Azaphilones: chemistry and biology

Natural product driven diversity via skeletal remodeling of caryophyllene β-lactam

(-)-β-Caryophyllene was decorated with a privileged β-lactam motif and subsequently converted into highly diverse scaffolds via remodeling of the ring system. The structures were defined by spectroscopic data, X-ray diffraction analysis, and experimental and calculated ECD data. Compound 19 displayed the most potent activity against the rice blast fungus, while 6 had a more potent α-glucosidase inhibition than the drug acarbose. These findings demonstrate a concise protocol to exploit natural product-driven diversity.

Structural Basis of a Broadly Selective Acyltransferase from the Polyketide Synthase of Splenocin

Polyketides are a large family of pharmaceutically important natural products, and the structural modification of their scaffolds is significant for drug development. Herein, we report high-resolution X-ray crystal structures of the broadly selective acyltransferase (AT) from the splenocin polyketide synthase (SpnD-AT) in the apo form and in complex with benzylmalonyl and pentynylmalonyl extender unit mimics. These structures revealed the molecular basis for the stereoselectivity and substrate specificity of SpnD-AT, and enabled the engineering of the industrially important Ery-AT6 to broaden its substrate scope to include three new types of extender units.

Structural Diversity and Biological Activities of Novel Secondary Metabolites from Endophytes

Exploration of structurally novel natural products greatly facilitates the discovery of biologically active pharmacophores that are biologically validated starting points for the development of new drugs. Endophytes that colonize the internal tissues of plant species, have been proven to produce a large number of structurally diverse secondary metabolites. These molecules exhibit remarkable biological activities, including antimicrobial, anticancer, anti-inflammatory and antiviral properties, to name but a few. This review surveys the structurally diverse natural products with new carbon skeletons, unusual ring systems, or rare structural moieties that have been isolated from endophytes between 1996 and 2016. It covers their structures and bioactivities. Biosynthesis and/or total syntheses of some important compounds are also highlighted. Some novel secondary metabolites with marked biological activities might deserve more attention from chemists and biologists in further studies.

Chlorinated Azaphilone Pigments with Antimicrobial and Cytotoxic Activities Isolated from the Deep Sea Derived Fungus Chaetomium sp. NA-S01-R1

Four novel compounds, chaephilone C (1), chaetoviridides A–C (2–4), were obtained from the culture of a deep sea derived fungus Chaetomium sp. NA-S01-R1, together with four known compounds—chaetoviridin A (5), chaetoviridine E (6), chaetomugilin D (7) and cochliodone A (8). Their structures, including absolute configurations, were assigned based on NMR, MS and time-dependent density functional theory (TD-DFT) ECD calculations. A plausible biogenetic pathway for compounds 1–3 was proposed. Compounds 2 and 3 exhibited antibacterial activities against Vibrio rotiferianus and Vibrio vulnificus. Compounds 1, 3 and 4 displayed similar anti-methicillin resistant Staphylococcus aureus (anti-MRSA) activities in comparison to chloramphenicol. Compound 2 showed the most potent cytotoxic activities towards the Hep G2 cell and compounds 1 and 3 demonstrated relatively stronger cytotoxic activities than the other compounds against the HeLa cell.

Polyoxygenated Cyclohexenoids with Promising α-Glycosidase Inhibitory Activity Produced by Phomopsis sp. YE3250, an Endophytic Fungus Derived from Paeonia delavayi

Seven new polyoxygenated cyclohexenoids, namely, phomopoxides A-G (1-7), were isolated from the fermentation broth extract of an endophytic fungal strain Phomopsis sp. YE3250 from the medicinal plant Paeonia delavayi Franch. The structures of these compounds were established by spectroscopic interpretation. The absolute configurations of compounds 1 and 4 were confirmed by X-ray crystallographic analysis and chemical derivative approach. All isolated compounds showed weak cytotoxic activities toward three human tumor cell lines (Hela, MCF-7, and NCI-H460) and weak antifungal activities against five pathogenic fungi (Candida albicans, Aspergillus niger, Pyricularia oryzae, Fusarium avenaceum, and Hormodendrum compactum). In addition, compounds 1-7 showed a promising α-glycosidase inhibitory activity with IC₅₀ values of 1.47, 1.55, 1.83, 2.76, 2.88, 3.16, and 2.94 mM, respectively, as compared with a positive control of acarbose (IC₅₀ = 1.22 mM).

Polyoxygenated cyathane diterpenoids from the mushroom Cyathus africanus, and their neurotrophic and anti-neuroinflammatory activities

In a previous study, we reported ten new polyoxygenated cyathane diterpenoids, neocyathins A-J, and their anti-neuroinflammatory effects from the liquid culture of the medicinal Basidiomycete Cyathus africanus. In the present study, eight new highly polyoxygenated cyathane diterpenoids, named neocyathins K-R (1-8), were isolated from the solid culture of C. africanus cultivated on cooked rice, together with three known congeners (9-11). The structures and the absolute configurations of the new compounds were elucidated through comprehensive NMR and HRESIMS spectroscopic data, electronic circular dichroism (ECD) data, and chemical conversion. Compounds 1 and 2 represent the first reported naturally occurring compounds with 4,9-seco-cyathane carbon skeleton incorporating an unprecedented medium-sized 9/7 fused ring system, while the 3,4-seco-cyathane derivative (3) was isolated from Cyathus species for the first time. All compounds were evaluated for their neurotrophic and anti-neuroinflammatory activity. All the isolates at 1-25 μM displayed differential nerve growth factor (NGF)-induced neurite outgrowth-promoting activity in PC-12 cells, while one of the compounds, allocyathin B₂ (11), inhibited NO production in lipopolysaccharide (LPS)-stimulated microglia BV-2 cells. In addition, molecular docking studies showed that compound 11 generated interactions with the inducible nitric oxide synthase (iNOS) protein.

Secondary Metabolites of Mangrove-Associated Strains of Talaromyces

Boosted by the general aim of exploiting the biotechnological potential of the microbial component of biodiversity, research on the secondary metabolite production of endophytic fungi has remarkably increased in the past few decades. Novel compounds and bioactivities have resulted from this work, which has stimulated a more thorough consideration of various natural ecosystems as conducive contexts for the discovery of new drugs. Thriving at the frontier between land and sea, mangrove forests represent one of the most valuable areas in this respect. The present paper offers a review of the research on the characterization and biological activities of secondary metabolites from manglicolous strains of species belonging to the genus Talaromyces. Aspects concerning the opportunity for a more reliable identification of this biological material in the light of recent taxonomic revisions are also discussed.

Monascuspigment rubropunctatin derivative FZU-H reduces Aβ(1-42)-induced neurotoxicity in Neuro-2A cells

Alzheimer's disease (AD) is an extremely complex disease, characterized by several pathological features including oxidative stress and amyloid-β (Aβ) aggregation. Blockage of Aβ-induced injury has emerged as a potential therapeutic approach for AD. Our previous efforts resulted in the discovery of Monascus pigment rubropunctatin derivative FZU-H with potential neuroprotective effects. This novel lead compound significantly diminishes toxicity induced by Aβ(1-42) in Neuro-2A cells. Our further mechanism investigation revealed that FZU-H inhibited Aβ(1-42)-induced caspase-3 protein activation and the loss of mitochondrial membrane potential. In addition, treatment of FZU-H was proven to attenuate Aβ(1-42)-induced cell redox imbalance and Tau hyperphosphorylation which caused by okadaic acid in Neuro-2A cells. These results indicated that FZU-H shows promising neuroprotective effects for AD.

Monascus pigment rubropunctatin derivative FZU-H shows promising neuroprotective effects for AD.

Penicilazaphilones D and E: two new azaphilones from a sponge-derived strain of the fungus Penicillium sclerotiorum

Two new azaphilones, penicilazaphilones D (1) and E (2), along with four known analogs (3–6), were obtained from the sponge-derived fungus Penicillium sclerotiorum.

Production of Monascus pigments as extracellular crystals by cell suspension culture

It is generally accepted that Monascus pigments are predominantly cell-bound, including both intracellular and surface-bound pigments. This long-term misconception was corrected in the present work. Production of extracellular crystal pigments by submerged culture of Monascus sp. was confirmed by microscopic observation and collection of Monascus pigments from extracellular broth by direct membrane filtration. Following up the new fact, the bioactivity of mycelia as whole-cell biocatalyst for biosynthesis and biodegradation of Monascus pigments had been detailedly examined in both an aqueous solution and a nonionic surfactant micelle aqueous solution. Based on those experimental results, cell suspension culture in an aqueous medium was developed as a novel strategy for accumulation of high concentration of Monascus pigments. Thus, glucose feeding during submerged culture in the aqueous medium was carried out successfully and high orange Monascus pigments concentration of near 4 g/L was achieved.

Rosoloactone: A natural diterpenoid inducing apoptosis in human cervical cancer cells through endoplasmic reticulum stress and mitochondrial damage

Natural diterpenoids have been previously reported to induce tumor cell apoptosis. We identified a diterpenoid metabolite as rosoloactone that was isolated from the endophytic fungus Trichothecium roseum and displayed significant antitumor activity in vitro. In this study, we report the antitumor effect of rosoloactone on human cervical cancer HeLa cells and its mechanism of action. Our data indicate that rosoloactone induces strong anti-proliferative and pro-apoptotic effects in human cervical cancer HeLa cells, leads to significant apoptotic morphological characteristics, and increases the number of Annexin V-positive stained cells. These effects were associated with endoplasmic reticulum stress (ERS) and mitochondrial damage. More specifically, rosoloactone caused accumulation of misfolded or unfolded proteins in the ER lumen, leading to excessive ERS, as well as mitochondrial damage followed by release of cytochrome c into the cytosol, activation of caspase-9 and -3, and subsequent activation of mitochondria-mediated apoptosis. Furthermore, the effects of rosoloactone were likely accompanied by marked reactive oxygen species (ROS) production. Altogether our results showed that rosoloactone mediates pro-apoptotic effects in human cervical cancer HeLa cells likely via the activation of ERS-associated apoptosis and the mitochondria-mediated apoptotic pathway.

Ferrocene Derived Bifunctional Phosphine-Catalyzed Asymmetric Oxa-[4+2] Cycloaddition of α-Substituted Allenones with Enones

An efficient ferrocene-derived bifunctional phosphine-catalyzed enantioselective oxa-[4+2] cycloaddition of α-substituted allenones with a broad range of enones is investigated for the preparation of stereodefined dihydropyrans in good to excellent yields (up to 99 %) and excellent enantioselectivity (up to 99 % ee). Furthermore, a series of valuable chiral polyheterocyclic frameworks can be efficiently achieved in good yields with excellent enantioselectivities.

Determination of two potential toxicity metabolites derived from the disruption of the pksCT gene in Monascus aurantiacus Li As3.4384

BACKGROUND

We previously demonstrated that disruption of the pksCT gene of Monascus led to a greater than 98% decrease in its citrinin production capacity in Monascus (PHDS26). Two potentially toxic compounds, monascopyridine A (MPA) and monascopyridine B (MPB), were found in the fermentation products of the pksCT gene-disrupted Monascus. Moreover, a rapid and reliable high-performance liquid chromatography method was developed for the simultaneous determination of MPA and MPB. We studied the effects of various extraction parameters and designed an orthogonal experiment to investigate the importance of each factor.

RESULTS

The optimal extraction conditions were: methanol concentration, 90%; extraction temperature, 40 °C; extraction time, 10 min; two extraction cycles; and a solid-liquid ratio of 1:25. Under the optimal chromatographic conditions, good linearity was reached over the concentration ranges 0.5-200 µg mL^-1 and 0.5-300 µg mL^-1 for MPA and MPB, respectively, and the corresponding determination coefficients were 0.9999 and 0.9997. The percentage relative standard deviation values of within-day and between-day precision for MPA were 2.0% and 2.1%, respectively; the corresponding values for MPB were 4.8% and 4.6%. The average recovery for MPA and MPB was 99.9% and 94%, respectively.

CONCLUSION

Maximum MPA and MPB yields (2073.7 and 1961.7 µg g^-1 , respectively) were observed after 16 days of cultivation. © 2017 Society of Chemical Industry.

Polyketides with different post-modifications from desert endophytic fungus Paraphoma sp

Three new polyketides 4,6,8-trihydroxy-5-methyl-3,4-dihydronaphthalen-1(2H)-one (1), 5,7-dihydroxy-3-(1-hydroxyethyl)-3,4-dimethylisobenzofuran-1(3H)-one (2) and 1-(4-hydroxy-6-methoxy-1,7-dimethyl-3-oxo-1,3-dihydroisobenzofuran-1-yl) ethyl acetate (3) together with seven known analogues (4-10) were isolated from desert endophytic fungus Paraphoma sp. The structures of these compounds were elucidated by analysis of NMR data. The absolute configuration of (1-3) was established on the basis of CD experiments. The possible biosynthetic pathway of compounds (1-10) was suggested, which implied that these secondary metabolites might be originated from polyketide biosynthesis with different post-modification reactions. Compounds 2, and 5-8 were evaluated for bioactivities against plant pathogen A. solani, whereas none of them displayed any biological effects. In addition, compounds 1, 2 and 5-10 were also tested for cytotoxic activities against three human cancer cell lines (HepG2 cells, MCF-7 cells and Hela cells) without biological effects.

Bioactive Azaphilone Derivatives from the Fungus Talaromyces aculeatus

Six new azaphilone derivatives, talaraculones A-F (1-6), together with five known analogues (7-11), were obtained from the saline soil-derived fungus Talaromyces aculeatus. The absolute configurations of 1 and 6 were assigned by quantum chemical calculations of the electronic circular dichroism (ECD) spectra. Compounds 1 and 5 represent the first reported azaphilone derivatives with a C4 aliphatic side chain and a methylal group at C-3, respectively. Talaraculones A and B (1 and 2) exhibited stronger inhibitory activity against α-glucosidase than the positive control acarbose (IC₅₀ = 101.5 μM), with IC₅₀ values of 78.6 and 22.9 μM, respectively.

New alkenylated tetrahydropyran derivatives from the marine sediment-derived fungus Westerdykella dispersa and their bioactivities

Six new alkenylated tetrahydropyran derivatives belonged to polyketides, designated as (12R,13R)-dihydroxylanomycinol (1), (12S,13S)-dihydroxylanomycinol (2), (12R,13S)-dihydroxylanomycinol (3) and (12S,13R)-dihydroxylanomycinol (4), (12S,13R)-N-acetyl-dihydroxylanomycin (5) and (12S,13S)-N-acetyl-dihydroxylanomycin (6), together with one related known compound lanomycinol (7) were isolated from the liquid cultures of Westerdykella dispersa obtained from the marine sediments. Their structures and absolute configurations were determined on the basis of extensive analysis of NMR spectra combined with comparison of NMR data to those of known compound, and computational method via calculation of the electronic circular dichroism (ECD). The anti-agricultural pathogenic fungal and antibacterial activities of all isolated compounds were evaluated. Compounds 1-7 exhibited moderate antifungal activities selectively against tested fungal strains with minimum inhibitory concentration (MIC) values ranging from 12.5 to 50μg/mL, and weak antibacterial activities selectively against tested antibacterial strains with MIC value at 100μg/mL.

Preparation, Structure, and Potent Antifouling Activity of Sclerotioramine Derivatives

A series of 30 sclerotioramine derivatives (2-31) of the natural compound, (+)-sclerotiorin (1), has been successfully semi-synthesized by a one-step reaction with high yields (up to 80%). The structures of these new derivatives were established by extensive spectroscopic methods and single-crystal X-ray diffraction analysis for 3, 6, and 10. (+)-Sclerotiorin (1) and its semisynthetic derivatives (2-31) were evaluated for their antifouling activity. Most of them except 6, 7, 8, 12, and 28 showed potent antifouling activity against the larval settlement of the barnacle Balanus amphitrite. More interestingly, most of the aromatic amino-derivatives (13-17, 19-21, 23, 25-27, and 29-31) showed strong antifouling activity; however, only two aliphatic amino-derivatives (5 and 10) had the activity.

Antifungal and Antiviral Cyclic Peptides from the Deep-Sea-Derived Fungus Simplicillium obclavatum EIODSF 020

A new linear peptide simplicilliumtide I (1) and four new cyclic peptides simplicilliumtides J-M (2-5) together with known analogues verlamelins A and B (6 and 7) were isolated from the deep-sea-derived fungal strain Simplicillium obclavatum EIODSF 020. Their structures were elucidated by spectroscopic analysis, and their absolute configurations were further confirmed by chemical structural modification, Marfey's and Mosher's methods. Compounds 2, 6, and 7 showed significant antifungal activity toward Aspergillus versicolor and Curvularia australiensis and also had obvious antiviral activity toward HSV-1 with IC₅₀ values of 14.0, 16.7, and 15.6 μM, respectively. The structure-bioactivity relationship of this type of cyclic peptide was also discussed. This is the first time to discuss the effects of the lactone linkage and the substituent group of the fatty acid chain fragment on the bioactivity of this type of cyclic peptides. This is also the first time to report the antiviral activity of these cyclic peptides.

Minutellins A - D, azaphilones from the stromata of Annulohypoxylon minutellum (Xylariaceae)

During the course of our screening for new metabolites with chemotaxonomic importance from stromata of fungi from the family Xylariaceae, we characterized several interesting metabolites in the fungus Annulohypoxylon minutellum. Extraction of the fruiting bodies and purification by preparative HPLC resulted in the isolation of five metabolites. The main compound was identified as the known metabolite hinnulin A (5), while four minor compounds were found to represent previously undescribed azaphilones, named minutellins A - D (1-4). Their planar structures were elucidated using NMR and HRESIMS data; absolute stereochemistry was assigned by CD data and Mosher's method. Compounds 1, 3 and 5 showed cytotoxic effects against murine and human cells. As the production of 1-5 is restricted to a group of closely related Annulohypoxylon species, they serve well as chemotaxonomic marker.

Penicilones A-D, Anti-MRSA Azaphilones from the Marine-Derived Fungus Penicillium janthinellum HK1-6

Four new azaphilones, penicilones A-D (1-4), were isolated from the mangrove rhizosphere soil-derived fungus Penicillium janthinellum HK1-6. Their planar structures and absolute configurations were determined by extensive analysis of NMR spectroscopic data, ECD spectra, the modified Mosher's method, and chemical conversions. Interestingly, 1 and 2 had the opposite configuration at C-7 compared to the closely related chloro analogues 3 and 4. Ester hydrolysis of 2 and 4 afforded their parental azaphilones, named penicilones E (5) and F (6). Compounds 1-6 were evaluated for their antibacterial activities in vitro. Penicilones B-D (2-4) showed potent anti-MRSA (Staphylococcus aureus ATCC 43300, ATCC 33591) activities with MIC values ranging from 3.13 to 6.25 μg/mL.

The fungal natural product azaphilone-9 binds to HuR and inhibits HuR-RNA interaction in vitro

The RNA-binding protein Hu antigen R (HuR) binds to AU-rich elements (ARE) in the 3'-untranslated region (UTR) of target mRNAs. The HuR-ARE interactions stabilize many oncogenic mRNAs that play important roles in tumorigenesis. Thus, small molecules that interfere with the HuR-ARE interaction could potentially inhibit cancer cell growth and progression. Using a fluorescence polarization (FP) competition assay, we identified the compound azaphilone-9 (AZA-9) derived from the fungal natural product asperbenzaldehyde, binds to HuR and inhibits HuR-ARE interaction (IC50 ~1.2 μM). Results from surface plasmon resonance (SPR) verified the direct binding of AZA-9 to HuR. NMR methods mapped the RNA-binding interface of HuR and identified the involvement of critical RNA-binding residues in binding of AZA-9. Computational docking was then used to propose a likely binding site for AZA-9 in the RNA-binding cleft of HuR. Our results show that AZA-9 blocks key RNA-binding residues of HuR and disrupts HuR-RNA interactions in vitro. This knowledge is needed in developing more potent AZA-9 derivatives that could lead to new cancer therapy.

Structure and Biosynthesis of Isatropolones, Bioactive Amine-Scavenging Fluorescent Natural Products from Streptomyces Gö66

The natural products isatropolone A-C (1-3) were reisolated from Streptomyces Gö66, with 1 and 3 showing potent activity against Leishmania donovani. They contain a rare tropolone ring derived from a type II polyketide biosynthesis pathway. Their biosynthesis was elucidated by labeling experiments, analysis of the biosynthesis gene cluster, its partial heterologous expression, and structural characterization of various intermediates. Owing to their 1,5-diketone moiety, they can react with ammonia, amines, lysine, and lysine-containing peptides and proteins, which results in the formation of a covalent bond and subsequent pyridine ring formation. Their fluorescence properties change upon amine binding, enabling the simple visualization of reacted amines including proteins.

Potential allelopathic azaphilones produced by the endophytic Chaetomium globosum TY1 inhabited in Ginkgo biloba using the one strain-many compounds method

On the basis of the one strain-many compounds strategy, seven azaphilones, including Chaetomugilin A (1), D (2), S (3), I (4), J (5), Q (6) and O (7), were isolated from the endophytic Chaetomium globosum TY1. Their structures were identified by NMR and HRESIMS spectrometry data. All azaphilones were evaluated for plant growth regulation using eight species of herbaceous plant seeds seedling growth bioassay, which showed the plant growth influence of the seedling. Among these compounds tested, Chaetomugilin O (7) with tetrahydrofuran exhibited higher response index and lower IC50 values than positive control glyphosate, a broad-spectrum systemic herbicide. 1-3 also showed better or similar inhibit activity to glyphosate. The structure-allelopathic activity relationship analysis of these isolated azaphilones indicates that both tetrahydrofuran and tetrahydrofuran combine with lactones ring groups give potent inhibition of seedling growth. Chaetomugilin O and Chaetomugilin A, D, S could be used to develop natural eco-friendly herbicides.

Montagnuphilones A-G, Azaphilones from Montagnulaceae sp. DM0194, a Fungal Endophyte of Submerged Roots of Persicaria amphibia

Seven azaphilones, montagnuphilones A-G (1-7), together with previously known azaphilones 8-11, were encountered in Montagnulaceae sp. DM0194, an endophytic fungus isolated from submerged roots of Persicaria amphibia. The structures of 1-7 were elucidated on the basis of their MS and NMR spectroscopic analysis. Compounds 1-8 were evaluated for their cytotoxicity and ability to inhibit nitric oxide (NO) production in lipopolysaccharide-activated RAW264.7 macrophage cells. Among these, none were found to be cytotoxic to RAW264.7 cells up to 100.0 μM, but 8, 5, and 2 showed NO inhibitory activity with IC₅₀ values of 9.2 ± 0.9, 25.5 ± 1.1, and 39.6 ± 1.8 μM, respectively.

New prenylxanthones, polyketide hemiterpenoid pigments from the endophytic fungus Emericella sp. XL029 and their anti-agricultural pathogenic fungal and antibacterial activities

Four new prenylxanthones and five known compounds were isolated from the plant endophytic fungusEmericellasp. XL029. Biological assays revealed that the compounds showed selective inhibitory activity against bacterial and fungal strains.

Exploring sesquiterpene alkaloid-like scaffolds via Beckmann-transannular remodelling of beta-caryophyllene

Cascaded Beckmann-transannular protocol transformed macrocyclic beta-caryophyllene into poly-heterocyclic unnatural skeletal types.

Highly oxygenated caryophyllene-type and drimane-type sesquiterpenes from Pestalotiopsis adusta, an endophytic fungus of Sinopodophyllum hexandrum

Four new highly oxidized caryophyllene-type sesquiterpenes (1–4), and two new drimane-type sesquiterpenes (6, 7), along with nine known compounds have been isolated from an endophytic fungus Pestalotiopsis adusta.

Fluorescent natural products as probes and tracers in biology

Fluorescence is a remarkable property of many natural products in addition to their medicinal and biological value. Herein, we provide a review of these peculiar secondary metabolites to stimulate prospecting of them as original fluorescent tracers, endowed with unique photophysical properties and with applications in most fields of biology.

Electronic effects on a one-pot aromatization cascade involving alkynyl-Prins cyclization, Friedel–Crafts alkylation and dehydration to tricyclic benzo[f]isochromenes

A short, efficient cyclization/aromatization cascade affords tricyclic 1,4-dihydro-2H-benzo[f]isochromenes. Electronic factors suggest concerted alkynyl-Prins and Friedel–Crafts reactions in the sequence.

α-Glucosidase inhibitors and phytotoxins from Streptomyces xanthophaeus

Twenty-four metabolites 1-24 were isolated from the fermentation broth of Streptomyces xanthophaeus. Their structures were elucidated on the basis of spectroscopic analysis and by comparison of their NMR data with literature data reported. Daidzein (1), genistein (2) and gliricidin (3) inhibited α-glucosidase in vitro with IC₅₀ values of 174.2, 36.1 and 47.4 μM, respectively, more potent than the positive control, acarbose. Docking study revealed that the amino acid residue Thr 215 is the essential binding site for active ligands 2. In addition, the phytotoxic effects of all compounds were assayed on radish seedlings, five of which, 3, 8, 13, 15 and 18, inhibited the growth of radish (Raphanus sativus) seedlings with inhibitory rates of >60% at a concentration of 100 ppm, which was comparable or superior to the positive control glyphosate. This is the first report of the phytotoxicity of the compounds.

Tau-directed approaches for the treatment of Alzheimer's disease: focus on leuco-methylthioninium

Small molecular weight compounds able to inhibit formation of tau oligomers and fibrils have already been tested for Alzheimer's disease (AD) treatment. The most advanced tau aggregation inhibitor (TAI) is methylthioninium (MT), a drug existing in equilibrium between a reduced (leuco-methylthioninium) and oxidized form (MT(+)). MT chloride (also known as methylene blue) was investigated in a 24-week Phase II study in 321 mild-to-moderate AD patients at the doses of 69, 138, and 228 mg/day. This trial failed to show significant positive effects of MT in the overall patient population. The dose of 138 mg/day showed potential benefits on cognitive performance of moderately affected patients and cerebral blood flow in mildly affected patients. A follow-up compound (TRx0237) claimed to be more bioavailable and less toxic than MT, is now being developed. Phase III clinical trials on this novel TAI in AD and in the behavioral variant of frontotemporal dementia are underway.