Naphthyridine derivatives

A naphthyridine compound represented by the following general formula (1):

• wherein R1 represents a hydrogen atom or a lower alkyl group;
• R2 represents a hydrogen atom, a lower alkyl group, a cycloalkyl group, phenyl group, or a phenyl-lower alkyl group optionally having 1 to 3 lower alkoxy groups on the phenyl ring;
• R3 and R4 each independently represent the group —Y—O—Z—R5 (wherein Y is a lower alkylene group, Z is a single bond or a lower alkylene group, and R5 is phenyl group optionally having 1 to 3 substituents selected from the group consisting of halogen atoms, lower alkoxy groups, lower alkyl groups, halogen-substituted lower alkyl groups, methylenedioxy group, hydroxyl group, 2,2-di(lower alkoxy-carbonyl)ethyl groups and 2,2-di(lower alkoxy-carbonyl)vinyl groups, or one of R3 and R4 is the group —Y—O—Z—R5 (wherein Y, Z and R5 are as above) and the other is a lower alkyl group, phenyl group, or a phenyl-lower alkyl group;
• with the proviso that the case where R2 is a phenyl-lower alkyl group optionally having 1 to 3 lower alkoxy groups on the phenyl ring and at least one of R3 and R4 is a benzyloxy-lower alkyl group having 1 to 3 lower alkoxy groups on the benzene ring is excluded.