A compound of formula I: wherein: W is 0 or NH; R 1 is selected from: (i) H; (ii) C 3-6 cycloalkyl; (iii) C 3-7 heterocyclyl optionally substituted with a group selected from: methyl; and ester; and (iv) linear or branched C 1-4 alkyl optionally substituted with a group selected from: alkoxy; amino; amido. acylamido; acyloxy; alkyl carboxyl ester; alkyl carbamoyl; alkyl carbamoyl ester; phenyl; phosphonate ester; C 3-7 heterocyclyl optionally substituted with a group selected from methyl and oxo; and a naturally occurring amino acid, optionally N-substituted with a group selected from methyl, acetyl and boc; A 1 is CR A or N; A 2 is CR B or N; A 3 is CR c or N; A 4 is CR D or N; where no more than two of A 1, A 2, A 3, and A 4 may be N; one or two of R A, R B, R c and R D, (if present) are selected from H, F, Cl, Br, Me, CF 3, cyclopropyl, cyano, OMe, OEt, CH 2 OH, CH 2 OMe and OH; the remainder of R A, R B, R c and R D, (if present) are H; R N1 is H or Me; one of R C2 and R C3 is C(=O)NH 2; the other is selected from H, CI, F, Br, Me, OMe, OEt, cyano, CF 3, CH 2 OH, CH 2 OMe, C 2-4 alkenyl and Csheterocyclyl; R C1 and R C4 are independently selected from H, CI, F, Br, Me, OMe, OEt, cyano, CF 3, CH 2 OH, CH 2 OMe, C 2-4 alkenyl and Csheterocyclyl. W is 0 or NH; R 1 is selected from: (i) H; (ii) C 3-6 cycloalkyl; (iii) C 3-7 heterocyclyl optionally substituted with a group selected from: methyl; and ester; and (iv) linear or branched C 1-4 alkyl optionally substituted with a group selected from: alkoxy; amino; amido. acylamido; acyloxy; alkyl carboxyl ester; alkyl carbamoyl; alkyl carbamoyl ester; phenyl; phosphonate ester; C 3-7 heterocyclyl optionally substituted with a group selected from methyl and oxo; and a naturally occurring amino acid, optionally N-substituted with a group selected from methyl, acetyl and boc; (i) H; (ii) C 3-6 cycloalkyl; (iii) C 3-7 heterocyclyl optionally substituted with a group selected from: methyl; and ester; and methyl; and ester; and (iv) linear or branched C 1-4 alkyl optionally substituted with a group selected from: alkoxy; amino; amido. acylamido; acyloxy; alkyl carboxyl ester; alkyl carbamoyl; alkyl carbamoyl ester; phenyl; phosphonate ester; C 3-7 heterocyclyl optionally substituted with a group selected from methyl and oxo; and a naturally occurring amino acid, optionally N-substituted with a group selected from methyl, acetyl and boc; alkoxy; amino; amido. acylamido; acyloxy; alkyl carboxyl ester; alkyl carbamoyl; alkyl carbamoyl ester; phenyl; phosphonate ester; C 3-7 heterocyclyl optionally substituted with a group selected from methyl and oxo; and a naturally occurring amino acid, optionally N-substituted with a group selected from methyl, acetyl and boc; A 1 is CR A or N; A 2 is CR B or N; A 3 is CR c or N; A 4 is CR D or N; where no more than two of A 1, A 2, A 3, and A 4 may be N; one or two of R A, R B, R c and R D, (if present) are selected from H, F, Cl, Br, Me, CF 3, cyclopropyl, cyano, OMe, OEt, CH 2 OH, CH 2 OMe and OH; the remainder of R A, R B, R c and R D, (if present) are H; R N1 is H or Me; one of R C2 and R C3 is C(=O)NH 2; the other is selected from H, CI, F, Br, Me, OMe, OEt, cyano, CF 3, CH 2 OH, CH 2 OMe, C 2-4 alkenyl and Csheterocyclyl; R C1 and R C4 are independently selected from H, CI, F, Br, Me, OMe, OEt, cyano, CF 3, CH 2 OH, CH 2 OMe, C 2-4 alkenyl and Csheterocyclyl.