Thienothiopyran-2-sulfonamides: a novel class of water-soluble carbonic anhydrase inhibitors

A Simple Representation of Three-Dimensional Molecular Structure

Statistical and machine learning approaches predict drug-to-target relationships from 2D small-molecule topology patterns. One might expect 3D information to improve these calculations. Here we apply the logic of the extended connectivity fingerprint (ECFP) to develop a rapid, alignment-invariant 3D representation of molecular conformers, the extended three-dimensional fingerprint (E3FP). By integrating E3FP with the similarity ensemble approach (SEA), we achieve higher precision-recall performance relative to SEA with ECFP on ChEMBL20 and equivalent receiver operating characteristic performance. We identify classes of molecules for which E3FP is a better predictor of similarity in bioactivity than is ECFP. Finally, we report novel drug-to-target binding predictions inaccessible by 2D fingerprints and confirm three of them experimentally with ligand efficiencies from 0.442-0.637 kcal/mol/heavy atom.

Thioether benzenesulfonamide inhibitors of carbonic anhydrases II and IV: structure-based drug design, synthesis, and biological evaluation

A novel series of potent thioether benzenesulfonamide inhibitors of carbonic anhydrases II and IV was discovered using structure-based drug design. Synthesis, structure-activity relationship, and optimization of physicochemical properties are described. Low nanomolar potency was achieved, and selected compounds with improved thermodynamic solubility showed promising in vitro inhibition of carbonic anhydrase activity in rabbit iris ciliary body homogenate.

Molecular design for enhancement of ocular penetration

Over the past two decades, many oral drugs have been designed in consideration of physicochemical properties to attain optimal pharmacokinetic properties. This strategy significantly reduced attrition in drug development owing to inadequate pharmacokinetics during the last decade. On the other hand, most ophthalmic drugs are generated from reformulation of other therapeutic dosage forms. Therefore, the modification of formulations has been used mainly as the approach to improve ocular pharmacokinetics. However, to maximize ocular pharmacokinetic properties, a specific molecular design for ocular drug is preferable. Passive diffusion of drugs across the cornea membranes requires appropriate lipophilicity and aqueous solubility. Improvement of such physicochemical properties has been achieved by structure optimization or prodrug approaches. This review discusses the current knowledge about ophthalmic drugs adapted from systemic drugs and molecular design for ocular drugs. I propose the approaches for molecular design to obtain the optimal ocular penetration into anterior segment based on published studies to date.

Theoretical study of gas-phase acidity, pKa, lipophilicity, and solubility of some biologically active sulfonamides

The geometries of 19 biologically active substituted sulfonamides (including clinically useful acetazolamide, methazolamide, ethoxzolamide, dichlorophenamide, dorzolamide, and brinzolamide) in both neutral and deprotonated forms, were optimized using Becke3LYP/6-311+G(d,p) method (compounds 1-6) and two-layered ONIOM (B3LYP 6-311+G(d,p): MNDO) method (compounds 7-19). The investigated sulfonamides are weak acids with calculated acidity of about 1320-1420 kJ mol(-1). Of acids studied the highest gas-phase acidity (1324 kJ mol(-1)) possesses methazolamide. This drug is, according to the computed pKa value (5.9), also in water solution the most acidic compound of the sulfonamides investigated. The computed pKa values varied between 5.9 and 12.6 and correlate well with the available experimental pKa's found in the literature. Cancerostatic aromatic sulfonamides 16-19 are generally weak acids with the acidity comparable or slightly lower than the lead sulfanilamide. The available experimental partition coefficients of sulfonamides investigated are best reproduced by the IA LOGP method. Computed partition coefficients for antiglaucoma sulfonamides 1-13 varied between -0.47 and 2.61 (IA LOGP). Thus these compounds are only slightly or moderate lipophilic. The lipophilicity of the cancerostatic sulfonamides 14-18 is from relatively narrow interval between -0.07 and 1.68 (IA LOGP). The most potent CAI 10-13 are also the most lipophilic compounds among the antiglaucomatics studied. The available experimental solubilities are best reproduced by the IA LOGS method. The computed solubilities qualitatively correlate with the corresponding lipophilicities, logS increasing as logP declines. The analysis of molecular descriptors defined by Lipinski have been shown that all of the sulfonamides studied obey 'Rule of 5'. Therefore, in the early stages of the design of antiglaucoma sulfonamides, it is becoming more important to determine the pKa, lipophilicity, water solubility, and other physicochemical properties associated with a drug, before synthetic work is undertaken, with the aim of avoiding the synthesis of compounds that are predicted to have poor biopharmaceutical characteristics.

Quantitative structure-activity relationships of carbonic anhydrase inhibitors

A review is presented of quantitative structure-activity relationships (QSARs) of different categories of carbonic anhydrase (CA) inhibitors, which are basically benzenesulfonamides, heterocyclic sulfonamides and aliphatic sulfonamides. The review shows that in all categories, the inhibition potency depends largely on the electronic properties of the sulfonamide group, which can be affected by the electronic characteristics of the substituents present on the nucleus (benzene or heterocyclic ring) of the sulfonamide molecules. Substituents themselves can be involved, along with the nucleus, in some dispersion interaction with the enzyme. Based on this review, a schematic model is presented to represent the interaction of sulfonamides with the CA.

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.

Phototriggered delivery of hydrophobic carbonic anhydrase inhibitors

We have developed a versatile tool for the delivery of inhibitors of carbonic anhydrase II, which allows modification of a hydrophobic drug with either a water-solubilizing, photolabile cage or a hydrophobic, photolabile cage. The former mask is useful for direct delivery of hydrophobic molecules in an aqueous prodrug form. The latter may find application if delivery from a surface is desirable. In our system, where the target enzyme is found in the eye, both approaches may be useful for the delivery of hydrophobic drugs having subnanomolar dissociation constants from the enzyme.

Successful virtual screening for novel inhibitors of human carbonic anhydrase: strategy and experimental confirmation

Virtual screening of compound libraries is an alternative and complementary approach to high-throughput screening in the lead discovery process. A new strategy is described to search for possible leads of human carbonic anhydrase II, applying a protocol of several consecutive hierarchical filters involving a preselection based on functional group requirements and fast pharmacophore matching. A suitable pharmacophore is derived by a sophisticated "hot spot" analysis of the binding site to detect regions favorable for protein-ligand interactions. In subsequent steps, molecular similarity with known reference ligands is used to rerank the hits from the pharmacophore matching. Finally the best scored candidates are docked flexibly into the protein binding pocket. After examination of the affinity predictions, 13 compounds were selected for experimental testing. Of these 13, three could be shown to be subnanomolar, one is nanomolar, while a further seven are micromolar inhibitors. The binding mode of two hits could be confirmed by crystal structure analysis. The novelty of the discovered leads is best supported by the fact that a search in the patent literature showed the newly discovered subnanomolar compounds to comprise scaffolds not yet covered by existing patents.

Cleavage of beta-lactone ring by serine protease. Mechanistic implications

Both enantiomers of 3-benzyl-2-oxetanone (1) were found to be slowly hydrolyzed substrates of alpha-chymotrypsin having k(cat) values of 0.134+/-0.008 and 0.105+/-0.004 min(-1) for (R)-1 and (S)-1, respectively, revealing that alpha-CT is virtually unable to differentiate the enantiomers in the hydrolysis of 1. The initial step to form the acyl-enzyme intermediate by the attack of Ser-195 hydroxyl on the beta-lactone ring at the 2-position in the hydrolysis reaction may not be enzymatically driven, but the relief of high ring strain energy of beta-lactone may constitute a major driving force. The deacylation step is also attenuated, which is possibly due to the hydrogen bond that would be formed between the imidazole nitrogen of His-57 and the hydroxyl group generated during the acylation in the case of (R)-1, but in the alpha-CT catalyzed hydrolysis of (S)-1 the imidazole nitrogen may form a hydrogen bond with the ester carbonyl oxygen.

Carbonic anhydrase inhibitors: perfluoroalkyl/aryl-substituted derivatives of aromatic/heterocyclic sulfonamides as topical intraocular pressure-lowering agents with prolonged duration of action

Reaction of perfluoroalkyl/arylsulfonyl chlorides or perfluoroalkyl/arylcarbonyl chlorides with aromatic/heterocyclic sulfonamides possessing a free amino/imino/hydrazino/hydroxy group afforded compounds with the general formula C(x)()F(y)()Z-A-SO(2)NH(2), where Z = SO(2)NH, SO(3), CONH, or CO(2) and A = aromatic/heterocyclic moiety. The sulfonyl chlorides used in synthesis included: CF(3)SO(2)Cl, n-C(4)F(9)SO(2)Cl, n-C(8)F(17)SO(2)Cl, and C(6)F(5)SO(2)Cl, whereas the acyl chlorides were C(8)F(17)COCl and C(6)F(5)COCl. A total of 25 different sulfonamides have been derivatized by means of the above-mentioned perfluorosulfonyl/acyl halides. These new series of sulfonamides showed strong affinities toward isozymes I, II, and IV of carbonic anhydrase (CA). For a given sulfonamide derivatized by the above procedures, inhibitory power was greater for the alkyl/arylsulfonylated compounds, as compared to the corresponding perfluoroalkyl/arylcarbonylated ones. In vitro inhibitory activity generally increased with the number of carbon atoms in the molecule of the acylating/sulfonylating agent, with a maximum for the perfluorophenylsulfonylated and perfluorobenzoylated derivatives. Some of the prepared CA inhibitors displayed very good water solubility (in the range of 2%) and strongly lowered intraocular pressure (IOP) when applied topically, directly into the normotensive/glaucomatous rabbit eye, as 2% water solutions. The good water solubility of these new classes of CA inhibitors, correlated with the neutral pH of their solutions used in the ophthalmologic applications, makes them attractive candidates for developing novel types of antiglaucoma drugs devoid of unpleasant ocular side effects.

2H-Thieno[3,2-e]- and [2,3-e]-1,2-thiazine-6-sulfonamide 1,1-dioxides as ocular hypotensive agents: synthesis, carbonic anhydrase inhibition and evaluation in the rabbit

Novel non-chiral 2H-thieno[3,2-e]- and [2,3-e]-1,2-thiazine-6-sulfonamide 1,1-dioxides were synthesized for evaluation as potential candidates for the treatment of glaucoma. All of the compounds prepared were potent high affinity inhibitors of human carbonic anhydrase II, Ki < 0.5 nM. Additionally, inhibition of recombinant human carbonic anhydrase IV was determined for selected compounds; these were shown to be moderate to potent inhibitors of this isozyme with IC50 values ranging from 4.25 to 73.6 nM. Of the compounds evaluated for their ability to lower intraocular pressure in naturally hypertensive Dutch-belted rabbits, 5a, 17a3, 17b1, 17b2, 17h2 and 17i1 showed significant efficacy (> 20% decrease) in this model following topical ocular administration.

Carbonic anhydrase inhibitors: topical sulfonamide antiglaucoma agents incorporating secondary amine moieties

Reaction of aromatic/heterocyclic sulfonamides possessing free amino, imino or hydrazino moieties with 7-chloro-4-chloromethylcoumarin afforded a series of N-[(7-chloro-4-coumarinyl)-methyl]- derivatives which showed effective inhibition of three carbonic anhydrase (CA) isozymes. Topical application within the rabbit eye of some of these compounds led to effective intraocular pressure lowering due to CA inhibition within the ocular tissues, and reduced aqueous humor production.

Carbonic anhydrase inhibitors - part 78(#). Synthesis of water-soluble sulfonamides incorporating beta-alanyl moieties, possessing long lasting-intraocular pressure lowering properties via the topical route

Reaction of 26 aromatic/heterocyclic sulfonamides containing amino, imino, hydrazino or hydroxyl groups with N-tert-butyloxycarbonyl-beta-alanine (Boc-beta-ala; Boc = t-butoxycarbonyl) in the presence of carbodiimide derivatives afforded, after removal of the protecting group, a series of water-soluble compounds (as salts of strong acids, such as hydrochloric, trifluoroacetic or trifluoromethane sulfonic). The new derivatives were assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA), and more precisely of three of its isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form), involved in important physiological processes. Good inhibition was observed against all three isozymes, but especially against CA II and CA IV (in the nanomolar range), the two isozymes known to play a critical role in aqueous humour secretion within the ciliary processes of the eye. Some of the best inhibitors synthesized were applied as 2% aqueous solutions into the eyes of normotensive or glaucomatous albino rabbits, when strong and long-lasting intraocular pressure (IOP) lowering was observed with many of them. Thus, the amino acyl groups conferring water solubility to these sulfonamide CA inhibitors, coupled with their strong enzyme inhibitory properties and balanced lipid solubility seem to be the key factors for obtaining compounds with effective topical antiglaucoma activity.

Carbonic anhydrase inhibitors. Part 79. Synthesis of topically acting sulfonamides incorporating GABA moieties in their molecule, with long-lasting intraocular pressure-lowering properties

Reaction of 26 aromatic/heterocyclic sulfonamides containing amino, imino, hydrazino or hydroxyl groups with N-tert-butoxycarbonyl-gamma-aminobutyric acid (Boc-GABA; Boc=t-butoxycarbonyl) in the presence of carbodiimide derivatives, afforded after removal of the protecting group, a series of water-soluble compounds (as salts of strong acids, such as hydrochloric, trifluoroacetic or trifluoromethane sulfonic). The new derivatives were assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA), and more precisely of three of its isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form), involved in important physiological processes. Some of the new compounds effectively inhibited CA II and CA IV (in the nanomolar range), the two isozymes known to play a critical role in aqueous humor secretion within the ciliary processes of the eye. Some of the best inhibitors obtained as described above were applied as 2% water solutions into the eye of normotensive or glaucomatous albino rabbits, when strong and long-lasting intraocular pressure (IOP) lowering has been evidenced. Thus, the amino acyl tail conferring water solubility to these sulfonamides, coupled with their strong enzyme inhibitory properties and balanced lipid solubility seem to be the key factors for obtaining compounds with effective topical antiglaucoma activity from the class of the carbonic anhydrase inhibitors.

Carbonic anhydrase inhibitors: synthesis of water-soluble, topically effective intraocular pressure lowering aromatic/heterocyclic sulfonamides containing 8-quinoline-sulfonyl moieties: is the tail more important than the ring?

Reaction of 20 aromatic/heterocyclic sulfonamides containing a free amino, imino, hydrazino or hydroxyl group, with 8-quinoline-sulfonyl chloride afforded a series of water-soluble (as hydrochloride or triflate salts) compounds. The new derivatives were assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA), and more precisely of three of its isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form), involved in important physiological processes. Efficient inhibition was observed against all three isozymes, but especially against CA II (in nanomolar range), which is the isozyme known to play a critical role in aqueous humor secretion within the ciliary processes of the eye. Some of the best inhibitors synthesized were topically applied as 2% water solutions onto the eye of normotensive and glaucomatous albino rabbits, when strong and long-lasting intraocular pressure (IOP) lowering was observed with many of them. This result prompted us to reanalyze the synthetic work done by other groups for the design of water soluble, topically effective antiglaucoma sulfonamides. According to these researchers, the IOP lowering effect is due to the intrinsic nature of the specific heterocyclic sulfonamide considered, among which the thienothiopyran-2-sulfonamide derivatives represent the best studied case. Indeed, the first agents developed for such applications, such as dorzolamide, are derivatives of this ring system. In order to prove that the tail (in this case the 8-quinoline-sulfonyl moiety) conferring water solubility to a sulfonamide CA inhibitor is more important than the ring to which the sulfonamido group is grafted, we also prepared a dorzolamide derivative to which the 8-quinoline-sulfonyl moiety was attached. This new compound is quite water soluble as hydrochloride salt, behaves as a strong CA II inhibitor, and fared better than the parent molecule in lowering IOP in experimental animals. Thus, the tail conferring water solubility to such an enzyme inhibitor is more important for its topical activity as antiglaucoma drug than the heterocyclic/aromatic ring to which the sulfonamido moiety is grafted.

Carbonic anhydrase inhibitors. Water-soluble, topically effective intraocular pressure lowering agents derived from isonicotinic acid and aromatic/heterocyclic sulfonamides: is the tail more important than the ring?

Reaction of twenty aromatic/heterocyclic sulfonamides containing a free amino, imino, hydrazino or hydroxyl group, with isonicotinoyl chloride afforded a series of water-soluble compounds (as hydrochloride or triflate salts). The new derivatives were examined as inhibitors of three carbonic anhydrase (CA) isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form). Efficient inhibition was observed against all three isozymes, but especially against CA II and CA IV (K(I) in the nanomolar range), the two isozymes known to play a critical role in aqueous humor secretion within the ciliary processes of the eye. Some of the most potent inhibitors synthesized were applied as 2% water solutions directly into the eye of normotensive or glaucomatous albino rabbits. Very strong intraocular pressure (IOP) lowering was observed for many of them, and the active drug was detected in eye tissues and fluids. According to others the IOP lowering effect of topically effective antiglaucoma sulfonamides is due to the intrinsic nature of the specific heterocyclic sulfonamide considered, among which the thienothiopyran-2-sulfonamide derivatives represent the best studied case e.g. dorzolamide. In order to prove that the tail (in this case the isonicotinoyl moiety) conferring water solubility to a sulfonamide CA inhibitor is more important than the ring to which the sulfonamido group is grafted a dorzolamide derivative to which the isonicotinoyl moiety was attached was also prepared. This new compound is more water soluble than dorzolamide (as hydrochloride salt), behaves as a strong CA II inhibitor and acts similarly to the parent derivative in lowering IOP in experimental animals. Thus, it seems that the tail conferring water solubility is more important for topical activity as an antiglaucoma drug than the heterocyclic/aromatic ring to which the sulfonamido moiety is attached.

Carbonic anhydrase inhibitors: synthesis of water-soluble, aminoacyl/dipeptidyl sulfonamides possessing long-lasting intraocular pressure-lowering properties via the topical route

Reaction of 26 aromatic/heterocyclic sulfonamides containing amino, imino, hydrazino, or hydroxyl groups with Boc-Gly, Boc-Sar, TrS-Crt, or Boc-Gly-Gly (Sar = sarcosine, N-Me-Gly; Crt = creatine, N-amidinosarcosine; TrS = tritylsulfenyl; Boc = tert-butoxycarbonyl) in the presence of carbodiimide derivatives afforded after removal of the protecting groups a series of water-soluble compounds (as salts of strong acids, such as hydrochloric, trifluoroacetic, or trifluoromethanesulfonic). The new derivatives were assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA) and more precisely of three of its isozymes, CA I, II (cytosolic forms), and IV (membrane-bound form), involved in important physiological processes. Efficient inhibition was observed against all three isozymes and especially against CA II and IV (in the nanomolar range), the two isozymes known to play a critical role in aqueous humor secretion within the ciliary processes of the eye. Some of the best inhibitors synthesized were applied as 2% water solutions into the eye of normotensive or glaucomatous albino rabbits, when strong and long-lasting intraocular pressure (IOP) lowering was observed with many of them. Thus, the aminoacyl/dipeptidyl tail conferring water solubility to these sulfonamide CA inhibitors coupled with strong enzyme inhibitory properties and balanced lipid solubility seem to be the key factors for obtaining compounds with effective topical antiglaucoma activity.

Carbonic anhydrase inhibitors. Part 71. Synthesis and ocular pharmacology of a new class of water-soluble, topically effective intraocular pressure lowering sulfonamides incorporating picolinoyl moieties

Reaction of 20 aromatic/heterocyclic sulfonamides containing a free amino, imino, hydrazino or hydroxyl group, with picolinic acid in the presence of carbodiimide derivatives afforded a series of water-soluble (as hydrochloride or triflate salts) compounds. The new derivatives were assayed as inhibitors of three carbonic anhydrase (CA) isozymes, CA I, II (cytosolic forms) and IV (membrane-bound form). Efficient inhibition was observed against all three isozymes, but especially against CA II and CA IV (in nanomolar range), the two isozymes known to play a critical role in aqueous humor secretion within the ciliary processes of the eye. Some of the best inhibitors synthesized were applied as 2% water solutions directly into the eye of normotensive or glaucomatous albino rabbits. Very strong intraocular pressure (IOP) lowering was observed for many of them, and the active drug was detected in eye tissues and fluids. This result prompted us to reanalyze the synthetic work done by other groups for the design of water soluble, topically effective antiglaucoma sulfonamides. According to these researchers, the IOP lowering effect is due to the intrinsic nature of the specific heterocyclic sulfonamide considered, among which the thienothiopyran-2-sulfonamide derivatives represent the best studied case. Indeed, the first agents developed for such applications, such as dorzolamide, are derivatives of this ring system. In order to prove that the tail (in this case the picolinoyl moiety) conferring water solubility to a sulfonamide CA inhibitor is critically important for its topical effectiveness, similarly to the ring to which the sulfonamido group is grafted, we also prepared a dorzolamide derivative to which the picolinoyl moiety was attached. This new compound is more water soluble than dorzolamide (as hydrochloride salt), behaves as a strong CA II inhibitor, and acts similarly to the parent derivative in lowering IOP in experimental animals. Thus, it seems that the tail conferring water solubility is more important for topical activity as antiglaucoma drug, than the heterocyclic/aromatic ring to which the sulfonamido moiety is grafted.

A caged hydrophobic inhibitor of carbonic anhydrase II

[formula: see text] A tight-binding, hydrophobic inhibitor of carbonic anhydrase II has been masked with a water-solubilizing, photolabile group derived from o-nitrophenylglycine. This caged inhibitor represents our first effort at the site-specific delivery of prodrugs that can be activated by light. Via this approach, we have begun to address the problems of water insolubility and systemic side effects on administration of tight-binding inhibitors of carbonic anhydrase.

Carbonic anhydrase inhibitors. Synthesis of water-soluble, topically effective, intraocular pressure-lowering aromatic/heterocyclic sulfonamides containing cationic or anionic moieties: is the tail more important than the ring?

Reaction of several aromatic/heterocyclic sulfonamides containing a free amino, imino, hydrazino, or hydroxyl group, with 2, 3-pyridinedicarboxylic anhydride or 2,6-pyridinedicarboxylic acid in the presence of carbodiimide derivatives, afforded two series of water-soluble (as hydrochloride, triflate, or carboxylate salts) compounds. The new derivatives were assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA) and more precisely of three of its isozymes, CA I, II (cytosolic forms), and IV (membrane-bound form), involved in important physiological processes. Efficient inhibition was observed against all three isozymes, but especially against CA II and IV (in nanomolar range), the two isozymes known to play a critical role in aqueous humor secretion within the ciliary processes of the eye. Some of the best inhibitors synthesized were applied as 2% water solutions directly into the eye of normotensive and glaucomatous albino rabbits. Very strong and long-lasting intraocular pressure (IOP) lowering was observed with many of them. This result prompted us to reanalyze the synthetic work done by other groups for the design of water-soluble, topically effective antiglaucoma sulfonamides. According to these researchers, the IOP-lowering effect is due to the intrinsic nature of the specific heterocyclic sulfonamide considered, among which the thienothiopyran-2-sulfonamide derivatives represent the best-studied case. Indeed, the first agents developed for topical application, such as dorzolamide, are derivatives of this ring system. To prove that the tail (in this case the pyridinecarboxylic moieties) conferring water solubility to a sulfonamide CA inhibitor is more important than the ring to which the sulfonamido group is grafted, we also prepared dorzolamide derivatives incorporating such moieties. These new compounds possess good water solubility as hydrochloride or carboxylate salts, balanced by a relatively modest lipid solubility. They are strong CA II inhibitors and are able to lower IOP in experimental animals more than the parent derivatives. Our conclusion is that the tail conferring water solubility to such an enzyme inhibitor is more important for topical activity as an antiglaucoma drug, than the heterocyclic/aromatic ring to which the sulfonamido moiety is grafted.

Structural analysis of inhibitor binding to human carbonic anhydrase II

X-ray crystal structures of carbonic anhydrase II (CAII) complexed with sulfonamide inhibitors illuminate the structural determinants of high affinity binding in the nanomolar regime. The primary binding interaction is the coordination of a primary sulfonamide group to the active site zinc ion. Secondary interactions fine-tune tight binding in regions of the active site cavity >5 A away from zinc, and this work highlights three such features: (1) advantageous conformational restraints of a bicyclic thienothiazene-6-sulfonamide-1,1-dioxide inhibitor skeleton in comparison with a monocyclic 2,5-thiophenedisulfonamide skeleton; (2) optimal substituents attached to a secondary sulfonamide group targeted to interact with hydrophobic patches defined by Phe131, Leu198, and Pro202; and (3) optimal stereochemistry and configuration at the C-4 position of bicyclic thienothiazene-6-sulfonamides; the C-4 substituent can interact with His64, the catalytic proton shuttle. Structure-activity relationships rationalize affinity trends observed during the development of brinzolamide (Azopt), the newest carbonic anhydrase inhibitor approved for the treatment of glaucoma.

The discovery and structure-activity relationships of nonpeptide, low molecular weight antagonists selective for the endothelin ET(B) receptor

The systematic modification of the ETA selective N-(5-isoxazolyl)benzene-sulfonamide endothelin antagonists to give ETB selective antagonists is reported. The reversal in selectivity was brought about by substitution of the 4-position with aryl and substituted aryl groups. Of all the aromatic substituents studied, the para-tolyl group gave rise to the most active and selective ETB antagonist. Larger substituents caused a decrease in both ETB activity and selectivity. A similar trend was observed by substitution at the 5-position of the N-(5-isoxazolyl)-2-thiophenesulfonamide ETA receptor antagonists. The para-tolyl group was again found to be optimal for the ETB activity and selectivity. The structural features that were found to be favorable for binding to the ETB receptor, that is, the presence of a linear, conjugated pi-system of definite shape and size, have been successfully incorporated into the design of ETB selective polycyclic aromatic sulfonamides antagonists.

Dorzolamide: development and clinical application of a topical carbonic anhydrase inhibitor

Systemic carbonic anhydrase inhibitors are among the most powerful agents to lower intraocular pressure. Unfortunately, their use is frequently accompanied by undesired side effects. Some are due to the relatively large amounts of drug that have to be systemically administered to inhibit the carbonic anhydrase in the ciliary processes. Recently, dorzolamide, a topical carbonic anhydrase inhibitor, has become commercially available for clinical use. This article reviews the development of topical carbonic anhydrase inhibitors with special reference to dorzolamide. When administered three-times daily, dorzolamide lowers intraocular pressure in a clinically useful manner. Ocular side-effects include frequent stinging and burning and allergy can develop. Systemic side effects have not been observed that could definitively be related to inhibition of extraocular carbonic anhydrase. Blood dyscrasias have not yet been observed. Absence of cardiovascular and pulmonary side effects, as can occur with beta adrenergic antagonists, and lack of pupillary and accommodative stimulation, as occur with cholinergic agonists, might make dorzolamide first-line medical treatment for elevated intraocular pressure.

Penetration into the anterior chamber via the conjunctival/scleral pathway

The importance of the conjunctival/scleral pathway as a route of entry into the ciliary body, and in particular uptake and deposition by vessels, was investigated. A constant concentration of methazolamide analogs as well as 6-carboxyfluorescein (6-CB) and rhodamine B (RB) was maintained on either the cornea or the conjunctiva/sclera tissue, the latter excluding the cornea. The solutions were applied with the use of a cylindrical well affixed to the cornea of an anesthetized white rabbit. After two hours, concentrations of drug or dye were measured in cornea, aqueous humor or iris/ciliary body for both routes of entry. Confocal microscopy methods were used to determine reflected fluorescence images for 6-CB and RB. Carbonic anhydrase inhibition, partitioning, solubility and intraocular pressure (IOP) measurements were also determined. Permeability calculations were estimated for drug diffusing against aqueous flow within the posterior chamber. The conjunctival/scleral route of entry produced higher iris/ciliary body concentrations for all compounds except for the lipophilic RB. Confocal microscopy results suggested that drug is gaining entry into the ciliary body through vessel uptake in the sclera. Following entry of drug into the conjunctival/scleral tissue, a significant portion enters scleral vessels and deposits within the ciliary body. Calculations are given that indicate that once drug penetrates the cornea it is highly unlikely drug diffuses through the pupil against aqueous flow to enter the posterior chamber and reach the ciliary body.