Carbonic anhydrase inhibitors: inhibition of isozymes I, II and IV by sulfamide and sulfamic acid derivatives

Chemoselective Reactions of Functionalized Sulfonyl Halides

Chemoselective transformations of functionalized sulfonyl fluorides and chlorides are surveyed comprehensively. It is shown that sulfonyl fluorides provide an excellent selectivity control in their reactions. Thus, numerous conditions are tolerated by the SO2 F group - from amide and ester formation to directed ortho-lithiation and transition-metal-catalyzed cross-couplings. Meanwhile, sulfur (VI) fluoride exchange (SuFEx) is also compatible with numerous functional groups, thus confirming its title of "another click reaction". On the contrary, with a few exceptions, most transformations of functionalized sulfonyl chlorides typically occur at the SO2 Cl moiety.

Cloning, characterization and anion inhibition studies of a new γ-carbonic anhydrase from the Antarctic bacterium Pseudoalteromonas haloplanktis

A new γ-class carbonic anhydrase (CA, EC 4.2.1.1) was cloned, purified and characterized from the Antarctic bacterium Pseudoalteromonas haloplanktis, PhaCAγ. The enzyme has a medium-low catalytic activity for the physiologic reaction of CO2 hydration to bicarbonate and protons, with a kcat of 1.4×10(5)s(-1) and a kcat/Km of 1.9×10(6)M(-1)s(-1). An anion inhibition study of PhaCAγ with inorganic anions and small molecule inhibitors is also reported. Many anions present in sea water, such as chloride, fluoride, sulfate, iodide, but also others such as azide, perchlorate and tetrafluoroborate did not inhibit this enzyme. Pseudohalides such as cyanate, thiocyanate, cyanide, selenocyanide, and also bicarbonate, nitrate, nitrite and many complex inorganic anions showed inhibition in the millimolar range (KI in the range of 1.7-9.3mM). The best PhaCAγ inhibitors detected in this study were diethyldithiocarbamate (KI of 0.96 mM) as well as sulfamide, sulfamate, phenylboronic acid and phenylarsonic acid (KI in the range of 82-91 μM). Since γ-CAs are poorly understood at this moment, being present in carboxysomes and thus involved in photosynthesis, this study may be relevant for a better understanding of these processes in Antarctic bacteria/cyanobacteria.

Hydrophobic substituents of the phenylmethylsulfamide moiety can be used for the development of new selective carbonic anhydrase inhibitors

A new series of compounds containing a sulfamide moiety as zinc-binding group (ZBG) has been synthesized and tested for determining inhibitory properties against four human carbonic anhydrase (hCA) isoforms, namely, CAs I, II, IX, and XII. The X-ray structure of the cytosolic dominant isoform hCA II in complex with the best inhibitor of the series has also been determined providing further insights into sulfamide binding mechanism and confirming that such zinc-binding group, if opportunely derivatized, can be usefully exploited for obtaining new potent and selective CAIs. The analysis of the structure also suggests that for drug design purposes the but-2-yn-1-yloxy moiety tail emerges as a very interesting substituent of the phenylmethylsulfamide moiety due to its capability to establish strong van der Waals interactions with a hydrophobic cleft on the hCA II surface, delimited by residues Phe131, Val135, Pro202, and Leu204. Indeed, the complementarity of this tail with the cleft suggests that different substituents could be used to discriminate between isoforms having clefts with different sizes.

Removal of nitrite with sulfamic acid for nitrate N and O isotope analysis with the denitrifier method

In environmental water samples that contain both nitrate (NO3-) and nitrite (NO2-), isotopic analysis of nitrate alone by all currently available methods requires pretreatment to remove nitrite. Sulfamic acid addition, used previously for this purpose (Wu JP, Calvert SE, Wong CS. Deep-Sea Research Part I - Oceanographic Research Papers 1997; 44: 287), is shown here to be compatible with the denitrifier method for both N and O isotope analysis of nitrate. Sulfamic acid at a pH of approximately 1.7 reduces nitrite to N2. Samples are then neutralized with base prior to isotope analysis, to alleviate the buffering demands of the bacterial media and as a precaution to prevent modification of nitrate during storage with the residual sulfamic acid at low pH. Under appropriate reaction conditions, nitrite is completely removed within minutes. Sulfamic acid treatment does not compromise the completeness of the conversion of nitrate into N2O or the precision and accuracy of N and O isotope measurements by the denitrifier method. Nitrite concentrations upwards of 7 times the ambient nitrate can be removed without affecting the isotope composition of nitrate. The method is applied to analyses of the coupled N and O isotopes of nitrate and nitrite in waters of the Mexican Margin, to illustrate its efficacy and utility when employed either in the field upon sample collection or in the lab after months of frozen sample storage.

Therapeutic potential of sulfamides as enzyme inhibitors

Sulfamide, a quite simple molecule incorporating the sulfonamide functionality, widely used by medicinal chemists for the design of a host of biologically active derivatives with pharmacological applications, may give rise to at least five types of derivatives, by substituting one to four hydrogen atoms present in it, which show specific biological activities. Recently, some of these compounds started to be exploited for the design of many types of therapeutic agents. Among the enzymes for which sulfamide-based inhibitors were designed, are the carbonic anhydrases (CAs), a large number of proteases belonging to the aspartic protease (HIV-1 protease, gamma-secretase), serine protease (elastase, chymase, tryptase, and thrombin among others), and metalloprotease (carboxypeptidase A (CPA) and matrix metalloproteinases (MMP)) families. Some steroid sulfatase (STS) and protein tyrosine phosphatase inhibitors belonging to the sulfamide class of derivatives have also been reported. In all these compounds, many of which show low nanomolar affinity for the target enzymes for which they have been designed, the free or substituted sulfamide moiety plays important roles for the binding of the inhibitor to the active site cavity, either by directly coordinating to a metal ion found in some metalloenzymes (CAs, CPA, STS), usually by means of one of the nitrogen atoms present in the sulfamide motif, or as in the case of the cyclic sulfamides acting as HIV protease inhibitors, interacting with the catalytically critical aspartic acid residues of the active site by means of an oxygen atom belonging to the HN-SO2-NH motif, which substitutes a catalytically essential water molecule. In other cases, the sulfamide moiety is important for inducing desired physico-chemical properties to the drug-like compounds incorporating it, such as enhanced water solubility, better bioavailability, etc., because of the intrinsic properties of this highly polarized moiety when attached to an organic scaffold. This interesting motif is thus of great value for the design of pharmacological agents with a lot of applications.

Integrated approach using protein and ligand information to analyze selectivity- and affinity-determining features of carbonic anhydrase isozymes

The application and comparison of selected protein- and ligand-based approaches to elucidate factors important for affinity and selectivity towards the carbonic anhydrase isozymes I, II, and IV are described. Carbonic anhydrases are abundant in pro- and eukaryotes. These enzymes catalyze the reversible hydration of carbon dioxide to bicarbonate and H(+) ions and are thus involved in many important physiological and pathophysiological processes. Due to the fact that the human carbonic anhydrase family consists of 16 closely related isozymes, the design of selective inhibitors is a special challenge for medicinal chemists. In order to extract selectivity-determining features, we applied purely ligand-based 3D QSAR techniques as well as qualitative comparative molecular field analyses of the targets' binding sites using consensus principal component analysis (CPCA). The dataset for the QSAR studies was deliberately compiled from 1,748 inhibitors and comprises about 140 ligands, mainly of the sulfonamide type. Additionally, we employed the novel AFMoC approach, which intrinsically combines protein and ligand information. The simultaneous use of these different techniques gives deeper insight into selectivity and affinity-determining features and provides quantitative models for prediction.

Carbonic anhydrase inhibitors. Inhibition of Plasmodium falciparum carbonic anhydrase with aromatic sulfonamides: towards antimalarials with a novel mechanism of action?

The malarial parasite Plasmodium falciparum encodes for an alpha-carbonic anhydrase (CA) enzyme possessing catalytic properties distinct of that of the human host, which was only recently purified. A series of aromatic sulfonamides, most of which were Schiff's bases derived from sulfanilamide/homosulfanilamide/4-aminoethylbenzenesulfonamide and substituted-aromatic aldehydes, or ureido-substituted such sulfonamides, were investigated for in vitro inhibition of the malarial parasite enzyme (pfCA) and the growth of P. falciparum. Several inhibitors with affinity in the micromolar range (K(I)'s in the range of 0.080-1.230 microM) were detected, whereas the most potent such derivatives were the clinically used sulfonamide CA inhibitor acetazolamide, and 4-(3,4-dichlorophenyl-ureidoethyl)-benzenesulfonamide, which showed an inhibition constant of 80 nM against pfCA, being four times more effective an inhibitor as compared to acetazolamide (K(I) of 315 nM). The lipophilic 4-(3,4-dichlorophenylureido-ethyl)-benzenesulfonamide was also an effective in vitro inhibitor for the growth of P. falciparum (IC50 of 2 microM), whereas acetazolamide achieved the same level of inhibition at 20 microM. This is the first study proving that antimalarials possessing a novel mechanism of action can be obtained, by inhibiting a critical enzyme for the life cycle of the parasite. Indeed, by inhibiting pfCA, the synthesis of pyrimidines mediated by carbamoylphosphate synthase is impaired in P. falciparum but not in the human host. Sulfonamide CA inhibitors have the potential for the development of novel antimalarial drugs.

Carbonic anhydrases: current state of the art, therapeutic applications and future prospects

Carbonic anhydrases (CAs, EC 4.2.1.1) are wide-spread enzymes, present in mammals in at least 14 different isoforms. Some of these isozymes are cytosolic (CA I, CA II, CA III, CA VII, CA XIII), others are membrane-bound (CA IV, CA IX, CA XII and CA XIV), CA V is mitochondrial and CA VI is secreted in the saliva and milk. Three cytosolic acatalytic forms are also known (CARP VIII, CARP X and CARP XI). The catalytically active isoforms, which play important physiological and patho-physiological functions, are strongly inhibited by aromatic and heterocyclic sulfonamides. The catalytic and inhibition mechanisms of these enzymes are understood in great detail, and this greatly helped the design of potent inhibitors, some of which possess important clinical applications. The use of such CA inhibitors (CAIs) as antiglaucoma drugs are discussed in detail, together with the recent developments that led to isozyme-specific and organ-selective inhibitors. A recent discovery is connected with the involvement of CAs and their sulfonamide inhibitors in cancer: many potent CAIs were shown to inhibit the growth of several tumor cell lines in vitro and in vivo, thus constituting interesting leads for developing novel antitumor therapies. Future prospects for drug design of inhibitors of these ubiquitous enzymes are dealt with. Although activation of CAs has been a controversial issue for some time, recent kinetic, spectroscopic and X-ray crystallographic experiments offered an explanation of this phenomenon, based on the catalytic mechanism. It has been demonstrated recently, that molecules that act as carbonic anhydrase activators (CAAs) bind at the entrance of the enzyme active site participating in facilitated proton transfer processes between the active site and the reaction medium. In addition to CA II-activator adducts, X-ray crystallographic studies have been also reported for ternary complexes of this isozyme with activators and anion (azide) inhibitors. Structure-activity correlations for diverse classes of activators is discussed for the isozymes for which the phenomenon has been studied, i.e., CA I, II, III and IV. The possible physiological relevance of CA activation/inhibition is also addressed, together with recent pharmacological/ biomedical applications of such compounds in different fields of life sciences.

Carbonic anhydrase inhibitors

At least 14 different carbonic anhydrase (CA, EC 4.2.1.1) isoforms were isolated in higher vertebrates, where these zinc enzymes play crucial physiological roles. Some of these isozymes are cytosolic (CA I, CA II, CA III, CA VII), others are membrane-bound (CA IV, CA IX, CA XII, and CA XIV), CA V is mitochondrial and CA VI is secreted in saliva. Three acatalytic forms are also known, which are denominated CA related proteins (CARP), CARP VIII, CARP X, and CARP XI. Several important physiological and physio-pathological functions are played by many CA isozymes, which are strongly inhibited by aromatic and heterocyclic sulfonamides as well as inorganic, metal complexing anions. The catalytic and inhibition mechanisms of these enzymes are understood in detail, and this helped the design of potent inhibitors, some of which possess important clinical applications. The use of such enzyme inhibitors as antiglaucoma drugs will be discussed in detail, together with the recent developments that led to isozyme-specific and organ-selective inhibitors. A recent discovery is connected with the involvement of CAs and their sulfonamide inhibitors in cancer: several potent sulfonamide inhibitors inhibited the growth of a multitude of tumor cells in vitro and in vivo, thus constituting interesting leads for developing novel antitumor therapies. Furthermore, some other classes of compounds that interact with CAs have recently been discovered, some of which possess modified sulfonamide or hydroxamate moieties. Some sulfonamides have also applications as diagnostic tools, in PET and MRI or as antiepileptics or for the treatment of other neurological disorders. Future prospects for drug design applications for inhibitors of these ubiquitous enzymes are also discussed.