Thiazine or pyrazine derivatives

A compound represented by the following formula [I] or a salt thereof,

• wherein
• X is R6—(A2)n—N,
• R1 and R2, being the same or different, are hydrogen, lower alkyl, cycloalkyl or aryl,
• R3 and R4, being the same or different, are hydrogen, lower alkyl, cycloalkyl, aryl or an aromatic heterocycle,
• R5 is hydrogen, lower alkyl, cycloalkyl, aryl or —A3—A4—R7,
• R6 is hydrogen, lower alkyl, cycloalkyl, hydroxy, lower alkoxy, aryl, aryloxy or an aromatic heterocycle,
• R7 is hydrogen, lower alkyl, hydroxy, lower alkoxy, aryl, aryloxy, amino, lower alkylamino, arylamino, an aromatic heterocycle or a nonaromatic heterocycle,
• n is 0 or 1,
• A1 is lower alkylene,
• A2 is carbonyl or sulfonyl,
• A3 is lower alkylene,
• A4 is carbonyl or oxalyl,
• each lower alkyl defined above is unsubstituted or substituted by halogen, hydroxy, lower alkoxy, aryl or aryloxy,
• each lower alkoxy defined above is unsubstituted or substituted by aryl, and
• each lower alkylene defined above is unsubstituted or substituted by aryl.