Benzenesulfonamide Group Research Articles

Molecular modeling and cytotoxic activity of newly synthesized benzothiazole-thiazole conjugates

In the dynamic area of drug development, researchers have been urged to uncover and test novel compounds with better effectiveness and fewer side effects in order to find more effective cancer treatments. In this comprehensive study, the synthesis and anticancer efficacy of new benzothiazole-thiazole have been displayed. Initially, a series of benzothiazole-thiazole conjugates 5a-c, 7a-b, and 8 were carefully designed and synthesized from the versatile 6-acetyl-2-phenylsulfonamidobenzothiazole (2), following the guidelines of rational design principles. The DFT/B3LYP approach showed that the synthesized hybrids had a non-planar configuration, where the benzene-sulfonamide group was oriented almost perpendicularly. The tested derivatives exhibited close HOMO-LUMO energies leading to small energy gaps (ΔEH-L = 1.54–2.97 eV). Additionally, the inhibitory effects of the newly synthesized conjugates were tested on four cancer cell lines, including HepG2, HCT-116, MCF-7, and WI38. Conjugates 5a and 8 had strong inhibitory effects on the HCT-116 and MCF-7 cell lines. Additionally, the synthesized conjugates showed inhibitory action against CAIX and CAXII, where conjugate 8 also effectively inhibited both isoforms, as well as, conjugate 5a. Molecular docking analysis was performed to study the binding affinities and interactions of the newly synthesized benzothiazole-thiazole conjugates with the target PDB: 5fl4 protein. Moreover, the ADME outlines of the inspected conjugates were displayed, and conjugates 2 and 6 showed suitable characteristics for GI absorption and minor violations of Lipinski’s rules; thus, they are promising lead compounds.

New amidine-benzenesulfonamides as iNOS inhibitors for the therapy of the triple negative breast cancer

Triple negative breast cancer (TNBC) is a specific breast cancer subtype, and poor prognosis is associated to this tumour when it is in the metastatic form. The overexpression of the inducible Nitric Oxide Synthase (iNOS) is considered a predictor of poor outcome in TNBC patients, and this enzyme is reported as a valuable molecular target to compromise TNBC progression. In this work, new amidines containing a benzenesulfonamide group were designed and synthesized as selective iNOS inhibitors. An in vitro biological evaluation was performed to assess compounds activity against both the inducible and constitutive NOSs. The most interesting compounds 1b and 2b were evaluated on MDA-MB-231 cells as antiproliferative agents, and 1b capability to counteract cell migration was also studied. Finally, an in-depth docking study was performed to shed light on the observed potency and selectivity of action of the most promising compounds.

Aromatic-Ring-Fused BOPPY Fluorophores: Synthesis, Spectral, Redox Properties, and Bioimaging Application.

Tetracoordinated organoboron dyes exhibiting strong fluorescence in either solution or the solid state are currently receiving much attraction in view of their photovoltaic, optoelectronic, and biological applications. Herein, a series of aromatic-ring-fused BOPPY dyes have been developed by one-pot condensation of formylated isoindoles or indoles and pyridinylhydrazine followed by subsequent borylation coordination. The facile synthesis provides excellent diversity of these unsymmetrical α-benzo- and β-benzothiophene-fused BOPPY dyes with intriguing photophysical properties owing to their rigid and planar structure and extended π-conjugation while containing a reactive site. They display intense green to orange fluorescence in solution and red-to-near-infrared emission in the solid state, with high fluorescence quantum yields up to 92 and 21%, respectively, relatively large Stokes shifts, and excellent photostability. Furthermore, two representative benzo-fused BOPPY probes with morpholine or benzenesulfonamide groups were developed and used to selectively "light up" the subcellular organelles such as lysosomes and endoplasmic reticulum under ultralow concentration, respectively.

Zinc(II) phthalocyanine substituted by sulfonamide derivative: Photophysical and photochemical properties

Synthesis of two different new compounds, (E)-4-((2‑hydroxy-3‑methoxy-5-nitro benzylidene)amino)-N-(pyridine-2-yl)benzenesulfonamide 1, (E)-4-((2-(3,4-dicyanophenoxy )-3‑methoxy-5-nitrobenzylidene)amino)-N-(pyridine-2-yl)benzenesulfonamide2and 2(3),9(10),16(17),23(24)-tetrakis-[(E)-4-((3‑methoxy-5-nitro-2-(λ1-oxidanyl)benzylidene) amino)-N-(pyridine-2-yl)benzene sulfonamid] zinc(II) phthalocyanine complex 3 was carried out. Their structures were characterized by spectroscopic methods such as Fourier transform infrared, Proton nuclear magnetic resonance, Carbon-13 nuclear magnetic resonance, Ultraviolet-visible, Fluorescence, Matrix-assisted laser desorption/ionization, Time-of-flight mass (except compounds 1 and 2), as well as Elemental analysis. The spectroscopic, photophysical, and photochemical properties of zinc(II) phthalocyanine complex 3, substituted with new benzenesulfonamide derivatives containing different functional groups, were explored in dimethylsulfoxide to determine its usability as a photosensitizer for photodynamic therapy. The effects of the presence of tetra-substituted new benzenesulfonamide groups from the peripheral positions of the zinc(II) phthalocyanine ring on the spectroscopic, photophysical, and photochemical properties were investigated and these properties were compared with the properties of the substituted and unsubstituted zinc(II) phthalocyanines. As a photosensitizer for photodynamic therapy, this new phthalocyanine 3 has well solubility in different kinds of solvents without aggregation sufficient fluorescence properties, ability to produce singlet oxygen, and photostability under appropriate light irradiation.

Synthesis of new 3-substituted quinolone derivatives with benzene sulfonamide group using hydrazine linker with their docking and antibacterial studies in vitro

Quinolones are among the prominent class of broad-spectrum antibiotics. In this work, a series of 1,4-dihydro-4-oxo-3-[3-{benzenesulfon}-2-hydrazino-1-oxo-]quinoline derivatives 6a-e were synthesized and tested for their antibacterial efficacy in vitro. Compounds 6a-e were characterized by NMR (1H,13C), HRMS and IR analysis. All these compounds confirmed bactericidal activity against tested bacterial strains. The MIC data have shown that compounds 6e (MIC = 7.5 mg/mL) displayed better activity against Staphylococcus aureus, Escherichia coli (ETEC) and Pseudomonas aeruginosa. Compounds 6b-e (MIC = 7.5 mg/mL) have similar activity as Norfloxacin against E. coli. Molecular docking studies was also conducted to explore binding interactions of our compounds at the active sites of the GyrB subunit of E. coli K-12.

Tellurides bearing benzensulfonamide as carbonic anhydrase inhibitors with potent antitumor activity

We evaluated in vitro a series of telluride containing compounds bearing the benzenesulfonamide group, as effective inhibitors of the physiologically relevant human (h) expressed Carbonic Anhydrase (CA; EC 4.2.1.1) enzymes I, II, IV VII and IX. The potent effects of such compounds against the tumor-associated hCA IX being low nanomolar inhibitors (KI 2.2 to 2.9 nM) and with good selectivity over the ubiquitous hCA II, gave the possibility to evaluate their lethal effect in vitro against a breast cancer cell line (MDA-MB-231). Among the series, both compounds 3a and 3g induced significant toxic effects against tumor cells after 48 h incubation. Under normoxic condition 3a showed high efficacy killing over 94% of tumor cells at 1 µM, and derivative 3g reached the tumor cell viability under the 5% at 10 µM. In hypoxic condition, these two compounds showed less effective although retained excellent cancer cell killer. These unusual features make them interesting lead compounds acting as antitumor agents also in tumor types not dependent from hCA IX overexpression.

Mn2+ Complexes Containing Sulfonamide Groups with pH-Responsive Relaxivity.

We present two ligands containing a N-ethyl-4-(trifluoromethyl)benzenesulfonamide group attached to either a 6,6'-(azanediylbis(methylene))dipicolinic acid unit (H3DPASAm) or a 2,2'-(1,4,7-triazonane-1,4-diyl)diacetic acid macrocyclic platform (H3NO2ASAm). These ligands were designed to provide a pH-dependent relaxivity response upon complexation with Mn2+ in aqueous solution. The protonation constants of the ligands and the stability constants of the Mn2+ complexes were determined using potentiometric titrations complemented by spectrophotometric experiments. The deprotonations of the sulfonamide groups of the ligands are characterized by protonation constants of log KiH = 10.36 and 10.59 for DPASAm3- and HNO2ASAm2-, respectively. These values decrease dramatically to log KiH = 6.43 and 5.42 in the presence of Mn2+, because of the coordination of the negatively charged sulfonamide groups to the metal ion. The higher log KiH value in [Mn(DPASAm)]- is related to the formation of a seven-coordinate complex, while the metal ion in [Mn(NO2ASAm)]- is six-coordinated. The X-ray crystal structure of Na[Mn(DPASAm)(H2O)]·2H2O confirms the formation of a seven-coordinate complex, where the coordination environment is fulfilled by the donor atoms of the two picolinate groups, the amine N atom, the N atom of the sulfonamide group, and a coordinated water molecule. The lower conditional stability of the [Mn(NO2ASAm)]- complex and the lower protonation constant of the sulfonamide group results in complex dissociation at relatively high pH (<7.0). However, protonation of the sulfonamide group in [Mn(DPASAm)]- falls into the physiologically relevant pH window and causes a significant increase in relaxivity from r1p = 3.8 mM-1 s-1 at pH 9.0 to r1p = 8.9 mM-1 s-1 at pH 4.0 (10 MHz, 25 °C).

Synthesis of Hydroxybenzofuranyl-pyrazolyl and Hydroxyphenyl-pyrazolyl Chalcones and Their Corresponding Pyrazoline Derivatives as COX Inhibitors, Anti-inflammatory and Gastroprotective Agents.

Five new series of hydroxybenzofuranyl-pyrazolyl chalcones 3a,b, hydroxyphenyl-pyrazolyl chalcones 6a-c and their corresponding pyrazolylpyrazolines 4a, d, 7a-c and 8a-f have been synthesized and evaluated for their in vitro cyclooxygenase (COX)-1 and COX-2 inhibitory activity. All the synthesized compounds exhibited dual COX-1 and COX-2 inhibitory activity with obvious selectivity against COX-2. The pyrazolylpyrazolines 4a-d and 8a-f bearing two vicinal aryl moieties in the pyrazoline nucleus showed more selectivity towards COX-2. Within these two series, derivatives 4c, d and 8d-f bearing the benzenesulfonamide group were the most selective. Compounds 4a-d and 8a-f were further subjected to in vivo anti-inflammatory screening, ulcerogenic liability and showed good anti-inflammatory activity with no ulcerogenic effect. In addition compounds 4c and 8d as examples showed prostaglandin (PG)E2 inhibition % 44.23 and 51.4 respectively, tumor necrosis factor α (TNFα) inhibition % 33.48 and 41.41 respectively and gastroprotective effect in ethanol induced rodent gastric ulcer model. In addition, to explore the binding mode and selectivity of our compounds, 8d and celecoxib were docked into the active site of COX-1 and COX-2. It was found that compound 8d exhibited a binding pattern and interactions similar to that of celecoxib with COX-2 active site, while bitter manner of interaction than celecoxib to COX-1 active site.

Structural investigation on thiazolo[5,4-d]pyrimidines to obtain dual-acting blockers of CD73 and adenosine A2A receptor as potential antitumor agents

Adenosine pathway, including its generating enzyme (CD73) and its receptors represents a key target for cancer immunotherapy. Here we aimed to search for novel compounds able to co-target the CD73 and the A2A adenosine receptor (A2A AR) as dual-blockers of adenosine generation and activity. The design project was to combine in the same molecule the thiazolo[5,4-d]pyrimidine core, an essential pharmacophoric feature to block the A2A AR, with a benzenesulfonamide group which is a characteristic group of CD73 inhibitors. Most of the reported compounds resulted in inverse agonists of the human (h) A2A AR endowed with high affinity, selectivity and potency. However they were weak inhibitors of CD73 enzyme. Nevertheless, this study can be considered as a starting point to develop more active compounds.

Synthesis of novel tellurides bearing benzensulfonamide moiety as carbonic anhydrase inhibitors with antitumor activity

We have synthetized a novel series of β-hydroxy tellurides bearing the benzenesulfonamide group as potent inhibitors of carbonic anhydrase enzymes. In a one pot procedure, we discovered both the ring opening reaction of the three-membered ring and the cleavage of the sulfonamide protecting moiety at the same time. Moreover, the first X-ray co-crystallographic structure of a β-hydroxy telluride derivative with hCA II is reported. The potent effects of these compounds against the tumor-associated hCA IX with low nanomolar constant inhibition values give the possibility to evaluate their activity in vitro using a breast cancer cell line (MDA-MB-231). Compounds 7e and 7g induced significant toxic effects against tumor cells after 48 h incubation in normoxic conditions killing over 50% of tumor cells at 3 μM, but their efficacy decreased in hypoxic conditions reaching the 50% of the tumor cell viability only at 30 μM. These unusual features make them interesting lead compounds to act as antitumor agents, not only as Carbonic Anhydrase IX inhibitors, but reasonably in different pathways, where hCA IX is not overexpressed.

Photoinduced electron-transfer reactions of tris(2,2′-bipyridine)ruthenium(II)-based carbonic anhydrase inhibitors tethering plural binding sites

AbstractTris(2,2′‐bipyridine)ruthenium(II) complex‐based carbonic anhydrase (CA) inhibitors, [Ru(bpy)2(bpydbs)]2+ {bpy = 2,2′‐bipyridine and bpydbs = 2,2′‐bipyridinyl‐4,4′‐dicarboxilic acid bis[(2‐{2‐[2‐(4‐sulfamoylbenzoylamino)ethoxy]ethoxy}ethyl)amide]} and [Ru(bpydbs)3]2+, tethering plural benzenesulfonamide groups have been prepared. The CA catalytic activity was effectively suppressed by these synthetic [Ru(bpy)2(bpydbs)]2+ and [Ru(bpydbs)3]2+ inhibitors, and their dissociation constants at pH = 7.2 and at 25°C were determined to be KI = 0.93 ± 0.02 μM and KI = 0.24 ± 0.03 μM, respectively. Next, 2 photoinduced electron‐transfer (ET) systems comprising a Ru2+‐CA complex and an electron acceptor, such as chloropentaamminecobalt(III) ([CoCl(NH3)5]2+) or methylviologen (MV2+) were studied. In the presence of CA and a sacrificial electron acceptor, such as pentaamminechlorocobalt(III) complex, the photoexcited triplet state of 3([Ru(II)]2+)* was quenched through an intermolecular photoinduced ET mechanism. In case of the [Ru(bpydbs)3]2+‐CA‐MV2+ system, the photoexcited triplet state of 3([Ru(bpydbs)3]2+)* was quenched by sacrificial quencher through an intermolecular photoinduced ET mechanism, giving the oxidized [Ru(bpydbs)3]3+. Then the following intramolecular ET from the amino acid residue, Tyr6, near the active site of CA proceeded. We observed a transient absorption around at 410 nm, arising from the formation of a Tyr•+ in the [Ru(bpydbs)3]2+‐CA‐MV2+ system. These artificial Ru(II)‐CA systems may clearly demonstrate both intermolecular and intramolecular photoinduced ET reactions of protein and could be one of the interesting models of the ET proteins. Their photophysical properties and the detailed ET mechanisms are discussed in order to clarify the multistep ET reactions.

Synthesis and Conformational Studies of Taa‐Containingo‐Nitrobenzenesulfonamide‐ (o‐Nosyl‐) Protected GS Analogs to Prove the Importance of 6RStereochemistry of Taa over 6S

AbstractGramicidin S (GS) is long known broad range antibiotic but limited to only topical application clinically due to its adverse hemolytic activity. We are reporting here the synthesis of Gramicidin S analogs where the turn unit D‐Phe‐Pro was replaced by suitably designed C6 substituted Tetrahydrofuran amino acid (Taa) moiety and side chain amine was protected as o‐nitro benzene sulfonamide group (o‐Nosyl). The detailed conformational analyses were also carried out by evaluating the structure activity relationship. Variation in the side chain and modification in the stereocentres of Taa play an important role towards the structure activity relationship in this class of compounds.

Synthesis, spectroscopic characterization, antimicrobial evaluation and molecular docking study of novel triazine-quinazolinone based hybrids

A new series of 1,3,5-triazine incorporating aromatic quinazolinone moieties as a potential antimicrobial agents is reported. The first chlorine group of the cyanuric chloride (1) was replaced by aniline and the second one was replaced by various aromatic amines. The prepared monochlorotriazine was allowed to react with hydrazine and subsequently it was reacted with 2-methyl-4H-benzo[1,3]oxazin-4-one to obtain novel triazine-quinazolinone based hybrids (9a-f). The chemical structure and purity of the hybrid compounds were evaluated by different techniques such as thin layer chromatography, melting point, Fourier-transform infrared (FTIR), 1H and 13C NMR spectra and elemental analysis. Antimicrobial activity of the hybrid compounds were study by three Gram-negative bacteria (Salmonella entritidis, Escherichia coli, Pseudomonas aeruginosa) and three Gram-positive bacteria (Staphylococcus aureus, Listeria monocitogenes, Bacillus subtilis) as well as Candida albicansas a yeast-like fungus using the serial broth dilution method. Among them, compound 9d with benzenesulfonamide group showed higher antimicrobial activity with a minimum inhibitory concentration (MIC) value of 16 μg/mL. Furthermore, compounds 5d, 9a and 9b showed good activity against several tested strains. In addition, docking simulation was perform to position best antibacterial compounds in to the S. aureus dihydrofolate reductase (DHFR) active site to determine the probable binding conformations.

Synthesis and biological evaluation of novel synthetic chalcone derivatives as anti-tumor agents targeting Cat L and Cat K

A series of chalcone derivatives bearing benzamide or benzenesulfonamide moieties were synthesized and evaluated for their anti-tumor effect on HCT116, MCF7 and 143B cell lines in vitro. SAR analysis showed that compounds bearing a benzenesulfonamide group had greater potency than those bearing a benzamide group. It was also shown that compounds with a mono-methyl or mono-halogen group at the 3-position on the terminal phenyl ring were more effective than those with trifluoromethyl or methoxy groups. Compound 8e exhibited the most potent anti-tumor activities against HCT116, MCF7 and 143B cell lines, with IC50 values of 0.597, 0.886 and 0.791μM, respectively. Molecular docking studies and enzymatic assays demonstrated that the anti-tumor activity of compound 8e might be regulated by Cat L and Cat K.

Discovery of simplified leucyladenylate sulfamates as novel leucyl-tRNA synthetase (LRS)-targeted mammalian target of rapamycin complex 1 (mTORC1) inhibitors

Leucyl-tRNA synthetase (LRS) has been reported to be a possible mediator of intracellular amino acids signaling to mTORC1. Given that mTORC1 is associated with cell proliferation and tumorigenesis, the LRS-mediated mTORC1 pathway may offer an alternative strategy in anticancer therapy. In this study, we developed a series of simplified analogues of leucyladenylate sulfamate (1) as LRS-targeted mTORC1 inhibitors. We replaced the adenylate group with a N-(3,4-dimethoxybenzyl)benzenesulfonamide (2a) or a N-(2-phenoxyethyl)benzenesulfonamide groups (2b) that can maintain specific binding, but has more favorable physicochemical properties such as reduced polarity and asymmetric centers. Among these simplified analogues, compound 16 and its constrained analogue 22 effectively inhibited S6K phosphorylation in a dose-dependent manner and exhibited cancer cell specific cytotoxicity against six different types of cancer cells. This result supports that LRS is a viable target for novel anticancer therapy.

Discovery and characterization of novel selective inhibitors of carbonic anhydrase IX.

Human carbonic anhydrase IX (CA IX) is highly expressed in tumor tissues, and its selective inhibition provides a potential target for the treatment of numerous cancers. Development of potent, highly selective inhibitors against this target remains an unmet need in anticancer therapeutics. A series of fluorinated benzenesulfonamides with substituents on the benzene ring was designed and synthesized. Several of these exhibited a highly potent and selective inhibition profile against CA IX. Three fluorine atoms significantly increased the affinity by withdrawing electrons and lowering the pKa of the benzenesulfonamide group. The bulky ortho substituents, such as cyclooctyl or even cyclododecyl groups, fit into the hydrophobic pocket in the active site of CA IX but not CA II, as shown by the compound's co-crystal structure with chimeric CA IX. The strongest inhibitor of recombinant human CA IX's catalytic domain in human cells achieved an affinity of 50 pM. However, the high affinity diminished the selectivity. The most selective compound for CA IX exhibited 10 nM affinity. The compound that showed the best balance between affinity and selectivity bound with 1 nM affinity. The inhibitors described in this work provide the basis for novel anticancer therapeutics targeting CA IX.

N-[(1,3-Benzodioxol-5-yl)methyl]benzenesulfonamide: an analogue of capsaicin

The title compound, C14H13NO4S, an analogue of capsaicin, differs from the latter by having a 1,3-benzodioxole ring rather than a 2-meth­oxy­phenol moiety, and having a benzene­sulfonamide group instead of an aliphatic amide chain. The five-membered ring is in an envelope conformation with the methyl­ene C atom lying 0.221 (6) Å out of the plane formed by the other four atoms. The dihedral angle between the phenyl ring and the mean plane of the 1,3-benzodioxole fused-ring system is 84.65 (4)°. In the crystal, mol­ecules aggregate into supra­molecular layers in the ac plane through C—H⋯O, N—H⋯O and C—H⋯π inter­actions.

Photoinduced Electron-Transfer Reactions of Carbonic Anhydrase Inhibitor Containing Tris(2,2′-bipyridine)ruthenium(II) Analogue

A ruthenium(II) complex-based carbonic anhydrase (CA) inhibitor, [Ru(bpy)2(bpybs)](2+) {bpy = 2,2'-bipyridine and bpybs = 4'-methyl-2,2'-bipyridinyl-4-carboxylic acid (2-{2-[(4-sulphamoylbenzoylamino)ethoxy]ethoxy}ethyl)amide}, tethering a benzenesulfonamide group and a [Ru(bpy)3](2+) moiety has been prepared. The CA activity was effectively suppressed by a synthetic [Ru(bpy)2(bpybs)](2+) inhibitor, and the dissociation constant at pH 7.2 and at 25 °C was determined to be KI = 1.9 ± 0.2 μM. Next, in the presence of CA and a sacrificial electron acceptor, such as pentaamminechlorocobalt(III) complex, the photoexcited triplet state of (3)([Ru(bpy)2(bpybs)](2+))* was quenched through an intermolecular photoinduced ET mechanism to form the oxidized [Ru(bpy)2(bpybs)](3+), followed by the intramolecular electron abstraction from an amino-acid residue near the active site of CA. The resulting oxidized CA was catalytically inactive. Kinetic experiments also revealed that the second-order rate constant for the initial step and the first-order rate constant for the second step under our experimental conditions were kq = 4.8 × 10(7) M(-1) s(-1) and kIET = 6.6 × 10(4) s(-1), respectively. Thus, the intramolecular ET between CA and [Ru(bpy)2(bpybs)](3+) is a crucial event to regulate CA activity by the visible light irradiation of a synthetic [Ru(bpy)3](2+)-type inhibitor.

Research on the structure–surface adsorptive activity relationships of triazolyl glycolipid derivatives for mild steel in HCl

Triazolyl glycolipid derivatives constructed via CuI-catalyzed azide-alkyne 1,3-dipolar cycloaddition reaction (Cue-AAC) represent a new range of carbohydrate-based scaffolds for use in many fields of the chemical research. Here the surface adsorptive ability of series of our previously prepared C1- or C6-triazole linked gluco- and galactolipid derivatives for mild steel in 1M HCl was studied via electrochemical impedance spectroscopy (EIS). Results indicated that these monosaccharide–fatty acid conjugates are weak inhibitors against HCl corrosion for mild steel. Moreover, some newly synthesized triazolyl disaccharide (maltose)–fatty alcohol conjugates failed to display enhanced activity, meaning that the structural enlargement of the sugar moiety does not favor the iron surface adsorption. However, a bis-triazolyl glycolipid derivative, which was realized by introducing a benzenesulfonamide group via Cue-AAC to the C6-position of a C1-triazolyl glucolipid analog, eventually showed significantly improved adsorptive potency compared to that of its former counterparts. The corrosion inhibitive modality of this compound for mild steel in HCl was subsequently studied via potentiodynamic polarization and thermodynamic calculations.

Fluoroalkyl and Alkyl Chains Have Similar Hydrophobicities in Binding to the “Hydrophobic Wall” of Carbonic Anhydrase

The hydrophobic effect, the free-energetically favorable association of nonpolar solutes in water, makes a dominant contribution to binding of many systems of ligands and proteins. The objective of this study was to examine the hydrophobic effect in biomolecular recognition using two chemically different but structurally similar hydrophobic groups, aliphatic hydrocarbons and aliphatic fluorocarbons, and to determine whether the hydrophobicity of the two groups could be distinguished by thermodynamic and biostructural analysis. This paper uses isothermal titration calorimetry (ITC) to examine the thermodynamics of binding of benzenesulfonamides substituted in the para position with alkyl and fluoroalkyl chains (H(2)NSO(2)C(6)H(4)-CONHCH(2)(CX(2))(n)CX(3), n = 0-4, X = H, F) to human carbonic anhydrase II (HCA II). Both alkyl and fluoroalkyl substituents contribute favorably to the enthalpy and the entropy of binding; these contributions increase as the length of chain of the hydrophobic substituent increases. Crystallography of the protein-ligand complexes indicates that the benzenesulfonamide groups of all ligands examined bind with similar geometry, that the tail groups associate with the hydrophobic wall of HCA II (which is made up of the side chains of residues Phe131, Val135, Pro202, and Leu204), and that the structure of the protein is indistinguishable for all but one of the complexes (the longest member of the fluoroalkyl series). Analysis of the thermodynamics of binding as a function of structure is compatible with the hypothesis that hydrophobic binding of both alkyl and fluoroalkyl chains to hydrophobic surface of carbonic anhydrase is due primarily to the release of nonoptimally hydrogen-bonded water molecules that hydrate the binding cavity (including the hydrophobic wall) of HCA II and to the release of water molecules that surround the hydrophobic chain of the ligands. This study defines the balance of enthalpic and entropic contributions to the hydrophobic effect in this representative system of protein and ligand: hydrophobic interactions, here, seem to comprise approximately equal contributions from enthalpy (plausibly from strengthening networks of hydrogen bonds among molecules of water) and entropy (from release of water from configurationally restricted positions).