Three-step Cascade Research Articles

Control of Stereoselectivity in Diverse Hapalindole Metabolites is Mediated by Cofactor-Induced Combinatorial Pairing of Stig Cyclases.

Stereospecific polycyclic core formation of hapalindoles and fischerindoles is controlled by Stig cyclases through a three-step cascade involving Cope rearrangement, 6-exo-trig cyclization, and a final electrophilic aromatic substitution. Reported here is a comprehensive study of all currently annotated Stig cyclases, revealing that these proteins can assemble into heteromeric complexes, induced by Ca2+ , to cooperatively control the stereochemistry of hapalindole natural products.

Hydrogen-bonding-assisted redox-neutral construction of tetrahydroquinolines via hydride transfer.

The hydrogen-bonding-assisted construction of tetrahydroquinolines decorated with structurally diverse 3,3'-difunctional groups has been realized via a hydride transfer-involved three-step cascade reaction in the presence of morpholine. This protocol solves the limitation of acyclic 1,3-dicarbonyl compounds by one-pot synthesis of tetrahydroquinolines, featuring operational simplicity, broadly applicable substrates, and metal- and acid-free conditions with EtOH as a hydrogen-bonding donor.

Design of an in vitro biocatalytic cascade for the manufacture of islatravir.

Enzyme-catalyzed reactions have begun to transform pharmaceutical manufacturing, offering levels of selectivity and tunability that can dramatically improve chemical synthesis. Combining enzymatic reactions into multistep biocatalytic cascades brings additional benefits. Cascades avoid the waste generated by purification of intermediates. They also allow reactions to be linked together to overcome an unfavorable equilibrium or avoid the accumulation of unstable or inhibitory intermediates. We report an in vitro biocatalytic cascade synthesis of the investigational HIV treatment islatravir. Five enzymes were engineered through directed evolution to act on non-natural substrates. These were combined with four auxiliary enzymes to construct islatravir from simple building blocks in a three-step biocatalytic cascade. The overall synthesis requires fewer than half the number of steps of the previously reported routes.

Mild, Modular, and Convergent Synthesis of Helical Naphtho[2,1-c]chromenes via a Multistep Cyclization/Aromatization Cascade Sequence.

Tetracyclic 6H-naphtho[2,1-c]chromenes are expeditiously synthesized through a BF3·OEt2-mediated, three-step cascade reaction, creating new central pyran and aromatic rings. The cascade involves the addition of phenol-derived alkynyl substrates to BF3-activated aldehydes followed by alkyne-Prins cyclization, Friedel-Crafts reaction, and final elimination. Aliphatic and electron-deficient aromatic aldehydes afford the products in 50-74% isolated yields, but benzaldehyde and tolualdehyde resulted in lower yields. X-ray analysis of a p-bromophenyl derivative (5aA) shows the two aromatic moieties are twisted by 28° to create a helical backbone.

Synthesis of Indolizine and Pyrrolo[1,2-a]azepine Derivatives via a Gold(I)-Catalyzed Three-Step Cascade.

Linear N-alkenyl or alkynyl N-sulfonyl 1-aminobut-3-yn-2-ones are converted into bicyclic indolizines and pyrrolo[1,2-a]azepine-type alkaloids upon gold(I) catalysis (17 examples, 10-85%). The reaction cascade allowed formation of C-N, O-S, and C-C bonds via a cycloisomerization/sulfonyl migration/cyclization process using 10 mol % of [(2-biphenyl)di-tert-butylphosphine]gold(I) triflimide complex in dichloromethane.

Implications of dark matter cascade decay from DAMPE, HESS, Fermi-LAT and AMS02 data

Abstract Recent high-energy cosmic e± measurement from the DArk Matter Particle Explorer (DAMPE) satellite confirms the deviation of total cosmic ray electron spectrum above 700-900 GeV from a simple power law. In this paper we demonstrate that the cascade decay of dark matter can account for DAMPE’s TeV e+e− spectrum. We select the least constraint DM decay channel into four muons as the benchmark scenario, and perform an analysis with propagation variance in both DM signal and the Milky Way’s electron background. The best-fit of the model is obtained for joint DAMPE, Fermi-LAT, H.E.S.S. high energy electron data sets, and with an $\mathcal {O}(10^{26})$ second decay lifetime, which is consistent with existing gamma ray and cosmic microwave background limits. We compare the spectral difference between the cascade decay of typical final-state channels. The least constrained 4μ channels give good fits to the electron spectrum’s TeV scale down-turn, yet their low energy spectrum has tension with sub-TeV positron data from AMS02. We also consider a three-step cascade decay into eight muons, and also a gamma-ray constrained 4μ, 4b mixed channel, to demonstrate that a further softened cascade decay signal would be required for the agreement with all the data sets.

2570 Capecitabine-Induced Ileitis: A Case Report

INTRODUCTION: Capecitabine is a fluoropyrimidine chemotherapy agent used in the treatment of colorectal cancer. Gastrointestinal side effects are common, including diarrhea, nausea, vomiting, abdominal pain, severe hepatic impairment, and decreased appetite. Here we report a case of Capecitabine-induced ileitis with severe diarrhea leading to hypovolemic shock and acute kidney injury. The patient was admitted to the intensive care unit (ICU) twice during hospitalization and required cessation of capecitabine. CASE DESCRIPTION/METHODS: Our patient is an 82-year-old male with a history of prostate cancer now with stage IIA rectal adenocarcinoma who was started on Capecitabine neoadjuvant chemotherapy without radiation due to previous pelvic radiotherapy for the prostate cancer. He tolerated the first treatment cycle without any side effects. At the beginning of the 2nd cycle, he reported eight watery non-bloody bowel movements a day. CT abdomen showed wall thickening of multiple loops of the distal small bowel. He was admitted to the ICU, started on vasopressor therapy and broad-spectrum antibiotics, but diarrhea persisted. Physical exam showed mild diffuse abdominal tenderness. Laboratory studies were notable for elevated creatinine but stool culture, ova and parasites, and Clostridium difficile PCR were negative. Antibiotics were stopped and loperamide was started without significant improvement. Gastroenterology was consulted and colonoscopy showed linear ulcers at terminal ileum and ulceration at ileocecal valve - pathology showed active ileitis with ulceration. Diarrhea improved with supportive management and cessation of Capecitabine. DISCUSSION: Although Capecitabine's side effects are mostly well tolerated, they can occasionally lead to prolonged hospitalization and even ICU admission. Capecitabine is not a cytotoxic drug in itself, it is absorbed from the intestine and metabolized in the liver then in the tumor cells by three-step enzymatic cascade to be converted to 5-FU. Capecitabine-induced ileitis has been reported in the literature and was diagnosed by a combination of symptoms, CT scan, colonoscopy, and/or histopathology. The mechanism is reported to be due to the susceptibility of the intestinal vascular endothelium to 5-FU by the generation of free radicals which may lead to a hypercoagulable state. In summary, treating physicians should be aware of this critical side effect and intervene early when diarrhea is reported.

TSSCM: A synergism-based three-step cascade model for influence maximization on large-scale social networks.

Identification of the most influential spreaders that maximize information propagation in social networks is a classic optimization problem, called the influence maximization (IM) problem. A reasonable diffusion model that can accurately simulate information propagation in social networks is the key step to efficiently solving the IM problem. Synergism of neighbor nodes plays an important role in information propagation dynamics. Some known diffusion models have considered the reinforcement mechanism in defining the activation threshold. Most of these models focus on the synergetic effects of nodes on their common neighbors, but the accumulation of synergism has been neglected in previous studies. Inspired by these facts, we first discuss the catalytic role of synergism in the spreading dynamics of social networks and then propose a novel diffusion model called the synergism-based three-step cascade model (TSSCM) based on the above analysis and the three-degree influence theory. Finally, we devise an algorithm for solving the IM problem based on the TSSCM. Experiments on five real large-scale social networks demonstrate the efficacy of our method, which achieves competitive results in terms of influence spreading compared to the four other algorithms tested.

Cascade synthesis of uridine-5\u2032-diphosphate glucuronic acid by coupling multiple whole cells expressing hyperthermophilic enzymes

BackgroundEnzymatic glycan synthesis has leapt forward in recent years and a number of glucuronosyltransferase (EC 2.4.1.17) have been identified and prepared, which provides a guide to an efficient approach to prepare glycans containing glucuronic acid (GlcA) residues. The uridine 5′-diphosphate (UDP) activated form, UDP-GlcA, is the monosaccharide donor for these glucuronidation reactions.ResultsTo produce UDP-GlcA in a cost-effective way, an efficient three-step cascade route was developed using whole cells expressing hyperthermophilic enzymes to afford UDP-GlcA from starch. By coupling a coenzyme regeneration system with an appropriate expression level with UDP-glucose 6-dehydrogenase in a single strain, the cells were able to meet NAD+ requirements. Without addition of exogenous NAD+, the reaction produced 1.3 g L−1 UDP-GlcA, representing 100% and 46% conversion of UDP-Glc and UTP respectively. Finally, an anion exchange chromatography purification method was developed. UDP-GlcA was successfully obtained from the cascade system. The yield of UDP-GlcA during purification was about 92.0%.ConclusionsThis work built a de novo hyperthermophilic biosynthetic cascade into E. coli host cells, with the cells able to meet NAD+ cofactor requirements and act as microbial factories for UDP-GlcA synthesis, which opens a door to large-scale production of cheaper UDP-GlcA.

One-pot, three-step cascade synthesis of D-danshensu using engineered Escherichia coli whole cells

D-danshensu (D-DSS), extracted from the plant Salvia miltiorrhiza (Danshen), is widely used to treat cardiovascular and cerebrovascular diseases. Here we engineered Escherichia coli strains to produce D-DSS from catechol, pyruvate and ammonia by one-pot biotransformation. Tyrosin-phenol lyase (TPL), L-amino acid deaminase (aadL), D-lactate dehydrogenase (ldhD) and glucose dehydrogenase (gdh) genes were overexpressed in Escherichia coli strain. First, the expression of genes was regulated by different copy number plasmids combination, the result of E. coli TALG6, with strong overexpression of TPL, aadL, ldhD and moderate overexpression of gdh, exhibited 253.7% increase D-DSS production compared to E. coli TALG1. Second, the optimum concentration of catechol was found to be 50 mM. Finally, a fed-batch biotransformation strategy was proposed, namely the amount of catechol was added to 50 mM every 2 h. The total production of D-DSS reached 55.35 mM within 14 h, which was 1.7 times that without feeding.

An Enzyme Cascade Synthesis of Vanillin

A novel approach for the synthesis of vanillin employing a three-step two-enzymatic cascade sequence is reported. Cytochrome P450 monooxygenases are known to catalyse the selective hydroxylation of aromatic compounds, which is one of the most challenging chemical reactions. A set of rationally designed variants of CYP102A1 (P450 BM3) from Bacillus megaterium at the amino acid positions 47, 51, 87, 328 and 437 was screened for conversion of the substrate 3-methylanisole to vanillyl alcohol via the intermediate product 4-methylguaiacol. Furthermore, a vanillyl alcohol oxidase (VAO) variant (F454Y) was selected as an alternative enzyme for the transformation of one of the intermediate compounds via vanillyl alcohol to vanillin. As a proof of concept, the bi-enzymatic three-step cascade conversion of 3-methylanisole to vanillin was successfully evaluated both in vitro and in vivo.

E3 ubiquitin ligases in B-cell malignancies

Ubiquitylation is a post-translational modification (PTM) that controls various cellular signaling pathways. It is orchestrated by a three-step enzymatic cascade know as the ubiquitin proteasome system (UPS). E3 ligases dictate the specificity to the substrates, primarily leading to proteasome-dependent degradation. Deregulation of the UPS components by various mechanisms contributes to the pathogenesis of cancer. This review focuses on E3 ligase-substrates pairings that are implicated in B-cell malignancies. Understanding the molecular mechanism of specific E3 ubiquitin ligases will present potential opportunities for the development of targeted therapeutic approaches.

Mechanism design of data management system for nuclear power

The data management system (DMS) developed in SNERDI is a central platform for data collection, storage, control, configuration, display, and application of all engineering data, serving for project design and management. The four-layer architecture of the DMS is proposed, and considering the specialty of nuclear power design data, key mechanisms on data modeling and storage, data collection, full text search, data visualization, and plant information model configuration are studied and solutions are presented. Specifically, the data is stored by a “name-value separation” method in which metadata and value is separately modeled and stored. Design data is collected through interfaces which acquire data either by standard template or by data extraction from engineering documents and 3D models. For full text search, all the documents are converted into plain text files, and the DMS database is “content-restored” into JSON-formatted files. Data visualization solves the problem of data display friendly and graphically, as well as 3D models navigation. The plant information model is configured by a three-step cascade style.

Enantioselective Synthesis of Pharmaceutically Active γ-Aminobutyric Acids Using a Tailor-Made Artificial Michaelase in One-Pot Cascade Reactions.

Chiral γ-aminobutyric acid (GABA) analogues represent abundantly prescribed drugs, which are broadly applied as anticonvulsants, as antidepressants, and for the treatment of neuropathic pain. Here we report a one-pot two-step biocatalytic cascade route for synthesis of the pharmaceutically relevant enantiomers of γ-nitrobutyric acids, starting from simple precursors (acetaldehyde and nitroalkenes), using a tailor-made highly enantioselective artificial “Michaelase” (4-oxalocrotonate tautomerase mutant L8Y/M45Y/F50A), an aldehyde dehydrogenase with a broad non-natural substrate scope, and a cofactor recycling system. We also report a three-step chemoenzymatic cascade route for the efficient chemical reduction of enzymatically prepared γ-nitrobutyric acids into GABA analogues in one pot, achieving high enantiopurity (e.r. up to 99:1) and high overall yields (up to 70%). This chemoenzymatic methodology offers a step-economic alternative route to important pharmaceutically active GABA analogues, and highlights the exciting opportunities available for combining chemocatalysts, natural enzymes, and designed artificial biocatalysts in multistep syntheses.

Four-component, three-step cascade reaction: an effective synthesis of indazole-fused triazolo[5,1-c]quinoxalines

An efficient four-component, three-step cascade synthesis of indazole-fused triazolo[5,1-c]quinoxalines has been described. Notable features of this protocol include simple starting materials, reduced synthetic steps, and good yields.

HIV prevention cascades: a unifying framework to replicate the successes of treatment cascades

Many countries are off track to meet targets for reducing new HIV infections. HIV prevention cascades have been proposed to assist in the implementation and monitoring of HIV prevention programmes by identifying gaps in the steps required for effective use of prevention methods, similar to HIV treatment cascades. However, lack of a unifying framework impedes widespread use of prevention cascades. Building on a series of consultations, we propose an HIV prevention cascade consisting of three key domains of motivation, access, and effective use in a priority population. This three-step cascade can be used for routine monitoring and advocacy, particularly by attaching 90-90-90-style targets. Further characterisation of reasons for gaps across motivation, access, or effective use allows for a comprehensive framework, guiding identification of relevant responses and platforms for interventions. Linking the prevention cascade, reasons for gaps, and interventions reconciles the different requirements of prevention cascades, providing a unifying framework.

Monitoring of successive phosphorylations of thymidine using free and immobilized human nucleoside/nucleotide kinases by Flow Injection Analysis with High-Resolution Mass Spectrometry

Nucleosides and their analogues play a crucial role in the treatment of several diseases including cancers and viral infections. Their therapeutic efficiency depends on their capacity to be converted to the active nucleoside triphosphates form through successive phosphorylation steps catalyzed by nucleoside/nucleotide kinases. It is thus mandatory to develop an easy, rapid, reliable and sensitive enzyme activity tests. In this study, we monitored the three-step phosphorylation of thymidine to thymidine triphosphate respectively by (1) human thymidine kinase 1 (hTK1), (2) human thymidylate kinase (hTMPK) and (3) human nucleoside diphosphate kinase (hNDPK). Free and immobilized kinase activities were characterized by using the Michaelis-Menten kinetic model. Flow Injection Analysis (FIA) with High-Resolution Mass Spectrometry (HRMS) was used as well as capillary electrophoresis (CE) with UV detection. The three-step cascade phosphorylation of thymidine was also monitored. FIA-HRMS allows a sensitive and rapid evaluation of the phosphorylation process. This study proposes simple, rapid, efficient and sensitive methods for enzyme kinetic studies and successive phosphorylation monitoring with immobilized enzymes.

Protease-Activatable Scaffold Proteins as Versatile Molecular Hubs in Synthetic Signaling Networks.

Protease signaling and scaffold-induced control of protein–protein interactions represent two important mechanisms for intracellular signaling. Here we report a generic and modular approach to control the activity of scaffolding proteins by protease activity, creating versatile molecular platforms to construct synthetic signaling networks. Using 14-3-3 proteins as a structurally well-characterized and important class of scaffold proteins, three different architectures were explored to achieve optimal protease-mediated control of scaffold activity, fusing either one or two monovalent inhibitory ExoS peptides or a single bivalent ExoS peptide to T14-3-3 using protease-cleavable linkers. Analysis of scaffolding activity before and after protease-induced cleavage revealed optimal control of 14-3-3 activity for the system that contained monovalent ExoS peptides fused to both the N-and C-terminus, each blocking a single T14-3-3 binding site. The protease-activatable 14-3-3 scaffolds were successfully applied to construct a three-step signaling cascade in which dimerization and activation of FGG-caspase-9 on an orthogonal supramolecular platform resulted in activation of a 14-3-3 scaffold, which in turn allowed 14-3-3-templated complementation of a split-luciferase. In addition, by combining 14-3-3-templated activation of caspase-9 with a caspase-9-activatable 14-3-3 scaffold, the first example of a synthetic self-activating protease signaling network was created. Protease-activatable 14-3-3 proteins thus represent a modular platform whose properties can be rationally engineered to fit different applications, both to create artificial in vitro synthetic molecular networks and as a novel signaling hub to re-engineer intracellular signaling pathways.

Three-step cascade over a single catalyst: synthesis of 5-(ethoxymethyl)furfural from glucose over a hierarchical lamellar multi-functional zeolite catalyst

Glucose conversion over hierarchical lamellar MFI–Sn/Al: accommodating a three-step reaction cascade over a single catalyst for a high yield of 5-(ethoxymethyl) furfural.

Enantioselective biocatalytic formal α-amination of hexanoic acid to l-norleucine.

A three-step one-pot biocatalytic cascade was designed for the enantioselective formal α-amination of hexanoic acid to l-norleucine. Regioselective hydroxylation by P450CLA peroxygenase to 2-hydroxyhexanoic acid was followed by oxidation to the ketoacid by two stereocomplementary dehydrogenases. Combination with final stereoselective reductive amination by amino acid dehydrogenase furnished l-norleucine in >97% ee.