P2X7 receptor antagonists and their use

A compound of formula (III)

• or a pharmaceutically acceptable salt thereof,
• wherein
• R1 is selected from halogen or C1-6 alkyl,
• X is C(O)NH or NHC(O);
• n is 1;
• each R5 and each R6 are independently selected from hydrogen or C1-3alkyl, or R5 and R6 together with the carbon atom to which they are both attached forms a C3-6cycloalkcyl ring,
• R2 is an optionally substituted cycloalkyl group containing 5 to 7 carbon atoms;
• and
• R3 is hydrogen, or a group R7, OR7, SR7, NR7R8, where R7 and R8 are independently selected from hydrogen, optionally substituted C1-10alkyl, an optionally substituted cycloalkyl or an optionally substituted heterocyclic group, or R7 and R8 together with the nitrogen to which they are attached form an optionally substituted heterocyclic ring which may contain additional heteroatoms, and may further comprise bridging groups.