A compound of formula I: wherein: W is O 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; Y is O, NH or CH 2; R Y is selected from: (a) wherein: Z 1 is CR Z1 or N; Z 2 is CR Z2 or N; Z 4 is CR Z4 or N; Z 5 is CR Z5 or N; where no more than two of Z 1, Z 2, Z 4 and Z 5 may be N; one or two of R Z1, R Z2, R Z4 and R Z5, (if present) are selected from H, F, Cl, Br, Me, OMe, cyano, CF 3, CH 2 OH, CH 2 OMe, C 2-4 alkenyl, and C 5 heterocyclyl; the remainder of R Z1, R Z2, R Z4 and R Z5, (if present) are H; (b) where R 12 is selected from H, F, Cl, Br, OMe, cyano and CF 3; with the proviso that when A 1 is CF; A 2, A 3 and A 4 are CH; Y is O or NH; R Y is RYA, where Z 1, Z 2, Z 4 and Z 5 are CH; R 1 is not Et; and when A 1 is CF; A 2, A 3 and A 4 are CH; Y is NH; R Y is RYA, where Z 1 and Z 5 are CH, one of Z 2 and Z 4 is CF, and the other of Z 2 and Z 4 is CH; R 1 is not Et. W is O 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; (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; 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; 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; Y is O, NH or CH 2; R Y is selected from: (a) wherein: Z 1 is CR Z1 or N; Z 2 is CR Z2 or N; Z 4 is CR Z4 or N; Z 5 is CR Z5 or N; (a) wherein: Z 1 is CR Z1 or N; Z 2 is CR Z2 or N; Z 4 is CR Z4 or N; Z 5 is CR Z5 or N; Z 1 is CR Z1 or N; Z 2 is CR Z2 or N; Z 4 is CR Z4 or N; Z 5 is CR Z5 or N; where no more than two of Z 1, Z 2, Z 4 and Z 5 may be N; one or two of R Z1, R Z2, R Z4 and R Z5, (if present) are selected from H, F, Cl, Br, Me, OMe, cyano, CF 3, CH 2 OH, CH 2 OMe, C 2-4 alkenyl, and C 5 heterocyclyl; the remainder of R Z1, R Z2, R Z4 and R Z5, (if present) are H; (b) where R 12 is selected from H, F, Cl, Br, OMe, cyano and CF 3; with the proviso that when A 1 is CF; A 2, A 3 and A 4 are CH; Y is O or NH; R Y is RYA, where Z 1, Z 2, Z 4 and Z 5 are CH; R 1 is not Et; and when A 1 is CF; A 2, A 3 and A 4 are CH; Y is NH; R Y is RYA, where Z 1 and Z 5 are CH, one of Z 2 and Z 4 is CF, and the other of Z 2 and Z 4 is CH; R 1 is not Et.