Syntheses of coumarin–tacrine hybrids as dual-site acetylcholinesterase inhibitors and their activity against butylcholinesterase,Aβ aggregation,and β-secretase

Exploring small-molecule acetylcholinesterase (AChE) inhibitors to slow the breakdown of acetylcholine (Ach) represents the mainstream direction for Alzheimer’s disease (AD) therapy. As the first acetylcholinesterase inhibitor approved for the clinical treatment of AD, tacrine has been widely used as a pharmacophore to design hybrid compounds in order to combine its potent AChE inhibition with other multi-target profiles. In present study, a series of novel tacrine–coumarin hybrids were designed, synthesized and evaluated as potent dual-site AChE inhibitors. Moreover, compound 1g was identified as the most potent candidate with about 2-fold higher potency (K_i = 16.7 nM) against human AChE and about 2-fold lower potency (K_i = 16.1 nM) against BChE than tacrine (K_i = 35.7 nM for AChE, K_i = 8.7 nM for BChE), respectively. In addition, some of the tacrine–coumarin hybrids showed simultaneous inhibitory effects against both Aβ aggregation and β-secretase. We therefore conclude that tacrine–coumarin hybrid is an interesting multifunctional lead for the AD drug discovery.     

NAD-based inhibitors with anticancer potential

Three classes of novel inhibitors of inosine monophosphate dehydrogenase have been prepared and their anti-proliferative properties were evaluated against several cancer cell lines.(1) Mycophenolic adenine dinucleotide analogues (8–13) containing a substituent at the C2 of adenine ring were found to be potent inhibitors of IMPDH (K_i’s in range of 0.6–82 nM) and sub-μM inhibitors of leukemic K562 cell proliferation. (2) Mycophenolic adenosine (d and l) esters (20 and 21) showed a potent inhibition of IMPDH2 (K_i = 102 and K_i = 231 nM, respectively) and inhibition of K562 cell growth (IC₅₀ = 0.5 and IC₅₀ = 1.6 μM). These compounds serve both as inhibitors of the enzyme and as a depot form of mycophenolic acid. The corresponding amide analogue 22, also a potent inhibitor of IMPDH (K_i = 84 nM), did not inhibit cancer cell proliferation. (3) Mycophenolic-(l)- and (d)-valine adenine di-amide derivatives 25 (K_i = 9 nM) and 28 (K_i = 3 nM) were found to be very potent enzymatically, but did not inhibit proliferation of cancer cells.     

Design,synthesis, and X-ray structural studies of BACE-1 inhibitors containing substituted 2-oxopiperazines as P1′-P2′ ligands

We report the design and synthesis of a series of BACE1 inhibitors incorporating mono- and bicyclic 6-substituted 2-oxopiperazines as novel P1′ and P2′ ligands and isophthalamide derivative as P2-P3 ligands. Among mono-substituted 2-oxopiperazines, inhibitor 5a with N-benzyl-2-oxopiperazine and isophthalamide showed potent BACE1 inhibitory activity (K_i = 2 nM). Inhibitor 5g, with N-benzyl-2-oxopiperazine and substituted indole-derived P2-ligand showed a reduction in potency. The X-ray crystal structure of 5g-bound BACE1 was determined and used to design a set of disubstituted 2-oxopiperazines and bicyclic derivatives that were subsequently investigated. Inhibitor 6j with an oxazolidinone derivative showed a BACE1 inhibitory activity of 23 nM and cellular EC₅₀ of 80 nM.     

Design,synthesis, X-ray studies,and biological evaluation of novel macrocyclic HIV-1 protease inhibitors involving the P1′-P2′ ligands

Design, synthesis, and evaluation of a new class of HIV-1 protease inhibitors containing diverse flexible macrocyclic P1′-P2′ tethers are reported. Inhibitor 5a with a pyrrolidinone-derived macrocycle exhibited favorable enzyme inhibitory and antiviral activity (K_i = 13.2 nM, IC₅₀ = 22 nM). Further incorporation of heteroatoms in the macrocyclic skeleton provided macrocyclic inhibitors 5m and 5o. These compounds showed excellent HIV-1 protease inhibitory (K_i = 62 pM and 14 pM, respectively) and antiviral activity (IC₅₀ = 5.3 nM and 2.0 nM, respectively). Inhibitor 5o also remained highly potent against a DRV-resistant HIV-1 variant.     

Selective inhibition of human carbonic anhydrases by novel amide derivatives of probenecid: Synthesis,biological evaluation and molecular modelling studies

Novel amide derivatives of probenecid, a well-known uricosuric agent, were synthesized and evaluated as inhibitors of human carbonic anhydrases (hCAs, EC 4.2.1.1). The transmembrane isoforms (hCA IX and XII) were potently and selectively inhibited by some of them. The proposed chemical modification led to a complete loss of hCA II inhibition (K_is > 10,000 nM) and enhanced the inhibitory activity against the tumour-associated hCA XII (compound 4 showed a K_i value of 15.3 nM). The enzyme inhibitory data have also been validated by docking studies of the compounds within the active site of hCA XII.     

Purification and biochemical properties of a Kunitz-type trypsin inhibitor from Entada acaciifolia (Benth.) seeds

A new trypsin inhibitor (EATI) was isolated from Entada acaciifolia (Benth.) seeds. EATI is a competitive inhibitor with a molecular mass of 20 kDa and an inhibition stoichiometry of 1:1 for bovine trypsin. The dissociation constant (K_i) calculated was 1.75 nmol/L, displaying a high affinity between enzyme and inhibitor. Both Native PAGE and RP-HPLC revealed that EATI is composed of four isoinhibitors that share the amino acid composition and the amino-terminal sequence homolog to Kunitz-type inhibitors. EATI is stable to denaturation by heat (up to 70 °C), pH (2–10), urea (8 mol/L) and its inhibitory activity was unaltered in different concentrations of DTT (up to 100 mmol/L). CD analysis revealed that EATI in reduced form underwent structural modifications associated with a decrease in thermal and pH stabilities, suggesting that their disulfide bonds are not involved in the structuring of its reactive site, but are important for maintenance of its conformational stability. This behavior makes EATI one of the few inhibitors described in the literature with high DTT resistance.     

Primary structure and specificity of the major serine proteinase inhibitor of amaranth (Amaranthus caudatus L.) seeds

A novel of the potato inhibitor I family of serine proteinase inactivating proteins has been isolated from seeds of grain amaranth (Amaranthus caudatus L.) and characterized. The mature form of the amaranth trypsin/subtilisin inhibitor (ATSI) with pI ≈ 8.3 and molecular mass 7887 Da contains 69 amino acids in a sequence showing 33–51% identity with members of the inhibitor I family from other plant families. A minor form with pI ≈ 7.8 and same inhibitory properties lacked the N-terminal dipeptide Ala-Arg. In accordance with the reactive-site bond Lys⁴⁵-Asp⁴⁶, which was identified by specific cleavage on a subtilisin column, ATSI is a potent inhibitor of trypsin (K_i ≈ 0.34 nM) and more weakly of plasmin (K_i ≈ 38 nM) and Factor XII_a (K_i ≈ 440 nM). However, ATSI also inactivates chymotrypsin (K_i ≈ 0.41 nM), cathepsin G (K_i ≈ 122 nM) and several alkaline microbial proteinases, including subtilisin NOVO (K_i ≈ 0.37 nM). Interestingly, ATSI contains a Trp residue instead of the highly conserved Arg in position 53 (P′_B), which is assumed to play a central role in stabilization of the active-site loop during complex formation. ATSI was immediately inactivated by peptsin and hardly represents an antinutritional component in foods or feeds.     

Synthesis and evaluation of novel azetidine analogs as potent inhibitors of vesicular [3H]dopamine uptake

Lobelane analogs that incorporate a central piperidine or pyrrolidine moiety have previously been reported by our group as potent inhibitors of VMAT2 function. Further central ring size reduction of the piperidine moiety in lobelane to a four-membered heterocyclic ring has been carried out in the current study to afford novel cis-and trans-azetidine analogs. These azetidine analogs (15a–15c and 22a–22c) potently inhibited [³H]dopamine (DA) uptake into isolated synaptic vesicles (K_i ? 66 nM). The cis-4-methoxy analog 22b was the most potent inhibitor (K_i = 24 nM), and was twofold more potent that either lobelane (2a, K_i = 45 nM) or norlobelane (2b, K_i = 43 nM). The trans-methylenedioxy analog, 15c (K_i = 31 nM), was equipotent with the cis-analog, 22b, in this assay. Thus, cis- and trans-azetidine analogs 22b and 15c represent potential leads in the discovery of new clinical candidates for the treatment of methamphetamine abuse.     

A new lysine derived glyoxal inhibitor of trypsin,its properties and utilization for studying the stabilization of tetrahedral adducts by trypsin

New trypsin inhibitors Z-Lys-COCHO and Z-Lys-H have been synthesised. K_i values for Z-Lys-COCHO, Z-Lys-COOH, Z-Lys-H and Z-Arg-COOH have been determined. The glyoxal group (–COCHO) of Z-Lys-COCHO increases binding ~300 fold compared to Z-Lys-H. The α-carboxylate of Z-Lys-COOH has no significant effect on inhibitor binding. Z-Arg-COOH is shown to bind ~2 times more tightly than Z-Lys-COOH. Both Z-Lys-¹³COCHO and Z-Lys-CO¹³CHO have been synthesized. Using Z-Lys-¹³COCHO we have observed a signal at 107.4 ppm by ¹³C NMR which is assigned to a terahedral adduct formed between the hydroxyl group of the catalytic serine residue and the ¹³C-enriched keto-carbon of the inhibitor glyoxal group. Z-Lys-CO¹³CHO has been used to show that in this tetrahedral adduct the glyoxal aldehyde carbon is not hydrated and has a chemical shift of 205.3 ppm. Hemiketal stabilization is similar for trypsin, chymotrypsin and subtilisin Carlsberg. For trypsin hemiketal formation is optimal at pH 7.2 but decreases at pHs 5.0 and 10.3. The effective molarity of the active site serine hydroxyl group of trypsin is shown to be 25300 M. At pH 10.3 the free glyoxal inhibitor rapidly (t_1/2=0.15 h) forms a Schiff base while at pH 7 Schiff base formation is much slower (t_1/2=23 h). Subsequently a free enol species is formed which breaks down to form an alcohol product. These reactions are prevented in the presence of trypsin and when the inhibitor is bound to trypsin it undergoes an internal Cannizzaro reaction via a C2 to C1 alkyl shift producing an α-hydroxycarboxylic acid.     

A Kazal-type serine proteinase inhibitor from chicken liver (clTI-1): Purification,primary structure,and inhibitory properties

Low-molecular-mass trypsin inhibitor (clTI-1; chicken liver Trypsin Inhibitor-1) was purified from chicken liver by extraction with perchloric acid, ammonium sulfate precipitation, a combination of ethanol-acetone fractionation followed by gel filtration, ion-exchange chromatography and RP-HPLC on a C18 column. The inhibitor occurs in two isoforms with molecular masses of 5938.56 and 6026.29 Da (determined by MALDI TOFF mass spectrometry). The complete amino acid sequences of both isoforms were determined (UniProtKB/Swiss-Prot P85000; ISK1L_CHICK). The inhibitor shows a high homology to Kazal-type family inhibitors, especially to trypsin/acrosin inhibitors and pancreatic secretory trypsin inhibitors. clTI-1 inhibits both bovine and porcine trypsin (K_a = 1.1 × 10⁹ M^?1 and 2.5 × 10⁹ M^?1, respectively). Significant differences were shown in the inhibition of the anionic and cationic forms of chicken trypsin (K_a = 4.5 × 10⁸ M^?1 and 1.2 × 10¹⁰ M^?1). Weak interaction with human plasmin (K_a = 1.2 × 10⁷ M^?1) was also revealed.     

Pyrrolidine analogs of GZ-793A: Synthesis and evaluation as inhibitors of the vesicular monoamine transporter-2 (VMAT2)

Central heterocyclic ring size reduction from piperidinyl to pyrrolidinyl in the vesicular monoamine transporter-2 (VMAT2) inhibitor GZ-793A and its analogs resulted in novel N-propane-1,2(R)-diol analogs 11a–i. These compounds were evaluated for their affinity for the dihydrotetrabenazine (DTBZ) binding site on VMAT2 and for their ability to inhibit vesicular dopamine (DA) uptake. The 4-difluoromethoxyphenethyl analog 11f was the most potent inhibitor of [³H]-DTBZ binding (K_i = 560 nM), with 15-fold greater affinity for this site than GZ-793A (K_i = 8.29 μM). Analog 11f also showed similar potency of inhibition of [³H]-DA uptake into vesicles (K_i = 45 nM) compared to that for GZ-793A (K_i = 29 nM). Thus, 11f represents a new water-soluble inhibitor of VMAT function.     

Design,synthesis and herbicidal activity study of aryl 2,6-disubstituted sulfonylureas as potent acetohydroxyacid synthase inhibitors

A series of sulfonylurea derivatives containing a 2,6-disubstituted aryl moiety were designed, synthesized and evaluated for their herbicidal activities. Most of these compounds showed excellent inhibitory rates against both monocotyledonous and dicotyledonous weeds, especially 10a, 10h and 10i. They exhibited equivalent or superior herbicidal efficiency than commercial chlorsulfuron at the dosage of 15 g/ha and the preliminary SAR was summarized. In order to illuminate the molecular mechanism of several potent compounds, their apparent inhibition constant (K_i^app) of Arabidopsis thaliana acetohydroxyacid synthase (AHAS) were determined and the results confirmed that these compounds were all potent AHAS inhibitors. 10i have a K_i^app of 11.5 nM, which is about 4 times as potent as chlorsulfuron (52.4 nM).     

Carbonic anhydrase inhibitors. Inhibition of human cytosolic isoforms I and II with (reduced) Schiff’s bases incorporating sulfonamide,carboxylate and carboxymethyl moieties

A library of Schiff bases was synthesized by condensation of aromatic amines incorporating sulfonamide, carboxylic acid or carboxymethyl functionalities as Zn²⁺-binding groups, with aromatic aldehydes incorporating tert-butyl, hydroxy and/or methoxy groups. The corresponding amines were thereafter obtained by reduction of the imines. These compounds were assayed for the inhibition of two cytosolic human carbonic anhydrase (hCA, EC 4.2.1.1) isoenzymes, hCA I and II. The K_i values of the Schiff bases were in the range of 7.0–21,400 nM against hCA II and of 52–8600 nM against hCA I, respectively. The corresponding amines showed K_i values in the range of 8.6 nM–5.3 μM against hCA II, and of 18.7–251 nM against hCA I, respectively. Unlike the imines, the reduced Schiff bases are stable to hydrolysis and several low-nanomolar inhibitors were detected, most of them incorporating sulfonamide groups. Some carboxylates also showed interesting CA inhibitory properties. Such hydrosoluble derivatives may show pharmacologic applications.     

Bioisosterism of urea-based GCPII inhibitors: Synthesis and structure–activity relationship studies

We report a strategy based on bioisosterism to improve the physicochemical properties of existing hydrophilic, urea-based GCPII inhibitors. Comprehensive structure–activity relationship studies of the P1′ site of ZJ-43- and DCIBzL-based compounds identified several glutamate-free inhibitors with K_i values below 20 nM. Among them, compound 32d (K_i = 11 nM) exhibited selective uptake in GCPII-expressing tumors by SPECT-CT imaging in mice. A novel conformational change of amino acids in the S1′ pharmacophore pocket was observed in the X-ray crystal structure of GCPII complexed with 32d.     

β-Secretase (BACE1)-inhibiting C-methylrotenoids from Abronia nana suspension cultures

Suspension cultures of Abronia nana were established to produce C-methylisoflavones. A new C-methylrotenoid, named abronione A (2), was isolated along with three known rotenoids, boeravinone D (1), boeravinone A methyl ether (3), and mirabijalone D (4). The IC₅₀ values of compounds 1, 2, and 4 on β-secretase (BACE1) were 4.77, 62.21, and 4.24 μM, respectively, whereas 3 was inactive. At concentrations up to 1.0 mM, the compounds did not inhibit other proteases such as trypsin, chymotrypsin, and elastase, indicating that they were specific inhibitors of β-secretase. Compounds 1 and 4 were non-competitive inhibitors based on the Dixon plot and with K_i values of 5.01 and 4.28 μM, respectively. At 50 μM, compound 4 inhibited Aβ_1–42 production by 43.7% in APP_SW-N2a cells.     

Discovery of novel α1-adrenoceptor ligands based on the antipsychotic sertindole suitable for labeling as PET ligands

The synthesis and in vitro preclinical profile of a series of 5-heteroaryl substituted analogs of the antipsychotic drug sertindole are presented. Compounds 1-(4-fluorophenyl)-3-(1-methylpiperidin-4-yl)-5-(pyrimidin-5-yl)-1H-indole (Lu AA27122, 3i) and 1-(4-fluorophenyl)-5-(1-methyl-1H-1,2,4-triazol-3-yl)-3-(1-methylpiperidin-4-yl)-1H-indole (3l) were identified as high affinity α_1A-adrenoceptor ligands with K_i values of 0.52 and 0.16 nM, respectively, and with a >100-fold selectivity versus dopamine D₂ receptors. Compound 3i showed almost equal affinity for α_1B- (K_i = 1.9 nM) and α_1D-adrenoceptors (K_i = 2.5 nM) as for α_1A, as well as moderate affinity for 5-HT_1B (K_i = 13 nM) and 5-HT₆ (K_i = 16 nM) receptors, whereas 3l showed >40-fold selectivity toward all other targets tested. Based on in vitro assays for assessment of permeability rates and extent, it is predicted that both compounds enter the brain of rats, non-human primates, as well as humans, and as such are good candidates to be carried forward for further evaluation as positron emission tomography (PET) ligands.     

Benzenesulfonamide bearing 1,2,4-triazole scaffolds as potent inhibitors of tumor associated carbonic anhydrase isoforms hCA IX and hCA XII

Three series of novel heterocyclic compounds (3a–3g, 4a–4g and 5a–5g) containing benzenesulfonamide moiety and incorporating a 1,2,4-triazole ring, have been synthesized and investigated as inhibitors against four isomers of the α-class carbonic anhydrases (CAs, EC 4.2.1.1), comprising hCAs I and II (cytosolic, ubiquitous isozymes) and hCAs IX and XII (transmembrane, tumor associated isozymes). Against the human isozymes hCA I and II, compounds of two series (3a–3g and 4a–4g) showed K_i values in the range of 84–868 nM and 5.6–390 nM, respectively whereas compounds of series 5a–5g were found to be poor inhibitors (K_i values exceeding 10,000 nM in some cases). Against hCA IX and XII, all the tested compounds exhibited excellent to moderate inhibitory potential with K_i values in the range of 2.8–431 nM and 1.3–63 nM, respectively. Compounds 3d, 3f and 4f exhibited excellent inhibitory potential against all of the four isozymes hCA I, II, IX and XII, even better than the standard drug acetazolamide (AZA) whereas compound of the series 5a–5g were comparatively less potent but more selective towards hCA IX and XII.     

Synthesis and monoamine transporter affinity of 3α-arylmethoxy-3β-arylnortropanes

A series of 3-arylnortrop-2-enes and 3α-arylmethoxy-3β-arylnortropanes were synthesized and evaluated for binding affinity at monoamine transporters. The 3-(3,4-dichlorophenyl)nortrop-2-ene (6e) exhibited high affinity for the SERT (K_i = 0.3 nM). The 3α-arylmethoxy-3β-arylnortropanes were generally SERT selective with the 3α-(3.4-dichlorophenylmethoxy)-3βphenylnortrop-2-ene (7c) possessing subnanomolar potency (K_i = 0.061 nM). However, 3α-(3,4-dichlorophenylmethoxy)-3β-phenylnortrop-2-ene (7b) exhibited high affinity at all three transporters [(DAT K_i = 22 nM), (SERT K_i = 6 nM) and (NET K_i = 101 nM)].     

A serine protease inhibitor from <Emphasis Type="Italic">Musca domestica</Emphasis> larva exhibits inhibitory activity against elastase and chymotrypsin

Objective

Insect-derived serine protease inhibitors (serpins) exhibit multiple inhibitory activities, but so far, no functional roles for serpins of Musca domestica have been identified. Here, the functional features of M. domestica serine protease inhibitor (MDSPI16) were characterized.

Results

Hundred forty seven differentially expressed genes including the MDSPI16 gene were screened by constructing the subtractive cDNA library. The 1154-bp full-length MDSPI16 gene was cloned, and the recombinant MDSPI16 serpin protein was expressed as a 42.6 kDa protein in an Escherichia coli expression system. The recombinant MDSPI16 protein was purified using Ni–NTA affinity chromatography, and the inhibitory activity of MDSPI16 was assessed. MDSPI16 did not inhibit trypsin, papain, or proteinase K but strongly inhibited elastase (K_i = 2.8 nM) and chymotrypsin (K_i = 28 nM). The inhibitory activity of MDSPI16 remained stable over from 37 to 100 °C and from pH 2 to 12.

Conclusions

The MDSPI16 exhibited inhibitory activity against elastase and chymotrypsin and the inhibitory activity remained stable.

     

Carbonic anhydrase inhibitors: Synthesis and inhibition of the human carbonic anhydrase isoforms I,II, IX and XII with benzene sulfonamides incorporating 4- and 3-nitrophthalimide moieties

A series of 4 and 5 nitro-1,3-dioxoisoindolin-2-yl benzenesulfonamide derivatives (compounds 1–8) was synthesized by reaction of benzenesulfonamide derivatives with 4 and 3-nitrophthalic anhydrides. These new sulfonamides were investigated as inhibitors of the zinc metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) and more specifically against the human (h) cytosolic isoforms hCA I and II and the transmembrane, tumor-associated hCA IX and XII. Most of the novel compounds were medium potency-weak hCA I inhibitors (K_is in the range of 295–10,000 nM), but were more effective hCA II inhibitors (K_is of 1.7–887 nM). The tumor-associated hCA IX was also inhibited, with K_is in the micromolar range, whereas against hCA XII the inhibition constants were in the range of 90–3746 nM. The structure–activity relationship (SAR) with this series of sulfonamides is straightforward, with the main features leading to good activity for each isoforms being established. The high sequence hCA alignment homology and molecular docking studies was performed in order to rationalize the activities reported and binding mode to different hCA as inhibitors.