Carbonic Anhydrase Inhibitors: Aliphatic N-phosphorylated Sulfamates--A Novel Zinc-anchoring Group Leading to Nanomolar Inhibitors

Aryl derivatives of 3H-1,2-benzoxaphosphepine 2-oxides as inhibitors of cancer-related carbonic anhydrase isoforms IX and XII

A range of 3H-1,2-benzoxaphosphepine 2-oxide aryl derivatives with various substitution patterns at positions 7, 8, or 9 of the scaffold was synthesised in five steps from the commercially available salicylaldehydes. All of the newly obtained compounds were studied for their inhibition potency against carbonic anhydrase (CA) isoforms I, II, IX, and XII. Delightfully, these compounds showed a striking selectivity for the cancer-associated CA IX and XII over the cytosolic CA I and II, whose inhibition may lead to side-effects. Overall, a structure-activity relationship (SAR) revealed that 7- and 8-substituted aryl derivatives were more effective inhibitors of CA IX and XII than 9-substituted derivatives. In addition, the fluorine-containing analogues emerged as the most potent CA IX/XII inhibitors in this series.

N-substituted glutamyl sulfonamides as inhibitors of glutamate carboxypeptidase II (GCP2)

Glutamate carboxypeptidase II (GCP2) is a membrane-bound cell-surface peptidase which is implicated in several neurological disorders and is also over-expressed in prostate tumor cells. There is a significant interest in the inhibition of GCP2 as a means of neuroprotection, while GCP2 inhibition as a method to treat prostate cancer remains a topic of further investigation. The key zinc-binding functional group of the well-characterized classes of GCP2 inhibitors (phosphonates and phosphoramidates) is tetrahedral and negatively charged at neutral pH, while glutamyl urea class of inhibitors possesses a planar and neutral zinc-binding group. This study introduces a new class of GCP2 inhibitors, N-substituted glutamyl sulfonamides, which possess a neutral tetrahedral zinc-binding motif. A library containing 15 secondary sulfonamides and 4 tertiary (N-methyl) sulfonamides was prepared and evaluated for inhibitory potency against purified GCP2 enzyme activity. While most inhibitors lacked potency at 100 μm, short alkyl sulfonamides exhibited promising low micromolar potency, with the optimal inhibitor in this series being glutamyl N-(propylsulfonamide) (2g). Lastly, molecular docking was used to develop a model to formulate an explanation for the relative inhibitory potencies employed for this class of inhibitors.

Design, synthesis, and docking studies of new 1,3,4-thiadiazole-2-thione derivatives with carbonic anhydrase inhibitory activity

A new series of 1,3,4-thiadiazole-2-thione derivatives have been prepared and assayed for the inhibition of three physiologically relevant carbonic anhydrase (CA, EC 4.2.1.1) isozymes, the cytosolic human isozymes I and II, and the transmembrane, tumor-associated hCA IX. Against hCA I the investigated thiones, showed inhibition constants in the range of 2.55-222 microM, against hCA II in the range of 2.0-433 microM, and against hCA IX in the range of 1.25-148 microM. Compound 5c, 4-(4,5-dihydro-5-thioxo-1,3,4-thiadiazol-2-yl)-1-(5-nitro-2-oxoindolin-3-ylidene)semicarbazide showed interesting inhibition of the tumor-associated hCA IX with K(I) value of 1.25 microM, being the first non-sulfonamide type inhibitor of such activity. This result is rather important taking into consideration the known antitumor activity of thiones. In addition, docking of the tested compounds into CA II active site was performed in order to predict the affinity and orientation of these compounds at the isozyme active site. The results showed similar orientation of the target compounds at CA II active site compared with reported sulfonamide type CAIs with the thione group acting as a zinc-binding moiety.

Carbonic anhydrase inhibitors: The X-ray crystal structure of the adduct of N-hydroxysulfamide with isozyme II explains why this new zinc binding function is effective in the design of potent inhibitors

N-Hydroxysulfamide is a 2000-fold more potent inhibitor of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1) as compared to sulfamide. It also inhibits other physiologically relevant isoforms, such as the tumor-associated CA IX and XII (K(I)s in the range of 0.865-1.34microM). In order to understand the binding of this inhibitor to the enzyme active site, the X-ray crystal structure of the human hCA II-N-hydroxysulfamide adduct was resolved. The inhibitor coordinates to the active site zinc ion by the ionized primary amino group, participating in an extended network of hydrogen bonds with amino acid residues Thr199, Thr200 and two water molecules. The additional two hydrogen bonds in which N-hydroxysulfamide bound to hCA II is involved as compared to the corresponding adduct of sulfamide may explain its higher affinity for the enzyme, also providing hints for the design of tight-binding CA inhibitors possessing an organic moiety substituting the NH group in the N-hydroxysulfamide structure.

Carbonic anhydrase inhibitors. N-cyanomethylsulfonamides--a new zinc binding group in the design of inhibitors targeting cytosolic and membrane-anchored isoforms

A series of N-cyanomethyl aromatic sulfonamides and bis-sulfonamides was prepared by reaction of arylsulfonyl halides with aminoacetonitrile. The obtained derivatives incorporated various aryl moieties, such as 4-halogeno/alkyl/aryl/nitro-substituted-phenyl, pentafluorophenyl or 2-naphthyl. Moderate inhibitory activity was detected for some compounds against the cytosolic human isoform II of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1), hCA II, with inhibition constants of 90, 180 and 560n M for the 4-nitrophenyl-, 4-iodophenyl- and pentafluorophenyl-N-cyanomethylsulfonamides, respectively. Other derivatives acted as weak inhibitors of isoforms hCA I (KIs of 720 nM-45 microM), hCA II (KIs of 1000-9800 nM) and hCA IX (KIs of 900-10200 nM). Thus, the N-cyanomethylsulfonamide zinc binding group is less effective than the sulfonamide, sulfamate or sulfamide ones for the design of effective CA inhibitors.

Carbonic anhydrase inhibitors. Inhibition of the cytosolic and tumor-associated carbonic anhydrase isozymes I, II, and IX with a series of 1,3,4-thiadiazole- and 1,2,4-triazole-thiols

A series of heterocyclic mercaptans incorporating 1,3,4-thiadiazole- and 1,2,4-triazole rings have been prepared and assayed for the inhibition of three physiologically relevant carbonic anhydrase (CA, EC 4.2.1.1) isozymes, the cytosolic human isozymes I and II, and the transmembrane, tumor-associated hCA IX. Against hCA I the investigated thiols showed inhibition constants in the range of 97 nM to 548 microM, against hCA II in the range of 7.9-618 microM, and against hCA IX in the range of 9.3-772 microM. Thiadiazoles were generally more active than triazoles against all investigated isozymes. Generally, the best inhibitors were the simple derivative 5-amino-1,3,4-thiadiazole-2-thiol and its N-acetylated derivative, which were anyhow at least two orders of magnitude less effective inhibitors when compared to the corresponding sulfonamides, acetazolamide, and its deacetylated derivative. An exception was constituted by 5-(2-pyridylcarboxamido)-1,3,4-thiadiazole-2-thiol, which is the first hCA I-selective inhibitor ever reported, possessing an inhibition constant of 97 nM against isozyme I, and being a 105 times less effective hCA II inhibitor, and 3154 times less effective hCA IX inhibitor. Thus, the thiol moiety may lead to effective CA inhibitors targeting isozyme I, whereas it is a less effective zinc-binding function for the design of CA II and CA IX inhibitors over the sulfonamide group.

Carbonic anhydrase inhibitors: synthesis and inhibition of cytosolic/tumor-associated carbonic anhydrase isozymes I, II, IX, and XII with N-hydroxysulfamides—a new zinc-binding function in the design of inhibitors

A small library of N-hydroxysulfamides was synthesized by an original approach in order to investigate whether this zinc-binding function is efficient for the design of inhibitors targeting the cytosolic (hCA I and II) and transmembrane, tumor-associated (hCA IX and XII) isozymes of carbonic anhydrase (CA, EC 4.2.1.1). The parent derivative, N-hydroxysulfamide was a more potent inhibitor as compared to sulfamide or sulfamic acid against all isozymes, with inhibition constants in the range of 473 nM-4.05 microM. Its substituted n-decyl-, n-dodecyl-, benzyl-, and biphenylmethyl-derivatives were less inhibitory against hCA I (K(I)s in the range of 5.8-8.2 microM) but more inhibitory against hCA II (K(I)s in the range of 50.5-473 nM). The same situation was true for the tumor-associated isozymes, with K(I)s in the range of 353-790 nM against hCA IX and 372-874 nM against hCA XII. Some sulfamides/sulfamates possessing similar substitution patterns have also been investigated for the inhibition of these isozymes, being shown that in some particular cases sulfamides are more efficient inhibitors as compared to the corresponding sulfamates. Potent CA inhibitors targeting the cytosolic or tumor-associated CA isozymes can thus be designed from various classes of sulfonamides, sulfamides, or sulfamates and their derivatives, considering the extensive interactions in which the inhibitor and the enzyme active site are engaged, based on recent X-ray crystallographic data.