Multigram Quantities Research Articles

Deoxofluorination of pyridinyloxoacetates by sulfur tetrafluoride

An effective scalable method for the synthesis of -, -, and -pyridinyloxoacetates has been developed, based on the interaction of the respective bromopyridines with diethyl oxalate in the presence of isopropylmagnesium chloride. This method enables the preparation of all isomeric pyridinyl oxoacetates with preparative yields in multigram quantities. The deoxofluorination process of isomeric pyridinyl oxoacetates with sulfur tetrafluoride was investigated. It was established that the deoxofluorination of - and -pyridinyloxoacetates with sulfur tetrafluoride leads to the formation of a mixture of -/-pyridinyldifluoroacetic acid esters and -/-pyridinyltetrafluorinated ethers, which can be separated chromatographically. It was found that when using an excess of sulfur tetrafluoride and prolonged heating of the reaction mixture, the fluorination of -/-pyridinyl oxoacetates results in the exclusive formation of -/-pyridinyltetrafluorinated ethers. On the other hand, in the case of deoxofluorination of -pyridinyloxoacetate with sulfur tetrafluoride, varying the temperature and the amount of fluorinating reagent allows for the selective formation of -pyridinyldifluoroacetic acid ester or -pyridinyltetrafluorinated ether. -/-/-Pyridinyltetrafluorinated ethers are new representatives of the small group of hetaryltetrafluorinated ethers and have potential applications in medicine and agrochemistry.

Considerations for safety assessment of intractable proteins expressed in genetically modified crops

Current requirements for safety assessment by regulatory agencies necessitate the production of multi-gram quantities of functionally active proteins newly expressed in genetically modified (GM) crops. This presents challenges for so-called intractable proteins (those that are difficult to isolate in an active form). Significant experience and knowledge have been gained by both GM crop developers and global regulatory agencies regarding the safety assessment of the newly expressed proteins (NEPs). By leveraging this knowledge and scientific data that have accumulated over the last several decades, the safety assessments of NEPs can be refined and improved. In this technical review, we examine the options for characterizing intractable NEPs and producing protein test substances from different sources to support the safety assessments of novel GM crops.

Continuous Flow Approach for Benzylic Photo-oxidations Using Compressed Air.

A continuous flow approach for the aerobic photo-oxidation of benzylic substrates to ketone and aldehyde products is presented. The resulting process exploits UV-A LEDs (375 nm) in combination with a Corning AFR reactor that ensures effective gas-liquid mixing and leads to short residence times of 1 min. A variety of benzylic substrates are converted to their corresponding carbonyl products, and scalability is demonstrated to produce multigram quantities of products within a few hours. Overall, this continuous flow approach offers several improvements over alternative oxidation methods due to the combined use of air as an oxidant and SAS (sodium anthraquinone-2 sulfonate) as a water-soluble photocatalyst. The use of greener and safer conditions together with process intensification principles renders this flow approach attractive for further industrial applications.

Mechanochemical Synthesis of Boroxine-linked Covalent Organic Frameworks.

We report a rapid, room-temperature mechanochemical synthesis of 2- and 3-dimensional boroxine covalent organic frameworks (COFs), enabled by using trimethylboroxine as a dehydrating additive to overcome the hydrolytic sensitivity of boroxine-based COFs. The resulting COFs display high porosity and crystallinity, with COF-102 being the first example of a mechanochemically prepared 3D COF, exhibiting a surface area of ca.2,500m2g-1. Mechanochemistry enabled a >20-fold reduction in solvent use and ~100-fold reduction in reaction time compared with solvothermal methods, providing target COFs quantitatively with no additional work-up besides vacuum drying. Real-time Raman spectroscopy permitted the first quantitative kinetic analysis of COF mechanosynthesis, while transferring the reaction design to Resonant Acoustic Mixing (RAM) enabled synthesis of multi-gram amounts of the target COFs (tested up to 10 g).

Large-scale purification of a deprotected macrocyclic peptide by supercritical fluid chromatography (SFC) integrated with liquid chromatography in discovery chemistry

A macrocyclic peptide A was successfully purified in large quantities (∼30 g) in >95 % purity by an integrated two-step orthogonal purification process combining supercritical fluid chromatography (SFC) with medium-pressure reverse-phase liquid chromatography (MP-RPLC). MP-RPLC was used to fractionate the crude peptide A, remove unwanted trifluoroacetic acid (TFA) originating from the peptide A cleavage off the resin, and convert the peptide A into ammonium acetate salt form, prior to the final purification by SFC. A co-solvent of methanol/acetonitrile containing ammonium acetate and water in CO2 was developed on a Waters BEH 2-Ethylpyridine column. The developed SFC method was readily scaled up onto a 5 cm diameter column to process multi-gram quantities of the MP-RPLC fraction to reach > 95 % purity with a throughput/productivity of 0.96 g/h. The incorporation of SFC with MP-RPLC has been demonstrated to have a broader application in other large-scale polypeptide purifications.

Diastereodivergent Synthesis of A-Ring Lactones Derived from Cholesterol and Diosgenin: A Convenient Solution for an Old Problem – NMR and X-ray Characterization

AbstractA convenient protocol for the synthesis of A-ring lactones derived from cholesterol was developed. A lactone reduction–lactol separation–reoxidation sequence, applied to the inseparable mixture of diastereomeric lactones, allows the production of multigram amounts of each lactone in pure form. The same sequence applied to A-ring lactones derived from diosgenin produced similar results. A detailed NMR characterization of all the obtained lactones is also provided. X-ray diffraction corroborated the structure of the obtained compounds.

A Fast and Efficient Molecular Networking Approach for Reactivity of Natural Products Exploration in Plant Extracts: Application to Diterpene Esters from Euphorbia dendroides.

Natural products represent a rich source of bioactive compounds, covering a large chemical space. Even if challenging, this diversity can be extended by applying chemical modifications. However, these studies generally require multigram amounts of isolated natural products and face frequent testing failures. To overcome this limitation, we propose a rapid and efficient approach that uses molecular networking (MN) to visualize the new chemical diversity generated by simple chemical modifications of natural extracts. Moreover, the strategy deployed enables the most appropriate reagents to be defined quickly upstream of a reaction on a pure compound, in order to maximize chemical diversity. This methodology was applied to the latex extract of Euphorbia dendroides to follow the reactivity toward a series of Brønsted and Lewis acids of three class of diterpene esters identified in this species: jatrophane, terracinolide, and phorbol. Through the molecular networking interpretation, with the aim to illustrate our approach, BF3·OEt2 was selected for chemical modification on isolated jatrophane esters. Three rearranged compounds (3-5) were obtained, showing that the most appropriate reagents can be selected by MN interpretation.

(Diazomethyl)dimethylphosphine Oxide - A Diazoalkane Reagent for [3+2] Cycloadditions.

A safe and efficient method for the in-situ preparation of (diazomethyl)dimethylphosphine oxide - a hereto unexplored diazoalkane reagent - is developed. The method is based on the diazotization of the corresponding P(O)Me2-substituted amine (readily available in multigram quantities) in non-aqueous media. The protocol provides the target product as ca. 1.5 M CHCl3 solution which is stable at -18 °C. The utility of the synthesized diazoalkane is illustrated by its [3+2] cycloaddition with electron-poor alkynes and alkenes providing the corresponding P(O)Me2-substituted pyrazoles and pyrazolines with moderate to good efficiency. In this view, the title compound represents and an important extension of medicinally relevant phosphine oxide reagents.

A continuous flow approach for the desulfurative bromination of sulfides

The preparation of alkyl bromides is a pivotal transformation in organic chemistry. The wide range of applications that bromides have as building blocks render this class of compounds a privileged motif widely used in the manufacture of active pharmaceutical ingredients. Traditionally prepared from the deoxygenation of alcohols, alkyl bromides have been recently obtained from sulfides in high yields, a transformation we have named desulfurative bromination. In order to improve the efficiency of this transformation, we report herein the investigation and optimisation of a continuous flow strategy. The influence of the flow rate; role of the brominating agent; and substrate scope have been studied delivering an in-flow protocol to access multigram quantities of these valuable intermediates.

Preparation of von Hippel-Lindau (VHL) E3 ubiquitin ligase ligands exploiting constitutive hydroxyproline for benzylic amine protection.

The von Hippel-Lindau (VHL) protein serves as the substrate recognition subunit of the multi-subunit Cullin-2 RING E3 ubiquitin ligase (CRL2VHL), which regulates intracellular concentrations of hypoxia inducible factors (HIFs) through a ubiquitin proteasome system (UPS) cascade. Strategic recruitment of CRL2VHL by bi- or trifunctional targeted protein degraders (e.g., PROTACs®) offers the prospect of promoting aberrant polyubiquitination and ensuing proteasomal degradation of disease-related proteins. Non-peptidic, l-hydroxyproline-bearing VHL ligands such as VH032 (1) and its chiral benzylic amine analog Me-VH032 (2), are functional components of targeted protein degraders commonly employed for this purpose. Herein, we compare two approaches for the preparation of 1 and 2 primarily highlighting performance differences between Pd(OAc)2 and Pd-PEPPSI-IPr for the key C-H arylation of 4-methylthiazole. Results from this comparison prompted the development of a unified, five-step route for the preparation of either VH032 (1) or Me-VH032 (2) in multigram quantities, resulting in yields of 56% and 61% for 1 and 2, respectively. Application of N-Boc-l-4-hydroxyproline rather than N-tert-butoxycarbonyl to shield the benzylic amine during the coupling step enhances step economy. Additionally, we identified previously undisclosed minor byproducts generated during arylation steps along with observations from amine deprotection and amidation reaction steps that may prove helpful not only for the preparation of 1 and 2, but for other VHL recruiting ligands, as well.

Synthesis, Structural Characterization and Hirshfeld Surface Analysis of a Novel Cd(II) Coordination Polymer with Mixed N- and O-donor Linker

In the present study, we report the room temperature synthesis of a novel two-dimensional (2D) coordination polymer (CP) having the formula {[Cd(H-PCA)2(H2O)].0.5(H2O).0.5(CH3OH)}n (CP1), where H-PCA represents 4-pyrazolecarboxylate. The synthesis of CP1 was achieved through a one-pot reaction, involving the self-assembly of Cd(OAc)2·2H2O and the multitopic mixed N- and O-donor ligand, 4-pyrazolecarboxylic acid (H2-PCA), in methanol. This method demonstrated high yield and purity, enabling the facile production of multigram quantities of CP1 within a short timeframe. Notably, the synthetic procedure selectively deprotonates the carboxylic acid group while retaining the pyrazole moiety in its protonated form.CP1 has been thoroughly characterized using various analytical techniques, including single-crystal X-ray diffraction, FTIR spectroscopy, elemental analysis, scanning electron microscopy, thermogravimetric analysis, and powder X-ray diffraction. The structural analysis revealed that CP1 features a 3, 5-connected binodal net with the point symbol {4.5.6}{4.55.63.7}, leading to a unique –ths net topology. Through hydrogen bonding connections between adjacent 2D sheets, CP1 further extends into a three-dimensional (3D) supramolecular network due to the presence of coordinated water molecules and the protonated pyrazole group. Additionally, a 3D Hirshfeld Surface analysis accompanied by quantitative 2D fingerprint plots was also investigated to explore the intermolecular interactions.

A novel Zn(II) coordination polymer with mixed N- and O-donor linker: Room temperature synthesis, comprehensive characterization and Hirshfeld surface analysis

The present study describes the room temperature synthesis of a new two-dimensional (2D) coordination polymer (CP) having the formula [Zn(H-PCA)2]n (CP1), where H-PCA stands for 4-pyrazolecarboxylate. The mixture of Zn(OAc)2·2H2O and multitopic mixed N- and O-donor 4-pyrazolecarboxylic acid (H2-PCA) were self-assembled in a one-pot in methanol. The synthesis produced good yield and purity, and this method makes it simple to obtain multigram quantities of CP1 within a short period. Notably, this synthetic method selectively deprotonates the carboxylic acid group while maintaining pyrazole moiety in its protonated form. CP1 has been characterized by single-crystal X-ray diffraction, FTIR spectroscopy, elemental analysis, scanning electron microscopy, thermogravimetric analysis and powder X-ray diffraction. CP1 exhibits a 4-connected, 2-fold interpenetrated 2D network with the point symbol {44.62} – sql net topology. Due to the presence of the protonated pyrazole, these 2D layers further extended into a three-dimensional (3D) non-porous supramolecular network through strong 'intermolecular' NH···O hydrogen bonds between adjacent layers. Additionally, a 3D Hirshfeld Surface analysis accompanied by quantitative 2D-fingerprint plots was also investigated to explore the 'intermolecular' interactions.

Development of a Continuous Flow Baldwin Rearrangement Process and Its Comparison to Traditional Batch Mode.

A new and highly efficient continuous flow process is presented for the synthesis of aziridines via the thermal Baldwin rearrangement. The process was initially explored using traditional batch synthesis techniques but suffered from moderate yields, long reaction times, and moderate diastereoselectivities. Here we demonstrate that the process can be greatly improved upon its transfer to continuous flow, which afforded the aziridine targets in high yields, short reaction times, and consistently high diastereoselectivities, with the high-throughput process rendering multigram quantities of product in short periods of time. In addition, flow processing extended the substrate scope including several examples that had failed in batch mode, thus demonstrating the value of this overlooked entry into valuable aziridine species.

The Synthesis and Acid-base Properties of α-(Fluoromethyl)- and α-(Difluoromethyl)-substituted Cyclobutane Building Blocks

Aim. To synthesize cyclobutane-derived amines and carboxylic acids bearing CH2F or CHF2 groups in the α position; to determine the regularities of the effect of fluoroalkyl substituents on the acid-base properties of the title compounds.Results and discussion. Synthetic approaches to 1-(fluoromethyl)- and 1-(difluoromethyl)cyclobutanamines, 1-(fluoromethyl)- and 1-(difluoromethyl)cyclobutanecarboxylic acids have been developed. It has been found that the pKa (pKa(H)) values measured for the title compounds, as well as for their non-substituted and CF3-substituted analogues, are consistent with the electron-withdrawing effect of the corresponding fluoroalkyl substituents.Experimental part. The synthesis of the title compounds commenced from the known ethyl 1-(hydroxymethyl)cyclobutanecarboxylate or the product of its Swern oxidation (the corresponding aldehyde) and included fluorination, alkaline ester hydrolysis (for carboxylic acids), and modified Curtius rearrangement (for amines). The pKa value was determined from the pre-equivalence point part of the titration curve using the standard acid-base titration.Conclusions. A newly developed synthetic approach to 1-(fluoromethyl)- and 1-(difluoromethyl)cyclobutanamines, 1-(fluoromethyl)- and 1-(difluoromethyl)cyclobutanecarboxylic acids allows to obtain the title compounds in multigram quantities (up to 97 g). With a single exception, the acid-base properties of these products, as well as their parent non-substituted and CF3-substituted analogues, change in a monotonous manner in accordance with inductive electronic effect of the fluorine atom(s).

Modular Photochemical Flow Synthesis of Structurally Diverse Benzyne and Triazine Precursors

AbstractBenzyne and related arynes are classical high‐energy species with a rich history of widespread applications in synthesis. However, despite several synthetic routes being available to generate arynes and their precursors, none represents an ideal entry to benzyne chemistry in view of safety, scalability, and sustainability. Here we report a new photochemical flow process allowing for the generation of benzyne precursors in high yields, and throughput, with easy isolation of multigram quantities of products. This process leverages a catalyst‐free photochemical rearrangement via a photoexcited nitro arene which involves a cyclic hydroxylamine intermediate that has been fully characterized. The resulting precursors were converted to benzynes via a second photochemical flow process generating heterocyclic targets upon trapping with azide and sydnone partners. Remarkably, when reacting the benzyne precursors with secondary amines, a wide range of aryl triazines is obtained in good yields via a third photo‐flow transformation. This represents a modular approach to synthesize these species, that avoids the use of potentially explosive diazonium salts. Ultimately, three photochemical flow processes using a single high‐power LED light source (365 nm, adjustable in‐put power) are presented with manifest benefits compared to batch processing. Moreover, the functionalization of a pendent carboxyl group to form sets of biologically relevant aryl triazine‐based amides highlights further applications of these unique and industrially relevant triazine entities.

Continuous-Flow Synthesis of Cyclobutenes Using LED Technology

AbstractCyclobutenes are highly strained ring systems of considerable synthetic interest that can be accessed via cycloaddition reactions between alkenes and alkynes. However, their traditional preparation relies on photochemical [2+2] cycloadditions that exploit low-wavelength UV radiation emitted from inefficient medium-pressure Hg lamps. This paper reports on the development of a modern approach using a high-power LED set-up emitting at the boundary of UV-A and visible light in conjunction with a continuous-flow reactor. The resulting flow process renders a series of cyclobutenes from maleimides and various commercial alkynes. This provides a more energy-efficient approach that is readily scalable to access multigram quantities of cyclobutenes in high chemical yields and short residence times. The value of these products is exemplified by flow-based hydrogenations yielding highly substituted cyclobutanes which represent sought after building blocks in modern medicinal chemistry programs.

Energetic Polymer Possessing Furazan, 1,2,3-Triazole, and Nitramine Subunits.

A [3 + 2] cycloaddition reaction using dialkyne and diazide comonomers, both bearing explosophoric groups, to synthesize energetic polymers containing furazan and 1,2,3-triazole ring as well as nitramine group in the polymer chain have been described. The developed solvent- and catalyst-free approach is methodologically simple and effective, the comonomers used are easily available, and the resulting polymer does not need any purification. All this makes it a promising tool for the synthesis of energetic polymers. The protocol was utilized to generate multigram quantities of the target polymer, which has been comprehensively investigated. The resulting polymer was fully characterized by spectral and physico-chemical methods. Compatibility with energetic plasticizers, thermochemical characteristics, and combustion features indicate the prospects of this polymer as a binder base for energetic materials. The polymer of this study surpasses the benchmark energetic polymer, nitrocellulose (NC), in a number of properties.

Dehydrogenative Imination of Low-Valent Sulfur Compounds-Fast and Scalable Synthesis of Sulfilimines, Sulfinamidines, and Sulfinimidate Esters.

Herein, we describe an electrochemical pathway for the synthesis of sulfilimines, sulfoximines, sulfinamidines, and sulfinimidate esters from readily available low-valent sulfur compounds and primary amides or their analogues. The combination of solvents and supporting electrolytes together act both as an electrolyte as well as a mediator, leading to efficient use of reactants. Both can be easily recovered, enabling an atom-efficient and sustainable process. A broad scope of sulfilimines, sulfinamidines, and sulfinimidate esters with N-EWGs is accessed in up to excellent yields with broad functional group tolerance. This fast synthesis can be easily scaled up to multigram quantities with high robustness for fluctuation of current densities of up to 3 orders of magnitude. The sulfilimines are converted into the corresponding sulfoximines in an ex-cell process in high to excellent yields using electro-generated peroxodicarbonate as a green oxidizer. Thereby, preparatively valuable NH sulfoximines are accessible.

Photochemical Synthesis of Pyrazolines from Tetrazoles in Flow

AbstractPyrazolines and their pyrazole congeners are important heterocyclic building blocks with numerous applications in the fine chemical industries. However, traditional routes towards these entities are based on multistep syntheses generating substantial amounts of chemical waste. Here we report an alternative approach using UV-light to convert tetrazoles into pyrazolines via a reagent-free photo-click strategy. This route generates nitrile imine dipoles in situ that are trapped with different dipolarophiles rendering a selection of these heterocyclic targets in high chemical yields. A continuous flow method is ultimately realized that generates multigram quantities of product in a safe and readily scalable manner thus demonstrating the value of this photochemical approach for future exploitations in industry.

Development of a multigram synthesis of the bradykinin receptor 2 agonist FR-190997 and analogs thereof.

Using Fujisawa's B2R agonist FR-190997, we recently demonstrated for the first time that agonism at the bradykinin receptor type 2 (B2R) produces substantial antiproliferative effects. FR-190997 elicited an EC50 of 80 nM in the triple-negative breast cancer cell line MDA-MB-231, a much superior performance to that exhibited by most approved breast cancer drugs. Consequently, we initiated a program aiming primarily at synthesizing adequate quantities of FR-190997 to support further in vitro and in vivo studies toward its repurposing for various cancers and, in parallel, enable the generation of novel FR-190997 analogs for an SAR study. Prerequisite for this endeavor was to address the synthetic challenges associated with the FR-190997 scaffold, which the Fujisawa chemists had constructed in 20 steps, 13 of which required chromatographic purification. We succeeded in developing a 17-step synthesis amenable to late-stage diversification that eliminated all chromatography and enabled access to multigram quantities of FR-190997 and novel derivatives thereof, supporting further anticancer research based on B2R agonists.