A compound of general formula I: or a pharmaceutically acceptable salt thereof, wherein: X is C, R 1 and R 2 are different and selected from H, F, I, Cl, -OH, -NH 2, -NO 2, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl wherein butyl, pentyl and hexyl are linear or branched, -O- C 1 -C 6 -alkyl, -O-benzyl (-O-Bn), wherein C 1 -C 6 -alkyl is linear or branched and wherein benzyl is unsubstituted or substituted with one or more halogen and/or one or more C 1 -C 6 -alkyl or -O-C 1 -C 6 -alkyl; or X is C, R 1 and R 2 are the same and selected from F, I, Cl, -OH, -NH 2, -NO 2, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl wherein butyl, pentyl and hexyl are linear or branched, -O- C 1 -C 6 -alkyl, -O-benzyl (-O-Bn), wherein C 1 -C 6 -alkyl is linear or branched and wherein benzyl is unsubstituted or substituted with one or more halogen and/or one or more C 1 -C 6 -alkyl or -O-C 1 -C e -alkyl; and R 3 is selected from -OH, -NH 2, -O-C 1 -C 6 -alkyl, -C 1 -C 6 -alkyl-O-C(=O)-C 1 -C 6 -alkyl, -NH-C 1 -C 6 -alkyl, - O-aryl, O-substituted aryl, -NH-aryl, -NH-substituted aryl, wherein C 1 -C 6 -alkyl is linear or branched, aryl is unsubstituted or substituted with one or more amino acid residues to form a compound in formula II illustrated with a substituted aryl being represented by phenylalanine: or a pharmaceutically acceptable salt thereof; provided that the compound is not one of the following, wherein X R 1 R 2 R 3 C Cl H OH C H Cl OH C OMe H OH C H OMe OH C Cl Cl OH C OBn H OH C H OBn OH or hydrochloride or TFA salts of compounds mentioned in the table above. or a pharmaceutically acceptable salt thereof, wherein: X is C, R 1 and R 2 are different and selected from H, F, I, Cl, -OH, -NH 2, -NO 2, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl wherein butyl, pentyl and hexyl are linear or branched, -O- C 1 -C 6 -alkyl, -O-benzyl (-O-Bn), wherein C 1 -C 6 -alkyl is linear or branched and wherein benzyl is unsubstituted or substituted with one or more halogen and/or one or more C 1 -C 6 -alkyl or -O-C 1 -C 6 -alkyl; or X is C, R 1 and R 2 are the same and selected from F, I, Cl, -OH, -NH 2, -NO 2, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl wherein butyl, pentyl and hexyl are linear or branched, -O- C 1 -C 6 -alkyl, -O-benzyl (-O-Bn), wherein C 1 -C 6 -alkyl is linear or branched and wherein benzyl is unsubstituted or substituted with one or more halogen and/or one or more C 1 -C 6 -alkyl or -O-C 1 -C e -alkyl; and X is C, R 1 and R 2 are different and selected from H, F, I, Cl, -OH, -NH 2, -NO 2, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl wherein butyl, pentyl and hexyl are linear or branched, -O- C 1 -C 6 -alkyl, -O-benzyl (-O-Bn), wherein C 1 -C 6 -alkyl is linear or branched and wherein benzyl is unsubstituted or substituted with one or more halogen and/or one or more C 1 -C 6 -alkyl or -O-C 1 -C 6 -alkyl; or X is C, R 1 and R 2 are the same and selected from F, I, Cl, -OH, -NH 2, -NO 2, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl wherein butyl, pentyl and hexyl are linear or branched, -O- C 1 -C 6 -alkyl, -O-benzyl (-O-Bn), wherein C 1 -C 6 -alkyl is linear or branched and wherein benzyl is unsubstituted or substituted with one or more halogen and/or one or more C 1 -C 6 -alkyl or -O-C 1 -C e -alkyl; R 3 is selected from -OH, -NH 2, -O-C 1 -C 6 -alkyl, -C 1 -C 6 -alkyl-O-C(=O)-C 1 -C 6 -alkyl, -NH-C 1 -C 6 -alkyl, - O-aryl, O-substituted aryl, -NH-aryl, -NH-substituted aryl, wherein C 1 -C 6 -alkyl is linear or branched, aryl is unsubstituted or substituted with one or more amino acid residues to form a compound in formula II illustrated with a substituted aryl being represented by phenylalanine: or a pharmaceutically acceptable salt thereof; provided that the compound is not one of the following, wherein X R 1 R 2 R 3 C Cl H OH C H Cl OH C OMe H OH C H OMe OH C Cl Cl OH C OBn H OH C H OBn OH or hydrochloride or TFA salts of compounds mentioned in the table above.