Enantioselective Total Synthesis of the Marine Macrolides Salarins A and C

Here we report the first total synthesis of the marine macrolide salarin C, a potent anticancer agent, and demonstrate the biomimetic oxidation-Wasserman rearrangement to access salarin A. This synthesis relies on L-proline catalysis to install a chlorohydrin function that masks the sensitive C16-C17 epoxide and potentially mimics the biosynthesis of these compounds where a related chlorohydrin may yield both THF- and epoxide-containing salarins. Additional and key features of the synthesis include (i) macrocycle formation via ring-closing metathesis, (ii) macrocyclic substrate-controlled epoxidation of the C12-C13 allylic alcohol, and (iii) a late-stage Julia-Kocienski olefination to install the side chain. Importantly, this work provides a platform for the synthesis of other salarins and analogues of these potentially important anticancer natural products.

sp3 -Rich Heterocycle Synthesis on DNA: Application to DNA-Encoded Library Production

DNA encoded library (DEL) synthesis represents a convenient means to produce, annotate and store large collections of compounds in a small volume. While DELs are well suited for drug discovery campaigns, the chemistry used in their production must be compatible with the DNA tag, which can limit compound class accessibility. As a result, most DELs are heavily populated with peptidomimetic and sp2 -rich molecules. Herein, we show that sp3 -rich mono- and bicyclic heterocycles can be made on DNA from ketochlorohydrin aldol products through a reductive amination and cyclization process. The resulting hydroxypyrrolidines possess structural features that are desirable for DELs and target a distinct region of pharmaceutically relevant chemical space.

Development and application of decatungstate catalyzed C-H 18F- and 19F-fluorination, fluoroalkylation and beyond

Over the past few decades, photocatalytic C-H functionalization reactions have received increasing attention due to the often mild reaction conditions and complementary selectivities to conventional functionalization processes. Now, photocatalytic C-H functionalization is a widely employed tool, supporting activities ranging from complex molecule synthesis to late-stage structure-activity relationship studies. In this perspective, we will discuss our efforts in developing a photocatalytic decatungstate catalyzed C-H fluorination reaction as well as its practical application realized through collaborations with industry partners at Hoffmann-La Roche and Merck, and extension to radiofluorination with radiopharmaceutical chemists and imaging experts at TRIUMF and the BC Cancer Agency. Importantly, we feel that our efforts address a question of utility posed by Professor Tobias Ritter in "Late-Stage Fluorination: Fancy Novelty or Useful Tool?" (ACIE, 2015, 54, 3216). In addition, we will discuss decatungstate catalyzed C-H fluoroalkylation and the interesting electrostatic effects observed in decatungstate-catalyzed C-H functionalization. We hope this perspective will inspire other researchers to explore the use of decatungstate for the purposes of photocatalytic C-H functionalization and further advance the exploitation of electrostatic effects for both rate acceleration and directing effects in these reactions.

A plastic scintillator and HPGe β-γ coincidence detection system

A network of specialist laboratories support the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) with re-measurements of radionuclide samples, including xenon gas. The measurement of four xenon fission product radionuclides (133Xe, 135Xe, 131mXe and 133mXe) can be used to detect an underground nuclear explosion. Laboratories use a range of techniques to measure the radionuclides, including beta-gamma (β-γ) coincidence spectrometry. These highly-sensitive measurements are capable of detecting concentrations of down to 500 atoms of 133Xe in a few cm3 of xenon. In some detector systems, detection of the metastable isomers (131mXe and 133mXe) can be more challenging due to interferences between the signatures of different radionuclides. Recent work has shown that using high-purity Germanium (HPGe) high-resolution gamma detectors, these interferences can be reduced, lowering the dependence of the detection limits on radionuclide sample isotopic composition. One downside of these detectors is the reduction in detection efficiency, which impacts the overall detection sensitivity; so assessing different detector systems is a priority for radionuclide laboratories. This work presents a coincidence detector system comprising of a plastic scintillator gas cell and a large-crystal high-purity germanium detector. The energy resolution, coincidence detection efficiency, MDA and interference factors are determined from measurements of synthetic radioxenon gas samples.

Human intestinal organoids from Cronkhite-Canada syndrome patients reveal link between serotonin and proliferation

Cronkhite-Canada Syndrome (CCS) is a rare, noninherited polyposis syndrome affecting 1 in every million individuals. Despite over 50 years of CCS cases, the etiopathogenesis and optimal treatment for CCS remains unknown due to the rarity of the disease and lack of model systems. To better understand the etiology of CCS, we generated human intestinal organoids (HIOs) from intestinal stem cells isolated from 2 patients. We discovered that CCS HIOs are highly proliferative and have increased numbers of enteroendocrine cells producing serotonin (also known as 5-hydroxytryptamine or 5HT). These features were also confirmed in patient tissue biopsies. Recombinant 5HT increased proliferation of non-CCS donor HIOs and inhibition of 5HT production in the CCS HIOs resulted in decreased proliferation, suggesting a link between local epithelial 5HT production and control of epithelial stem cell proliferation. This link was confirmed in genetically engineered HIOs with an increased number of enteroendocrine cells. This work provides a new mechanism to explain the pathogenesis of CCS and illustrates the important contribution of HIO cultures to understanding disease etiology and in the identification of novel therapies. Our work demonstrates the principle of using organoids for personalized medicine and sheds light on how intestinal hormones can play a role in intestinal epithelial proliferation.

Potent and Selective Cell-Active Iminosugar Inhibitors of Human α-N-Acetylgalactosaminidase (α-NAGAL)

Glycoside hydrolases (GHs) are a class of enzymes with emerging roles in various diseases. Selective GH inhibitors are sought to better understand their functions and assess the therapeutic potential of modulating their activities. Iminosugars are a promising class of GH inhibitors but typically lack the selectivity required to accurately perturb biological systems. Here, we describe a concise synthesis of iminosugar inhibitors of N-acetyl-α-galactosaminidase (α-NAGAL), the GH responsible for cleaving terminal α-N-acetylgalactosamine residues from glycoproteins and glycoconjugates. Starting from non-carbohydrate precursors, this modular synthesis supported the identification of a potent (490 nM) and α-NAGAL selective (~200-fold) guanidino-containing derivative DGJNGuan.  To illustrate the cellular activity of this new inhibitor, we developed a quantitative fluorescence image-based method to measure levels of the Tn-antigen, a cellular glycoprotein substrate of a-NAGAL. Using this assay we show that DGJGuan exhibits excellent inhibition of a-NAGAL within cells using patient derived fibroblasts (EC50 = 150 nM). Moreover, in vitro and in cell assays to assess levels of lysosomal b-hexosaminidase substrate ganglioside GM2 show that DGJGuan is selective whereas DGJNAc exhibits off-target inhibition both in vitro and within cells. DGJNGuan is a readily produced and selective tool compound that should prove useful for investigating the physiological roles of α-NAGAL.

An α-chloroaldehyde-based formal synthesis of eribulin

Eribulin (Halaven) is the most structurally complex non-peptidic drug made by total synthesis and has challenged preconceptions of synthetic feasibility in drug discovery and development. However, despite decades of research, the synthesis and manufacture of eribulin remains a daunting task. Here, we report syntheses of the most complex fragment of eribulin (C14-C35) used in two distinct industrial routes to this important anticancer drug. Our convergent strategy relies on a doubly diastereoselective Corey-Chaykovsky reaction to affect the union of two tetrahydrofuran-containing subunits. Notably, this process relies exclusively on enantiomerically enriched α-chloroaldehydes as building blocks for constructing the three densely functionalized oxygen heterocycles found in the C14-C35 fragment and all associated stereocenters. Overall, eribulin can now be produced in a total of 52 steps, which is a significant reduction from that reported in both academic and industrial syntheses.

Rapid 18 F- and 19 F-Difluoromethylation through Desulfurative Fluorination of Transient N-, O-, and C-Linked Dithioles

The difluoromethyl group plays an important role in modern medicinal and agrochemistry. While several difluoromethylation reagents have been reported, these typically rely on difluoromethyl carbenes or anions, or target specific processes. Here, we describe a conceptually unique and general process for O-H, N-H and C-H difluoromethylation that involves the formation of a transient dithiole followed by facile desulfurative fluorination using silver(I) fluoride. We also introduce the 5,6-dimethoxy-1,3-benzodithiole (DMBDT) function, which undergoes sufficiently rapid desulfurative fluorination to additionally support ¹⁸ F-difluoromethylation. This new process is compatible with the wide range of functional groups typically encountered in medicinal chemistry campaigns, and the use of Ag¹⁸ F is demonstrated in the production of ¹⁸ F-labeled derivatives of testosterone, perphenazine, and melatonin, 58.0±2.2, 20.4±0.3 and 32.2±3.6 MBq μmol^-1 , respectively. We expect that the DMBDT group and this ¹⁸ F/¹⁹ F-difluoromethylation process will inspire and support new efforts in medicinal chemistry, agrochemistry and radiotracer production.

Third international challenge to model the medium- to long-range transport of radioxenon to four Comprehensive Nuclear-Test-Ban Treaty monitoring stations

In 2015 and 2016, atmospheric transport modeling challenges were conducted in the context of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) verification, however, with a more limited scope with respect to emission inventories, simulation period and number of relevant samples (i.e., those above the Minimum Detectable Concentration (MDC)) involved. Therefore, a more comprehensive atmospheric transport modeling challenge was organized in 2019. Stack release data of Xe-133 were provided by the Institut National des Radioéléments/IRE (Belgium) and the Canadian Nuclear Laboratories/CNL (Canada) and accounted for in the simulations over a three (mandatory) or six (optional) months period. Best estimate emissions of additional facilities (radiopharmaceutical production and nuclear research facilities, commercial reactors or relevant research reactors) of the Northern Hemisphere were included as well. Model results were compared with observed atmospheric activity concentrations at four International Monitoring System (IMS) stations located in Europe and North America with overall considerable influence of IRE and/or CNL emissions for evaluation of the participants' runs. Participants were prompted to work with controlled and harmonized model set-ups to make runs more comparable, but also to increase diversity. It was found that using the stack emissions of IRE and CNL with daily resolution does not lead to better results than disaggregating annual emissions of these two facilities taken from the literature if an overall score for all stations covering all valid observed samples is considered. A moderate benefit of roughly 10% is visible in statistical scores for samples influenced by IRE and/or CNL to at least 50% and there can be considerable benefit for individual samples. Effects of transport errors, not properly characterized remaining emitters and long IMS sampling times (12-24 h) undoubtedly are in contrast to and reduce the benefit of high-quality IRE and CNL stack data. Complementary best estimates for remaining emitters push the scores up by 18% compared to just considering IRE and CNL emissions alone. Despite the efforts undertaken the full multi-model ensemble built is highly redundant. An ensemble based on a few arbitrary runs is sufficient to model the Xe-133 background at the stations investigated. The effective ensemble size is below five. An optimized ensemble at each station has on average slightly higher skill compared to the full ensemble. However, the improvement (maximum of 20% and minimum of 3% in RMSE) in skill is likely being too small for being exploited for an independent period.

Looking on the horizon; potential and unique approaches to developing radiation countermeasures for deep space travel

Future lunar missions and beyond will require new and innovative approaches to radiation countermeasures. The Translational Research Institute for Space Health (TRISH) is focused on identifying and supporting unique approaches to reduce risks to human health and performance on future missions beyond low Earth orbit. This paper will describe three funded and complementary avenues for reducing the risk to humans from radiation exposure experienced in deep space. The first focus is on identifying new therapeutic targets to reduce the damaging effects of radiation by focusing on high throughput genetic screens in accessible, sometimes called lower, organism models. The second focus is to design innovative approaches for countermeasure development with special attention to nucleotide-based methodologies that may constitute a more agile way to design therapeutics. The final focus is to develop new and innovative ways to test radiation countermeasures in a human model system. While animal studies continue to be beneficial in the study of space radiation, they can have imperfect translation to humans. The use of three-dimensional (3D) complex in vitro models is a promising approach to aid the development of new countermeasures and personalized assessments of radiation risks. These three distinct and unique approaches complement traditional space radiation efforts and should provide future space explorers with more options to safeguard their short and long-term health.

Origin, structure and functional transition of sex pheromone components in a false widow spider

Female web-building spiders disseminate pheromone from their webs that attracts mate-seeking males and deposit contact pheromone on their webs that induces courtship by males upon arrival. The source of contact and mate attractant pheromone components, and the potential ability of females to adjust their web’s attractiveness, have remained elusive. Here, we report three new contact pheromone components produced by female false black widow spiders, Steatoda grossa: N-4-methylvaleroyl-O-butyroyl-L-serine, N-4-methylvaleroyl-O-isobutyroyl-L-serine and N-4-methylvaleroyl-O-hexanoyl-L-serine. The compounds originate from the posterior aggregate silk gland, induce courtship by males, and web pH-dependently hydrolyse at the carboxylic-ester bond, giving rise to three corresponding carboxylic acids that attract males. A carboxyl ester hydrolase (CEH) is present on webs and likely mediates the functional transition of contact sex pheromone components to the carboxylic acid mate attractant pheromone components. As CEH activity is pH-dependent, and female spiders can manipulate their silk’s pH, they might also actively adjust their webs’ attractiveness.

Abstract 5078: Metaproteomic analysis of IBD associated colorectal cancer

Inflammatory bowel disease (IBD) increases the risk of developing colorectal cancer by 60%. The composition of gut flora and its interaction with mucosal cells plays a key role in the development of IBD and colorectal cancer. However, the actual cause-effect relationship between dysbiosis of the gut microbiome and human IBD and associated colorectal cancer has not been well established. In the current study, we sought to characterize colon mucosa adherent microbiota using metaproteomics to understand the colon micro-environment and the host-microbiome interactions. Three groups of colon biopsies were included in our analysis: healthy controls, Non-progressors (IBD patients without dysplasia or cancer) and Progressors (IBD patients who have dysplasia or cancer). The biopsy samples were analyzed by LC MS/MS and the bacterial proteins were identified using the Human Microbiome Project (HMP) human gut microbiome database. The inferences of bacterial taxonomy, bacterial enzymes and Gene ontology (GO) pathways were processed through Unipept. Examining bacterial composition between different sample groups showed no statistically significant difference at the levels of phyla and classes. However, a significant reduction of Holdemanella biformis was observed when comparing Progressors vs Non-progressors. Holdemanella biformis has recently been proposed to be endogenous anti-tumourigenic bacterial strains. Decrease of this bacterial species in Progressors suggested that it may be a protective bacteria preventing the progression of IBD associated colorectal cancer. Analysis of Gene Ontology (GO) biological processes identified GO terms that were significantly different among the Progressor, Non-progressor and healthy groups. For example, the GO term ‘detoxification of arsenic containing substances’ was significantly underrepresented in the Progressor group compared to healthy and Non-progressor groups. Furthermore, several bacterial enzymes were significantly different between the three groups. In particular, oxidoreductases were significantly decreased in the Progressor group compared to healthy and Non-progressor groups. While the implications of these significantly enriched or depleted bacterial biological processes and bacterial enzymes in the neoplastic progression of IBD warrant further investigation, the results from our current study provide new insight into understanding how gut microbiota as a modulator of microenvironment may contribute to progression of IBD-associated colorectal cancer.

Citation Format: Nobel Bhasin, Prerna Dabral, Victoria Poplaski, Lisa Lai, Hong-Yuan Tsai, Mary Bronner, Teresa Brentnall, John Valentine, Jordon March, Antone Opekun, Robert Britton, Pan Sheng, Ru Chen. Metaproteomic analysis of IBD associated colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5078.

Decatungstate Catalyzed Synthesis of Trifluoromethylthioesters from Aldehydes via a Radical Process

Here we report a mild and general method for the trifluoromethylthiolation of aldehydes using N-trifluoromethylthiosaccharin as the CF₃S radical source and sodium decatungstate (NaDT) as the photocatalyst. This reaction proceeds via hydrogen atom abstraction by photoactivated DT and features good functional groups and substrate tolerance. Generally, electron-rich aldehydes demonstrate better reactivity than electron-deficient ones and good selectivity is observed for the trifluoromethylthiolation of aldehydic C-H bonds over tertiary and benzylic C-H bonds. Preliminary mechanistic studies have shown that a free radical process is involved.

Crowdsourcing biocuration: The Community Assessment of Community Annotation with Ontologies (CACAO)

Experimental data about gene functions curated from the primary literature have enormous value for research scientists in understanding biology. Using the Gene Ontology (GO), manual curation by experts has provided an important resource for studying gene function, especially within model organisms. Unprecedented expansion of the scientific literature and validation of the predicted proteins have increased both data value and the challenges of keeping pace. Capturing literature-based functional annotations is limited by the ability of biocurators to handle the massive and rapidly growing scientific literature. Within the community-oriented wiki framework for GO annotation called the Gene Ontology Normal Usage Tracking System (GONUTS), we describe an approach to expand biocuration through crowdsourcing with undergraduates. This multiplies the number of high-quality annotations in international databases, enriches our coverage of the literature on normal gene function, and pushes the field in new directions. From an intercollegiate competition judged by experienced biocurators, Community Assessment of Community Annotation with Ontologies (CACAO), we have contributed nearly 5,000 literature-based annotations. Many of those annotations are to organisms not currently well-represented within GO. Over a 10-year history, our community contributors have spurred changes to the ontology not traditionally covered by professional biocurators. The CACAO principle of relying on community members to participate in and shape the future of biocuration in GO is a powerful and scalable model used to promote the scientific enterprise. It also provides undergraduate students with a unique and enriching introduction to critical reading of primary literature and acquisition of marketable skills.

Rational design of cell active C2-modified DGJ analogues for the inhibition of human α-galactosidase A (GALA)

We report the rational design and synthesis of C2-modified DGJ analogues to improve the selective inhibition of human GALA over other glycosidases. We prepare these analogues using a concise route from non-carbohydrate materials and demonstrate the most selective inhibitor 7c (∼100-fold) can act in Fabry patient cells to drive reductions in levels of the disease-relevant glycolipid Gb3.

All sugars ain't sweet: selection of particular mono-, di- and trisaccharides by western carpenter ants and European fire ants

Ants select sustained carbohydrate resources, such as aphid honeydew, based on many factors including sugar type, volume and concentration. We tested the hypotheses (H1-H3) that western carpenter ants, Camponotus modoc, seek honeydew excretions from Cinara splendens aphids based solely on the presence of sugar constituents (H1), prefer sugar solutions containing aphid-specific sugars (H2) and preferentially seek sugar solutions with higher sugar content (H3). We further tested the hypothesis (H4) that workers of both Ca. modoc and European fire ants, Myrmica rubra, selectively consume particular mono-, di- and trisaccharides. In choice bioassays with entire ant colonies, sugar constituents in honeydew (but not aphid-specific sugar) as well as sugar concentration affected foraging decisions by Ca. modoc. Both Ca. modoc and M. rubra foragers preferred fructose to other monosaccharides (xylose, glucose) and sucrose to other disaccharides (maltose, melibiose, trehalose). Conversely, when offered a choice between the aphid-specific trisaccharides raffinose and melezitose, Ca. modoc and M. rubra favoured raffinose and melezitose, respectively. Testing the favourite mono-, di- and trisaccharide head-to-head, both ant species favoured sucrose. While both sugar type and sugar concentration are the ultimate cause for consumption by foraging ants, strong recruitment of nest-mates to superior sources is probably the major proximate cause.

Systems biology evaluation of refractory Clostridioides difficile infection including multiple failures of fecal microbiota transplantation

BACKGROUND

Fecal microbiota transplantation (FMT) aims to cure Clostridioides difficile infection (CDI) through reestablishing a healthy microbiome and restoring colonization resistance. Although often effective after one infusion, patients with continued microbiome disruptions may require multiple FMTs. In this N-of-1 study, we use a systems biology approach to evaluate CDI in a patient receiving chronic suppressive antibiotics with four failed FMTs over two years.

METHODS

Seven stool samples were obtained between 2016-18 while the patient underwent five FMTs. Stool samples were cultured for C. difficile and underwent microbial characterization and functional gene analysis using shotgun metagenomics. C. difficile isolates were characterized through ribotyping, whole genome sequencing, metabolic pathway analysis, and minimum inhibitory concentration (MIC) determinations.

RESULTS

Growing ten strains from each sample, the index and first four recurrent cultures were single strain ribotype F078-126, the fifth was a mixed culture of ribotypes F002 and F054, and the final culture was ribotype F002. One single nucleotide polymorphism (SNP) variant was identified in the RNA polymerase (RNAP) β-subunit RpoB in the final isolated F078-126 strain when compared to previous F078-126 isolates. This SNV was associated with metabolic shifts but phenotypic differences in fidaxomicin MIC were not observed. Microbiome differences were observed over time during vancomycin therapy and after failed FMTs.

CONCLUSION

This study highlights the importance of antimicrobial stewardship in patients receiving FMT. Continued antibiotics play a destructive role on a transplanted microbiome and applies selection pressure for resistance to the few antibiotics available to treat CDI.

Total synthesis of biselide A

A total synthesis of the marine macrolide biselide A is described that relies on an enantiomerically enriched α-chloroaldehyde as the sole chiral building block. Several strategies to construct the macrocycle are presented including a macrocyclic Reformatsky reaction that ultimately provides access to the natural product in a longest linear sequence of 18 steps. Biological testing of synthetic biselide A suggests this macrolide disrupts cell division through a mechanism related to the regulation of microtubule cytoskeleton organization. Overall, this concise synthesis and insight gained into the mechanism of action should inspire medicinal chemistry efforts directed at structurally related anticancer marine macrolides.

Rational Design and Synthesis of Selective PRMT4 Inhibitors: A New Chemotype for Development of Cancer Therapeutics*

Protein arginine N-methyl transferase 4 (PRMT4) asymmetrically dimethylates the arginine residues of histone H3 and nonhistone proteins. The overexpression of PRMT4 in several cancers has stimulated interest in the discovery of inhibitors as biological tools and, potentially, therapeutics. Although several PRMT4 inhibitors have been reported, most display poor selectivity against other members of the PRMT family of methyl transferases. Herein, we report the structure-based design of a new class of alanine-containing 3-arylindoles as potent and selective PRMT4 inhibitors, and describe key structure-activity relationships for this class of compounds.

Enterobactin on a Bead: Parallel, Solid Phase Siderophore Synthesis Reveals Structure-Activity Relationships for Iron Uptake in Bacteria

A solid-phase platform for the precise and sequential synthesis of enterobactin analogues is described. This chemistry unites the power of solid-phase peptide synthesis with the unique opportunities and applications offered by siderophore chemistry. Here, a series of hybrid enterobactin hydroxamate/catecholate (HEHC) analogues were synthesized using both catechols and amino acid derived hydroxmate chelators. The HEHC analogues were evaluated for their ability to bind free iron and to promote growth in siderophore-auxotrophic mutant bacteria. We find that, in contrast to S. aureus or E. coli, a number of HEHC analogues promote growth in P. aeruginosa and structure-activity relationships (SARs) exist for the growth promotion via HEHC analogues in this organism.

Fluorodesulfurization of Thionobenzodioxoles with Silver(I) Fluoride

Difluorobenzodioxole is an important functional group found in both pharmaceuticals and agrochemicals. The late-stage introduction of this functional group is challenged by typical fluorination conditions of HF and strong oxidants. Here, we demonstrate that a range of difluorobenzodioxoles can be prepared from catechols in two steps through conversion into thionobenzodioxoles, followed by desulfurative fluorination with silver(I) fluoride. These mild reaction conditions are compatible with a variety of functional groups and enable access to a range of functionalized difluorobenzodioxoles.

Glycoside hydrolase stabilization of transition state charge: new directions for inhibitor design

Carbasugars are structural mimics of naturally occurring carbohydrates that can interact with and inhibit enzymes involved in carbohydrate processing. In particular, carbasugars have attracted attention as inhibitors of glycoside hydrolases (GHs) and as therapeutic leads in several disease areas. However, it is unclear how the carbasugars are recognized and processed by GHs. Here, we report the synthesis of three carbasugar isotopologues and provide a detailed transition state (TS) analysis for the formation of the initial GH-carbasugar covalent intermediate, as well as for hydrolysis of this intermediate, using a combination of experimentally measured kinetic isotope effects and hybrid QM/MM calculations. We find that the α-galactosidase from Thermotoga maritima effectively stabilizes TS charge development on a remote C5-allylic center acting in concert with the reacting carbasugar, and catalysis proceeds via an exploded, or loose, S_N2 transition state with no discrete enzyme-bound cationic intermediate. We conclude that, in complement to what we know about the TS structures of enzyme-natural substrate complexes, knowledge of the TS structures of enzymes reacting with non-natural carbasugar substrates shows that GHs can stabilize a wider range of positively charged TS structures than previously thought. Furthermore, this enhanced understanding will enable the design of new carbasugar GH transition state analogues to be used as, for example, chemical biology tools and pharmaceutical lead compounds.

Positive charge stabilized on remote C5-allylic center with catalysis occurring via a loose S_N2 transition state.

A short de novo synthesis of nucleoside analogs

Nucleoside analogs are commonly used in the treatment of cancer and viral infections. Their syntheses benefit from decades of research but are often protracted, unamenable to diversification, and reliant on a limited pool of chiral carbohydrate starting materials. We present a process for rapidly constructing nucleoside analogs from simple achiral materials. Using only proline catalysis, heteroaryl-substituted acetaldehydes are fluorinated and then directly engaged in enantioselective aldol reactions in a one-pot reaction. A subsequent intramolecular fluoride displacement reaction provides a functionalized nucleoside analog. The versatility of this process is highlighted in multigram syntheses of d- or l-nucleoside analogs, locked nucleic acids, iminonucleosides, and C2'- and C4'-modified nucleoside analogs. This de novo synthesis creates opportunities for the preparation of diversity libraries and will support efforts in both drug discovery and development.

Synergism of anisotropic and computational NMR methods reveals the likely configuration of phormidolide A

Characterization of the complex molecular scaffold of the marine polyketide natural product phormidolide A represents a challenge that has persisted for nearly two decades. In light of discordant results arising from recent synthetic and biosynthetic reports, a rigorous study of the configuration of phormidolide A was necessary. This report outlines a synergistic effort employing computational and anisotropic NMR investigation, that provided orthogonal confirmation of the reassigned side chain, as well as supporting a further correction of the C7 stereocenter.

Improving the sensitivity and reliability of radionuclide measurements at remote international monitoring stations

The Comprehensive Nuclear-Test-Ban Treaty is supported by a global network of monitoring stations that perform high-resolution gamma-spectrometry on air filter samples. The UK CTBT Radionuclide Laboratory has utilised cosmic veto systems to improve the sensitivity of measurements since 2010. During this study, a second detector system (with a cosmic veto) was deployed at the CTBT IMS station RN67, alongside the standard detector. This is an incredibly remote IMS station on the island of St Helena in the South Atlantic. A duplicate system was also tested at AWE to benchmark the remote systems performance. The cosmic veto system improved detection sensitivities by up to 10% across a range of radionuclides. As a system to re-measure samples 7 days after the primary measurement, detection sensitivities were improved by an order of magnitude, allowing a potentially crucial confirmation of signatures when timely transport to a laboratory is not feasible. Utilising the second detector in coincidence with the primary detector system (which would require reengineering of the shield), sensitivity improvements of up to two orders of magnitude can be achieved. These improvements are maintained even when the measurement takes place without any decay, potentially allowing a highly sensitive treaty measurement within 2 h of the end of collection.

Parenteral lipids shape gut bile acid pools and microbiota profiles in the prevention of cholestasis in preterm pigs

Multi-component lipid emulsions, rather than soy-oil emulsions, prevent cholestasis by an unknown mechanism. Here, we quantified liver function, bile acid pools, and gut microbial and metabolite profiles in premature parenterally fed pigs given a soy-oil lipid emulsion, Intralipid (IL), a multi component lipid emulsion, SMOFlipid (SMOF), a novel emulsion with a modified fatty-acid composition [experimental emulsion (EXP)], or a control enteral diet (ENT) for 22 days. We assayed serum cholestasis markers, measured total bile acid levels in plasma, liver, and gut contents, and analyzed colonic bacterial 16S rRNA gene sequences and metabolomic profiles. Serum cholestasis markers (i.e., bilirubin, bile acids, and γ-glutamyl transferase) were highest in IL-fed pigs and normalized in those given SMOF, EXP, or ENT. Gut bile acid pools were lowest in the IL treatment and were increased in the SMOF and EXP treatments and comparable to ENT. Multiple bile acids, especially their conjugated forms, were higher in the colon contents of SMOF and EXP than in IL pigs. The colonic microbial communities of SMOF and EXP pigs had lower relative abundance of several gram-positive anaerobes, including Clostridrium XIVa, and higher abundance of Enterobacteriaceae than those of IL and ENT pigs. Differences in lipid and microbial-derived compounds were also observed in colon metabolite profiles. These results indicate that multi-component lipid emulsions prevent cholestasis and restore enterohepatic bile flow in association with gut microbial and metabolomic changes. We conclude that sustained bile flow induced by multi-component lipid emulsions likely exerts a dominant effect in reducing bile acid-sensitive gram-positive bacteria.

Involvement of the Gut Microbiota and Barrier Function in Glucocorticoid-Induced Osteoporosis

Glucocorticoids (GCs) are potent immune-modulating drugs with significant side effects, including glucocorticoid-induced osteoporosis (GIO). GCs directly induce osteoblast and osteocyte apoptosis but also alter intestinal microbiota composition. Although the gut microbiota is known to contribute to the regulation of bone density, its role in GIO has never been examined. To test this, male C57/Bl6J mice were treated for 8 weeks with GC (prednisolone, GC-Tx) in the presence or absence of broad-spectrum antibiotic treatment (ABX) to deplete the microbiota. Long-term ABX prevented GC-Tx-induced trabecular bone loss, showing the requirement of gut microbiota for GIO. Treatment of GC-Tx mice with a probiotic (Lactobacillus reuteri [LR]) prevented trabecular bone loss. Microbiota analyses indicated that GC-Tx changed the abundance of Verrucomicobiales and Bacteriodales phyla and random forest analyses indicated significant differences in abundance of Porphyromonadaceae and Clostridiales operational taxonomic units (OTUs) between groups. Furthermore, transplantation of GC-Tx mouse fecal material into recipient naïve, untreated WT mice caused bone loss, supporting a functional role for microbiota in GIO. We also report that GC caused intestinal barrier breaks, as evidenced by increased serum endotoxin level (2.4-fold), that were prevented by LR and ABX treatments. Enhancement of barrier function with a mucus supplement prevented both GC-Tx-induced barrier leakage and trabecular GIO. In bone, treatment with ABX, LR or a mucus supplement reduced GC-Tx-induced osteoblast and osteocyte apoptosis. GC-Tx suppression of Wnt10b in bone was restored by the LR and high-molecular-weight polymer (MDY) treatments as well as microbiota depletion. Finally, we identified that bone-specific Wnt10b overexpression prevented GIO. Taken together, our data highlight the previously unappreciated involvement of the gut microbiota and intestinal barrier function in trabecular GIO pathogenesis (including Wnt10b suppression and osteoblast and osteocyte apoptosis) and identify the gut as a novel therapeutic target for preventing GIO. © 2019 American Society for Bone and Mineral Research.

Quaternary Ammonium Trifluoromethoxide Salts as Stable Sources of Nucleophilic OCF3

The reaction of nucleophilic tertiary amines with trifluoromethyl and pentafluoroethyl methyl ethers provides quaternary ammonium trifluoromethoxide (NR₄OCF₃) and pentafluoroethoxide (NR₄OCF₂CF₃) salts, respectively, in good yields. The new trifluoromethoxide salts disclosed herein are uniquely stable for extended periods of time in both the solid state and in solution, which complements contemporary reagents. Here we describe the preparation of a range of NR₄OCF₃ salts, their long-term stability, and utility in substitution reactions.

A Convenient Synthesis of Difluoroalkyl Ethers from Thionoesters Using Silver(I) Fluoride

Herein we report the mild and rapid fluorodesulfurization of thionoesters using only silver(I) fluoride. This reaction demonstrates excellent functional group tolerance and complements existing strategies for difluoroalkyl ether synthesis, which rely on toxic and often dangerous reagents that demonstrate limited functional group compatibility. We additionally report the translation of this finding to the production of ¹⁸ F-labelled difluoroalkyl ethers using fluoride-derived [¹⁸ F]AgF. This new process should enable the synthesis of a wide range of difluoroalkyl ethers with applications in medicinal and materials chemistry, and radiotracer production.

Genetic and morphological analyses reveal a complex biogeographic pattern in the endemic barbel populations of the southern Italian peninsula

The Italian peninsula is a biodiversity hotspot, with its freshwater fish fauna characterized by high levels of local endemism. Two endemic fluvio-lacustrine fishes of the genus Barbus (barbel, family Cyprinidae) have allopatric distributions in the Tyrrhenian and Adriatic basins of Italy. Barbus plebejus inhabits the mid- to northern Adriatic basins, while B. tyberinus is widespread in all central-northern basins draining into the Tyrrhenian Sea. For basins in Southern Italy draining into the southern parts of these seas, there remains a knowledge gap on their barbel populations due to no previous genetic and morphological studies, despite their apparent biogeographic isolation. Correspondingly, this study quantified the presence and distribution of barbels in the Adriatic and Tyrrhenian basins of Southern Italy through genetic and morphological analyses of 197 fish sampled across eight populations. Testing of how local isolation has influenced the evolution and persistence of these populations was completed by examining sequence variation at two mitochondrial loci (cytochrome b and D-loop) and performing geometric morphometric analyses of body shape, plus measuring 11 morphometric and meristic characters. Phylogenetic and morphological analyses revealed the presence of two genetically distinct lineages that differed significantly from adjacent B. tyberinus and B. plebejus populations. These two new taxa, here described as SI1 and SI2 Barbus lineages, are highly structured and reflect a complex mosaic biogeographic pattern that is strongly associated with the underlying hydrographical scenarios of the basins. The geographic isolation of these basins thus has high evolutionary importance that has to be considered for maintaining endemism.

Isolation, Structure Elucidation, and Total Synthesis of Dolichovespulide, a Sesquiterpene from Dolichovespula Yellowjackets

As part of an ongoing program to identify sex attractant pheromone components that mediate sexual communication in yellowjacket wasps, a novel sesquiterpene was isolated from body surface extracts of virgin bald-faced hornet queens, Dolichovespula maculata. The gross structure of this sesquiterpene was proposed through microscale spectroscopic analyses, and the configuration of the central olefin was subsequently confirmed by total synthesis. This new natural product (termed here dolichovespulide) represents an important addition to the relatively small number of terpenoids reported from the taxonomic insect family Vespidae.

Probiotic Lactobacillus reuteri Prevents Postantibiotic Bone Loss by Reducing Intestinal Dysbiosis and Preventing Barrier Disruption

Antibiotic treatment, commonly prescribed for bacterial infections, depletes and subsequently causes long-term alterations in intestinal microbiota composition. Knowing the importance of the microbiome in the regulation of bone density, we investigated the effect of postantibiotic treatment on gut and bone health. Intestinal microbiome repopulation at 4-weeks postantibiotic treatment resulted in an increase in the Firmicutes:Bacteroidetes ratio, increased intestinal permeability, and notably reduced femoral trabecular bone volume (approximately 30%, p < 0.01). Treatment with a mucus supplement (a high-molecular-weight polymer, MDY-1001 [MDY]) prevented the postantibiotic-induced barrier break as well as bone loss, indicating a mechanistic link between increased intestinal permeability and bone loss. A link between the microbiome composition and bone density was demonstrated by supplementing the mice with probiotic bacteria. Specifically, Lactobacillus reuteri, but not Lactobacillus rhamnosus GG or nonpathogenic Escherichia coli, reduced the postantibiotic elevation of the Firmicutes:Bacteroidetes ratio and prevented femoral and vertebral trabecular bone loss. Consistent with causing bone loss, postantibiotic-induced dysbiosis decreased osteoblast and increased osteoclast activities, changes that were prevented by both L. reuteri and MDY. These data underscore the importance of microbial dysbiosis in the regulation of intestinal permeability and bone health, as well as identify L. reuteri and MDY as novel therapies for preventing these adverse effects. © 2018 American Society for Bone and Mineral Research.

18F-Branched-Chain Amino Acids: Structure-Activity Relationships and PET Imaging Potential

The large, neutral L-type amino acid transporters (LAT1-LAT4) are sodium-independent transporters that are widely distributed throughout the body. LAT expression levels are increased in many types of cancer, and their expression increases as cancers progress, leading to high expression levels in high-grade tumors and metastases. Because of the key role and overexpression of LAT in many types of cancer, radiolabeled LAT substrates are promising candidates for nuclear imaging of malignancies that are not well revealed by conventional radiotracers. The goal of this study was to examine the structure-activity relationships of a series of ¹⁸F-labeled amino acids that were predicted to be substrates of the LAT transport system. Methods: Using a photocatalytic radical fluorination, we prepared a series of 11 fluorinated branched-chain amino acids and evaluated them and their nonfluorinated parents in a cell-based LAT affinity assay. We radiofluorinated selected branched-chain amino acids via the same radical fluorination reaction and evaluated tumor uptake in U-87 glioma xenograft-bearing mice. Results: Structure-activity relationship trends observed in a LAT affinity assay were maintained in further in vitro studies, as well as in vivo using a U-87 xenograft model. LAT1 uptake was tolerant of fluorinated amino acid stereochemistry and chain length. PET imaging and biodistribution studies showed that the tracer (S)-5-¹⁸F-fluorohomoleucine had rapid tumor uptake, favorable in vivo kinetics, and good stability. Conclusion: By using an in vitro affinity assay, we could predict LAT-mediated cancer cell uptake in a panel of fluorinated amino acids. These predictions were consistent when applied to different cell lines and murine tumor models, and several new tracers may be suitable for further development as oncologic PET imaging agents.

A counterintuitive stereochemical outcome from a chelation-controlled vinylmetal aldehyde addition leads to the configurational reassignment of phormidolide A

Detailed NMR spectroscopic comparisons of a series of synthetic C10–C23 fragments with a known derivative of phormidolide A resulted in the configurational reassignment of seven of its 11 stereocentres.

Base-Catalyzed Transesterification of Thionoesters

Here we report a convenient synthesis of thionoesters by base-catalyzed transesterification. Benzyl and alkyl thionobenzoates and thionoheterobenzoates were efficiently prepared using various alcohols catalyzed by the corresponding sodium alkoxide. This methodology features a broad substrate scope, good to excellent yields, short reaction times, while simultaneously driving the reaction toward completion through the removal of the methanol byproduct. We also report the conversion of a small collection of thionobenzoates into the corresponding α,α-difluorobenzyl ethers to demonstrate the conversion of alcohols into difluorobenzyl or difluoroheterobenzyl ethers, a process that could prove useful for lead optimization in medicinal chemistry.

Site-Selective, Late-Stage C-H 18 F-Fluorination on Unprotected Peptides for Positron Emission Tomography Imaging

Peptides are often ideal ligands for diagnostic molecular imaging due to their ease of synthesis and tuneable targeting properties. However, labelling unmodified peptides with ¹⁸ F for positron emission tomography (PET) imaging presents a number of challenges. Here we show the combination of photoactivated sodium decatungstate and [¹⁸ F]-N-fluorobenzenesulfonimide effects site-selective ¹⁸ F-fluorination at the branched position in leucine residues in unprotected and unaltered peptides. This streamlined process provides a means to directly convert native peptides into PET imaging agents under mild aqueous conditions, enabling rapid discovery and development of peptide-based molecular imaging tools.