The present invention relates to a compound represented by formula (I), an optical isomer thereof, a pharmaceutically acceptable salt thereof, wherein X is a hydrogen atom or a halogen atom R1 is a hydrogen atom or -(CnH2n)-R [wherein n is an integer of 1 to 5 and R is a hydrogen atom, a group COOR" or -COR" of a substituent on any one of the n carbon atoms, wherein R" is a hydrogen atom or a C1-4alkyl group and R" is a pyridyl group, an amino group substituted with a C1-4alkyl group, a phenoxyalkyl group having a halogen atom on the carbon atoms of the benzene ring or a phenyl group having a C1-4 alkoxy group or a C1-4 alkoxycarbonyl group on the carbon atoms of the benzene ring) R2 is a hydrogen atom or a C1-4alkyl group R3 is -CHO or -COOH and R4 is -CH=CH-(CH2)P-CH3 (wherein p is an integer of 1 to 12), -CH(OH)-(CH2) q-CH3 (wherein q is an integer of 1 to 13), -CH(OH)-CH2-CH(CH3)-(CH2) 2-CH=C(CH3) 2, -CH=CH-CH(CH3)-(CH2)3-CH(CH3) 2, -(CH2) 2-CH(CH3)-(CH2)3-CH(CH3) 2, or -(CH2)8-CH3].
