Reduction and oxidation are cornerstone transformations in organic synthesis. While reagents have traditionally been used to effect organic redox reactions, recent advances in electrochemical methodology have offered an attractive alternative approach. In principle, the electrification of these processes could minimize stoichiometric waste, supply arbitrarily tunable potentials, and leverage sustainable energy. However, the practical realization of these advantages is hampered by the need to use organic solvents, which originates from the insolubility of typical substrates in water. As a result, many electrosynthetic reactions require superstoichiometric organic supporting electrolytes, operate under constant current conditions with limited potential control at each electrode, and function under high Ohmic resistance and therefore low efficiencies. Here, we demonstrate a biphasic aqueous-organic approach to electrosynthesis enables the efficient, metal-free, and selective reduction of nitrogen centers. This hybrid format combines the highly optimized performance of aqueous electrochemical platforms with the synthetic versatility of organic media. By integrating reaction and separation into a single process, we minimize byproduct formation, bypass chromatographic purification, and recycle the metal-free redox mediator – either in sequential batch experiments or in continuous flow – with minimal loss (<1% per cycle). Mechanistic experiments demonstrate that reduction proceeds through hydrogen atom transfer in a thin zone near the phase boundary, with the overall process achieving near-perfect Faradaic efficiency and high current density. The concept of biphasic electrosynthesis readily generalizes to other redox transformations, offering more sustainable and more ideal options for both discovery and manufacturing

Stereochemical editing strategies have recently enabled the transformation of readily accessible substrates into rare and valuable products. Typically, site selectivity is achieved by minimizing kinetic complexity by using protecting groups to suppress reactivity at undesired sites (substrate control) or by using catalysts with tailored shapes to drive reactivity at the desired site (catalyst control). We propose “network control,” a contrasting paradigm that exploits hidden interactions between rate constants to greatly amplify modest intrinsic biases and enable precise multisite editing. When network control is applied to the photochemical isomerization of hexoses, six of the eight possible diastereomers can be selectively obtained. The amplification effect can be viewed as a mesoscale phenomenon between the limiting regimes of kinetic control in simple chemical systems and metabolic regulation in complex biological systems.

Autonomous process optimization (APO) is a technology that has recently found utility in a multitude of process optimization challenges. In contrast to most APO examples in microflow reactor systems, we recently presented a system capable of optimization in high-throughput batch reactor systems. The drawback of APO in a high-throughput batch reactor system is the reliance on reaction sampling at a predetermined static timepoint rather than a dynamic endpoint. Static timepoint sampling can lead to the inconsistent capture of the process performance under each process parameter permutation. This is important because critical process behaviors such as rate acceleration accompanied by decomposition could be missed entirely. To address this drawback, we implemented a dynamic reaction endpoint determination strategy to capture the product purity once the process stream stabilized. We accomplished this through the incorporation of a real-time plateau detection algorithm into the APO workflow to measure and report the product purity at the dynamically determined reaction endpoint. We then applied this strategy to the autonomous optimization of a photobromination reaction towards the synthesis of a pharmaceutically relevant intermediate. In doing so, we not only uncovered process conditions to access the desired monohalogenation product in 85 UPLC area % purity with minimal decomposition risk, but also measured the effect of each parameter on the process performance. Our results highlight the advantage of incorporating dynamic sampling in APO workflows to drive optimization toward a stable and high-performing process.

The discorhabdin natural products are a large subset of pyrroloiminoquinone alkaloids with a myriad of biological activities. Despite garnering much synthetic attention, few members have thus far been completed, with none featuring a bridging carbon–nitrogen bond that is found in numerous discorhabdins, including discorhabdin V. Here we report the first total synthesis and full stereochemical assignment of (+)-discorhabdin V in 13 linear steps. To access the pyrroloiminoquinone we developed a convergent N-alkylation/oxidative aminocyclization/bromination cascade that joins two key components, which are both made on multigram scale. An intramolecular Heck reaction then forms the quaternary carbon center in an intermediate containing the carbon–nitrogen bridge, and a reductive N,O-acetal cyclization sequence introduces the final piperidine ring. Furthermore, we have established the relative stereochemistry of (+)-discorhabdin V through experimental NOESY data and DP4 NMR probability calculations. The absolute configuration of the natural product has also been determined via circular dichroism and the use of an amino acid-derived chiral starting material. Our work represents the first report of a total synthesis of a nitrogen-bridged discorhabdin and paves the way for future biological evaluation of such compounds.

This manuscript describes the detailed evaluation of more than 40 phosphine reductants via automated and nonautomated high-throughput experimentation approaches with the goal of identifying selective reductants for cleaving the disulfide bonds of capped, engineered cysteines in a proprietary monoclonal antibody (mAb). As a point of reference, this study included phosphines that have previously been documented in the literature [4-diphenylphosphino benzoic acid (DPPBA), tris(3-sulfophenyl)phosphine (TSPP), and 3-(diphenylphosphino)benzenesulfonate (diPPBS)]; however, all known reductants showed the formation of undesired side products upon reduction (detectable by IEX), especially at higher phosphine loadings. The high-throughput study also revealed several phosphines with potential for selective reduction that had not been previously studied for this type of transformation. These initial hits were further evaluated with regard to the phosphine/mAb ratio, solubility in aqueous media, and air oxidation behavior. The best phosphine identified (1-(4-(diphenylphosphanyl)benzyl)-1-methylpyrrolidin-1-ium bromide (P10)) was then employed in a sequence of high-throughput studies that established efficient one-pot reduction/conjugation reaction conditions. Overall, the work detailed herein demonstrates how high-throughput experimental design enables rapid and resource-sparing insights into mAb reduction and conjugation reactivity with phosphine-based reductants.

Liquid-liquid extraction (LLE) screening can be a very labor-intensive exercise during commercial process development, particularly when workup challenges such as poor partitioning or emulsion formation arise. An automated platform for LLE has the potential to both accelerate process development and deliver a more optimized process, thereby reducing the burden on downstream purification requirements. To address this need, a fully automated liquid-liquid extraction workflow was designed and implemented to optimize extraction unit operations during process development. This workflow leverages commercially available hardware and software to perform extractions, identify phase boundaries, and prepare samples for analysis. A data visualization tool was also developed to streamline the processing of visual and quantitative data. Application of the automated LLE workflow on two case studies will be presented: one highlighting the development of an effective enzyme removal strategy for a biocatalytic cascade reaction and the other demonstrating the identification of operating parameters for workup of an intermediate with a tendency to partition into an oil layer.

In carbonyl–olefin metathesis, two π-bonds undergo a cycloaddition-cycloreversion process to form valuable alkenes from simple precursors. Although this synthetic methodology has advanced significantly, further improvements would be greatly facilitated by a clear understanding of whether Lewis-acid-catalyzed carbonyl–olefin metathesis reactions occur via a stepwise or concerted pathway. Here we use 12C/13C kinetic isotope effects (KIEs), 1H/2H KIEs, and Hammett studies to show that prototypical iron(III)-catalyzed ring-closing carbonyl–olefin metathesis reactions of aryl ketones are stepwise. Despite this strong experimental evidence, typical computational models incorrectly predict a concerted mechanism. We trace this failure to the use of conventional implicit solvation models and demonstrate that when solvent molecules are explicitly represented, the correct stepwise mechanism is predicted. These results call into question prior computational proposals of concerted carbonyl-olefin metathesis, highlight the importance of explicit solvent representations for charged intermediates, and have broad implications for how all polar reactions are studied.

Research in the field of asymmetric catalysis over the past half century has resulted in landmark advances, enabling the efficient synthesis of chiral building blocks, pharmaceuticals and natural products(1-3). A small number of asymmetric catalytic reactions have been identified that display high selectivity across a broad scope of substrates; not coincidentally, these are the reactions that have the greatest impact on how enantioenriched compounds are synthesized(4-8). We postulate that substrate generality in asymmetric catalysis is rare not simply because it is intrinsically difficult to achieve, but also because of the way chiral catalysts are identified and optimized(9). Typical discovery campaigns rely on a single model substrate, and thus select for high performance in a narrow region of chemical space. Here we put forth a practical approach for using multiple model substratesto select simultaneously for both enantioselectivity and generality in asymmetric catalytic reactions from the outset(10,11). Multisubstrate screening is achieved by conducting high-throughput chiral analyses by supercritical fluid chromatography-mass spectrometry with pooled samples. When applied to Pictet-Spengler reactions, the multisubstrate screening approach revealed a promising and unexpected lead for the general enantioselective catalysis of this important transformation, which even displayed high enantioselectivity for substrate combinations outside of the screening set.

Redox flow batteries based on quinone-bearing aqueous electrolytes have emerged as promising systems for energy storage from intermittent renewable sources. The lifetime of these batteries is limited by quinone stability. Here, we confirm that 2,6-dihydroxyanthrahydroquinone tends to form an anthrone intermediate that is vulnerable to subsequent irreversible dimerization. We demonstrate quantitatively that this decomposition pathway is responsible for the loss of battery capacity. Computational studies indicate that the driving force for anthrone formation is greater for anthraquinones with lower reduction potentials. We show that the decomposition can be substantially mitigated. We demonstrate that conditions minimizing anthrone formation and avoiding anthrone dimerization slow the capacity loss rate by over an order of magnitude. We anticipate that this mitigation strategy readily extends to other anthraquinone-based flow batteries and is thus an important step toward realizing renewable electricity storage through long-lived organic flow batteries.

We report a strategy for effecting catalytic, enantioselective carbocationic rearrangements through the intermediacy of alkyl iodanes as stereodefined carbocation equivalents. Asymmetric Wagner–Meerwein rearrangements of β-substituted styrenes are catalyzed by the C2-symmetric aryl iodide 1 to provide access to enantioenriched 1,3-difluorinated molecules possessing interesting and well-defined conformational properties. Hammett and kinetic isotope effect studies, in combination with computational investigations, reveal that two different mechanisms are operative in these rearrangement reactions, with the pathway depending on the identity of the migrating group. In reactions involving alkyl-group migration, intermolecular fluoride attack is product- and enantio-determining. In contrast, reactions in which aryl rearrangement occurs proceed through an enantiodetermining intramolecular 1,2-migration prior to fluorination. The fact that both pathways are promoted by the same chiral aryl iodide catalyst with high enantioselectivity provides a compelling illustration of generality across reaction mechanisms in asymmetric catalysis.

Understanding the mechanism of small molecules is a critical challenge in chemical biology and drug discovery. Medicinal chemistry is essential for elucidating drug mechanism, enabling variation of small molecule structure to gain structure-activity relationships (SARs). However, the development of complementary approaches that systematically vary target protein structure could provide equally informative SARs for investigating drug mechanism and protein function. Here we explore the ability of CRISPR-Cas9 mutagenesis to profile the interactions between lysine-specific histone demethylase 1 (LSD1) and chemical inhibitors in the context of acute myeloid leukemia (AML). Through this approach, termed CRISPR-suppressor scanning, we elucidate drug mechanism of action by showing that LSD1 enzyme activity is not required for AML survival and that LSD1 inhibitors instead function by disrupting interactions between LSD1 and the transcription factor GFI1B on chromatin. Our studies clarify how LSD1 inhibitors mechanistically operate in AML and demonstrate how CRISPR-suppressor scanning can uncover novel aspects of target biology.

Here we demonstrate that highly β-selective glycosylation reactions can be achieved when the electronics of a sulfonyl chloride activator and the reactivity of a glycosyl donor hemiacetal are matched. While these reactions are compatible with the acid- and base-sensitive protecting groups that are commonly used in oligosaccharide synthesis, these protecting groups are not relied upon to control selectivity. Instead, β-selectivity arises from the stereoinversion of an α-glycosyl arylsulfonate in an SN2-like mechanism. Our mechanistic proposal is supported by NMR studies, kinetic isotope effect (KIE) measurements, and DFT calculations.

Cancer drivers require statistical modeling to distinguish them from passenger events, which accumulate during tumorigenesis but provide no fitness advantage to cancer cells. The discovery of driver genes and mutations relies on the assumption that exact positional recurrence is unlikely by chance; thus, the precise sharing of mutations across patients identifies drivers. Examining the mutation landscape in cancer genomes, we found that many recurrent cancer mutations previously designated as drivers are likely passengers. Our integrated bioinformatic and biochemical analyses revealed that these passenger hotspot mutations arise from the preference of APOBEC3A, a cytidine deaminase, for DNA stem-loops. Conversely, recurrent APOBEC-signature mutations not in stem-loops are enriched in well-characterized driver genes and may predict new drivers. This demonstrates that mesoscale genomic features need to be integrated into computational models aimed at identifying mutations linked to diseases.

Nucleophilic aromatic substitution (SNAr) is one of the most widely applied reaction classes in pharmaceutical and chemical research, providing a broadly useful platform for the modification of aromatic ring scaffolds. The generally accepted mechanism for SNAr reactions involves a two-step addition–elimination sequence via a discrete, non-aromatic Meisenheimer complex. Here we use 12C/13C kinetic isotope effect (KIE) studies and computational analyses to provide evidence that prototypical SNAr reactions in fact proceed through concerted mechanisms. The KIE measurements were made possible by a new technique that leverages the high sensitivity of 19F as an NMR nucleus to quantitate the degree of isotopic fractionation. This sensitive technique permits the measurement of KIEs on 10 mg of natural abundance material in one overnight acquisition. As a result, it provides a practical tool for performing detailed mechanistic analyses of reactions that form or break C–F bonds. Nucleophilic aromatic substitution reactions have long been thought to occur primarily via stepwise mechanisms. New and sensitive methodology for measuring carbon kinetic isotope effects now shows that most such substitutions actually occur through concerted mechanisms.

Carbohydrates are involved in nearly all aspects of biochemistry, but their complex chemical structures present long-standing practical challenges to their synthesis. In particular, stereochemical outcomes in glycosylation reactions are highly dependent on the steric and electronic properties of coupling partners; thus, carbohydrate synthesis is not easily predictable. Here we report the discovery of a macrocyclic bis-thiourea derivative that catalyzes stereospecific invertive substitution pathways of glycosyl chlorides. The utility of the catalyst is demonstrated in the synthesis of trans-1,2-, cis-1,2-, and 2-deoxy-β-glycosides. Mechanistic studies are consistent with a cooperative mechanism in which an electrophile and a nucleophile are simultaneously activated to effect a stereospecific substitution reaction.

Polarization transfer is demonstrated as a sensitive technique for the measurement of isotopic fractionation of protonated carbons at natural abundance. This method allows kinetic isotope effects (KIEs) to be determined with substantially less material or shorter acquisition time compared with traditional experiments. Computations quantitatively reproduce the KIEs in a Diels-Alder reaction and a catalytic glycosylation. The glycosylation is shown to occur by an effectively concerted mechanism.

Synthesis of non-activated electron-rich and sterically hindered 18F-arenes remains a major challenge due to limitations of existing radiofluorination methodologies. Herein, we report on our mechanistic investigations of spirocyclic iodonium(III) ylide precursors for arene radiofluorination, including their reactivity, selectivity, and stability with no-carrier-added [18F]fluoride. Benchmark calculations at the G2[ECP] level indicate that pseudorotation and reductive elimination at iodine(III) can be modeled well by appropriately selected dispersion-corrected density functional methods. Modeling of the reaction pathways show that fluoride-iodonium(III) adduct intermediates are strongly activated and highly regioselective for reductive elimination of the desired [18F]fluoroarenes (difference in barriers, ΔΔG‡ > 25 kcal·mol-1). The advantage of spirocyclic auxiliaries is further supported by NMR spectroscopy studies, which bolster evidence for underlying decomposition processes which can be overcome for radiofluorination of iodonium(III) precursors. Using a novel adamantyl auxiliary, sterically hindered iodonium ylides have been developed to enable highly efficient radiofluorination of electron-rich arenes, including fragments of pharmaceutically relevant nitrogen-containing heterocycles and tertiary amines. Furthermore, this methodology has been applied for the syntheses of the radiopharmaceuticals 6-[18F]fluoro-meta-tyrosine ([18F]FMT, 11 ± 1% isolated radiochemical yield, non-decay-corrected (RCY, n.d.c.; n = 3), and meta-[18F]fluorobenzylguanidine ([18F]mFBG, 14 ± 1% isolated RCY, n.d.c., n = 3) which cannot be directly radiolabeled using conventional nucleophilic aromatic substitution with [18F]fluoride.

We describe a computer algorithm that searches for substitution rules on a set of triangles, the angles of which are all integer multiples of π/n. We find new substitution rules admitting 7-fold rotational symmetry at many different inflation factors.

NMR spectroscopy is a crucial tool in organic chemistry for the routine characterization of small molecules, structural elucidation of natural products, and study of reaction mechanisms. Although there is evidence that thermal motions strongly affect observed resonances, conventional predictions are performed only on stationary structures. Here we show that quasiclassical molecular dynamics provides a highly accurate and broadly applicable method for improving shielding predictions. Gas-phase values of the absolute shieldings of protons and carbons are predicted to nearly within experimental uncertainty, while the chemical shifts of large systems such as natural products are closely reproduced. Importantly, these results are obtained without the use of any empirical corrections. Our analysis suggests that the linear scaling factors currently employed are primarily a correction for vibrational effects. As a result, our method extends the reach of prediction methods to the study of molecules with unusual dynamics such as the iconic and controversial [18]annulene. Our predictions agree closely with experiment at both low and high temperatures and provide strong evidence that the equilibrium structure of [18]annulene is planar and aromatic.