Phenol derivatives and antitrypanosoma preventive/therapeutic agent comprising the same as active ingredient

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 C1-4 alkyl group;
• and R′″ is a pyridyl group, an amino group substituted with a C1-4 alkyl 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 C1-4 alkyl 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].