Abstract: Cyclic compounds and oligopeptide compounds that selectively inhibit KRAS were found. Oligopeptide compounds and non-natural amino acids useful for producing a cyclic compound were also found. Moreover, cyclic compounds and oligopeptide compounds were found to interact with an amino acid residue specific to KRAS.

Abstract: Solid-phase synthesis of a peptide has a problem that a desired elongation reaction is prevented from proceeding by diketopiperazine and a 6-membered diamine skeleton compound formed when a protective group at the N-terminal is removed. The present inventors have found that when in production of a peptide by a solid-phase method, a peptide in which an amino group at the N-terminal is protected with a protective group having an Fmoc skeleton is treated in a specific solvent with a base having a pKa of 23 or more in acetonitrile as a conjugate acid, and a peptide chain is then elongated, it is possible to solve the problem described above.