Adamantane derivative and use thereof

A compound represented by Formula (I):

• wherein R1 represents a hydrogen atom or (C1-6 alkyl)carbonyl optionally substituted with one or more halogen atoms;
• R2 represents a hydrogen atom or (C1-6 alkyl)carbonyl optionally substituted with one or more halogen atoms;
• X represents O or NR5;
• R3 represents phenyl optionally substituted with one or more substituents selected from X1, 5- or 6-membered heteroaryl optionally substituted with one or more substituents selected from X1, or COOR6;
• R4 represents a hydrogen atom, a halogen atom, azido, —OR7 or —NHR8;
• R5 represents a hydrogen atom or C1-6 alkyl;
• R6 represents a hydrogen atom or C1-6 alkyl;
• R7 represents a hydrogen atom, C1-6 alkyl, C1-6 alkoxy-C1-6 alkyl or (C1-6 alkyl)carbonyl optionally substituted with one or more halogen atoms;
• R8 represents a hydrogen atom, C1-6 alkyl or (C1-6 alkyl)carbonyl optionally substituted with one or more halogen atoms;
• and
• X1 represents C1-6 alkyl, a halogen atom, C1-6 alkoxy, nitro or cyano,
• an enantiomer thereof, a diastereomer thereof, or a pharmaceutically acceptable salt thereof.