Synthesis of 4-sulfamoylphenyl-benzylamine derivatives with inhibitory activity against human carbonic anhydrase isoforms I,II, IX and XII

Imine derivatives were obtained by condensation of sulfanilamide with substituted aromatic aldehydes. The Schiff bases were thereafter reduced with sodium borohydride, leading to the corresponding amines, derivatives of 4-sulfamoylphenyl-benzylamine. These sulfonamides were investigated as inhibitors of the human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms hCA I and II (cytosolic isozymes), as well as hCA IX and XII (transmembrane, tumor-associated enzymes). We noted that the compounds incorporating secondary amine moieties showed a better inhibitory activity against all CA isozymes compared to the corresponding Schiff bases. Low nanomolar CA II, IX and XII inhibitors were detected, whereas the activity against hCA I was less potent. The secondary amines incorporating sulfonamide or similar zinc-binding groups, poorly investigated chemotypes for designing metalloenzyme inhibitors, may offer interesting opportunities in the field due to the facile preparation and possibility to explore a vast chemical space.     

Carbonic anhydrase inhibitors: synthesis and inhibition of cytosolic/tumor-associated carbonic anhydrase isozymes I, II, and IX with sulfonamides incorporating 1,2,4-triazine moieties

A series of benzenesulfonamide derivatives incorporating triazine moieties in their molecules was obtained by reaction of cyanuric chloride with sulfanilamide, homosulfanilamide, or 4-aminoethylbenzenesulfonamide. The dichlorotriazinyl-benzenesulfonamides intermediates were subsequently derivatized by reaction with various nucleophiles, such as water, methylamine, or aliphatic alcohols (methanol and ethanol). The library of sulfonamides incorporating triazinyl moieties was tested for the inhibition of three physiologically relevant carbonic anhydrase (CA, EC 4.2.1.1) isozymes, the cytosolic hCA I and II, and the transmembrane, tumor-associated hCA IX. The new compounds reported here inhibited hCA I with K(I)s in the range of 75-136nM, hCA II with K(I)s in the range of 13-278nM, and hCA IX with K(I)s in the range of 0.12-549nM. The first hCA IX-selective inhibitors were thus detected, as the chlorotriazinyl-sulfanilamide and the bis-ethoxytriazinyl derivatives of sulfanilamide/homosulfanilamide showed selectivity ratios for CA IX over CA II inhibition in the range of 166-706. Furthermore, some of these compounds have subnanomolar affinity for hCA IX, with K(I)s in the range 0.12-0.34nM. These derivatives are interesting candidates for the development of novel unconventional anticancer strategies targeting the hypoxic areas of tumors. Clear renal cell carcinoma, which is the most lethal urologic malignancy and is both characterized by very high CA IX expression and chemotherapy unresponsiveness, could be the leading candidate of such novel therapies.     

Carbonic anhydrase inhibitors: novel sulfonamides incorporating 1,3,5-triazine moieties as inhibitors of the cytosolic and tumour-associated carbonic anhydrase isozymes I, II and IX

A new series of aromatic benzenesulfonamides incorporating 1,3,5-triazine moieties in their molecules is reported. This series was obtained by reaction of cyanuric chloride with sulfanilamide, homosulfanilamide or 4-aminoethylbenzenesulfonamide. The prepared dichlorotriazinyl-benzenesulfonamides were subsequently derivatized by reacting them with various nucleophiles, such as ammonia, hydrazine, primary and secondary amines, amino acid derivatives or phenol. The library of sulfonamides incorporating triazinyl moieties was tested for the inhibition of three physiologically relevant carbonic anhydrase (CA, EC 4.2.1.1) isozymes, the cytosolic hCA I and II, and the transmembrane, tumour-associated hCA IX. The new compounds inhibited hCA I with inhibition constants in the range of 31-8500 nM, hCA II with inhibition constants in the range of 14-765 nM and hCA IX with inhibition constants in the range of 1.0-640 nM. Structure-activity relationship was straightforward and rather simple in this class of CA inhibitors, with the compounds incorporating compact moieties at the triazine ring (such as amino, hydrazino, ethylamino, dimethylamino or amino acyl) being the most active ones, and the derivatives incorporating such bulky moieties (n-propyl, n-butyl, diethylaminoethyl, piperazinylethyl, pyridoxal amine or phenoxy) being less effective hCA I, II and IX inhibitors. Some of the new derivatives also showed selectivity for inhibition of hCA IX over hCA II (selectivity ratios of 23.33-32.00), thus constituting excellent leads for the development of novel approaches for the management of hypoxic tumours.     

Carbonic anhydrase inhibitors: inhibition of the tumor-associated isozymes IX and XII with a library of aromatic and heteroaromatic sulfonamides

The inhibition of the two transmembrane, tumor-associated isozymes of carbonic anhydrase (CA, EC 4.2.1.1) of human origin, hCA IX and XII, with a library of aromatic and heteroaromatic sulfonamides has been investigated. Most of them were sulfanilamide, homosulfanilamide, and 4-aminoethyl-benzenesulfonamide derivatives, to which tails that should induce diverse physico-chemical properties have been attached at the amino moiety, whereas several of these compounds were derived from metanilamide, benzene-1,3-disulfonamide or the 1,3,4-thiadiazole/thiadiazoline-2-sulfonamides. The tails were of the alkyl/aryl-carboxamido/sulfonamido-, ureido or thioureido type. Against hCA IX the investigated compounds showed inhibition constants in the range of 3-294 nM, whereas against hCA XII in the range of 1.9-348 nM, respectively. The best hCA IX inhibitors were ureas/thioureas incorporating 4-aminoethyl-benzenesulfonamide and metanilamide moieties. The best hCA XII inhibitors were 1,3,4-thiadiazole/thiadiazoline-2-sulfonamides incorporating 5-acylamido or 5-arylsulfonylamido moieties. These compounds also inhibited appreciably the cytosolic isozymes hCA I and II, but some selectivity for the transmembrane, tumor-associated isozymes was observed for some of them, which is an encouraging result for the design of novel therapies targeting hypoxic tumors, in which these carbonic anhydrases are highly overexpressed.     

Phenylethynylbenzenesulfonamide regioisomers strongly and selectively inhibit the transmembrane, tumor-associated carbonic anhydrase isoforms IX and XII over the cytosolic isoforms I and II

A series of compounds incorporating regioisomeric phenylethynylbenzenesulfonamide moieties has been investigated for the inhibition of four human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, hCA I, II, IX and XII. Inhibition between the low nanomolar to the milliomolar range has been observed against them, with several low nanomolar and tumor-CA selective inhibitors detected. The position of the sulfamoyl group with respect to the alkyne functionality, and the nature of the moieties substituting the second aromatic ring were the principal structural features influencing CA inhibition. The para-sulfamoyl-substituted derivatives were effective inhibitors of CA IX and XII, the meta-substituted regioisomers of CA I, IX and XII, whereas the ortho-substituted sulfonamides were weak inhibitors of CA I, II and IX, but inhibited significantly CA XII.     

Carbonic anhydrase inhibitors. Inhibition of cytosolic/tumor-associated carbonic anhydrase isozymes I, II, IX, and XII with Schiff's bases incorporating chromone and aromatic sulfonamide moieties, and their zinc complexes

A series of Schiff's bases was prepared by reaction of 3-formyl-chromone or 6-methyl-3-formyl-chromone with aromatic sulfonamides, such as sulfanilamide, homosulfanilamide, 4-aminoethyl-benzenesulfonamide, a pyrimidinyl-substituted sulfanilamide derivative, sulfaguanidine and 4-amino-6-trifluoromethyl-benzene-1,3-disulfonamide. The zinc complexes of these sulfonamides have also been obtained. The new derivatives and their Zn(II) complexes were investigated for the inhibition of four physiologically relevant isozymes of carbonic anhydrase (CA, EC 4.2.1.1): the cytosolic isoforms I and II, as well as the tumor-associated, transmembrane isozymes CA IX and XII. Except for the sulfaguanidine-derived compounds which were devoid of activity against all isozymes, the other sulfonamides and their metal complexes showed interesting inhibitory activity. Against isozyme CA I, the inhibition constants were in the range of 13-100 nM, against isozyme CA II in the range of 1.9-102 nM, against isozyme CA IX in the range of 6.3-48nM, and against CA XII in the range of 5.9-50nM. Generally, the formyl-chromone derived compounds were better CA inhibitors as compared to the corresponding 6-methyl-chromone derivatives, and for the simple, benzenesulfonamide derivatives activity increased with an increase of the spacer from sulfanilamide to homosulfanilamide and 4-aminoethylbenzenesulfonamide derivatives, respectively. Some of these compounds may show applications for the development of therapies targeting hypoxic tumors in which CA IX and XII are often highly overexpressed.     

Carbonic anhydrase inhibitors: Benzenesulfonamides incorporating cyanoacrylamide moieties are low nanomolar/subnanomolar inhibitors of the tumor-associated isoforms IX and XII

A series of benzenesulfonamides incorporating cyanoacrylamide moieties (tyrphostine analogues) have been obtained by reaction of sulfanilamide with ethylcyanoacetate followed by condensation with aromatic/heterocyclic aldehydes, isothiocyanates or diazonium salts. The new compounds have been investigated as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4. 2.1.1), and more specifically against the cytosolic human (h) isoforms hCA I and II, as well as the transmembrane, tumor-associated ones CA IX and XII, which are validated antitumor targets. Most of the new benzenesulfonamides were low nanomolar or subnanomolar CA IX/XII inhibitors whereas they were less effective as inhibitors of CA I and II. The structure–activity relationship for this class of effective CA inhibitors is also discussed. Generally, electron donating groups in the starting aldehyde reagent favored CA IX and XII inhibition, whereas halogeno, methoxy and dimethylamino moieties led to very potent CA XII inhibitors.     

7-Aryl-triazolyl-substituted sulfocoumarins are potent,selective inhibitors of the tumor-associated carbonic anhydrase IX and XII

Sulfocoumarins behave as interesting inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). Here, we report a new series of 7-substituted derivatives which were obtained by the click chemistry approach from 7-propargyloxy-sulfocoumarin and aryl azides incorporating halogens, hydroxy, methoxy and carboxyl moieties in their molecules. The new compounds were screened for the inhibition on four physiologically relevant human CA (hCA) isoforms, the cytosolic hCA I and II and the transmembrane tumor-associated hCA IX and XII. The new compounds did not inhibit the cytosolic isoforms but were low nanomolar inhibitors of the tumor-associated ones hCA IX and XII.     

Carbonic anhydrase inhibitors: synthesis and inhibition of cytosolic/tumor-associated carbonic anhydrase isozymes I, II, and IX with sulfonamides incorporating thioureido-sulfanilyl scaffolds

The tumor-associated transmembrane carbonic anhydrase (CA, EC 4.2.1.1) isozyme IX (CA IX) is overexpressed in hypoxic tumors and appears to be involved in acidification of the tumor microenvironment, a process correlated with cancer progression and bad prognosis. The acidification may be reduced by inhibiting the enzyme with potent sulfonamide/sulfamate CA inhibitors. A series of such aromatic sulfonamides incorporating thioureido-sulfanilyl moieties has been prepared and investigated for its interaction with the catalytic domain of the human isozyme hCA IX. The key intermediates in the synthesis were obtained by reacting sulfanilamide, homosulfanilamide, or 4-aminoethylbenzenesulfonamide with 4-acetamido-benzenesulfonyl chloride followed by deacetylation and reaction with thiophosgene. The obtained isothiocyanato sulfonamides were reacted with aliphatic or aromatic primary amines or hydrazines, leading to the corresponding thioureas. Some of these compounds showed excellent inhibitory properties against isozymes I, II, and IX, with several inhibitors also presenting selectivity for the inhibition of CA IX over that of the ubiquitous isozyme CA II. Such sulfonamides may constitute interesting candidates for the development of novel antitumor therapies based on the inhibition of the CA isozymes overexpressed in hypoxic tumors. Due to the highest expression of CA IX in clear renal cell carcinoma and its chemo/radioresistance, our efforts are first of all directed to generate effective therapeutic strategies for the cure of this malignancy.     

Synthesis of novel benzenesulfonamide bearing 1,2,3-triazole linked hydroxy-trifluoromethylpyrazolines and hydrazones as selective carbonic anhydrase isoforms IX and XII inhibitors

A series of twenty four hydroxy-trifluoromethylpyrazoline-carbonyl-1,2,3-triazoles and four hydrazones bearing benzenesulfonamide moieties was obtained by condensation of carboxyhydrazides with substituted 1,3-diketones. All the newly synthesized compounds were investigated as inhibitors of physiologically and pharmacologically relevant human (h) carbonic anhydrsae (CA, EC 4.2.1.1) cytosolic isoforms hCA I and II, as well as transmembrane tumor-assosciated isoforms hCA IX and XII. These compounds exhibited excellent CA inhibitory potency against the four CA isoenzymes as compared to clinically used reference drug acetazolamide (AAZ). Some compounds bearing bulkier group at C-5′ position of 1,2,3-triazoles ring were weaker inhibitors of hCA I. Inhibition assay against hCA II indicates, that several derivatives exhibited upto 27-fold more effective inhibitory activity compared to AAZ. Five of the assayed compounds displayed low nanomolar potency (K_i ≤ 10 nM) against hCA IX, whereas five compounds were found to be endowed with excellent inhibitory potencies (K_i ≤ 5 nM) against hCA XII. The biological activity profile presented herein will be useful for designing new leads and provide candidates for preclinical investigations.     

Carbonic anhydrase inhibitors: inhibition of the human transmembrane isozyme XIV with a library of aromatic/heterocyclic sulfonamides

The first inhibition study of the transmembrane carbonic anhydrase (CA, EC 4.2.1.1) isozymes hCA XIV with a library of aromatic and heteroaromatic sulfonamides synthesized earlier is reported. Most of the inhibitors were sulfanilamide, homosulfanilamide and 4-aminoethyl-benzenesulfonamide derivatives, to which tails that would induce diverse physicochemical properties have been attached at the amino moiety. Several of these compounds were metanilamide, benzene-1,3-disulfonamide or the 1,3,4-thiadiazole/thiadiazoline-2-sulfonamide derivatives. The tails incorporated in these molecules were of the alkyl/aryl-carboxamido/ sulfonamido-, ureido- or thioureido-types. The sulfanilamides acylated at the 4-amino group with short aliphatic/aromatic moieties incorporating 2-6 carbon atoms showed modest hCA XIV inhibitory activity (K(I)-s in the range of 1.25-4.2 microM) which were anyhow better than that of sulfanilamide (K(I) of 5.4 microM). Better activity showed the homosulfanilamide and 4-aminoethyl-benzenesulfonamide derivatives bearing arylsulfonamido/ureido and thioureido moieties, with K(I)'s in the range of 203-935 nM. The best activity was observed for the heteroaromatic compounds incorporating 1,3,4-thiadiazole/thiadiazoline-2-sulfonamide and 5-arylcarboxamido/sulfonamido moieties, with K(I)'s in the range of 10-85 nM. All these compounds were generally also much better inhibitors of the other two transmembrane CA isozyme, hCA IX and XII. Thus, highly potent hCA XIV inhibitors were detected, but isozyme-specific inhibitors were not discovered for the moment.     

Carbonic anhydrase inhibitors. Selective inhibition of human tumor-associated isozymes IX and XII and cytosolic isozymes I and II with some substituted-2-mercapto-benzenesulfonamides

A series of 2-mercapto-substituted-benzenesulfonamides has been prepared by a unique two-step procedure starting from the corresponding 2-chloro-substituted benzenesulfonamides. Compounds bearing an unsubstituted mercapto group and the corresponding S-benzoyl derivatives were investigated as inhibitors of four isoforms of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1), i.e., the cytosolic, ubiquitous isozymes CA I and II, as well as the transmembrane, tumor associated isozymes CA IX and XII. These derivatives were medium potency hCA I inhibitors (K(I)s in the range of 1.5-5.7 microM), two derivatives were strong hCA II inhibitors (K(I)s in the range of 15-16 nM), whereas the others showed weak activity. These compounds inhibited hCA IX with inhibition constants in the range 160-1950 nM and hCA XII with inhibition constants in the range 1.2-413 nM. Some of these derivatives showed a certain degree of selectivity for inhibition of the tumor-associated over the cytosolic isoforms, being thus interesting leads for the development of potentially novel applications in the management of hypoxic tumors which overexpress CA IX and XII.     

Inhibition of carbonic anhydrase isoforms I,II, IX and XII with secondary sulfonamides incorporating benzothiazole scaffolds

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyze the fundamental reaction of CO₂ hydration in all living organisms, being actively involved in the regulation of a plethora of patho/physiological conditions. A series of benzothiazole-based sulfonamides were synthesized and tested as possible CA inhibitors. Their inhibitory activity was assessed against the cytosolic human isoforms hCA I and hCA II and the transmembrane hCA IX and hCA XII. Several of the investigated derivatives showed interesting inhibition activity and selectivities for inhibiting hCA IX and hCA XII over the off-target ones hCA I and hCA II. Furthermore, computational procedures were used to investigate the binding mode of this class of compounds, within the active site of hCA IX.     

Carbonic anhydrase inhibitors. Selective inhibition of human tumor-associated isozymes IX and XII and cytosolic isozymes I and II with some substituted-2-mercapto-benzenesulfonamides

A series of 2-mercapto-substituted-benzenesulfonamides has been prepared by a unique two-step procedure starting from the corresponding 2-chloro-substituted benzenesulfonamides. Compounds bearing an unsubstituted mercapto group and the corresponding S-benzoyl derivatives were investigated as inhibitors of four isoforms of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1), i.e., the cytosolic, ubiquitous isozymes CA I and II, as well as the transmembrane, tumor associated isozymes CA IX and XII. These derivatives were medium potency hCA I inhibitors (K_Is in the range of 1.5–5.7 μM), two derivatives were strong hCA II inhibitors (K_Is in the range of 15–16 nM), whereas the others showed weak activity. These compounds inhibited hCA IX with inhibition constants in the range 160–1950 nM and hCA XII with inhibition constants in the range 1.2–413 nM. Some of these derivatives showed a certain degree of selectivity for inhibition of the tumor-associated over the cytosolic isoforms, being thus interesting leads for the development of potentially novel applications in the management of hypoxic tumors which overexpress CA IX and XII.     

Carbonic anhydrase inhibitors. Inhibition of cytosolic isoforms I and II, and extracellular isoforms IV, IX, and XII with sulfamides incorporating sugar moieties

A series of glycosylated sulfamides possessing a diverse substitution pattern, with benzylated, peracetylated, and unsaturated six- and five-membered ring sugar moieties attached to the NHSO(2)NH(2) zinc binding group is reported. These derivatives were tested for the inhibition of five human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, hCA I, II, IV, IX, and XII. Against hCA I the sulfamides behaved as weak inhibitors, whereas they showed low nanomolar activity against hCA II, IX, and XII, being slightly less effective as hCA IV inhibitors. One compound showed selectivity for inhibiting the tumor-associated isoforms hCA IX and XII over the ubiquitous cytosolic hCA II. The sulfamide zinc binding group may thus indeed lead to very effective glycosylated inhibitors targeting several physiologically relevant isozymes.     

Inhibition of human carbonic anhydrase isoforms I–XIV with sulfonamides incorporating fluorine and 1,3,5-triazine moieties

Reaction of cyanuryl fluoride with sulfanilamide or 4-aminoethylbenzenesulfonamide afforded triazinyl-substituted benzenesulfonamides incorporating fluorine, which were further derivatized by reaction with amines, amino alcohols, amino acids or amino acid esters. Inhibition studies of all the human (h) carbonic anhydrase (CA, EC 4.2.1.1) isoforms, hCA I–XIV with these compounds revealed that they show moderate-weak inhibition of hCA III, IV, VA and XIII, rather moderate inhibition against hCA I, VI, and IX, and excellent inhibition of the physiologically relevant hCA II, VII and XII. The inhibition profile of these fluorine containing triazinyl sulfonamides is thus very different from the corresponding analogs incorporating chlorine, which were previously investigated as inhibitors of some of these enzymes.     

Synthesis and exploration of 2-morpholino-4-phenylthiazol-5-yl acrylamide derivatives for their effects against carbonic anhydrase I,II, IX and XII isoforms as a non-sulfonamide class of inhibitors

Novel series of 2-morpholino-4-phenylthiazol-5-yl acrylamide derivatives (8a–s) have been synthesized and explored as a non-sulfonamide class of carbonic anhydrase (CA, EC 4.2.1.1) inhibitors. The newly synthesized molecules were evaluated for their CA inhibitory potency against four isoforms: the cytosolic isozyme hCA I, II as well as trans-membrane tumor associated isoform hCA IX and hCA XII taking acetazolamide (AAZ) as standard drug. The results revealed that most of the compounds showed good activity against hCA II, IX, and XII whereas none of them were active against hCA I (K_i >100 μM). It is observed that the physiologically most important cytosolic isoform hCA II was inhibited by these molecules in the range of K_i 9.3–77.7 μM. It is also found the both the transmembrane isoforms hCA IX and XII were also inhibited with K_is ranging between 54.7–96.7 μM and 4.6–8.8 μM, respectively. The binding modes of the active compounds within the catalytic pockets of hCA II, IX and XII were evaluated by docking studies. This new non-sulfonamide class of selective inhibitors of hCA II, IX and XII over the hCA I isoform may be used for further understanding the physiological roles of some of these isoforms in various pathologies.     

Carbonic anhydrase inhibitors. Diazenylbenzenesulfonamides are potent and selective inhibitors of the tumor-associated isozymes IX and XII over the cytosolic isoforms I and II

A series of diazenylbenzenesulfonamides, azo-dye derivatives of sulfanilamide or metanilamide incorporating phenol and amine moieties, were tested for inhibition of the tumor-associated isozymes of carbonic anhydrase (CA, EC 4.2.1.1), CA IX and XII. These compounds showed moderate-low inhibitory activities against the cytosolic isoforms CA I and II (offtargets) and excellent, low nanomolar inhibitory activity against the transmembrane CA IX and XII (K_Is in the range of 3.5–63 nM against CA IX and 5.0–69.4 nM against CA XII, respectively). The selectivity ratio for inhibiting the tumor-associated CA IX over the offtarget CA II was in the range of 15–104 for these diazenylbenzenesulfonamides, making them among the most isoform-selective inhibitors targeting tumor-associated CAs (over the ubiquitous CA II). Since CA IX/XII were recently shown to be both therapeutic and diagnostic targets for hypoxic solid tumors overexpressing these proteins, such compounds held promise for the management of hypoxic tumors, which are largely non-responsible to classical chemo- and radio-therapy.     

Sulfonamides incorporating heteropolycyclic scaffolds show potent inhibitory action against carbonic anhydrase isoforms I,II, IX and XII

Three series of polycyclic compounds possessing either primary sulfonamide or carboxylic acid moieties as zinc-binding groups were investigated as inhibitors of four physiologically relevant CA isoforms, the cytosolic hCA I and II, as well as the transmembrane hCA IX and XII. Most of the new sulfonamides reported here showed excellent inhibitory effects against isoforms hCA II, IX and XII, but no highly isoform-selective inhibition profiles. On the other hand, the carboxylates selectively inhibited hCA IX (K_Is ranging between 40.8 and 92.7 nM) without inhibiting significantly the other isoforms. Sulfonamides/carboxylates incorporating polycyclic ring systems such as benzothiopyranopyrimidine, pyridothiopyranopyrimidine or dihydrobenzothiopyrano[4,3-c]pyrazole may be considered as interesting candidates for exploring the design of isoform-selective CAIs with various pharmacologic applications.     

Aryl derivatives of 3H-1,2-benzoxathiepine 2,2-dioxide as carbonic anhydrase inhibitors

Abstract

A new series of homosulfocoumarins (3H-1,2-benzoxathiepine 2,2-dioxides) possessing various substitution patterns and moieties in the 7, 8 or 9 position of the heterocylic ring were prepared by original procedures and investigated for the inhibition of four physiologically relevant carbonic anhydrase (CA, EC 4.2.1.1) isoforms, the human (h) hCA I, II, IX and XII. The 8-substituted homosulfocoumarins were the most effective hCA IX/XII inhibitors followed by the 7-substituted derivatives, whereas the substitution pattern in position 9 led to less effective binders for the transmembrane, tumour-associated isoforms IX/XII. The cytosolic isoforms hCA I and II were not inhibited by these compounds, similar to the sulfocoumarins/coumarins investigated earlier. As hCA IX and XII are validated anti-tumour targets, with one sulphonamide (SLC-0111) in Phase Ib/II clinical trials, finding derivatives with better selectivity for inhibiting the tumour-associated isoforms over the cytosolic ones, as the homosulfocoumarins reported here, is of crucial importance.