1,2,3,4,6-penta-O-galloyl-β-d-glucose: A cholinesterase inhibitor from Terminalia chebula

The search for a novel pharmacotherapy from medicinal plants for neurodegenerative disorders has significantly advanced. Therefore, the present study was performed to evaluate the anticholinesterase activities of one hundred medicinal plants in Korea, where Terminalia chebula (T. chebula) fruits showed significant acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitions. Further bioassay monitored phytochemical exploration led to the isolation of 1,2,3,4,6-penta-O-galloyl-β-d-glucose (compound 1), which showed significant AChE and BChE inhibitory effects with IC₅₀ values of 29.9 ± 0.3 µM and 27.6 ± 0.2 µM, respectively. The inhibitory effect of compound 1 towards acetylcholinesterase was also evaluated using TLC and compared with tacrine as the positive control; the positive effect was confirmed. Furthermore, compound 1 also displayed strong antioxidant activity by the FRAP assay (IC₅₀ = 4.6 ± 0.2 µM). In conclusion, compound 1 may prove to be a potential natural anti-Alzheimer source based on noteworthy AChE and BChE inhibitions, and strong antioxidant activity.     

Molecular modeling based approach, synthesis and in vitro assay to new indole inhibitors of hepatitis C NS3/4A serine protease

In an attempt to identify potential HCV NS3 protease inhibitors lead compounds, a series of novel indoles (10a-g) was designed. Molecular modeling study, including fitting to a 3D-pharmacophore model of the designed molecules (10a-g), with HCV NS3 protease hypothesis using catalyst program was fulfilled. Also, the molecular docking into the NS3 active site was examined using Discovery Studio 2.5 software. Several compounds showed significant high simulation docking score and fit values. The designed compounds with high docking score and fit values were synthesized and biologically evaluated in vitro using an NS3 protease binding assay. It appears that most of the tested compounds reveal promising inhibitory activity against NS3 protease. Of these, compounds 10a and 10b demonstrated potent HCV NS3 protease inhibitors with IC₅₀ values of 9 and 12 ??g/mL, respectively. The experimental serine protease inhibitor activities of compounds 10a-g were consistent with their molecular modeling results. Inhibitors from this class have promising characteristics for further development as anti-HCV agents.     

Synthesis, biological assessment and molecular modeling of 14-aryl-10,11,12,14-tetrahydro-9H-benzo[5,6]chromeno[2,3-b]quinolin-13-amines

The synthesis and pharmacological evaluation of racemic 14-aryl-10,11,12,14-tetrahydro-9H-benzo[5,6]chromeno[2,3-b]quinolin-13-amines (19-28), prepared by Friedländer reaction of 3-amino-1-aryl-1H-benzo[f]chromene-2-carbonitriles (10-18) with suitable cycloalkanones is described. These molecules are potent, in the nanomolar range [IC₅₀ (EeAChE) = 7-101 nM], and selective inhibitors of acetylcholinesterase (AChE). The most potent inhibitor, 4-(13-amino-10,11,12,14-tetrahydro-9H-benzo[5,6]chromeno[2,3-b]quinolin-14-yl)phenol (20) [IC₅₀ (EeAChE) = 7 ± 2 nM] is four-fold more active than tacrine. Kinetic studies on compound 20 showed that this is a mixed-type inhibitor of EeAChE with a K_i of 5.00 nM. However, racemic 20 was unable to displace propidium iodide, suggesting that the inhibitor does not strongly bind to the peripheral anionic site (PAS) of AChE. Docking, molecular dynamics stimulations, and MM-GBSA calculations agree well with this behavior.     

Time-resolved single-turnover of ba3 oxidase from Thermus thermophilus

The kinetics of the oxidation of fully-reduced ba₃ cytochrome c oxidase from Thermus thermophilus by oxygen were followed by time-resolved optical spectroscopy and electrometry. Four catalytic intermediates were resolved during this reaction. The chemical nature and the spectral properties of three intermediates (compounds A, P and O) reproduce the general features of aa₃-type oxidases. However the F intermediate in ba₃ oxidase has a spectrum identical to the P state. This indicates that the proton taken up during the P → F transition does not reside in the binuclear site but is rather transferred to the covalently cross-linked tyrosine near that site. The total charge translocation associated with the F → O transition in ba₃ oxidase is close to that observed during the F → O transition in the aa₃ oxidases. However, the P_R → F transition is characterized by significantly lower charge translocation, which probably reflects the overall lower measured pumping efficiency during multiple turnovers.     

α-Glucosidase inhibition and antihyperglycemic activity of prenylated xanthones from Garcinia mangostana

An ethanol extract of the fruit case of Garcinia mangostan, whose most abundant chemical species are xanthones, showed potent α-glucosidase inhibitory activity (IC₅₀ = 3.2 μg/ml). A series of isolated xanthones (1-16) demonstrated modest to high inhibition of α-glucosidase with IC₅₀ values of 1.5-63.5 μM. In particular, one hitherto unknown xanthone 16 has a very rare 2-oxoethyl group on C-8. Kinetic enzymatic assays with a p-nitrophenyl glucopyranoside indicated that one of them, compound (9) exhibited the highest activity (K_i = 1.4 μM) and mixed inhibition. Using, a physiologically relevant substrate, maltose, as substrate, many compounds (6, 9, 14, and 15) also showed potent inhibition which ranged between 17.5 and 53.5 μM and thus compared favorably with deoxynojirimycin (IC₅₀ = 68.8 μM). Finally, the actual pharmacological potential of the ethanol extract was demonstrated by showing that it could elicit reduction of postprandial blood glucose levels. Furthermore, the most active α-glucosidase inhibitors (6, 9, and 14) were proven to be present in high quantities in the native seedcase by a HPLC chromatogram.     

Sesquiterpene lactones from the endemic Cape Verdean Artemisia gorgonum

Leaves and flowers of Artemisia gorgonum (Asteraceae) collected in Fogo, Cape Verde islands, were phytochemically investigated and resulted in isolation and characterization of three guaianolides 1, 2, 5, and a secoguainolide 4, in addition to eight known guaianolides 6-11 and two known germacranolides 12, 13. Structures were elucidated by 1D and 2D NMR experiments. Careful examination of the ¹³C NMR spectrum led to revision of the structure of a previously described guaianolide from 2 to 3. Most compounds exhibited mild antiplasmodial activities, ridentin (13) being the most interesting with an IC₅₀ of 3.8 ± 0.7 μg ml⁻¹ against Plasmodium falciparum FcB1 and weak cytotoxicity in a vero cell line (IC₅₀ 71.0 ± 3.9 μg ml⁻¹).     

Cytotoxic and antioxidant activities of diterpenes and sterols from the Vietnamese soft coral Lobophytum compactum

Two new diterpenes, lobocompactols A (1) and B (2), and five known compounds (3-7) were isolated from the methanol extract of the soft coral Lobophytum compactum using combined chromatographic methods and identified based on NMR and MS data. Each compound was evaluated for cytotoxic activity against A549 (lung) and HL-60 (acute promyelocytic leukemia) human cancer cell lines. Among them, compound 5 exhibited strong cytotoxic activity against the A549 cell line with an IC₅₀ of 4.97 ± 0.06 μM. Compounds 3, 4, and 7 showed moderate activity with IC₅₀ values of 23.03 ± 0.76, 31.13 ± 0.08, and 36.45 ± 0.01 μM, respectively. The cytotoxicity of 5 on the A549 cells was comparable to that of the positive control, mitoxantrone (MX). All compounds exhibited moderate cytotoxicity against the HL-60 cell line, with IC₅₀ values ranging from 17.80 ± 1.43 to 59.06 ± 2.31 μM. Their antioxidant activity was also measured using oxygen radical absorbance capacity method, compounds 1 and 2 exhibiting moderate peroxyl radical scavenging activity of 1.4 and 1.3 μM Trolox equivalents, respectively, at a concentration of 5 μM.     

Cholinergic and neuroprotective drugs for the treatment of Alzheimer and neuronal vascular diseases. II. Synthesis, biological assessment, and molecular modelling of new tacrine analogues from highly substituted 2-aminopyridine-3-carbonitriles

The synthesis, biological assessment, and molecular modelling of new tacrine analogues 11-22 is described. Compounds 11-22 have been obtained by Friedländer-type reaction of 2-aminopyridine-3-carbonitriles 1-10 with cyclohexanone or 1-benzyl-4-piperidone. The biological evaluation showed that some of these molecules were good AChE inhibitors, in the nanomolar range, and quite selective regarding the inhibition of BuChE, the most potent being 5-amino-2-(dimethylamino)-6,7,8,9-tetrahydrobenzo[1,8-b]-naphthyridine-3-carbonitrile (11) [IC₅₀ (EeAChE: 14 nM); IC₅₀ (eqBuChE: 5.2 ??M]. Kinetic studies on the easily available and potent anticholinesterasic compound 5-amino-2-(methoxy)-6,7,8,9-tetrahydrobenzo[1,8-b]-naphthyridine-3-carbonitrile (16) [IC₅₀ (EeAChE: 64 nM); IC₅₀ (eqBuChE: 9.6 ??M] showed that this compound is a mixed-type inhibitor (K_i = 69.2 nM) of EeAChE. Molecular modelling on inhibitor 16 confirms that this compound, as expected and similarly to tacrine, binds at the catalytic active site of EeAChE. The neuroprotective profile of molecules 11-22 has been investigated in SH-SY5Y neuroblastoma cells stressed with a mixture of oligomycin-A/rotenone. Compound 16 was also able to rescue by 50% cell death induced by okadaic acid in SH-SY5Y cells. From these results we conclude that the neuroprotective profile of these molecules is moderate, the most potent being compounds 12 and 17 which reduced cell death by 29%. Compound 16 does not affect ACh- nor K⁺-induced calcium signals in bovine chromaffin cells. Consequently, tacrine analogues 11-22 can be considered attractive therapeutic molecules on two key pharmacological targets playing key roles in the progression of Alzheimer, that is, cholinergic dysfunction and oxidative stress, as well as in neuronal cerebrovascular diseases.     

NF kappa B inhibitors and antitrypanosomal metabolites from endophytic fungus Penicillium sp. isolated from Limonium tubiflorum

Chemical investigation of the endophytic fungus Penicillium sp. isolated from Limonium tubiflorum growing in Egypt afforded four new compounds of polyketide origin, including two macrolides, penilactone (1) and 10,11-epoxycurvularin (2), a dianthrone, neobulgarone G (7), and a sulfinylcoumarin, sulfimarin (14), along with twelve known metabolites (3-6, 8-13, 15 and 16). The structures of all compounds were assigned by comprehensive spectral analysis (1D and 2D NMR) and mass spectrometry. Compounds 3, 4, 13 and 16 showed pronounced antitrypanosomal activity with mean MIC values ranging from 4.96 to 9.75 ??M. Moreover, when tested against a panel of three human tumor cell lines compounds 3, 4, 6 and 12 showed selective growth inhibition against Jurkat and U937 cell lines with IC₅₀ values ranging from 1.8 to 13.3 ??M. The latter compounds also inhibited TNF??-induced NF-??B activity in K562 cells with IC₅₀ values ranging from 1.6 to 10.1 ??M, respectively.     

New class of acetylcholinesterase inhibitors from the stem bark of Knema laurina and their structural insights

Bioassay-guided extraction of the stem bark of Knema laurina showed the acetylcholinesterase (AChE) inhibitory activity of DCM and hexane fractions. Further repeated column chromatography of hexane and DCM fractions resulted in the isolation and purification of five alkenyl phenol and salicylic acid derivatives. New compounds, (+)-2-hydroxy-6-(10′-hydroxypentadec-8′(E)-enyl)benzoic acid (1) and 3-pentadec-10′(Z)-enylphenol (2), along with known 3-heptadec-10′(Z)-enylphenol (3), 2-hydroxy-6-(pentadec-10′(Z)-enyl)benzoic acid (4), and 2-hydroxy-6-(10′(Z)-heptadecenyl)benzoic acid (5) were isolated from the stem bark of this plant. Compounds (1-5) were tested for their acetylcholinesterase inhibitory activity. The structures of these compounds were elucidated by the 1D and 2D NMR spectroscopy, mass spectrometry and chemical derivatizations. Compound 5 showed strong acetylcholinesterase inhibitory activity with IC₅₀ of 0.573 ± 0.0260 μM. Docking studies of compound 5 indicated that the phenolic compound with an elongated side chain could possibly penetrate deep into the active site of the enzyme and arrange itself through π-π interaction, H-bonding, and hydrophobic contacts with some critical residues along the complex geometry of the active gorge.     

Reaction of wild-type and Glu243Asp variant yeast cytochrome c oxidase with O2

We have studied internal electron transfer during the reaction of Saccharomyces cerevisiae mitochondrial cytochrome c oxidase with dioxygen. Similar absorbance changes were observed with this yeast oxidase as with the previously studied Rhodobacter sphaeroides and bovine mitochondrial oxidases, which suggests that the reaction proceeds along the same trajectory. However, notable differences were observed in rates and electron-transfer equilibrium constants of specific reaction steps, for example the ferryl (F) to oxidized (O) reaction was faster with the yeast (0.4 ms) than with the bovine oxidase (~ 1 ms) and a larger fraction Cu_A was oxidized with the yeast than with the bovine oxidase in the peroxy (P_R) to F reaction. Furthermore, upon replacement of Glu243, located at the end of the so-called D proton pathway, by Asp the P_R → F and F → O reactions were slowed by factors of ~ 3 and ~ 10, respectively, and electron transfer from Cu_A to heme a during the P_R → F reaction was not observed. These data indicate that during reduction of dioxygen protons are transferred through the D pathway, via Glu243, to the catalytic site in the yeast mitochondrial oxidase. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.     

Mononuclear and dinuclear model hydrolases of nickel and cobalt

Reaction between the dinuclear model hydrolases [M₂(μ-OAc)₂(OAc)₂(μ-H₂O)(tmen)₂]; M = Ni (1); M = Co (2) and trimethylsilyltrifluoromethanesulphonate (TMS-OTf) under identical reaction conditions gives the mononuclear complex [Ni(OAc)(H₂O)₂(tmen)][OTf] · H₂O (3) in the case of nickel and the dinuclear complex [Co₂(μ-OAc)₂(μ-H₂O)₂(tmen)₂][OTf]₂ (4) in the case of cobalt.Reaction of (3) with urea gives the previously reported [Ni(OAc)(urea)₂(tmen)][OTf] (5), whereas (4) gives [Co₂(OAc)₃(urea)(tmen)₂][OTf] (6) previously obtained by direct reaction of (2) with urea. Both (3) and (4) react with monohydroxamic acids (RHA) to give the dihydroxamate bridged dinuclear complexes [M₂(μ-OAc)(μ-RA)₂(tmen)₂][OTf]; M = Ni (7); M = Co (8) previously obtained by the reaction of (1) and (2) with RHA, illustrating the greater ability of hydroxamic acids to stabilize dinuclear complexes over that of urea by means of their bridging mode, and offering a possible explanation for the inhibiting effect of hydroxamic acids by means of their displacing bridging urea in a possible intermediate invoked in the action of urease.     

β-Diiminatolanthanoid(III) halides revisited

The crystalline compounds [LnCl₂(L)(thf)₂] [Ln = Ce (1), Tb (2), Yb (3)], [NdI₂(L)(thf)₂] (4), [LnCl(L′)₂] [Ln = Tb (5), Yb (6) (a known compound)] and [YbCl(L′′)(μ-Cl)₂Li(OEt₂)₂] (7) have been prepared [L = {N(C₆H₃Prⁱ₂-2,6)C(H)}₂CPh, L′ = {N(SiMe₃)C(Ph)}₂CH, L′′ = {N(SiMe₃)C(C₆H₄Ph-4)}₂CH]. The X-ray molecular structures of 2-7 have been established; in each, the monoanionic ligand L, L′ or L′′ is N,N′-chelating and essentially π-delocalised. Each of 1-7 was prepared from the appropriate LnCl₃, or for 4 [NdI₃(thf)₂], and an equivalent portion of the appropriate alkali metal [Li for 7, Na for 2, 3 and 5, or K for 1, 4 and 6] β-diiminate in thf; the isolation of exclusively 5 and 6 (rather than the L′ analogues of 2 or 3) is noteworthy, as is the structure of 7 which has no precedent in Group 3 or 4f metal β-diiminato chemistry.     

3-Hydroxy-2-methylene-3-(4-nitrophenylpropanenitrile): A new highly active compound against epimastigote and trypomastigote form of Trypanosoma cruzi

We have synthesized the Morita-Baylis-Hillman adduct (MBHA) 3-hydroxy-2-methylene-3-(4-nitrophenyl)-propanenitrile (3) in quantitative yield and evaluated on Trypanosoma cruzi epimastigote and bloodstream trypomastigote forms. Compound 3 strongly inhibited epimastigote growth, with IC₅₀/72 h of 28.5 μM and also caused intense trypomastigotes lysis, with an IC₅₀/24 h of 25.5 μM. Ultrastructural analysis showed significant morphological changes on both parasite forms treated with 3, including increase of cell volume and rounding of cell body as well as intense intracellular disorganization. Morphological changes indicative of apoptosis, autophagy or necrosis were observed in most affected cells. Docking calculations of 1, 2 and 3 pointed out the possibility of T. cruzi Farnesyl Pyrophosphate Synthase (TcFPPS) enzyme inhibition in 3 mechanism of action.     

Unusual stilbenoids and a stilbenolignan from seeds of Syagrus romanzoffiana

Stilbenoids, syagrusins A-B (1-2), and a stilbenolignan, 5-hydroxyaiphanol (3), along with three known phenylpropanoids (4-6), were isolated from seeds of Syagrus romanzoffiana. Compounds 1 and 2 possess unusual 1,4,4a,9a-tetrahydrofluoren-9-one and bicyclo[3.3.0]octanedione skeletons, respectively, whereas compound 3 is a stilbenolignan belonging to a very rare structural class of plant secondary metabolites. Their structures were elucidated by spectroscopic analyses. Compounds 1-3 exhibited moderate inhibitory activity against α-glucosidase with IC₅₀ values of 16.9 μM (1), 23.7 μM (2) and 12.8 μM (3), respectively.     

Prenylated C6-C3 compounds with molecular diversity from the roots of Illicium oligandrum

Eleven prenylated C₆-C₃ compounds, illioliganpyranone A (1), illioliganfunone A-D (2-5), and illioliganone D-I (6-11), together with five known prenylated C₆-C₃ compounds (12-16), were isolated from roots of Illicium oligandrum. The structures of 1-11 were elucidated by spectroscopic methods including 1D and 2D NMR, HRESIMS, and CD experiments. Possible biosynthetic pathways to compounds 1-16 derived from a common precursor of 5-allylbenzene-1,2,4-triol were postulated. All compounds were evaluated for cytotoxic activities against five human cancer cell lines (HCT-8, Bel-7402, BGC-823, A549 and A2780). Compound 15 exhibited significant cytotoxicity against HCT-8, BGC-823, A549, and A2780 cell lines with IC₅₀ values of 0.30-2.57 μM. Compound 16 showed moderate selective cytotoxicity against sensitive A2780 cells with IC₅₀ value of 1.38 μM.     

Fellutamide B is a potent inhibitor of the Mycobacterium tuberculosis proteasome

Via high-throughput screening of a natural compound library, we have identified a lipopeptide aldehyde, fellutamide B (1), as the most potent inhibitor of the Mycobacterium tuberculosis (Mtb) proteasome tested to date. Kinetic studies reveal that 1 inhibits both Mtb and human proteasomes in a time-dependent manner under steady-state condition. Remarkably, 1 inhibits the Mtb proteasome in a single-step binding mechanism with K_i = 6.8 nM, whereas it inhibits the human proteasome β5 active site following a two-step mechanism with K_i = 11.5 nM and  = 0.93 nM. Co-crystallization of 1 bound to the Mtb proteasome revealed a structural basis for the tight binding of 1 to the active sites of the Mtb proteasome. The hemiacetal group of 1 in the Mtb proteasome takes the (R)-configuration, whereas in the yeast proteasome it takes the (S)-configuration, indicating that the pre-chiral CHO group of 1 binds to the active site Thr1 in a different orientation. Re-examination of the structure of the yeast proteasome in complex with 1 showed significant conformational changes at the substrate-binding cleft along the active site. These structural differences are consistent with the different kinetic mechanisms of 1 against Mtb and human proteasomes.     

Phenolic compounds with NF-κB inhibitory effects from the fungus Phellinus baumii

Chemical investigation of the fungus Phellinus baumii has resulted in characterization of five previously undescribed hispidin derivatives, phellibaumins A-E (1-5), as well as two pairs of new non-equivalent epimeric benzyl dihydroflavones, methylphelligrin A (9), epi-methylphelligrin A (10), methylphelligrin B (11), and epi-methylphelligrin B (12), together with five known compounds, interfungin B (6), phelligridin H (7), phelligridimer A (8), phelligrin A (13), and epi-phelligrin A (14). Phellibaumin A (1) was a novel hispidin derivative with a unique 3,4-dihydroxybenzofuran unit. These compounds exhibited NF-κB inhibitory activity with IC₅₀ values of 52.96 μM (1), 41.40 μM (2), 52.92 μM (5), 36.44 μM (9 and 10), and 22.46 μM (11 and 12), respectively.     

A novel alkaloid, aristopyridinone A and anti-inflammatory phenanthrenes isolated from Aristolochia manshuriensis

A novel alkaloid, aristopyridinone A (1) and a new phenanthrene, aristolamide II (2), were isolated from Aristolochia manshuriensis (Guanmutong) together with eight known phenanthrenes (3-10). All structures were elucidated by spectroscopic methods. Compound 2 showed a selective inhibitory effect on elastase release by human neutrophils in response to fMLP with an IC₅₀ value of 4.11 μg/mL. Compound 7 exhibited significant inhibitory effects on superoxide anion generation and elastase release with IC₅₀ values of 0.12 and 0.20 μg/mL, respectively.