Patent ID: 7723524

Claim:
A compound represented by formula (1): wherein R 1 represents a C1-C6 alkyl group, a C2-C6 alkenyl group, a C1-C6 halogenoalkyl group, a C3-C6 cycloalkyl group which may have a substituent, a C6-C20 aryl group which may have a substituent, a C3-C5 heteroaryl group which may have a substituent, a C1-C6 alkoxy group, or a C1-C6 alkylamino group; R 2 represents a hydrogen atom, a phenyl group, an acetoxymethyl group, a pivaloyloxymethyl group, an ethoxycarbonyl group, a choline group, a dimethylaminoethyl group, a 5-indanyl group, a phthalidinyl group, a 5-alkyl-2-oxo-1,3-dioxol-4-ylmethyl group, a 3-acetoxy-2-oxobutyl group, a C1-C6 alkyl group, a C2-C7 alkoxymethyl group, or a phenylalkyl group formed of a C1-C6 alkylene group and a phenyl group; R 3 and R 4 each independently represent a hydrogen atom or a C1-C6 alkyl group, or a substituted carboxyl group derived from an amino acid, a dipeptide, or a tripeptide, and, in the case where each of R 3 and R 1 represents a C1-C6 alkyl group, the alkyl group may be substituted by one or more atoms or groups selected from among a hydroxyl group, a halogen atom, a C1-C6 alkylthio group, and a C1-C6 alkoxy group; and n denotes an integer of 1 to 3, or a salt thereof.