Pharmacologically active piperazino derivatives

New piperazino derivatives of formula ##STR1## in which R is a phenyl radical substituted with at least one sulphonamido group or a substituted nitrogenated heterocyclic ring, and A is CO, CH2, SO2, possessing inhibiting activity towards carbonic anhydrase. The new products are prepared from compounds of formula R-A-X in which X is OH, SH, halogen, OR"" or SR"" in which R"" is methyl, ethyl, phenyl, carbomethoxy, carboethoxy, and from a piperazino derivative of formula ##STR2## The R' group can also be introduced on termination of the reaction, by removing and substituting a protective group present at the nitrogen. R is 2-methoxy-5-sulphamoyl-phenyl, 2-sulphamoylimidazyl, 2-amino-1,3,4-thiadiazole or 2-acetamido-1,3,4-thiadiazole; R' is H, linear or branched C.sub.1 -C.sub.6 alkyl; linear or branched C.sub.2 -C.sub.6 alkenyl; alkyl-phenyl or alkenyl-phenyl, wherein phenyl is optionally monosubstituted with halogen, trihalomethyl, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkoxy, or sulphonamido; C.sub.2 -C.sub.6 aliphatic acyl; C.sub.3 -C.sub.6 alkylcarboxyalkoxy; alkyl-carboxyamino in which the alkyl is C.sub.1 -C.sub.3 and the amine is mono or disubstituted by linear or branched C.sub.1 -C.sub.6 alkyl and; R" is H, or together with R' forms a 5 or 6 membered ring condensed with the piperazine; provided that when R is a substituted phenyl group and A is CO, R' is other than H, C.sub.1 -C.sub.4 alkyl or benzyl.