A compound of Formula or a pharmaceutically acceptable tautomer, salt or solvate thereof, wherein: represents a single bond linking R C to the double bond either with a - or -stereochemistry; X represents halo, acetate, trifluoroacetate or triflate; R A and R B are independently selected from alkyl; R C represents hydrogen, alkyl, alkoxy or haloalkyl; R 1, R 2, R 3 and R 4 are independently selected from hydrogen, hydroxyl, alkoxy, halo, haloalkyl, haloalkyloxy, amino, alkylamino, aminoalkyl, alkyloxycarbonyl and COOH; or R 1 and R 2, or R 2 and R 3, or R 3 and R 4 form together with the carbon atoms to which they are attached a 5- or 6-membered aryl ring, a 5- or 6-membered heteroaryl ring, a 5- or 6-membered cycloalkyl ring, a 5- or 6-membered heterocyclyl ring, said rings being optionally substituted by one or more substituent selected from hydroxyl, alkoxy, halo, haloalkyl, haloalkyloxy, amino, alkylamino, aminoalkyl, alkyloxycarbonyl and COOH; R 1', R 2', R 3', R 4', R 5' and R 6' are independently either absent or selected from hydrogen, hydroxyl, alkoxy, halo, haloalkyl, haloalkyloxy, amino, alkylamino, aminoalkyl, alkyloxycarbonyl and COOH; or R 1' and R 2', or R 2' and R 3', or R 3' and R 4', or R 5' and R 6', form together with the carbon atoms to which they are attached a 5- or 6-membered aryl ring, a 5- or 6-membered heteroaryl ring, a 5- or 6-membered cycloalkyl ring, a 5- or 6-membered heterocyclyl ring, said rings being optionally substituted by one or more substituent selected from hydroxyl, alkoxy, halo, haloalkyl, haloalkyloxy, amino, alkylamino, aminoalkyl, alkyloxycarbonyl and COOH; or R A and R 5' form together with atoms to which they are attached a 6-membered heteroaryl ring optionally substituted by one or more substituent selected from alkyl, hydroxyl, alkoxy, halo, haloalkyl, haloalkyloxy, amino, alkylamino, aminoalkyl, alkyloxycarbonyl and COOH; wherein at least one of R 1, R 2, R 3, R 4, R 1', R 2', R 3', R 4', R 5' or R 6' is other than hydrogen. represents a single bond linking R C to the double bond either with a - or -stereochemistry; X represents halo, acetate, trifluoroacetate or triflate; R A and R B are independently selected from alkyl; R C represents hydrogen, alkyl, alkoxy or haloalkyl; R 1, R 2, R 3 and R 4 are independently selected from hydrogen, hydroxyl, alkoxy, halo, haloalkyl, haloalkyloxy, amino, alkylamino, aminoalkyl, alkyloxycarbonyl and COOH; or R 1 and R 2, or R 2 and R 3, or R 3 and R 4 form together with the carbon atoms to which they are attached a 5- or 6-membered aryl ring, a 5- or 6-membered heteroaryl ring, a 5- or 6-membered cycloalkyl ring, a 5- or 6-membered heterocyclyl ring, said rings being optionally substituted by one or more substituent selected from hydroxyl, alkoxy, halo, haloalkyl, haloalkyloxy, amino, alkylamino, aminoalkyl, alkyloxycarbonyl and COOH; R 1', R 2', R 3', R 4', R 5' and R 6' are independently either absent or selected from hydrogen, hydroxyl, alkoxy, halo, haloalkyl, haloalkyloxy, amino, alkylamino, aminoalkyl, alkyloxycarbonyl and COOH; or R 1' and R 2', or R 2' and R 3', or R 3' and R 4', or R 5' and R 6', form together with the carbon atoms to which they are attached a 5- or 6-membered aryl ring, a 5- or 6-membered heteroaryl ring, a 5- or 6-membered cycloalkyl ring, a 5- or 6-membered heterocyclyl ring, said rings being optionally substituted by one or more substituent selected from hydroxyl, alkoxy, halo, haloalkyl, haloalkyloxy, amino, alkylamino, aminoalkyl, alkyloxycarbonyl and COOH; or R A and R 5' form together with atoms to which they are attached a 6-membered heteroaryl ring optionally substituted by one or more substituent selected from alkyl, hydroxyl, alkoxy, halo, haloalkyl, haloalkyloxy, amino, alkylamino, aminoalkyl, alkyloxycarbonyl and COOH; wherein at least one of R 1, R 2, R 3, R 4, R 1', R 2', R 3', R 4', R 5' or R 6' is other than hydrogen.