A compound having the structure of formula I: or a pharmaceutically acceptable salt thereof, wherein: R 1 is R 2 is selected from the group consisting of -(CR 5 R 6) n R 7,-C(=X)NR 10 (CR 5 R 6) n R 7 and -C(=X)(CR 5 R 6) n R 7; R 3 is selected from the group consisting of H and Me; R 4 is selected from the group consisting of unsubstituted carbocyclyl, substituted or unsubstituted heterocyclyl, -(CR 5 R 6) n R 7 and -C(=NR 8)(CR 5 R 6) n R 7, with the proviso that R 4 is not Me; each R 5 is independently selected from the group consisting of H, F, amino, aminoC 1-6 alkyl, OH, -C 1-6 alkylOR 12 and C 1-6 alkyl; each R 6 is independently selected from the group consisting of H, F, aminoC 1-6 alkyl, -C 1-6 alkylOR 12 and C 1-6 alkyl, provided that each CR 5 R 6 unit does not comprise two OH, two NH 2, one OH and one NH 2, one F and one NH 2, or one F and one OH; each R 7 is selected from the group consisting of H, OR 12, NR 9 R 10 and - NHC(=NR 8)R 14; alternatively R 5 and R 7 or R 6 and R 7 are taken together with the atom or atoms to which they are attached to form a four, five or six membered substituted or unsubstituted heterocyclyl ring; alternatively R 5 and R 6 are taken together with the atom or atoms to which they are attached to form a three, four, five or six membered substituted or unsubstituted carbocyclyl or a substituted or unsubstituted heterocyclyl ring; each R 8 is independently selected from the group consisting of H, OR 12, CN and C 1-6 alkyl; with the proviso that at least one of R 5, R 6, R 7 and R 8 is not H; each R 9 is independently selected from the group consisting of H and - (CR 5 R 6) n R 13; each R 10 is independently selected from the group consisting of H and - (CR 5 R 6) m R 13; each R 12 is independently selected from the group consisting of H, C 1-6 alkyl, C 2-6 alkylOH and C 2-6 alkylamino; each R 13 is independently selected from the group consisting of OH and NH 2; each R 14 is independently selected from the group consisting of H and NR 9 R 10; each X is independently selected from O and NR 8; each m is independently an integer from 0 to 5; each n is independently an integer from 1 to 5. R 1 is R 2 is selected from the group consisting of -(CR 5 R 6) n R 7,-C(=X)NR 10 (CR 5 R 6) n R 7 and -C(=X)(CR 5 R 6) n R 7; R 3 is selected from the group consisting of H and Me; R 4 is selected from the group consisting of unsubstituted carbocyclyl, substituted or unsubstituted heterocyclyl, -(CR 5 R 6) n R 7 and -C(=NR 8)(CR 5 R 6) n R 7, with the proviso that R 4 is not Me; each R 5 is independently selected from the group consisting of H, F, amino, aminoC 1-6 alkyl, OH, -C 1-6 alkylOR 12 and C 1-6 alkyl; each R 6 is independently selected from the group consisting of H, F, aminoC 1-6 alkyl, -C 1-6 alkylOR 12 and C 1-6 alkyl, provided that each CR 5 R 6 unit does not comprise two OH, two NH 2, one OH and one NH 2, one F and one NH 2, or one F and one OH; each R 7 is selected from the group consisting of H, OR 12, NR 9 R 10 and - NHC(=NR 8)R 14; alternatively R 5 and R 7 or R 6 and R 7 are taken together with the atom or atoms to which they are attached to form a four, five or six membered substituted or unsubstituted heterocyclyl ring; alternatively R 5 and R 6 are taken together with the atom or atoms to which they are attached to form a three, four, five or six membered substituted or unsubstituted carbocyclyl or a substituted or unsubstituted heterocyclyl ring; each R 8 is independently selected from the group consisting of H, OR 12, CN and C 1-6 alkyl; with the proviso that at least one of R 5, R 6, R 7 and R 8 is not H; each R 9 is independently selected from the group consisting of H and - (CR 5 R 6) n R 13; each R 10 is independently selected from the group consisting of H and - (CR 5 R 6) m R 13; each R 12 is independently selected from the group consisting of H, C 1-6 alkyl, C 2-6 alkylOH and C 2-6 alkylamino; each R 13 is independently selected from the group consisting of OH and NH 2; each R 14 is independently selected from the group consisting of H and NR 9 R 10; each X is independently selected from O and NR 8; each m is independently an integer from 0 to 5; each n is independently an integer from 1 to 5.