A compound of formula: wherein: Y is O and Z is N, or Y is N and Z is O; X is O, S, SO 2 or NH; R1 is hydrogen or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, heterocyclyl and aryl; R2 is -NR'R" or -OR', wherein R' and R" are, each independently, hydrogen or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, heterocyclyl, heterocyclylalkyl, aryl and arylalkyl, or, together with the nitrogen atom to which they are bonded, R' and R" may form a 5 to 6 membered heteroaryl or heterocyclyl group, optionally containing one additional heteroatom selected among N, O and S; A is a divalent group selected from -(CH 2) 2 -, -CH 2 -C(CH 3) 2 -, -C(CH 3) 2 -CH 2 - and -CH=CH-; and the pharmaceutically acceptable salts thereof; wherein any of the above R1, R' and R" group may be optionally substituted, in any of their free positions, by one or more groups, for instance 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; and, in their turn, each of the above substituent may be further substituted by one or more of the aforementioned groups. Y is O and Z is N, or Y is N and Z is O; X is O, S, SO 2 or NH; R1 is hydrogen or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, heterocyclyl and aryl; R2 is -NR'R" or -OR', wherein R' and R" are, each independently, hydrogen or a group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 7 cycloalkyl, cycloalkyl-alkyl, heterocyclyl, heterocyclylalkyl, aryl and arylalkyl, or, together with the nitrogen atom to which they are bonded, R' and R" may form a 5 to 6 membered heteroaryl or heterocyclyl group, optionally containing one additional heteroatom selected among N, O and S; A is a divalent group selected from -(CH 2) 2 -, -CH 2 -C(CH 3) 2 -, -C(CH 3) 2 -CH 2 - and -CH=CH-; and the pharmaceutically acceptable salts thereof; wherein any of the above R1, R' and R" group may be optionally substituted, in any of their free positions, by one or more groups, for instance 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; and, in their turn, each of the above substituent may be further substituted by one or more of the aforementioned groups.