Novel coumarins and 2-thioxo-coumarins as inhibitors of the tumor-associated carbonic anhydrases IX and XII

Abstract

A series of coumarins incorporating tert-butyl-dimethylsilyloxy- or allyoxy- moieties in positions 4-, 6 or 7 of the heterocyclic ring have been synthesized and then converted to the corresponding 2-thioxo-coumarins. Other derivatives incorporating hydroxyethyloxy-, tosylethoxy- and 2-fluroethyloxy- moieties in position 7 of the coumarin ring were synthesized together with derivatives of 4-methyl-7-amino coumarin incorporating acetamido, 3,5-dimethylphenylureido- and tert-butyloxycarbonylamido functionalities. All these compounds were assayed as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). The human (h) cytosolic isoforms hCA I and II were weakly inhibited (hCA I) or not inhibited at all (hCA II) by these (thioxo)coumarins whereas the tumor-associated transmembrane isoforms hCA IX and XII were inhibited with efficiencies from the submicromolar to the low micromolar range by many of these derivatives. The structure–activity relationship for these classes of less investigated CA inhibitors are delineated, with the potential of using them as leads to obtain isoform-selective inhibitors with excellent affinity for CA IX and XII (validated antitumor targets) which do not significantly inhibit the cytosolic offtarget isoforms hCA I and II.