Heterocyclic compound

A compound represented by the formula (I):

• wherein
• R1 and R2 are each independently a hydrogen atom or a substituent, or R1 and R2 are bonded to each other to form, together with the adjacent nitrogen atom, an optionally further substituted non-aromatic nitrogen-containing heterocycle,
• X is CR4 or N,
• R3, R4, R5 and R6 are each independently a hydrogen atom, a halogen atom, an optionally substituted C1-6 alkyl group or an optionally substituted C1-6 alkoxy group, and Ring A is a 6-membered aromatic ring optionally further substituted by 1 to 4 substituents selected from (i) a halogen atom, (ii) a C1-6 alkyl group and (iii) a C1-6 alkoxy group, or a salt thereof.