A compound of the formula: or an ionic, salt or solvate form thereof, wherein: R 1 is selected from: H and wherein: R N1 is selected from H, C 1-3 alkyl and C(=O)Me; R N2 is selected from H, C 1-3 alkyl and C(=O)Me; R N3 is selected from H, C 1-3 alkyl and C(=O)Me; R N4 is selected from H and CH 3; R N7 and R N8 are independently selected from H and CH 3; R N9 is selected from H, C 1-3 alkyl and C(=O)Me; R N10 is selected from H, C 1-3 alkyl and C(=O)Me; R N11 is selected from H, C 1-3 alkyl and C(=O)Me; R 2 is selected from H and wherein: R N5 is selected from H, C 1-3 alkyl and C(=O)Me; R N6 is selected from H, C 1-3 alkyl and C(=O)Me; and wherein only one of R 1 and R 2 is H; or R 1 and R 2 together form the group -CH 2 -N(R N12)-C 2 H 4 -, where R N12 is selected from H, C 1-3 alkyl and C(=O)Me; R 4 is selected from CF 3, halo, CF 2 H and CN; and R 5 is selected from groups of the following formulae: wherein: R 6 is selected from H, (CHR C1) n1 C N(R N13)Z 1 and (CH 2) n2 C OZ 2; wherein: n1 is 1; R C1 is H or Me; R N13 is H or CH 3; Z 1 is H, CH 3 or OCH 3; n2 is 1; and Z 2 is CH 3; and where only one of R N13 and Z 1 can be CH 3, R 7, if present, is selected from H, and (CH 2) m1 C N(R M1)Y 1, wherein: m1 is 0 or 1; R M1 is H; and Y 1 is H, Me or OCH 3; and one of R 6 and R 7 is not H; and R 8, if present, is H or, when R 7 is C(=O)NH 2, R 8 is selected from H and C 1-2 alkyl. R 1 is selected from: H and wherein: R N1 is selected from H, C 1-3 alkyl and C(=O)Me; R N2 is selected from H, C 1-3 alkyl and C(=O)Me; R N3 is selected from H, C 1-3 alkyl and C(=O)Me; R N4 is selected from H and CH 3; R N7 and R N8 are independently selected from H and CH 3; R N9 is selected from H, C 1-3 alkyl and C(=O)Me; R N10 is selected from H, C 1-3 alkyl and C(=O)Me; R N11 is selected from H, C 1-3 alkyl and C(=O)Me; R N1 is selected from H, C 1-3 alkyl and C(=O)Me; R N2 is selected from H, C 1-3 alkyl and C(=O)Me; R N3 is selected from H, C 1-3 alkyl and C(=O)Me; R N4 is selected from H and CH 3; R N7 and R N8 are independently selected from H and CH 3; R N9 is selected from H, C 1-3 alkyl and C(=O)Me; R N10 is selected from H, C 1-3 alkyl and C(=O)Me; R N11 is selected from H, C 1-3 alkyl and C(=O)Me; R 2 is selected from H and wherein: R N5 is selected from H, C 1-3 alkyl and C(=O)Me; R N6 is selected from H, C 1-3 alkyl and C(=O)Me; and wherein only one of R 1 and R 2 is H; or R 1 and R 2 together form the group -CH 2 -N(R N12)-C 2 H 4 -, where R N12 is selected from H, C 1-3 alkyl and C(=O)Me; R N5 is selected from H, C 1-3 alkyl and C(=O)Me; R N6 is selected from H, C 1-3 alkyl and C(=O)Me; and wherein only one of R 1 and R 2 is H; or R 1 and R 2 together form the group -CH 2 -N(R N12)-C 2 H 4 -, where R N12 is selected from H, C 1-3 alkyl and C(=O)Me; R 4 is selected from CF 3, halo, CF 2 H and CN; and R 5 is selected from groups of the following formulae: wherein: R 6 is selected from H, (CHR C1) n1 C N(R N13)Z 1 and (CH 2) n2 C OZ 2; wherein: n1 is 1; R C1 is H or Me; R N13 is H or CH 3; Z 1 is H, CH 3 or OCH 3; n2 is 1; and Z 2 is CH 3; and where only one of R N13 and Z 1 can be CH 3, R 7, if present, is selected from H, and (CH 2) m1 C N(R M1)Y 1, wherein: m1 is 0 or 1; R M1 is H; and Y 1 is H, Me or OCH 3; and one of R 6 and R 7 is not H; and R 8, if present, is H or, when R 7 is C(=O)NH 2, R 8 is selected from H and C 1-2 alkyl. R 6 is selected from H, (CHR C1) n1 C N(R N13)Z 1 and (CH 2) n2 C OZ 2; wherein: n1 is 1; R C1 is H or Me; R N13 is H or CH 3; Z 1 is H, CH 3 or OCH 3; n2 is 1; and Z 2 is CH 3; and where only one of R N13 and Z 1 can be CH 3, n1 is 1; R C1 is H or Me; R N13 is H or CH 3; Z 1 is H, CH 3 or OCH 3; n2 is 1; and Z 2 is CH 3; R 7, if present, is selected from H, and (CH 2) m1 C N(R M1)Y 1, wherein: m1 is 0 or 1; R M1 is H; and Y 1 is H, Me or OCH 3; and one of R 6 and R 7 is not H; and m1 is 0 or 1; R M1 is H; and Y 1 is H, Me or OCH 3; R 8, if present, is H or, when R 7 is C(=O)NH 2, R 8 is selected from H and C 1-2 alkyl.