1,2-Benzisothiazol-3-one 1,1-dioxide inhibitors of human mast cell tryptase

Novel saccharin analogs as promising antibacterial and anticancer agents: synthesis, DFT, POM analysis, molecular docking, molecular dynamic simulations, and cell-based assay

Saccharine is a pharmacologically significant active scaffold for various biological activities, including antibacterial and anticancer activities. Herein, saccharinyl hydrazide (1) was synthesized and converted into 2-[(2Z)-2-(1,1-dioxo-1,2-dihydro-3H-1λ⁶,2- benzothiazole-3-ylidene) hydrazinyl] acetohydrazide (5), which was employed as a key precursor for synthesizing a novel series of small molecules bearing different moieties of monosaccharides, aldehydes, and anhydrides. Potent biological activities were found against Staphylococcus and Escherichia coli, and the results indicated that compounds 6c and 10a were the most active analogs with an inhibition zone diameter of 30–35 mm. In cell-based anticancer assay over Ovcar-3 and M-14 cell lines, compound 10a was the most potent analog with IC₅₀ values of 7.64 ± 0.01 and 8.66 ± 0.01 µM, respectively. The Petra Orisis Molinspiration (POM) theoretical method was used to calculate the drug score of tested compounds and compare them with their experimental screening data. Theoretical DFT calculations were carried out in a gas phase in a set of B3LYP 6-311G (d,p). Molecular docking studies utilizing the MOE indicated the best binding mode with the highest energy interaction within the binding sites. The molecular docking for Ovcar-3 was carried out on the ovarian cancer protein (3W2S), while the molecular docking for M-14 melanoma was carried out on the melanoma cancer protein (2OPZ). The MD performed about 2ns simulations to validate selected compounds’ theoretical studies.

An imazamox-based herbicide causes apoptotic changes in rat liver and pancreas

We studied the acute toxicity of an imazamox-based herbicide at 12, 24 and 36 mg/kg body (bw) weight imazamox equivalent dose on the liver and pancreatic tissue in Sprague Dawley rats. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, glucose, calcium as well as creatinine, were determined in blood samples, which were collected after 24, 48 and 72 h exposure. Caspase 3 and anti-insulin expression and immunopositivity were evaluated using in situ hybridization and immunohistochemistry, respectively. The imazamox-based herbicide evaluated in this study induced toxic effects even from the lowest dose tested (12 mg/kg bw). The two highest doses caused a statistically significant cytotoxicity on the Langerhans islet cells. Necrotic and degenerative changes were detected in hepatocytes at the two highest doses. Imazamox is considered to be poorly toxic to the liver. Nevertheless, the imazamox-based herbicide formulation tested here reduced the size of the β-islet cells, induced an elevation in serum glucose and calcium. Our data shows that commercial formulations of imazamox containing various co-formulants can have hepatic and pancreatic toxic effects.

Crystal structure of 2-(4-(2-(4-(2-fluorophenyl)piperazin-1-yl)ethyl)benzyl)benzo[d]isothiazol-3(2H)-one 1,1-dioxide, C26H26FN3O3S – a saccharin dervative

C26H26F1N3O3S1, triclinic, P1̅ (no. 2), a = 7.0252(14) Å, b = 9.3017(19) Å, c = 19.388(4) Å, α = 97.80(3)°, β = 97.77(3)°, γ = 106.84(3)°, V = 1180.9(5) Å3, Z = 2, R gt(F) = 0.0729, wR ref(F 2) = 0.1854, T = 296.15 K.

Synthesis and Antitumor Activity of Novel Arylpiperazine Derivatives Containing the Saccharin Moiety

Prostate cancer is a major public health problem worldwide. For the development of potential anti-prostate cancer agents, a series of novel arylpiperazine derivatives containing the saccharin moiety based on previous studies was designed, synthesized, and evaluated in prostate (PC-3, LNCaP, and DU145) cancer cell lines for their anticancer activities. The majority of the compounds exhibited excellent selective activity for the tested cancer cells. Compounds 4 and 12 exhibited strong cytotoxic activities against DU145 cells (half maximal inhibitory concentration (IC₅₀) < 2 μM). The structure–activity relationship (SAR) of these arylpiperazine derivatives was also discussed based on the obtained experimental data. This work provides a potential lead compound for anticancer agent development focusing on prostate cancer therapy.

Design of Benzoxathiazin-3-one 1,1-Dioxides as a New Class of Irreversible Serine Hydrolase Inhibitors: Discovery of a Uniquely Selective PNPLA4 Inhibitor

The design and examination of 4,1,2-benzoxathiazin-3-one 1,1-dioxides as candidate serine hydrolase inhibitors are disclosed, and represent the synthesis and study of a previously unexplored heterocycle. This new class of activated cyclic carbamates provided selective irreversible inhibition of a small subset of serine hydrolases without release of a leaving group, does not covalently modify active site catalytic cysteine and lysine residues of other enzyme classes, and was found to be amenable to predictable structural modifications that modulate intrinsic reactivity or active site recognition. Even more remarkable and within the small pilot series of candidate inhibitors examined in an initial study, an exquisitely selective inhibitor for a poorly characterized serine hydrolase (PNPLA4, patatin-like phospholipase domain-containing protein 4) involved in adipocyte triglyceride homeostasis was discovered.

Exploring the Photophysical and Photochemical Properties of N-(Thioalkyl)-saccharins as an Alternative Route to the Synthesis of Tricyclic Sultams

Photocyclization of N-(thioalkyl)-saccharin was carried out to obtain different polycyclic sultams in good yields. These photoreactions were efficient under inert atmosphere and acetone triplet-sensitized conditions indicating that the triplet excited state is directly involved in the formation of annulated products. The presence of molecular oxygen changes product distribution, and only photo-oxygenation products (sulfoxides and sulfones) were found. This result is especially valuable since, by simple changing from nitrogen- to oxygen-saturated solvent conditions, the reaction outcome can be tuned from cyclized to sulfur oxidation products. Additionally, steady-state photolysis, electrochemistry, and laser time-resolved spectroscopic studies confirmed that these reactions mainly proceeded by intramolecular electron transfer (ET) between the triplet excited saccharin moiety and sulfur atom.

2015 Philip S. Portoghese Medicinal Chemistry Lectureship. Curing Hepatitis C Virus Infection with Direct-Acting Antiviral Agents: The Arc of a Medicinal Chemistry Triumph

The development of direct-acting antiviral agents that can cure a chronic hepatitis C virus (HCV) infection after 8-12 weeks of daily, well-tolerated therapy has revolutionized the treatment of this insidious disease. In this article, three of Bristol-Myers Squibb's HCV programs are summarized, each of which produced a clinical candidate: the NS3 protease inhibitor asunaprevir (64), marketed as Sunvepra, the NS5A replication complex inhibitor daclatasvir (117), marketed as Daklinza, and the allosteric NS5B polymerase inhibitor beclabuvir (142), which is in late stage clinical studies. A clinical study with 64 and 117 established for the first time that a chronic HCV infection could be cured by treatment with direct-acting antiviral agents alone in the absence of interferon. The development of small molecule HCV therapeutics, designed by medicinal chemists, has been hailed as "the arc of a medical triumph" but may equally well be described as "the arc of a medicinal chemistry triumph".

Peroxodisulfate-mediated selenoamination of alkenes yielding amidoselenide-containing sulfamides and azoles

A novel intermolecular selenoamination of alkenes has been successfully developed and a series of structurally diverse vicinal amidoselenides were effectively obtained under mild heating.

Heparin makes differences: a molecular dynamics simulation study on the human βII-tryptase monomer

Human β-tryptase, an enzyme with trypsin-like activity in mast cells, is an important target for the treatment of inflammatory and allergy related diseases. Heparin has been inferred to play a vital role in the stabilization of the tryptase structure and the maintenance of its active form. Up to now, the structure-function relationship between heparin and the βII-tryptase monomer has not been studied with atomic resolution due to the lack of a complex structure of tryptase and heparin. To this end, the exact effect of heparin bonding to the βII-tryptase monomer structure has been investigated using molecular docking and molecular dynamics (MD) simulation. The MD simulation results combined with MM-GB/SA calculations showed that heparin stabilized the β-tryptase structure mainly through salt bridge interaction. The averaged noncovalent interaction (aNCI) method was employed for the visualization of nonbonding interactions. A crucial loop, which is located in the core region of βII-tryptase monomer structure, has been found. Arg188 and Asp189 from this loop act as a salt bridge intermediary between 4-mer heparin and 0GX. The observation of a salt bridge between Asp189 and P1 groups of 0GX confirms the supposed interaction between these two groups. These two residues have been proved to be responsible for the direction of the P1 group of 0GX. Our study revealed that how heparin affected the activity of the human βII-tryptase monomer (hBTM) through salt bridge interactions. The knowledge of heparin binding characteristics and the key residue contributions in this study may enlighten further the inhibitor design of this enzyme and may also improve our understanding of inflammatory and allergy related diseases.

Efficient imidation of C(sp3)–H bonds adjacent to oxygen atoms of aryl ethers under metal-free conditions

A metal-free intermolecular oxidative C–N formation reaction of aryl ethers with saccharins was realized for the first time.

Cavities tell more than sequences: exploring functional relationships of proteases via binding pockets

Computational approaches play an increasingly important role for the analysis and prediction of selectivity profiles. As most of the successfully administered small molecule drugs bind in depressions on the surface of proteins, physicochemical properties of the pocket-exposed amino acids play a central role in ligand recognition during the binding event. Cavbase is an approach to describe binding sites in terms of the exposed physicochemical properties and to compare them independent of their sequence and fold homology. Classification of proteins by means of their binding-site properties is a promising approach to obtain information necessary for selectivity modeling. For this purpose, the workflow clusterScore has been developed to explore the important parameters of a clustering procedure, which will allow an accurate classification of proteins. It has been successfully applied on two diverse and challenging data sets. The predicted number of clusters, as suggested by clusterScore and the subsequent clustering of proteins are in agreement with the EC and Merops classifications. Furthermore, putative cross-reactivity mapped between calpain-1 and cysteine cathepsins on structural level has so far only been described based on ligand data. In a benchmark study using ligand topology, binding site, and sequence information of eleven serine proteases, the emerging clusters indicate a pronounced correlation between the cavity and ligand data. These results emphasize the importance of binding-site information which should be considered for ligand design during lead optimization cycles. The program clusterScore is freely available and can be downloaded from our Web site www.agklebe.de.

A β-tryptase inhibitor with a tropanylamide scaffold to improve in vitro stability and to lower hERG channel binding affinity

Tropanylamide was investigated as a possible scaffold for β-tryptase inhibitors with a basic benzylamine P1 group and a substituted thiophene P4 group. Comparing to piperidinylamide, the tropanylamide scaffold is much more rigid, which presents less opportunity for the inhibitor to bind with off-target proteins, such as cytochrome P450, SSAO, and hERG potassium channel. The proposed binding mode was further confirmed by an in-house X-ray structure through co-crystallization.

Inhibitors of the salicylate synthase (MbtI) from Mycobacterium tuberculosis discovered by high-throughput screening

A simple steady-state kinetic high-throughput assay was developed for the salicylate synthase MbtI from Mycobacterium tuberculosis, which catalyzes the first committed step of mycobactin biosynthesis. The mycobactins are small-molecule iron chelators produced by M. tuberculosis, and their biosynthesis has been identified as a promising target for the development of new antitubercular agents. The assay was miniaturized to a 384-well plate format and high-throughput screening was performed at the National Screening Laboratory for the Regional Centers of Excellence in Biodefense and Emerging Infectious Diseases (NSRB). Three classes of compounds were identified comprising the benzisothiazolones (class I), diarylsulfones (class II), and benzimidazole-2-thiones (class III). Each of these compound series was further pursued to investigate their biochemical mechanism and structure-activity relationships. Benzimidazole-2-thione 4 emerged as the most promising inhibitor owing to its potent reversible inhibition.

Development of tryptase inhibitors derived from thalidomide

A novel series of tryptase inhibitors with a N-phenylphthalimide skeleton structurally derived from thalidomide (1) has been developed. Structure-activity relationship studies led to a potent and selective tryptase inhibitor, 2-(4-cyanophenyl)isoindole-1,3-dione-5-yl 3-(2-aminopyridin-5-yl)propanoate (7), with the IC50 value of 78 nM.

Structure-guided design of peptide-based tryptase inhibitors

Improved peptide-based inhibitors of human beta tryptase were discovered using information gleaned from tripeptide library screening and structure-guided design methods, including fragment screening. Our efforts sought to improve this class of inhibitors by replacing the traditional Lys or Arg P1 element. The optimized compounds display low nanomolar potency against the mast cell target and several hundred-fold selectivity with respect to serine protease off targets. Thus, replacement of Lys/Arg at P1 in a peptide-like scaffold does not need to be accompanied by a loss in target affinity.

1,2,5-Thiadiazolidin-3-one 1,1-dioxide-based heterocyclic sulfides are potent inhibitors of human tryptase

We describe herein the design, synthesis, and in vitro biochemical evaluation of a series of potent, time-dependent inhibitors of the mast cell-derived serine protease tryptase. The inhibitors were readily obtained by attaching various heterocyclic thiols, as well as a basic primary specificity residue P(1), to the 1,2,5-thiadiazolidin-3-one 1,1-dioxide scaffold. The inhibitors were found to be devoid of any inhibitory activity toward a neutral (elastase) or cysteine (papain) protease, however they were also fairly efficient inhibitors of bovine trypsin. The differential inhibition observed with trypsin suggests that enzyme selectivity can be optimized by exploiting differences in the S' subsites of the two enzymes. The results described herein demonstrate the versatility of the heterocyclic scaffold in fashioning mechanism-based inhibitors of neutral, basic, and acidic (chymo)trypsin-like serine proteases.

Inhibition of human β-tryptase by Bowman–Birk inhibitor derived peptides: creation of a new tri-functional inhibitor

Bowman-Birk inhibitor proteins (BBIs), which are potent inhibitors of chymotrypsin-like proteases, do not inhibit human beta-tryptase despite this protein having a chymotrypsin-like fold. We have reported previously that, in contrast, BBI-derived peptides (whose sequences incorporate the solvent exposed reactive site loop motif) are able to inhibit human beta-tryptase. This is due to their small size, which allows them to access the restricted active site(s) of tryptase, which has an unusual tetrameric arrangement with four active sites flanking a central pore. In this paper, we have examined the possibility of creating additional interactions within this pore by adding extensions to the BBI-peptide motif. We have taken the core disulfide-bridged sequence SCTKSIPPQCY and examined a series of extensions, at both the C- and N-termini, that bear a second positively charged Lys residue at their end. The aim was to construct inhibitors that could make additional interactions in tryptase by spanning the gap between adjacent active sites in the enzyme, producing a double-headed inhibitor; a positively charged group was used as the dominant specificity of this enzyme is for a positively charged P1 residue. Both N- and C-terminal extensions are found to produce inhibitors of much increased potency, with a strong dependence of potency on chain length. Moreover, it was found that the C- and N-terminal extensions were able to synergise, with their combination on the same peptide producing an even better inhibitor with a potency 10(4)-fold greater than the original sequence. We suggest that the C- and N-terminal extensions are picking up interactions with separate additional sites on the tryptase, making the doubly extended BBI peptide a tri-functional tryptase inhibitor.

Mechanism-based inactivation of human leukocyte elastase via an enzyme-induced sulfonamide fragmentation process

We describe herein the design and in vitro biochemical evaluation of a novel class of mechanism-based inhibitors of human leukocyte elastase (HLE) that inactivate the enzyme via an unprecedented enzyme-induced sulfonamide fragmentation cascade. The inhibitors incorporate in their structure an appropriately functionalized saccharin scaffold. Furthermore, the inactivation of the enzyme by these inhibitors was found to be time-dependent and to involve the active site. Biochemical, HPLC, and mass spectrometric studies show that the interaction of these inhibitors with HLE results in the formation of a stable acyl complex and is accompanied by the release of (L) phenylalanine methyl ester. The data are consistent with initial formation of a Michaelis-Menten complex and subsequent formation of a tetrahedral intermediate with the active site serine (Ser(195)). Collapse of the tetrahedral intermediate with tandem fragmentation results in the formation of a highly reactive conjugated sulfonyl imine which can either react with water to form a stable acyl enzyme and/or undergo a Michael addition reaction with an active site nucleophilic residue (His(57)). It is also demonstrated herein that this class of compounds can be used in the design of inhibitors of serine proteases having either a neutral or basic primary substrate specificity. Thus, the results suggest that these inhibitors constitute a potential general class of mechanism-based inhibitors of (chymo)trypsin-like serine proteases.

Design, synthesis and biological activity of a targeted library of potential tryptase inhibitors

We have designed, synthesized, and tested two small collections of potential tryptase inhibitors. The first library consists of diversely N-substituted 3-aminopiperidin-2-ones 6, and the second (compounds 7) was prepared by dimerising compounds 6 through the 3-amino function using diverse carbon chains. We have established efficient routes for obtaining 6 both in solution and on solid supports. We have also compared the dimerisation on-resin and in solution. Four of the compounds showed a high degree of tryptase inhibition at 1 microM, but none surpassed the tryptase inhibition activity of BABIM.

Solid-phase synthesis and SAR of 4-carboxy-2-azetidinone mechanism-based tryptase inhibitors

A series of nonguanidine N1-activated C4-carboxy azetidinone tryptase inhibitors was prepared by solid-phase methodology to quickly assess the SAR associated with distal functionality on the N1-activating group. From these studies, potent inhibitors with improved specificity were discovered.

Synthesis and SAR of 4-carboxy-2-azetidinone mechanism-based tryptase inhibitors

A series of N1-activated C4-carboxy azetidinones was prepared and tested as inhibitors of human tryptase. The key stereochemical and functional features required for potency, serine protease specificity and aqueous stability were determined. From these studies compound 2, BMS-262084, was identified as a potent and selective tryptase inhibitor which, when dosed intratracheally in ovalbumin-sensitized guinea pigs, reduced allergen-induced bronchoconstriction and inflammatory cell infiltration into the lung.

Monocharged inhibitors of mast cell tryptase derived from potent and selective dibasic inhibitors

Truncation of potent and selective dibasic inhibitors afforded monocharged inhibitors of human mast-cell tryptase. Using two classes of analogues as lead structures, several monocharged derivatives were identified with K(i) values ranging from 0.084 to 0.21 microM against the enzyme.

Synthesis of cyclic sulfonamides via intramolecular copper-catalyzed reaction of unsaturated iminoiodinanes

Olefinic primary sulfonamides were treated with iodobenzene diacetate and potassium hydroxide in methanol to give intermediate iminoiodinanes. Catalytic copper(I) or (II) triflate then provided intramolecular nitrene delivery leading to aziridine formation except in one case where a rare copper-catalyzed C-H insertion was observed. The aziridines could be opened by various nucleophiles (methanol, thiophenol, allylmagnesium bromide, benzylamine) to give the corresponding substituted cyclic sulfonamides.

Potent selective nonpeptidic inhibitors of human lung tryptase

Human lung tryptase, a homotetrameric serine protease unique to mast cell secretory granules, has been implicated in the pathogenesis of asthma. A hypothesis that tethered symmetrical inhibitors might bridge two adjacent active sites was explored via a rationally designed series of bisbenzamidines. These compounds demonstrated a remarkable distanced-defined structure-activity relationship against human tryptase with one series possessing subnanomolar potencies. Additional evidence supporting the concept of active-site bridging is also presented.

Solid-phase synthesis of benzisothiazolones as serine protease inhibitors

An efficient solid-phase synthesis of benzisothiazolone-1,1-dioxide-based serine protease inhibitors involving alkylation of carboxylic acids with N-(bromomethyl)benzisothiazolone-1,1-dioxide has been developed. An example using this procedure for preparation of a library of human mast cell tryptase inhibitors is described.