Patent ID: 7629471

Claim:
A compound of the following formula or a pharmaceutically acceptable salt of the compound or optical isomers thereof: (wherein R 1 represents one of the following two groups: R 2 represents —(CH 2 ) n —CHR 5 R 6 (wherein R 5 represents a hydrogen atom, an amino group, an amino group substituted with one or two C 1-6 alkyl groups, or a C 1-6 alkyl group substituted with phenyl, R 6 represents a carboxyl group, —CONH 2 , or —COOR 7 (wherein R 7 represents a substituted or unsubstituted C 1-6 alkyl group), and n represents 0 or an integer of 1 to 6) or a residue formed by removing NH 2 ftom any amino acid, R 3 represents a hydrogen atom, a substituted or unsubstituted C 1-6 alkyl group, a substituted or unsubstituted C 2-6 alkenyl group, a substituted or unsubstituted C 2-6 alkynyl group, a substituted or unsubstituted C 3-8 cycloalkyl group, an acyl group, an aryl group or a carboxyl group, and R 4 represents a hydrogen atom, a substituted or unsubstituted C 1-6 alkyl group, a substituted or unsubstituted C 2-6 alkenyl group, a substituted or unsubstituted C 2-6 alkynyl group, a substituted or unsubstituted C 3-8 cycloalkyl group, an acyl group, an aryl group or a carboxyl group).