A compound of formula: wherein: one selected from R1 and R2 is hydrogen and the other is ethynyl-R7, wherein: R7 is hydrogen, trialkylsylyl or an optionally substituted group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, aryl-alkyl, heterocyclyl and heterocyclyl-alkyl; R3 and R4 are independently hydrogen or an optionally substituted group selected from straight or branched C 1 -C 6 alkyl, straight or branched C 2 -C 6 alkenyl, straight or branched C 2 -C 6 alkynyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, arylalkyl, heterocyclyl and heterocyclyl-alkyl, or R3 and R4, taken together with the nitrogen atom to which they are bonded, may form an optionally substituted 5 to 7 membered heterocyclyl group optionally containing one additional heteroatom selected from N, O and S; R5 is an optionally substituted aryl; R6 is hydrogen, an optionally substituted straight or branched C 1 -C 6 alkyl or NR8R9, wherein: R8 and R9 are independently hydrogen or an optionally substituted group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, heterocyclyl and heterocyclyl-alkyl, or R8 and R9, taken together with the nitrogen atom to which they are bonded, may form an optionally substituted 5 to 7 membered heterocyclyl group optionally containing one additional heteroatom selected from N, O and S; or a pharmaceutically acceptable salt thereof. one selected from R1 and R2 is hydrogen and the other is ethynyl-R7, wherein: R7 is hydrogen, trialkylsylyl or an optionally substituted group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, aryl-alkyl, heterocyclyl and heterocyclyl-alkyl; R3 and R4 are independently hydrogen or an optionally substituted group selected from straight or branched C 1 -C 6 alkyl, straight or branched C 2 -C 6 alkenyl, straight or branched C 2 -C 6 alkynyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, arylalkyl, heterocyclyl and heterocyclyl-alkyl, or R3 and R4, taken together with the nitrogen atom to which they are bonded, may form an optionally substituted 5 to 7 membered heterocyclyl group optionally containing one additional heteroatom selected from N, O and S; R5 is an optionally substituted aryl; R6 is hydrogen, an optionally substituted straight or branched C 1 -C 6 alkyl or NR8R9, wherein: R8 and R9 are independently hydrogen or an optionally substituted group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, heterocyclyl and heterocyclyl-alkyl, or R8 and R9, taken together with the nitrogen atom to which they are bonded, may form an optionally substituted 5 to 7 membered heterocyclyl group optionally containing one additional heteroatom selected from N, O and S; or a pharmaceutically acceptable salt thereof. R7 is hydrogen, trialkylsylyl or an optionally substituted group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, aryl-alkyl, heterocyclyl and heterocyclyl-alkyl; R3 and R4 are independently hydrogen or an optionally substituted group selected from straight or branched C 1 -C 6 alkyl, straight or branched C 2 -C 6 alkenyl, straight or branched C 2 -C 6 alkynyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, arylalkyl, heterocyclyl and heterocyclyl-alkyl, or R3 and R4, taken together with the nitrogen atom to which they are bonded, may form an optionally substituted 5 to 7 membered heterocyclyl group optionally containing one additional heteroatom selected from N, O and S; R5 is an optionally substituted aryl; R6 is hydrogen, an optionally substituted straight or branched C 1 -C 6 alkyl or NR8R9, wherein: R8 and R9 are independently hydrogen or an optionally substituted group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, heterocyclyl and heterocyclyl-alkyl, or R8 and R9, taken together with the nitrogen atom to which they are bonded, may form an optionally substituted 5 to 7 membered heterocyclyl group optionally containing one additional heteroatom selected from N, O and S; or a pharmaceutically acceptable salt thereof.