A compound of Formula I or a pharmaceutically acceptable salt, solvate or ester thereof, wherein: R is H; R 1 is selected from the group consisting of aryl, heterocyclyl and -C(=O)-NR 5 R 6; R 2 is H or alkyl; X is selected from the group consisting of -NR 7, -C(R 8)(R 9)-, -O-, -S-, -S(=O)-, and -S(=O) 2; each R 3 independently is selected from the group consisting of alkyl, aryl, hydroxyl, and - S-alkyl, or wherein two R 3 groups together with the same carbon atom to which both are attached form -C(=O)-; m is 0, 1, or 2; n is 0 or 1; R 4 is selected from the group consisting of H, alkyl, aryl, -C(=O)-aryl, and -C(=O)-O-alkyl; R 5, R 6, and R 7 independently are H or alkyl; R 8 and R 9 independently are H, alkyl or aryl; or -C(R 8)(R 9)- together is heterocyclyl; alkyl is unsubstituted or substituted by one or more substituents which may be the same or different, each substituent being independently selected from the group consisting of halo, alkyl, aryl, cycloalkyl, heteroaryl, cyano, hydroxy, alkoxy, alkylthio, amino, -NH(alkyl), - NH(cycloalkyl), -N(alkyl) 2, -O-C -alkyl, -O-C -aryl, -O-C -cycloalkyl, carboxy and - C O-alkyl; aryl is unsubstituted or substituted by one or more substituents which may be same or different, each substituent being independently selected from the group consisting of alkyl, alkenyl, alkynyl, aryl, heteroaryl, hydroxyl, hydroxyalkyl, alkoxy, aryloxy, acyl, aroyl, halo, nitro, cyano, carboxy, alkoxycarbonyl, aryloxycarbonyl, alkylsulfonyl, arylsulfonyl, heteroarylsulfonyl, alkylthio, arylthio, heteroarylthio, cycloalkyl, heterocyclyl, -C(=N-CN)-NH 2, -C(=NH)-NH 2, -C(=NH)-NH(alkyl), Y 1 Y 2 N-, Y 1 Y 2 N-alkyl-, Y 1 Y 2 NC -, Y 1 Y 2 NSO 2 - and - SO 2 NY 1 Y 2, wherein Y 1 and Y 2 can be the same or different and are independently selected from the group consisting of hydrogen, alkyl, aryl, cycloalkyl, heterocyclyl and heteroaryl; wherein the following compound is excluded: R is H; R 1 is selected from the group consisting of aryl, heterocyclyl and -C(=O)-NR 5 R 6; R 2 is H or alkyl; X is selected from the group consisting of -NR 7, -C(R 8)(R 9)-, -O-, -S-, -S(=O)-, and -S(=O) 2; each R 3 independently is selected from the group consisting of alkyl, aryl, hydroxyl, and - S-alkyl, or wherein two R 3 groups together with the same carbon atom to which both are attached form -C(=O)-; m is 0, 1, or 2; n is 0 or 1; R 4 is selected from the group consisting of H, alkyl, aryl, -C(=O)-aryl, and -C(=O)-O-alkyl; R 5, R 6, and R 7 independently are H or alkyl; R 8 and R 9 independently are H, alkyl or aryl; or -C(R 8)(R 9)- together is heterocyclyl; alkyl is unsubstituted or substituted by one or more substituents which may be the same or different, each substituent being independently selected from the group consisting of halo, alkyl, aryl, cycloalkyl, heteroaryl, cyano, hydroxy, alkoxy, alkylthio, amino, -NH(alkyl), - NH(cycloalkyl), -N(alkyl) 2, -O-C -alkyl, -O-C -aryl, -O-C -cycloalkyl, carboxy and - C O-alkyl; aryl is unsubstituted or substituted by one or more substituents which may be same or different, each substituent being independently selected from the group consisting of alkyl, alkenyl, alkynyl, aryl, heteroaryl, hydroxyl, hydroxyalkyl, alkoxy, aryloxy, acyl, aroyl, halo, nitro, cyano, carboxy, alkoxycarbonyl, aryloxycarbonyl, alkylsulfonyl, arylsulfonyl, heteroarylsulfonyl, alkylthio, arylthio, heteroarylthio, cycloalkyl, heterocyclyl, -C(=N-CN)-NH 2, -C(=NH)-NH 2, -C(=NH)-NH(alkyl), Y 1 Y 2 N-, Y 1 Y 2 N-alkyl-, Y 1 Y 2 NC -, Y 1 Y 2 NSO 2 - and - SO 2 NY 1 Y 2, wherein Y 1 and Y 2 can be the same or different and are independently selected from the group consisting of hydrogen, alkyl, aryl, cycloalkyl, heterocyclyl and heteroaryl; wherein the following compound is excluded: