A compound represented by formula (Ia) or (Ib) wherein R is a group -COR a, -CONHR a or -CONR a R b wherein R a and R b are, each independently, hydrogen or an optionally substituted group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl, aryl, arylalkyl, heterocyclyl or heterocyclylalkyl, wherein the R a and R b groups may be optionally substituted, in any of their free positions, by one or more groups independently selected from: halogen, nitro, oxo groups (=O), cyano, alkyl, polyfluorinated alkyl, polyfluorinated alkoxy, alkenyl, alkynyl, hydroxyalkyl, aryl, arylalkyl, hetrocyclyl, cycloalkyl, hydroxy, alkoxy, aryloxy, heterocyclyloxy, methylenedioxy, alkylcarbonyloxy, arylcarbonyloxy, cycloalkenyloxy, alkylideneaminooxy, carboxy, alkoxycarbonyl, aryloxycarbonyl, cycloalkyloxycarbonyl, amino, ureido, alkylamino, dialkylamino, arylamino, diarylamino, formylamino, alkylcarbonylamino, arylcarbonylamino, heterocyclylcarbonylamino, alkoxycarbonylamino, alkoxyimino, alkylsulfonylamino, arylsulfonylamino, formyl, alkylcarbonyl, arylcarbonyl, cycloalkylcarbonyl, heterocyclylcarbonyl, aminocarbonyl, alkylaminocarbonyl, dialkylaminocarbonyl, alkylsulfonyl, arylsulfonyl, aminosulfonyl, alkylaminosulfonyl, dialkylaminosulfonyl, arylthio and alkylthio; or, together with the nitrogen atom to which they are bonded, R a and R b may form an optionally substituted 5 or 6 membered heterocycle optionally containing one additional heteroatom or heteroatomic group selected among N, NH, O or S; R 1 is selected from the group consisting of straight or branched C 3 -C 4 alkyl; or pharmaceutically acceptable salts thereof. R is a group -COR a, -CONHR a or -CONR a R b wherein R a and R b are, each independently, hydrogen or an optionally substituted group selected from straight or branched C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl, aryl, arylalkyl, heterocyclyl or heterocyclylalkyl, wherein the R a and R b groups may be optionally substituted, in any of their free positions, by one or more groups independently selected from: halogen, nitro, oxo groups (=O), cyano, alkyl, polyfluorinated alkyl, polyfluorinated alkoxy, alkenyl, alkynyl, hydroxyalkyl, aryl, arylalkyl, hetrocyclyl, cycloalkyl, hydroxy, alkoxy, aryloxy, heterocyclyloxy, methylenedioxy, alkylcarbonyloxy, arylcarbonyloxy, cycloalkenyloxy, alkylideneaminooxy, carboxy, alkoxycarbonyl, aryloxycarbonyl, cycloalkyloxycarbonyl, amino, ureido, alkylamino, dialkylamino, arylamino, diarylamino, formylamino, alkylcarbonylamino, arylcarbonylamino, heterocyclylcarbonylamino, alkoxycarbonylamino, alkoxyimino, alkylsulfonylamino, arylsulfonylamino, formyl, alkylcarbonyl, arylcarbonyl, cycloalkylcarbonyl, heterocyclylcarbonyl, aminocarbonyl, alkylaminocarbonyl, dialkylaminocarbonyl, alkylsulfonyl, arylsulfonyl, aminosulfonyl, alkylaminosulfonyl, dialkylaminosulfonyl, arylthio and alkylthio; or, together with the nitrogen atom to which they are bonded, R a and R b may form an optionally substituted 5 or 6 membered heterocycle optionally containing one additional heteroatom or heteroatomic group selected among N, NH, O or S; R 1 is selected from the group consisting of straight or branched C 3 -C 4 alkyl; or pharmaceutically acceptable salts thereof.