Substituted nitrated catechols, their use in the treatment of some central and peripheral nervous system disorders and pharmaceutical compositions containing them

A compound of formula I:

• 3
• where R1 and R2 are the same or different and signify hydrogen, optionally substituted lower aikanoyl or aroyl, optionally substituted lower alkoxycarbonyl, or optionally substituted lower alkylcarbamoyl;
• R3 signifies hydrogen or optionally substituted alkanoyl or aroyl group;
• R4 signifies optionally substituted saturated or partially unsaturated lower alkyl or ary group, or taken together with R3 signifies an optionally substituted saturated or partially unsaturated carbocyclic ring;
• A signifies oxygen or NR5 group, where R5 signifies NHR6 where R6 signifies optionally substituted lower alkyl or aryl group, or OR7 group where R7 signifies hydrogen, lower alkyl or lower alkanoyl, or A signifies an optionally substituted alkylidene when R4 signifies OR8 group where R8 signifies optionally substituted lower alkanoyl or aroyl group, and pharmaceutically acceptable salts thereof.