Patent ID: 8268789

Claim:
A compound represented by the general formula (1) or a salt thereof: wherein R 1 represents a hydrogen atom, a halogen atom, or a group represented by the following formula (2): wherein R 11 represents a C 1 to C 6 straight-chain or branched alkylene group, R 12 and R 13 together with the nitrogen atom adjacent to them form a 5- to 7-member ring structure, 1 to 2 carbon atoms in the ring may be substituted with a nitrogen atom or an oxygen atom, and the ring may be substituted with a C 1 to C 6 straight-chain or branched alkyl group; R 2 represents a C 1 to C 6 straight-chain or branched alkyl group, a C 3 to C 6 cycloalkyl group, a C 1 to C 6 straight-chain or branched alkyl group substituted with a C 3 to C 6 cycloalkyl group, or a C 7 to C 12 aralkyl group which may be substituted with 1 to 3 halogen atoms or with a C 1 to C 6 straight-chain or branched alkyl group; each of R 3 and R 4 independently represents a hydrogen atom or a C 7 to C 21 , aralkyl group which may be substituted with 1 to 3 halogen atoms or with a C 1 to C 6 straight-chain or branched alkyl group; A 1 represents an α-amino acid selected from the group consisting of glycine, alanine and cyclohexylalanine; A 2 represents an α-amino acid selected from the group consisting of α,γ-diaminobutyric acid and lysine; and A 3 represents an α-amino acid selected from the group consisting of phenylalanine, valine, and β-naphthylalanine.