Addressing Atropisomerism in the Development of Sotorasib, a Covalent Inhibitor of KRAS G12C: Structural, Analytical, and Synthetic Considerations

Unlocking Enol-Ugi-Derived Conformationally Restricted Peptidomimetic Motifs

The enol-Ugi condensation, a versatile multicomponent reaction, provides a rapid and efficient route to enamine peptidomimetics. In this study, we investigated the factors influencing the conformational behavior of three enol-Ugi adducts with distinct structural features. Through DFT calculations and NCI analysis, we identified that noncovalent interactions, including hydrogen bonds and π-π interactions, play a pivotal role in restricting conformational flexibility. While six-membered cyclic enamines 6 and 7 exhibited varying degrees of rotational freedom, the indanone-derived enamine 8 displayed a locked conformation resembling a retropeptidic turn. These findings highlight the potential of tailoring enol-Ugi adducts to mimic biologically relevant peptidic motifs, opening new avenues for drug discovery and design.

Identification of Structurally Novel KRASG12C Inhibitors through Covalent DNA-Encoded Library Screening

Covalent inhibition of the KRASG12C oncoprotein has emerged as a promising therapeutic approach for the treatment of nonsmall cell lung cancer (NSCLC). The identification of KRASG12C inhibitors has typically relied on the high-throughput screening (HTS) of libraries of cysteine-reactive small molecules or on the attachment of cysteine-reactive warheads to noncovalent binders of KRAS. Such screening approaches have historically been limited in the size and diversity of molecules that could be effectively screened. DNA-encoded library (DEL) screening has emerged as a promising approach to accelerate the preparation and screening of incredibly large and diverse chemical libraries. Here, we describe the design and synthesis of a covalent DEL to screen ∼16 million compounds against KRASG12C. We additionally describe the hit identification, validation, and structure-based optimization that culminated in the identification of a series of structurally novel, potent, and selective covalent inhibitors of KRASG12C with good pharmacokinetic profiles and promising in vivo pharmacodynamic effects.

Discovery of Novel Spirocyclic MAT2A Inhibitors Demonstrating High In Vivo Efficacy in MTAP-Null Xenograft Models

Synthetic lethality offers a robust strategy for discovering the next generation of precision medicine therapies tailored for molecularly defined patient populations. MAT2A inhibition is synthetically lethal in several cancers that exhibit a homozygous deletion of S-methyl-5'-thioadenosine phosphorylase (MTAP). Herein, we report the identification of novel MAT2A inhibitors featuring a spiral ring to circumvent the C-N atropisomeric chirality utilizing structure-based drug design. The Hit compound 9 exhibited high potency in enzymatic activity (IC50 = 7 nM) and in HCT-116 MTAP(-/-) cell potency (IC50 = 17 nM). Further optimization has led to the identification of two new lead compounds: a brain-penetrant compound, 29-1, and a potent but limited brain-penetrant compound, 39. Both of these lead compounds demonstrate increased plasma drug exposure and exhibit significant efficacy in xenograft models that are depleted of MTAP. We hope that identifying a brain-penetrant MAT2A inhibitor will create new opportunities to explore the potential therapeutic effects of S-adenosylmethionine modulation in the central nervous system.

Novel non-peptide uracil-derived human gonadotropin-releasing hormone receptor antagonists

Gonadotropin-releasing hormone (GnRH) is the main regulator of the reproductive system, acting on gonadotropic cells by binding to the GnRH1 receptor (GnRH1R). Traditionally, therapies targeting this receptor have relied on peptide modulators, which required subcutaneous or intramuscular injections. Due to the limitations of the parenteral administrations, there is a growing interest in developing oral small molecule modulators of GnRH1R as more convenient therapeutic alternatives. In this study, we examined the potential of chemically modifying elagolix, the first approved non-peptide, orally active GnRH1R antagonist, to increase its atropisomeric properties by introducing new moieties. We designed and synthesized the thio-uracil (1) and cytosine (2) derivatives of elagolix, both demonstrating GnRH1R antagonistic activities, with EC50 values of 39 and 110 nM, respectively. The atropisomers of 1 and 2 were efficiently separated using silica gel chromatography, and extensive NMR investigation, supported by Density Functional Theory (DFT) calculations, allowed us to define their conformations and rotational barriers. Docking and Molecular Dynamics (MD) studies revealed that 1 and 2 bind to GnRH1R with ΔG values comparable to elagolix, but through distinct binding modes. These results highlight the potential of non-peptide modulators to effectively modulate GnRH1R activity and pave the way for developing novel modulators.

Enantioselective synthesis of molecules with multiple stereogenic elements

This review explores the fascinating world of molecules featuring multiple stereogenic elements, unraveling the different strategies designed over the years for their enantioselective synthesis. Specifically, (dynamic) kinetic resolutions, desymmetrisations and simultaneous installation of stereogenic elements exploiting either metal- or organo-catalysis are the principal approaches to efficiently create and control the three-dimensional shapes of these attractive molecules. Although most molecules presented in this review possess a stereogenic carbon atom in combination with a stereogenic axis, other combinations with helices or planes of chirality have started to emerge, as well as molecules displaying more than two different stereogenic elements.

High Resolution Ion Mobility Enables the Structural Characterization of Atropisomers of GDC-6036, a KRAS G12C Covalent Inhibitor

GDC-6036 is a covalent KRAS G12C inhibitor that demonstrates high potency and selectivity. Structurally, GDC-6036 consists of several motifs that make the analytical characterization of this molecule challenging, including a highly basic pyrrolidine motif bonded to a quinazoline ring via an ether bond and an atropisomeric carbon-carbon bond between functionalized pyridine and quinazoline groups. Structurally, the desired atropisomer was synthesized via an atroposelective Negishi coupling with very high yield. However, having a direct way to analyze and confirm the presence of the atropisomeric species remained challenging in routine analytical workflows. In this study, both variable temperature nuclear magnetic resonance (VT-NMR) and two different approaches of in-line ion mobility coupled to liquid chromatography mass spectrometry (LC-MS) workflows were evaluated for the characterization of GDC-6036 and its undesired atropisomer (Compound B) to support synthetic route development. Briefly, both VT-NMR and traveling wave ion mobility spectrometry (TWIMS) enabled by structures for lossless ion manipulation (SLIM) technology coupled to high resolution MS (HRMS) are able to elucidate the structures of the atropisomers in a complex mixture. Drift tube IMS (DTIMS) was also evaluated, but lacked the resolving power to demonstrate separation between the two species in a mixture, but did show slight differences in their arrival times when multiplexed and injected separately. The determined resolving power (Rp) by multiplexing the ions via DTIMS was 67.3 and 60.5 for GDC-6036 and Compound B, respectively, while the two peak resolving power (Rpp) was determined to be 0.41, indicating inadequate resolution between the two species. Alternatively, the SLIM-IM studies showed Rp of 103.8 and 99.4, with a Rpp of 2.64, indicating good separation between the atropisomers. Furthermore, the CCS/z for GDC-6036 and Compound B was determined to be 231.2 Å2/z and 235.0 Å2/z, respectively. Quantitative experiments demonstrate linearity (R2 >0.99) for both GDC-6036 and Compound B while maintaining separation via SLIM-IM. Spike recoveries of one atropisomer relative to the other yielded strong recoveries (98.7% to 102.5%) while maintaining reproducibility (<7% RSD). The study herein describes the analytical process for evaluating new technologies and strategies for implementation in routine biopharmaceutical characterization workflows.

Atroposelective Synthesis of Axial Biaryls by Dynamic Kinetic Resolution Using Engineered Imine Reductases

Axially chiral biaryl compounds are ubiquitous scaffolds in natural products, bioactive molecules, chiral ligands and catalysts, but biocatalytic methods for their asymmetric synthesis are limited. Herein, we report a highly efficient biocatalytic route for the atroposelective synthesis of biaryls by dynamic kinetic resolution (DKR). This DKR approach features a transient six-membered aza-acetal-bridge-promoted racemization followed by an imine reductase (IRED)-catalyzed stereoselective reduction to construct the axial chirality under ambient conditions. Directed evolution of an IRED from Streptomyces sp. GF3546 provided a variant (S-IRED-Ss-M11) capable of catalyzing the DKR process to access a variety of biaryl aminoalcohols in high yields and excellent enantioselectivities (up to 98 % yield and >99 : 1 enantiomeric ratio). Molecular dynamics simulation studies on the S-IRED-Ss-M11 variant revealed the origin of its improved activity and atroposelectivity. By exploiting the substrate promiscuity of IREDs and the power of directed evolution, our work further extends the biocatalysts' toolbox to construct challenging axially chiral molecules.

High Rotational Barrier Atropisomers

Atropisomers have attracted a great deal of attention lately due to their numerous applications in organic synthesis and to their employment in drug discovery. However, the synthetic arsenal at our disposal with which to access them remains limited. The research described herein is two-pronged; we both demonstrate the use of MCR chemistry as a synthetic strategy for the de novo synthesis of a class of atropisomers having high barriers to rotation with the simultaneous insertion of multiple chiral elements and we study these unprecedented molecular systems by employing a combination of crystallography, NMR and DFT calculations. By fully exploiting the synthetic capabilities of our chemistry, we have been able to monitor a range of different types of interaction, i. e. π-π, CH-π, heteroatom-π and CD-π, in order to conduct structure-property studies. The results could be applied both to atroposelective synthesis and in drug discovery.

Enantioselective Synthesis of Heteroatom-Linked Non-Biaryl Atropisomers

Atropisomers hold significant fascination, not only for their prevalence in natural compounds but also for their biological importance and wide-ranging applications as chiral materials, ligands, and organocatalysts. While biaryl and heterobiaryl atropisomers are commonly studied, the enantioselective synthesis of less abundant heteroatom-linked non-biaryl atropisomers presents a formidable challenge in modern organic synthesis. Unlike classical atropisomers, these molecules allow rotation around two bonds, resulting in low barriers to enantiomerization through concerted bond rotations. In recent years the discovery of new configurationally stable rare non-biaryl scaffolds such as aryl amines, aryl ethers and aryl sulfones as well as innovative methodologies to control their configuration have been disclosed in the literature and constitute the topic of this minireview.

Impact of atropisomerism on a non-steroidal glucocorticoid receptor agonist

To investigate atropisomers of non-steroidal glucocorticoid receptor modulator GSK866, a virtual library of substituted benzoic acid analogues was enumerated. Compounds from this library were subjected to a torsion angle scan using Spartan'20 to calculate the torsion rotation energy barrier which identified compounds predicted to be stable as atropisomers. After synthesis of the library, analysis showed that compounds 13 and 14 existed as stable atropisomers 13a, 13b, 14a and 14b, in agreement with the earlier calculations. Screening in a glucocorticoid receptor cellular assay showed that one compound from each atropisomer pair was significantly more potent than the other. Docking in a public structure of the glucocorticoid receptor (PBD code 3E7C) enabled the stereochemistry of the two most potent compounds 13a and 14b to be assigned as (R a) and (S a), respectively.

The discovery of novel imidazo[1,2-a]pyridine derivatives as covalent anticancer agents

The success of targeted covalent inhibitors (TCIs) for treating cancers has spurred the search for novel scaffolds to install covalent warheads. In our endeavour, using a scaffold hopping strategy, we managed to utilize imidazo[1,2-a]pyridine as the core backbone and explored its potential for the development of covalent inhibitors, therefore, synthesizing a series of novel KRAS G12C inhibitors facilitated by the Groebke-Blackburn-Bienaymè reaction (GBB reaction). Preliminary bio-evaluation screening delivered compound I-11 as a potent anticancer agent for KRAS G12C-mutated NCI-H358 cells, whose effects were further clarified by a series of cellular, biochemical, and molecular docking experiments. These results not only indicate the potential of compound I-11 as a lead compound for the treatment of intractable cancers, but also validate the unique role of imidazo[1,2-a]pyridine as a novel scaffold suitable for the discovery of covalent anticancer agents.

The Target Therapy Hyperbole: "KRAS (p.G12C)"-The Simplification of a Complex Biological Problem

Kirsten Rat Sarcoma Viral Oncogene Homolog (KRAS) gene variations are linked to the development of numerous cancers, including non-small cell lung cancer (NSCLC), colorectal cancer (CRC), and pancreatic ductal adenocarcinoma (PDAC). The lack of typical drug-binding sites has long hampered the discovery of therapeutic drugs targeting KRAS. Since "CodeBreaK 100" demonstrated Sotorasib's early safety and efficacy and led to its approval, especially in the treatment of non-small cell lung cancer (NSCLC), the subsequent identification of specific inhibitors for the p.G12C mutation has offered hope. However, the CodeBreaK 200 study found no significant difference in overall survival (OS) between patients treated with Docetaxel and Sotorasib (AMG 510), adding another degree of complexity to this ongoing challenge. The current study compares the three-dimensional structures of the two major KRAS isoforms, KRAS4A and KRAS4B. It also investigates the probable structural changes caused by the three major mutations (p.G12C, p.G12D, and p.G12V) within Sotorasib's pocket domain. The computational analysis demonstrates that the wild-type and mutant isoforms have distinct aggregation propensities, resulting in the creation of alternate oligomeric configurations. This study highlights the increased complexity of the biological issue of using KRAS as a therapeutic target. The present study stresses the need for a better understanding of the structural dynamics of KRAS and its mutations to design more effective therapeutic approaches. It also emphasizes the potential of computational approaches to shed light on the complicated molecular pathways that drive KRAS-mediated oncogenesis. This study adds to the ongoing efforts to address the therapeutic hurdles presented by KRAS in cancer treatment.

Carbene-Catalyzed Atroposelective Construction of Chiral Diaryl Ethers

Atropoisomeric chemotypes of diaryl ethers-related scaffolds are prevalent in naturally active compounds. Nevertheless, there remains considerable research to be carried out on the catalytic asymmetric synthesis of these axially chiral molecules. In this instance, we disclose an N-heterocyclic carbene (NHC)-catalyzed synthesis of axially chiral diaryl ethers via atroposelective esterification of dialdehyde-containing diaryl ethers. NHC desymmetrization produces axially chiral diaryl ether atropisomers with high yields and enantioselectivities in moderate circumstances. Chiral diaryl ether compounds may be precursors for highly functionalized diaryl ethers with bioactivity and chiral ligands for asymmetric catalysis.

Conformation Analysis and Stereodynamics of Symmetrically ortho-Disubstituted Carvacrol Derivatives

The design and synthesis of analogs of natural products can be a valuable source of medicinal preparations for the pharmaceutical industry. In the present study, the structural elucidation of eleven derivatives of 2,4-dihalogeno substituted synthetic analogues of the natural compound carvacrol was carried out by means of NMR experiments, and of another thirteen by DFT calculations. By selective NOE experiments and the irradiation of CH signals of the isopropyl group, individual conformers were assigned as syn and anti. By comparing GIAO/B3LYP/6-311++G(d,p)-calculated and experimentally measured vicinal 3JCH spin-spin constants, this assignment was confirmed. An unusual relationship is reported for proton-carbon vicinal couplings: 3JCH (180°) < 3JCH (0°). The conformational mobility of carvacrols was studied by 2D EXSY spectra. The application of homonuclear decoupling technique (HOBS) to these spectra simplifies the spectra, improves resolution without reducing the sensitivity, and allows a systematic examination of the rotational barrier of all compounds via their CH signals of the isopropyl group in a wider temperature interval. The rate constants of the isopropyl rotation between syn and anti conformers were determined and the corresponding energy barriers (14-17 kcal/mol) were calculated. DFT calculations of the energy barriers in carvacrol derivatives allowed the determination of the steric origin of the restricted isopropyl rotation. The barrier height depends on the size of the 2- and 4-position substituents, and is independent of the derivatization of the OH group.

Atroposelective Chan-Evans-Lam Amination

The synthetic control of atropoisomerism along C-N bonds is a major challenge, and methods that allow C-N atroposelective bond formation are rare. This is a problem because each atropoisomer can feature starkly differentiated biological properties. Yet, among the three most practical and applicable classical amination methods available: 1) the Cu-catalyzed Ullmann-Goldberg reaction, 2) the Pd-catalyzed Buchwald-Hartwig reaction, and 3) the Cu-catalyzed Chan-Evans-Lam reaction, none has truly been rendered atroposelective at the newly formed C-N bond. The first ever Chan-Evans-Lam atroposelective amination is herein described with a simple copper catalyst and newly designed PyrOx chiral ligand. This method should find important applications in asymmetric synthesis, in particular for medicinal chemistry.

Chirality of New Drug Approvals (2013-2022): Trends and Perspectives

Many drugs are chiral with their chirality determining their biological interactions, safety, and efficacy. Since the 1980s, there has been a regulatory preference to bring single enantiomer to market. This perspective discusses trends related to chirality that have developed in the past decade (2013-2022) of new drug approvals. The EMA has not approved a racemate since 2016, while the average for the FDA is one per year from 2013 to 2022. These 10 include drugs which have been previously marketed elsewhere for several decades, analogues of pre-existing drugs, or drugs where the undefined stereocenter does not play a role in therapeutic activity. Two chiral switches were identified which were both combined with drug repurposing. This combination strategy has the potential to produce therapeutically valuable drugs in a faster time frame. Two class III atropisomers displaying axial chirality were approved between 2013 and 2022, one as a racemate and one as a single enantiomer.

Design and Catalytic Asymmetric Synthesis of Furan-Indole Compounds Bearing both Axial and Central Chirality

In the chemistry community, catalytic asymmetric synthesis of furan-based compounds bearing both axial and central chirality has proven to be a significant but challenging issue owing to the importance and difficulty in constructing such frameworks. In this work, we have realized the first catalytic asymmetric synthesis of five-five-membered furan-based compounds bearing both axial and central chirality via organocatalytic asymmetric (2+4) annulation of achiral furan-indoles with 2,3-indolyldimethanols with uncommon regioselectivity. By this strategy, furan-indole compounds bearing both axial and central chirality were synthesized in high yields with excellent regio-, diastereo-, and enantioselectivities. Moreover, theoretical calculations were conducted to provide an in-depth understanding of the reaction pathway, activation mode, and the origin of the selectivity.

Perspectives on Nuclear Magnetic Resonance Spectroscopy in Drug Discovery Research

The drug discovery landscape has undergone a significant transformation over the past decade, owing to research endeavors in a wide range of areas leading to strategies for pursuing new drug targets and the emergence of novel drug modalities. NMR spectroscopy has been a technology of fundamental importance to these research pursuits and has seen its use expanded both within and outside of traditional medicinal chemistry applications. In this perspective, we will present advancement of NMR-derived methods that have facilitated the characterization of small molecules and novel drug modalities including macrocyclic peptides, cyclic dinucleotides, and ligands for protein degradation. We will discuss innovations in NMR spectroscopy at the chemistry and biology interface that have broadened NMR's utility from hit identification through lead optimization activities. We will also discuss the promise of emerging NMR approaches in bridging our understanding and addressing challenges in the pursuit of the therapeutic agents of the future.

Catalytic Atroposelective Synthesis of Axially Chiral Azomethine Imines and Neuroprotective Activity Evaluation

Azomethine imines, as a prominent class of 1,3-dipolar species, hold great significance and potential in organic and medicinal chemistry. However, the reported synthesis of centrally chiral azomethine imines relies on kinetic resolution, and the construction of axially chiral azomethine imines remains unexplored. Herein, we present the synthesis of axially chiral azomethine imines through copper- or chiral phosphoric acid catalyzed ring-closure reactions of N'-(2-alkynylbenzylidene)hydrazides, showcasing high efficiency, mild conditions, broad substrate scope, and excellent enantioselectivity. Furthermore, the biological evaluation revealed that the synthesized axially chiral azomethine imines effectively protect dorsal root ganglia (DRG) neurons by inhibiting apoptosis induced by oxaliplatin, offering a promising therapeutic approach for chemotherapy-induced peripheral neuropathy (CIPN). Remarkably, the (S)- and (R)-atropisomers displayed distinct neuroprotective activities, underscoring the significance of axial stereochemistry.

Targeting ST8SIA6-AS1 counteracts KRASG12C inhibitor resistance through abolishing the reciprocal activation of PLK1/c-Myc signaling

BACKGROUND

KRASG12C inhibitors (KRASG12Ci) AMG510 and MRTX849 have shown promising efficacy in clinical trials and been approved for the treatment of KRASG12C-mutant cancers. However, the emergence of therapy-related drug resistance limits their long-term potential. This study aimed to identify the critical mediators and develop overcoming strategies.

METHODS

By using RNA sequencing, RT-qPCR and immunoblotting, we identified and validated the upregulation of c-Myc activity and the amplification of the long noncoding RNA ST8SIA6-AS1 in KRASG12Ci-resistant cells. The regulatory axis ST8SIA6-AS1/Polo-like kinase 1 (PLK1)/c-Myc was investigated by bioinformatics, RNA fluorescence in situ hybridization, RNA immunoprecipitation, RNA pull-down and chromatin immunoprecipitation. Gain/loss-of-function assays, cell viability assay, xenograft models, and IHC staining were conducted to evaluate the anti-cancer effects of co-inhibition of ST8SIA6-AS1/PLK1 pathway and KRAS both in vitro and in vivo.

RESULTS

KRASG12Ci sustainably decreased c-Myc levels in responsive cell lines but not in cell lines with intrinsic or acquired resistance to KRASG12Ci. PLK1 activation contributed to this ERK-independent c-Myc stability, which in turn directly induced PLK1 transcription, forming a positive feedback loop and conferring resistance to KRASG12Ci. ST8SIA6-AS1 was found significantly upregulated in resistant cells and facilitated the proliferation of KRASG12C-mutant cancers. ST8SIA6-AS1 bound to Aurora kinase A (Aurora A)/PLK1 and promoted Aurora A-mediated PLK1 phosphorylation. Concurrent targeting of KRAS and ST8SIA6-AS1/PLK1 signaling suppressed both ERK-dependent and -independent c-Myc expression, synergistically led to cell death and tumor regression and overcame KRASG12Ci resistance.

CONCLUSIONS

Our study deciphers that the axis of ST8SIA6-AS1/PLK1/c-Myc confers both intrinsic and acquired resistance to KRASG12Ci and represents a promising therapeutic target for combination strategies with KRASG12Ci in the treatment of KRASG12C-mutant cancers.

Stereodynamic Strategies to Induce and Enrich Chirality of Atropisomers at a Late Stage

Enantiomers, where chirality arises from restricted rotation around a single bond, are atropisomers. Due to the unique nature of the origins of their chirality, synthetic strategies to access these compounds in an enantioselective manner differ from those used to prepare enantioenriched compounds containing point chirality arising from an unsymmetrically substituted carbon center. In particular stereodynamic transformations, such as dynamic kinetic resolutions, thermodynamic dynamic resolutions, and deracemizations, which rely on the ability to racemize or interconvert enantiomers, are a promising set of transformations to prepare optically pure compounds in the late stage of a synthetic sequence. Translation of these synthetic approaches from compounds with point chirality to atropisomers requires an expanded toolbox for epimerization/racemization and provides an opportunity to develop a new conceptual framework for the enantioselective synthesis of these compounds.

Interrogating the configurational stability of atropisomers

Atropisomers are molecules whose stereogenicity arises from restricted rotation about a single bond. They are of current importance because of their applications in catalysis, medicine and materials science. The defining feature of atropisomeric molecules is that their stereoisomers are related to one another by bond rotation: as a result, evaluating their configurational stability (i.e., the rate at which their stereoisomers interconvert) is central to any work in this area. Important atropisomeric scaffolds include C-C linked biaryls, such as the ligand BINAP and the drug vancomycin, and C-N linked amine derivatives such as the drug telenzepine. This article focuses on the three most widely used experimental methods that are available to measure the rate of racemization in atropisomers, namely: (i) kinetic analysis of the racemization of an enantioenriched sample, (ii) dynamic HPLC and (iii) variable-temperature NMR. For each technique, an explanation of the theory is set out, followed by a detailed experimental procedure. A discussion is also included of which technique to try when confronted with a new molecular structure whose properties are not yet known. None of the three procedures require complex experimental techniques, and all can be performed by using standard analytical equipment (NMR and HPLC). The time taken to determine a racemization rate depends on which experimental method is required, but for a new compound it is generally possible to measure a racemization rate in <1 d.

Multiple Strategies to Develop Small Molecular KRAS Directly Bound Inhibitors

KRAS gene mutation is widespread in tumors and plays an important role in various malignancies. Targeting KRAS mutations is regarded as the "holy grail" of targeted cancer therapies. Recently, multiple strategies, including covalent binding strategy, targeted protein degradation strategy, targeting protein and protein interaction strategy, salt bridge strategy, and multivalent strategy, have been adopted to develop KRAS direct inhibitors for anti-cancer therapy. Various KRAS-directed inhibitors have been developed, including the FDA-approved drugs sotorasib and adagrasib, KRAS-G12D inhibitor MRTX1133, and KRAS-G12V inhibitor JAB-23000, etc. The different strategies greatly promote the development of KRAS inhibitors. Herein, the strategies are summarized, which would shed light on the drug discovery for both KRAS and other "undruggable" targets.

Organocatalytic Enantioselective Synthesis of Axially Chiral N,N'-Bisindoles

This study establishes the first organocatalytic enantioselective synthesis of axially chiral N,N'-bisindoles via chiral phosphoric acid-catalyzed formal (3+2) cycloadditions of indole-based enaminones as novel platform molecules with 2,3-diketoesters, where de novo indole-ring formation is involved. Using this new strategy, various axially chiral N,N'-bisindoles were synthesized in good yields and with excellent enantioselectivities (up to 87 % yield and 96 % ee). More importantly, this class of axially chiral N,N'-bisindoles exhibited some degree of cytotoxicity toward cancer cells and was derived into axially chiral phosphine ligands with high catalytic activity. This study provides a new strategy for enantioselective synthesis of axially chiral N,N'-bisindoles using asymmetric organocatalysis and is the first to realize the applications of such scaffolds in medicinal chemistry and asymmetric catalysis.

A Dynamic Kinetic Resolution Approach to Axially Chiral Diaryl Ethers by Catalytic Atroposelective Transfer Hydrogenation

Diaryl ethers are widespread in biologically active compounds, ligands and catalysts. It is known that the diaryl ether skeleton may exhibit atropisomerism when both aryl rings are unsymmetrically substituted with bulky groups. Despite recent advances, only very few catalytic asymmetric methods have been developed to construct such axially chiral compounds. We describe herein a dynamic kinetic resolution approach to axially chiral diaryl ethers via a Brønsted acid catalyzed atroposelective transfer hydrogenation (ATH) reaction of dicarbaldehydes with anilines. The desired diaryl ethers could be obtained in moderate to good chemical yields (up to 79 %) and high enantioselectivities (up to 95 % ee) under standard reaction conditions. Such structural motifs are interesting precursors for further transformations and may have potential applications in the synthesis of chiral ligands or catalysts.