid residue carrying a thiol group near its amino group with specific protecting groups being introduced to the thiol group and the amino group, it was found that not only the probability of initiation of amino acid translation reaction was improved, but also production of cleaved peptides was suppressed and translation efficiency and purity were improved. Furthermore, it was found that it is possible to efficiently promote the cyclization reaction of the peptide through amide bond formation. Based on these findings, the inventors discovered novel methods for preparing complexes between nucleic acids and peptides containing various unnatural amino acids and having an amide bond-mediated cyclized portion.