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In search of new anti-tuberculars compatible with anti-retroviral therapy we re-identified amicetin as a lead compound. Amicetin's binding to the 70S ribosomal subunit of Thermus thermophilus (Tth) has been unambiguously determined by crystallography and reveals it to occupy the peptidyl transferase center P-site of the ribosome. The amicetin binding site overlaps significantly with that of the well-known protein synthesis inhibitor balsticidin S. Amicetin, however, is the first compound structurally characterized to bind to the P-site with demonstrated selectivity for the inhibition of prokaryotic translation. The natural product-ribosome structure enabled the synthesis of simplified analogues that retained both potency and selectivity for the inhibition of prokaryotic translation.

We present data demonstrating the natural product mimic, zinaamidole A (ZNA), is a modulator of metal ion homeostasis causing cancer-selective cell death by specifically inducing cellular Zn(2+)-uptake in transformed cells. ZNA’s cancer selectivity was evaluated using metastatic, patient-derived breast cancer cells, established human breast cancer cell lines, and three-dimensional organoid models derived from normal and transformed mouse mammary glands. Structural analysis of ZNA demonstrated that the compound interacts with zinc through the N(2)-acyl-2-aminoimidazole core. Combination treatment with ZnSO(4) strongly potentiated ZNA’s cancer-specific cell death mechanism, an effect that was not observed with other transition metals. We show that Zn(2+)-dyshomeostasis induced by ZNA is unique and markedly more selective than other known Zn(2+)interacting compounds such as clioquinol. The in vivo bioactivity of ZNA was also assessed and revealed that tumor-bearing mice treated with ZNA had improved survival outcomes. Collectively, these data demonstrate that the N(2)-acyl-2aminoimidazole core of ZNA represents a powerful chemotype to induce cell death in cancer cells concurrently with a disruption in zinc homeostasis.

The intramolecular hydroamination of a guanidine on an eneyne unit affords a guanidine-substituted diene capable of reacting with dienophiles. These substrates undergo [4+2]-cycloaddition reactions to generate a series of complex cyclic- and spirocyclic-guanidines. Select substrates can further undergo a ring opening-elimination cascade that ultimately reveals a vinyl-2-aminoimidazole. As such this cascade reaction may find application in the synthesis of oroidin-type natural products and their analogues.

The bis-guanidinium ion family of natural products are revered for their utility in the study of ion channel physiology. While many congeners have been isolated with various oxidation and sulfation patterns, only two members of this family have been isolated bearing a carbon-carbon bond at C11, namely 11-saxitoxinethanoic acid and zetekitoxin AB. Herein we described a synthetic platform capable of efficiently targeting (+)-saxitoxin and 11-saxitoxinethanoic acid with an embedded C11 carbon-carbon bond. We demonstrate that this strategy enables direct enolate coupling in both an inter- and intramolecular fashion to create the C11-C15 carbon-carbon bond.

This paper details the design, fabrication, and characterization of highly uniform batch-fabricated sidewall etched vertical nanogap tunneling junctions for bio-sensing applications. The device consists of two vertically stacked gold electrodes separated by a partially etched sacrificial spacer layer of sputtered &alpha, Si and Atomic Layer Deposited (ALD) SiO2. A ~10 nm wide air-gap is formed along the sidewall by a controlled dry etch of the spacer. The thickness of the spacer layer can be tuned by adjusting the number of ALD cycles. The rigorous statistical characterization of the ultra-thin spacer films has also been performed. We fabricated nanogap electrodes under two design layouts with different overlap areas and spacer gaps, from ~4.0 nm to ~9.0 nm. Optical measurements reported an average non-uniformity of 0.46 nm (~8%) and 0.56 nm (~30%) in SiO2 and &alpha, Si film thickness respectively. Direct tunneling and Fowler&ndash, Nordheim tunneling measurements were done and the barrier potential of the spacer stack was determined to be ~3.5 eV. I&ndash, V measurements showed a maximum resistance of 46 &times, 103 G&Omega, and the average dielectric breakdown field of the spacer stack was experimentally determined to be ~11 MV/cm.

Wounds complicated by biofilms challenge even the best clinical care and can delay a return to duty for service members. A major component of treatment in wounded warriors includes infected wound management. Yet, all antibiotic therapy options have been optimized against planktonic bacteria, leaving an important gap in biofilm-related wound care. We tested the efficacy of a unique compound (CZ-01179) specifically synthesized to eradicate biofilms. CZ-01179 was formulated as the active agent in a hydrogel, and tested in vitro and in vivo in a pig excision wound model for its ability to treat and prevent biofilm-related wound infection caused by Acinetobacter baumannii. Data indicated that compared to a clinical standard—silver sulfadiazine—CZ-01179 was much more effective at eradicating biofilms of A. baumannii in vitro and up to 6 days faster at eradicating biofilms in vivo. CZ-01179 belongs to a broader class of newly-synthesized antibiofilm agents (referred to as CZ compounds) with reduced risk of resistance development, specific efficacy against biofilms, and promising formulation potential for clinical applications. Given its broad spectrum and biofilm-specific nature, CZ-01179 gel may be a promising agent to increase the pipeline of products to treat and prevent biofilm-related wound infections.

SUMMARY Isocitrate dehydrogenase 1 (IDH1) is the most commonly mutated gene in grade II–III glioma and secondary glioblastoma (GBM). A causal role for IDH1R132H in gliomagenesis has been proposed, but functional validation in vivo has not been demonstrated. In this study, we assessed the role of IDH1R132H in glioma development in the context of clinically relevant cooperating genetic alterations in vitro and in vivo. Immortal astrocytes expressing IDH1R132H exhibited elevated (R)-2-hydroxyglutarate levels, reduced NADPH, increased proliferation, and anchorage-independent growth. Although not sufficient on its own, IDH1R132H cooperated with PDGFA and loss of Cdkn2a, Atrx, and Pten to promote glioma development in vivo. These tumors resembled pro-neural human mutant IDH1 GBM genetically, histologically, and functionally. Our findings support the hypothesis that IDH1R132H promotes glioma development. This model enhances our understanding of the biology of IDH1R132H-driven gliomas and facilitates testing of therapeutic strategies designed to combat this deadly disease., In Brief Philip et al. show that mutant IDH1 cooperates with PDGFA and loss of Cdkn2a, Atrx, and Pten to promote gliomagenesis in vivo in a mouse model of glioma. These tumors resemble proneural human mutant IDH1 glioblastoma and exhibit enhanced sensitivity to PARP inhibition in combination with chemotherapy.

Scope: Lipotoxicity-induced endothelial dysfunction is an important vascular complication associated with diabetes. Clinical studies support the vascular benefits of blueberry anthocyanins, but the underlying mechanism is unclear. The hypothesis that metabolites of blueberry anthocyanins attenuate lipotoxicity-induced endothelial dysfunction was tested. Methods and results: Human aortic endothelial cells (HAECs) were treated for 6 h with either: (i) the parent anthocyanins (malvidin-3-glucoside and cyanidin-3-glucoside); or (ii) the blueberry metabolites (hydroxyhippuric acid, hippuric acid, benzoic acid-4-sulfate, isovanillic acid-3-sulfate, and vanillic acid-4-sulfate), at concentrations known to circulate in humans following blueberry consumption. For the last 5 h HAECs were treated with palmitate or vehicle. HAECs treated with palmitate displayed elevated reactive oxygen species generation, increased mRNA expression of NOX4, chemokines, adhesion molecules, and I?Ba, exaggerated monocyte binding, and suppressed nitric oxide production. Of note, the damaging effects of palmitate were ameliorated in HAECs treated with blueberry metabolites but not parent anthocyanins. Further, important translational relevance of these results was provided by our observation that palmitate-induced endothelial dysfunction was lessened in arterial segments that incubated concurrently with blueberry metabolites. Conclusion: The presented findings indicate that the vascular benefits of blueberry anthocyanins are mediated by their metabolites. Blueberries might complement existing therapies to lessen vascular complications.

IDH1 mutations are common in low-grade gliomas and secondary glioblastomas and cause overproduction of (R)-2HG. (R)-2HG modulates the activity of many enzymes, including some that are linked to transformation and some that are probably bystanders. Although prior work on (R)-2HG targets focused on 2OG-dependent dioxygenases, we found that (R)-2HG potently inhibits the 2OG-dependent transaminases BCAT1 and BCAT2, likely as a bystander effect, thereby decreasing glutamate levels and increasing dependence on glutaminase for the biosynthesis of glutamate and one of its products, glutathione. Inhibiting glutaminase specifically sensitized IDH mutant glioma cells to oxidative stress in vitro and to radiation in vitro and in vivo. These findings highlight the complementary roles for BCATs and glutaminase in glutamate biosynthesis, explain the sensitivity of IDH mutant cells to glutaminase inhibitors, and suggest a strategy for maximizing the effectiveness of such inhibitors against IDH mutant gliomas. Gliomas with IDH mutations show increased sensitivity to radiation in concert with glutaminase inhibition, offering a new approach to treating these tumors.

A regioselective base-mediated cyclization of mono-N-acylpropargylguanidines is reported. A related Ag(I)-catalyzed hydroamination strategy was recently employed to yield N3-Cbz-protected ene-guanidines, which found utility in the synthesis of naamidine A. Herein, we report the base-catalyzed hydroamination of mono-N-acylpropargylguanidines, which proceeds with the opposite regiochemistry to deliver isomerized N2-acyl-2-aminoimidazoles with broad substrate scope, circumventing the problematic regiospecific acylation of free 2-aminoimidazoles.

Bis -aryloxadiazoles are common scaffolds in medicinal chemistry due to their wide range of biological activities. Previously, we identified a 1,2,4-bis-aryloxadiazole that blocks mammary branching morphogenesis through activation of the aryl hydrocarbon receptor (AHR). In addition to defects in mammary differentiation, AHR stimulation induces toxicity in many other tissues. We performed a structure activity relationship (SAR) study of 1,2,4-bis-aryloxadiazole to determine which moieties of the molecule are critical for AHR activation. We validated our results with a functional biological assay, using desmosome formation during mammary morphogenesis to indicate AHR activity. These findings will aid the design of oxadiazole derivative therapeutics with reduced off-target toxicity profiles.

A synthesis of the 1,2-isoxazolidine fragment of the potent voltage gated sodium channel blocker, zetekitoxin AB is described. The synthesis utilizes an intramolecular nitrone –olefin 1,3-dipolar cycloaddition to establish the stereochemistry of the cis-1,2-isoxazolidine. The oxidative cleavage of an all anti-triol with the excision of the central carbon is central to using α-D-glucopyranoside as a traceless stereochemical template. This route furnishes a suitably protected synthon for the synthesis of zetekitoxin AB.

Cationic Rh(II) complexes are able to catalyze the regioselective hydroamination of propargyl ureas in a 6-endo fashion. This transformation permits access to interesting substitution patterns of dihydropyrimidines, which have found use as nucleotide exchange factor inhibitors.

The article discusses the synthesis of mono-N-acylguanidines, via acylation with acid chlorides or anhydrides is often complicated by over acylation due to the increased acidity of the initially formed mono-N-acylguanidine. Alternatively they can be accessed by the controlled hydrolysis of diacyl-protected guanidines. Several methods have also been developed for their synthesis from N-acyl-thioureas or N-acyl-pseudothioureas. The use of the monoprotected versions of the pyrazole transfer reagent have also been reported, but are unreactive or poorly reactive toward amines because of their decreased electrophilicity. The differentially protected pyrazole transfer reagent can be employed followed by removal of the Boc or Cbz protecting group. Keywords: Acetonitrile; Benzylamine; Benzyl chloroformate; N-Benzyl, N'-Cbz-guanidine; Carbonylbenzyloxycyanamide; Dichloromethane; Potassium benzyloxycarbonylcyanamide; Trimethylsilyl chloride

The identification of succinate dehydrogenase (SDH), fumarate hydratase (FH) and isocitrate dehydrogenase (IDH) mutations in human cancers has rekindled the idea that altered cellular metabolism can transform cells. Inactivating SDH and FH mutations cause the accumulation of succinate and fumarate, respectively, which can inhibit 2-oxoglutarate (2-OG)-dependent enzymes, including the EGLN prolyl 4-hydroxylases that mark the hypoxia inducible factor (HIF) transcription factor for polyubiquitylation and proteasomal degradation. Inappropriate HIF activation is suspected of contributing to the pathogenesis of SDH-defective and FH-defective tumours but can suppress tumour growth in some other contexts. IDH1 and IDH2, which catalyse the interconversion of isocitrate and 2-OG, are frequently mutated in human brain tumours and leukaemias. The resulting mutants have the neomorphic ability to convert 2-OG to the (R)-enantiomer of 2-hydroxyglutarate ((R)-2HG). Here we show that (R)-2HG, but not (S)-2HG, stimulates EGLN activity, leading to diminished HIF levels, which enhances the proliferation and soft agar growth of human astrocytes. These findings define an enantiomer-specific mechanism by which the (R)-2HG that accumulates in IDH mutant brain tumours promotes transformation and provide a justification for exploring EGLN inhibition as a potential treatment strategy.

A short and scalable synthesis of naamidine A, a marine alkaloid with a selective ability to inhibit epidermal growth factor receptor (EGFR)-dependent cellular proliferation, has been achieved. A key achievement in this synthesis was the development of a regioselective hydroamination of a monoprotected propargylguanidine to deliver N(3)-protected cyclic ene-guanidines. This permits the extension of this methodology to prepare N(2)-acyl analogues in a fashion that obviates the troublesome acylation of the free 2-aminoimidazoles, which typically yields mixtures of N(2)- and N(2),N(2)-diacylated products.

A concise stereoselective total synthesis of (+)-saxitoxin is described. A silver(I)-initiated hydroamination cascade constructs the bicyclic guanidinium ion core from a alkynyl bisguanidine. This sequence creates two C-N bonds, one C-O bond, and three rings and forms a single stereoisomer in a single synthetic transformation. This process enabled us to complete the synthesis of (+)-saxitoxin in 14 steps from N-Boc-l-serine methyl ester.

Syntheses of the reported structures of kealiinines B and C have been executed. An intermolecular electrophile-induced cyclization of a pendant arene on an ene–guanidine affords the tetracyclic, oxidized naphthimidazole cores.

A simple and efficient one-pot method for the synthesis of monoprotected guanidines is presented. Treatment of an acylcyanamide with chlorotrimethylsilane generates a reactive N-silylcarbodiimide capable of guanylating a variety of amines. Typically the reaction is complete in 15 min for primary and secondary aliphatic amines at rt. Hindered amines and anilines are also competent nucleophiles but require extended reaction times.

Cyclic and polycyclic guanidinium ion natural products have been shown to modulate a variety of important biological processes and their activities are often reliant on the unique hydrogen bond donor-acceptor topologies that these substructures display.1 While most synthetic methods to prepare guanidines rely on the addition of an amine (guanylation) of an activated thiourea or urea,2 alternative methodologies that generates peripheral C-N bonds from an intact guanidine nucleus have proven powerful for the preparation of polycyclic guanidine natural products.3a-e Our interest in the biological activity of guanidine natural products has prompted us to develop a synthetic platform that is capable of delivering cyclic guanidines having multiple ring sizes, substitution patterns, and oxidation states in short order. To this end we have been interested in the addition of guanidine N-H bonds across C-C π systems and recently reported a La(III) catalyzed tandem addition-hydroamination reaction of propargylcyanamides which required forcing conditions, and resulted in exclusive 5-exo-dig cyclization. 4 This led us to study the hydroamination of preformed di-Boc protected propargylguanidines of the type 1, in hopes of finding a 6-endo-dig selective process. Traditionally, metal catalyzed cyclizations on alkynes favor a 5-exo-dig pathway. This can be seen in Au(I) and Au(III) catalyzed cyclization of propargylcarbamates, propargylureas, and propargylamides, 5,6 as well as the Ti(IV)-amide hydroamination reactions of homopropargylamines. 7,8 Examples of cyclization of heteroatom nucleophiles onto alkynes leading to 6-endo-dig cyclization, although as synthetically significant as the 5-exo-dig products, are nevertheless much less common and usually observed with substrates in which the tether is largely sp2 hybridized. 9,10 During the preparation of this manuscript, Gin and co-workers described the AuCl3 catalyzed hydroamination of alkynes with 2-aminopyrimidines en route to the synthesis of crambedine.11 Their gold-catalyzed 6-exo-dig cyclization highlights the power of this approach in total synthesis. Achieving selectivity in these hydroaminations, particularly 5-exo-dig vs. 6-endo-dig, would present a valuable tool for the synthesis of complex guanidine containing natural products. This manuscript highlights the discovery of an unusual reactivity of dirhodium(II)-carboxylates as highly 6-endo-dig selective hydroamination catalysts in the cyclization of propargylguanidines, while Ag(I) is typically 5-exo-dig selective. We first examined the ability of traditional π-Lewis acids to catalyze the hydroamination of 1a (Table 1). Initial experiments highlighted that there were multiple reaction pathways available (entry 1). Cyclization of 1a in the presence of Cu(I) salts reliably gave a mixture of 6-endo-dig and 5-exo-dig products, 2a and 3a respectively, that are easily identified by the magnitude of either 3J or 4J coupling. From nOe experiments it was also confirmed that the 5-exo product 3a carried the Z-alkene configuration. The unanticipated product was the yne-guanidine 4, which may arise from a [1,3]-prototropic shift followed by isomerization as detailed by Gevorgyan for propargyl acetates.12 Table 1 Catalyst screen for propargylguanidine hydroamination. Ag(I) catalysis proved to be optimal for the generation of 3a with AgOAc giving a 1 : >20 ratio of 2a : 3a in 55% yield. It was further found that addition of AcOH to the AgOAc catalyzed reaction gave significant rate enhancements suggesting that protonolysis of the vinyl metal species was rate limiting, consistent with the known electrophilic hydroamination mechanism 13 Our first success in reversing the selectivity was found with gold (III) catalysts that favored the 6-endo product (entries 6-7). The sluggishness of the Au catalyzed reactions directed our attention to Rh(II). Dirhodium(II)-carboxylates have rarely been used to activate alkynes, however Murai has shown that Rh2(tfa)4 is a competent ene-ene-yne cycloisomerization catalyst and gives different product distributions than Pt(II) or Ru(II).14 Gratifyingly, Rh2(tfa)4 turned the selectivity over favoring the 6-endo product (entry 8). Quite to our surprise, given its decreased Lewis-acidity, Rh2(OAc)4 was a very selective catalyst favoring the 6-endo product 13 : 1 (entry 9). The reaction times were long and we suspected that this was due to catalyst solubility. The reaction was enhanced with Rh2(Oct)4 giving the 6-endo product in 81% isolated yield after 16 hours in > 20 : 1 (2a : 3a)selectivity as judged by 1H NMR (entry 10). Having identified a selective catalyst set, a substrate-selectivity profile was developed for the reaction (Table 2) and it was immediately apparent that the reactivity of the dirhodium(II)-carboxylates was quite unique. For example, cyclization of the p-methoxyphenyl alkyne (entry 1) with Ag(I) favored the 5-exo product, however with poor selectivity, consistent with the ability of this substituent to competitively stabilize a vinyl cation for 6-endo cyclization. In contrast, Rh(II) gave exclusively the 6-endo product 2b. Cyclization of electron poor aryl alkynes showed the opposite trend, with Ag(I) giving high 5-exo selectivity while Rh(II) was more modestly selective for the 6-endo product 2c (entry 2). Alkyl substituted alkynes gave the 6-endo products exclusively with Rh(II) (entries 3-7). This is in direct contrast to the Ag(I) catalyzed reactions, where modest selectivities for the 5-exo products are seen when the alkyne termini are electronically indistinguishable. Importantly for subsequent annulations and access to polycyclic skeletons, Rh2(Oct)4 tolerates useful functional groups (e.g. alcohols and alkyl chlorides, entries 4-7). These primary alkyl chlorides were also cleanly cyclized to the 5-exo-dig isomers 2g,h with Ag(I). Substitution is also permitted at the propargylic position wherein good selectivities are seen with Ag(I) for the 5-exo product and with Rh(II) for the 6-endo product (entry 8). Substituents on the guanidine nitrogen had modest effects on selectivity, with the 6-endo product always favored under Rh(II) catalysis (entries 9,10). The t-butyl alkyne 1l (entry 11) reacted well in the Ag(I) catalyzed process but was unreactive toward Rh(II), presumably due to the size of the Rh(II) catalyst. Table 2 Substrate scope for the Rh(II)-catalyzed hydroamination of propargylguanidines. The resultant cyclic eneguanidines contain a rich functional group handle for further manipulations (Scheme 1). For example bromination proceeds to give the 5-bromodihydropyrimidine 5 the structure of which was further confirmed by X-ray crystallography (Eq. 1). Oxidative cyclization of pendant nucleophiles gives the spirocyclic hemiaminal 6, reminiscent of the crambescidins (Eq. 2). Deprotection of the 5-membered ene-guanidine 2a under acidic conditions was accompanied by isomerization to give the 2-aminoimidazole 7 (Eq. 3). Reduction was also cleanly performed on 2b to give tetrahydropyrimidine 8 (Eq. 4). Scheme 1 Transformations of the resultant ene-guanidines. Examples of alkyne activation by dirhodium(II)-carboxylates are quite rare.8,15 Given the fact that reactions of internal alkynes have only been observed with Rh2(tfa)4 16 and that Rh2(Oct)4 is not able to activate alkynes independently,8 we were surprised that the dirhodium(II)-alkylcarboxylates were competent catalysts for this transformation especially at room temperature.17 This was especially true for the cyclization of electron deficient alkynes such as the pCF3Ph substituted alkyne 1c. We were even more surprised by the observation that 1c reacted ten times faster than the p-methoxy substituted alkyne 1b. Regardless of the poor π-Lewis aciditiy of these catalysts, this suggested that coordination of the alkyne was not rate limiting. Addition of 3 equivalents of acetic acid changed the selectivity from 5:1 to 1:1.7 (2c:3c, table 3 compare entries 1 and 2) suggesting that protonation of a vinyl-rhodium intermediate might be involved in the product determining step. The use of Rh2(tfa)4 as a catalyst also favored the 5-exo-dig product with 1c (entry 3). Taken together this may suggest a Curtin-Hammett scenario wherein the initial cyclization to form a 5- or 6-membered vinyl-rhodium anion is highly reversible and that perturbation of this pre-equilibrium by stabilizing the kinetically favored 5-exo-dig intermediate leads to poor selectivity.18 Table 3 Condition effects on selectivity. Mechanistically it is difficult to rationalize oxidation state changes in the dirhodium(II)-carboxylates upon arriving at a vinylrhodium intermediate (in this case the formation of Rh(I) in the dimer). This prompted us to examine better defined catalysts known to proceed through vinyl-rhodium intermediate.19 Although sluggish, Wilkinson’s catalyst promoted the cyclization and favored the 6-endo product in 10:1 selectivity (entry 4). Cationic Rh(I) however reversed the selectivity favoring the 5-exo product in 10:1 selectivity (entry 5). Again this may support the necessity for the initial cyclization event to be reversible in order to access the 6-endo product. More importantly this suggests access to more defined vinyl-rhodium intermediates that might be exploited for cascade reactivity. In conclusion we have demonstrated the unique ability of dirhodium(II)-carboxylates to catalyze the 6-endo-dig selective hydroamination of propargylguanidines. The resultant cyclic eneguanidines contain a rich latent functional group for the preparation of skeletally diverse cyclic guanidine natural product substructures. Studies to further understand the reactivity of dirhodium(II)-carboxylates and the application of these products to more complex targets are ongoing and will be reported in due course.