A compound of formula: wherein A is a group -(CH 2) 1-3 -X-R1; R1 is hydrogen, halogen or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, arylalkyl, heterocyclyl and heterocyclylalkyl; R2 is a group selected from C 2 -C 6 alkynyl, aryl, and heterocyclyl; R3 and R4 are each independently hydrogen, halogen, cyano or a group selected from C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, aryl, arylalkyl, heterocyclyl and heterocyclylalkyl; X is a single bond or a divalent radical selected from -NR'-, and -O-, wherein R' is hydrogen, COR5, C R5, S 2 R9, or a straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, arylalkyl, heterocyclyl and heterocyclylalkyl or, together with the nitrogen atom to which they are bound, R' and R1 may form a 5- to 7-membered heteroaryl or heterocyclyl group optionally containing one additional heteroatom selected from N, O and S; wherein: R5 is OR6, NR7R8 or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, aryl, arylalkyl, heterocyclyl and heterocyclylalkyl, wherein: R6 is a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, aryl and heterocyclyl; R7 and R8 are each independently hydrogen or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, aryl and heterocyclyl; R9 is a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, aryl and heterocyclyl; wherein any of the above R1-R9 and R' group may be optionally substituted, in any of their free positions, by 1 to 6 groups, independently selected from: halogen atom, nitro, oxo groups (=O), cyano, C 1 -C 6 alkyl, polyfluorinated alkyl, polyfluorinated alkoxy, alkenyl, alkynyl, hydroxyalkyl, aryl, arylalkyl, heterocyclyl, C 3 -C 7 cycloalkyl, hydroxy, alkoxy, aryloxy, heterocyclyloxy, methylenedioxy, alkylcarbonyloxy, arylcarbonyloxy, cycloalkenyloxy, heterocyclylcarbonyloxy, alkylideneaminooxy, carboxy, alkoxycarbonyl, aryloxycarbonyl, cycloalkyloxycarbonyl, heterocyclyloxycarbonyl, amino, ureido, alkylamino, dialkylamino, arylamino, diarylamino, heterocyclylamino, formylamino, alkylcarbonylamino, arylcarbonylamino, heterocyclylcarbonylamino, aminocarbonyl, alkylaminocarbonyl, dialkylaminocarbonyl, arylaminocarbonyl, heterocyclylaminocarbonyl, alkoxycarbonylamino, hydroxyaminocarbonyl alkoxyimino, alkylsulfonylamino, arylsulfonylamino, heterocyclylsulfonylamino, formyl, alkylcarbonyl, arylcarbonyl, cycloalkylcarbonyl, heterocyclylcarbonyl, alkylsulfonyl, arylsulfonyl, aminosulfonyl, alkylaminosulfonyl, dialkylaminosulfonyl, arylaminosulfonyl, heterocyclylaminosulfonyl, arylthio, alkylthio, phosphonate and alkylphosphonate; or a pharmaceutically acceptable salt thereof. A is a group -(CH 2) 1-3 -X-R1; R1 is hydrogen, halogen or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, arylalkyl, heterocyclyl and heterocyclylalkyl; R2 is a group selected from C 2 -C 6 alkynyl, aryl, and heterocyclyl; R3 and R4 are each independently hydrogen, halogen, cyano or a group selected from C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, aryl, arylalkyl, heterocyclyl and heterocyclylalkyl; X is a single bond or a divalent radical selected from -NR'-, and -O-, wherein R' is hydrogen, COR5, C R5, S 2 R9, or a straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, aryl, arylalkyl, heterocyclyl and heterocyclylalkyl or, together with the nitrogen atom to which they are bound, R' and R1 may form a 5- to 7-membered heteroaryl or heterocyclyl group optionally containing one additional heteroatom selected from N, O and S; wherein: R5 is OR6, NR7R8 or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, aryl, arylalkyl, heterocyclyl and heterocyclylalkyl, wherein: R6 is a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, aryl and heterocyclyl; R7 and R8 are each independently hydrogen or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, aryl and heterocyclyl; R9 is a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, aryl and heterocyclyl; R5 is OR6, NR7R8 or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, aryl, arylalkyl, heterocyclyl and heterocyclylalkyl, wherein: R6 is a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, aryl and heterocyclyl; R7 and R8 are each independently hydrogen or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, aryl and heterocyclyl; R6 is a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, aryl and heterocyclyl; R7 and R8 are each independently hydrogen or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, aryl and heterocyclyl; R9 is a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, aryl and heterocyclyl;