Enantioselective Cross-[4 + 2]-Cycloaddition/Decarboxylation of 2-Pyrones by Cooperative Catalysis of the Pd(0)/NHC Complex and Chiral Phosphoric Acid

Here, we describe a cooperative Pd(0)/chiral phosphoric acid catalytic system that allows us to realize the first chemo-, regio-, and enantioselective sequential cross-[4 + 2]-cycloaddition/decarboxylation reaction between 2-pyrones and unactivated acyclic 1,3-dienes. The key to the success of this transformation is the utilization of an achiral N-heterocyclic carbene (NHC) as the ligand and a newly developed chiral phosphoric acid as the cocatalyst. Experimental investigations and computational studies support the idea that the Pd(0)/NHC complex acts as a π-Lewis base to increase the nucleophilicity of 1,3-dienes via η2 coordination, while the chiral phosphoric acid simultaneously increases the electrophilicity of 2-pyrones by hydrogen bonding. By this synergistic catalysis, the sequential cross-[4 + 2]-cycloaddition and decarboxylation reaction proceeds efficiently, enabling the preparation of a wide range of chiral vinyl-substituted 1,3-cyclohexadienes in good yields and enantioselectivities. The synthetic utility of this reaction is demonstrated by synthetic transformations of the product to various valuable chiral six-membered carbocycles.

Pd(II)-Catalyzed enantioselective C-H olefination toward the synthesis of P-stereogenic phosphinamides

P-Stereogenic phosphorus compounds are important structural elements in chiral ligands or organocatalysts. Herein, we report a Pd(II)-catalyzed enantioselective C-H olefination toward the synthesis of P-stereogenic phosphinamides using cheap commercially available L-pGlu-OH as a chiral ligand. A broad range of P-stereogenic phosphinamides were gained in good yields with high enantioselectivities (33 examples, up to 77% yield, 99% ee) via desymmetrization and kinetic resolution.

Deciphering the Diversified Metabolic Behavior of Hydroxyalkyl Ferrocidiphenols as Anticancer Complexes

Ferrocidiphenols possessing appropriate substituents in the aliphatic chain have very promising anticancer properties, but a systematic approach to deciphering their diversified metabolic behavior has so far been lacking. Herein, we show that a series of novel ferrocidiphenols bearing different hydroxyalkyl substituents exhibit strong anticancer activity as revealed in a range of in vitro and in vivo experiments. Moreover, they display diversified oxidative transformation profiles very distinct from those of previous complexes, shown by the use of chemical and enzymatic methods and in cellulo and in vivo metabolism studies. In view of this phenomenon, unprecedented chemo-evolutionary sequences that connect all the ferrocidiphenol-related intermediates and analogues have been established. In addition, a comprehensive density functional theory (DFT) study has been performed to decipher the metabolic diversification profiles of these complexes and demonstrate the delicate modulation of carbenium ions by the ferrocenyl moiety, via either α- or β-positional participation.

Asymmetric Dearomatization of Indoles with Azodicarboxylates via Cascade Electrophilic Amination/Aza-Prins Cyclization/Phenonium-like Rearrangement

Herein, we report a highly efficient synthesis of enantioenriched aza-[3.3.1]-bicyclic enamines and ketones, a class of structural cores in many natural products, via asymmetric dearomatization of indoles with azodicarboxylates. The reaction is initiated by electrophilic amination and followed by aza-Prins cyclization/phenonium-like rearrangement. A newly developed fluorine-containing chiral phosphoric acid displays excellent activity in promoting this cascade reaction. The absence or presence of water as the additive directs the reaction pathway toward either enamine or ketone products in high yields (up to 93%) with high enantiopurity (up to 98% ee). Comprehensive density functional theory (DFT) calculations reveal the energy profile of the reaction and the origins of enantioselectivity and water-induced chemoselectivity.

Explicit Mechanism of Rh(I)-Catalyzed Asymmetric C-H Arylation and Facile Synthesis of Planar Chiral Ferrocenophanes

Mechanism-guided reaction development is a well-appreciated research paradigm in chemistry since the merging of mechanistic knowledge would accelerate the discovery of new synthetic methods. Low-valent transition metals such as Pd(0)- and Rh(I)-catalyzed C-H arylation with aryl (pseudo)halides is among the enabling reactions for the exclusive cross-coupling of two different aryl partners. However, different from the situation of Pd(0)-catalysis, the mechanism of Rh(I)-catalyzed C-H arylation is underexplored. The sequence of the elementary steps of aryl C-H activation and oxidative addition of aryl (pseudo)halides remains unclear. Herein, we report comprehensive experimental and computational studies toward explicit mechanistic understandings of Rh(I)-catalyzed intermolecular asymmetric C-H arylation between 2-pyridinylferrocenes and aryl bromides. The identification of each elementary step in the catalytic cycle and the structural characterization of the key intermediates and transition states allow the rational design and development of challenging intramolecular reactions. The successful realization of this reaction mode set the foundation for the facile synthesis of planar chiral [m]ferrocenophanes (m = 6-8), a class of rarely explored target molecules with strained structures and intriguing molecular topology.

Circulating tumour cell isolation, analysis and clinical application

BACKGROUND

Circulating tumour cells (CTCs) are cancer cells that circulate in the bloodstream after being shed from solid tumours. They can lead to tumour recurrence and metastasis. CTCs play a significant role as biomarkers for early diagnosis, therapy response monitoring, and prognostication. However, CTCs are rare and heterogeneous, with usually only a single-digit number in one millilitre of blood. Additionally, a circadian rhythm is involved in the release of CTCs into the peripheral circulation. Due to these biological properties, higher demands are placed on the isolation of CTCs, and current capture methods struggle to enrich all CTCs present in blood. As yet, these limitations have hampered the clinical application of CTCs.

CONCLUSIONS

In this review, we focus on the biological properties and clinical applications of CTCs and current CTC enrichment and isolation methods. Combined enrichment methods based on physical and biological properties are considered instrumental for the development of highly specific and sensitive CTC capture methods. The utilization of CTCs in conjunction with other liquid biopsy components (such as ctDNA) may yield more clinically useful information and the circadian rhythmicity of CTC release may change the way to evaluate and treat patients.

Cp*Co(III)-Catalyzed Enantioselective Hydroarylation of Unactivated Terminal Alkenes via C-H Activation

Enantioselective hydroarylation of unactivated terminal akenes constitutes a prominent challenge in organic chemistry. Herein, we reported a Cp*Co(III)-catalyzed asymmetric hydroarylation of unactivated aliphatic terminal alkenes assisted by a new type of tailor-made amino acid ligands. Critical to the chiral induction was the engaging of a novel noncovalent interaction (NCI), which has seldomly been disclosed in the C-H activation area, arising from the molecular recognition among the organocobalt(III) intermediate, the coordinated alkene, and the well-designed chiral ligand. A broad range of C2-alkylated indoles were obtained in high yields and excellent enantioselectivities. DFT calculations revealed the reaction mechanism and elucidated the origins of chiral induction in the stereodetermining alkene insertion step.

Towards Data-driven Design of Asymmetric Hydrogenation of Olefins: Database and Hierarchical Learning

Asymmetric hydrogenation of olefins is one of the most powerful asymmetric transformations in molecular synthesis. Although several privileged catalyst scaffolds are available, the catalyst development for asymmetric hydrogenation is still a time- and resource-consuming process due to the lack of predictive catalyst design strategy. Targeting the data-driven design of asymmetric catalysis, we herein report the development of a standardized database that contains the detailed information of over 12000 literature asymmetric hydrogenations of olefins. This database provides a valuable platform for the machine learning applications in asymmetric catalysis. Based on this database, we developed a hierarchical learning approach to achieve predictive machine leaning model using only dozens of enantioselectivity data with the target olefin, which offers a useful solution for the few-shot learning problem and will facilitate the reaction optimization with new olefin substrate in catalysis screening.

Atroposelective synthesis of N-aryl peptoid atropisomers via a palladium(ii)-catalyzed asymmetric C-H alkynylation strategy

The introduction of chirality into peptoids is an important strategy to determine a discrete and robust secondary structure. However, the lack of an efficient strategy for the synthesis of structurally diverse chiral peptoids has hampered the studies. Herein, we report the efficient synthesis of a wide variety of N-aryl peptoid atropisomers in good yields with excellent enantioselectivities (up to 99% yield and 99% ee) by palladium-catalyzed asymmetric C–H alkynylation. The inexpensive and commercially available l-pyroglutamic acid was used as an efficient chiral ligand. The exceptional compatibility of the C–H alkynylation with various peptoid oligomers renders this procedure valuable for peptoid modifications. Computational studies suggested that the amino acid ligand distortion controls the enantioselectivity in the Pd/l-pGlu-catalyzed C–H bond activation step.

The introduction of chirality into peptoids is an important strategy to determine a discrete and robust secondary structure.

Low-Temperature Nickel-Catalyzed C-N Cross-Coupling via Kinetic Resolution Enabled by a Bulky and Flexible Chiral N-Heterocyclic Carbene Ligand

The transition-metal-catalyzed C-N cross-coupling has revolutionized the construction of amines. Despite the innovations of multiple generations of ligands to modulate the reactivity of the metal center, ligands for the low-temperature enantioselective amination of aryl halides remain a coveted target of catalyst engineering. Designs that promote one elementary reaction often create bottlenecks at other steps. We here report an unprecedented low-temperature (as low as -50 °C), enantioselective Ni-catalyzed C-N cross-coupling of aryl chlorides with sterically hindered secondary amines via a kinetic resolution process (s factor up to >300). A bulky yet flexible chiral N-heterocyclic carbene (NHC) ligand is leveraged to drive both oxidative addition and reductive elimination with low barriers and control the enantioselectivity. Computational studies indicate that the rotations of multiple σ-bonds on the C₂ -symmetric chiral ligand adapt to the changing needs of catalytic processes. We expect this design would be widely applicable to diverse transition states to achieve other challenging metal-catalyzed asymmetric cross-coupling reactions.

Direct Synthesis of Ketones from Methyl Esters by Nickel-Catalyzed Suzuki-Miyaura Coupling

The direct conversion of alkyl esters to ketones has been hindered by the sluggish reactivity of the starting materials and the susceptibility of the product towards subsequent nucleophilic attack. We have now achieved a cross-coupling approach to this transformation using nickel, a bulky N-heterocyclic carbene ligand, and alkyl organoboron coupling partners. 65 alkyl ketones bearing diverse functional groups and heterocyclic scaffolds have been synthesized with this method. Catalyst-controlled chemoselectivity is observed for C(acyl)-O bond activation of multi-functional substrates bearing other bonds prone to cleavage by Ni, including aryl ether, aryl fluoride, and N-Ph amide functional groups. Density functional theory calculations provide mechanistic support for a Ni⁰ /Ni^II catalytic cycle and demonstrate how stabilizing non-covalent interactions between the bulky catalyst and substrate are critical for the reaction's success.

Enantioselective Synthesis of Atropisomeric Anilides via Pd(II)-Catalyzed Asymmetric C-H Olefination

Atropisomeric anilides have received tremendous attention as a novel class of chiral compounds possessing restricted rotation around an N-aryl chiral axis. However, in sharp contrast to the well-studied synthesis of biaryl atropisomers, the catalytic asymmetric synthesis of chiral anilides remains a daunting challenge, largely due to the higher degree of rotational freedom compared to their biaryl counterparts. Here we describe a highly efficient catalytic asymmetric synthesis of atropisomeric anilides via Pd(II)-catalyzed atroposelective C-H olefination using readily available L-pyroglutamic acid as a chiral ligand. A broad range of atropisomeric anilides were prepared in high yields (up to 99% yield) and excellent stereoinduction (up to >99% ee) under mild conditions. Experimental studies indicated that the atropostability of those anilide atropisomers toward racemization relies on both steric and electronic effects. Experimental and computational studies were conducted to elucidate the reaction mechanism and rate-determining step. DFT calculations revealed that the amino acid ligand distortion is responsible for the enantioselectivity in the C-H bond activation step. The potent applications of the anilide atropisomers as a new type of chiral ligand in Rh(III)-catalyzed asymmetric conjugate addition and Lewis base catalysts in enantioselective allylation of aldehydes have been demonstrated. This strategy could provide a straightforward route to access atropisomeric anilides, one of the most challenging types of axially chiral compounds.

Decarbonylative Suzuki-Miyaura Cross-Coupling of Aroyl Chlorides

Herein, we report a catalyst system for Pd-catalyzed decarbonylative Suzuki-Miyaura cross-coupling of aroyl chlorides with boronic acids to furnish biaryls. This strategy is suitable for a broad range of common aroyl chlorides and boronic acids. The synthetic utility is highlighted in the direct late-stage functionalization of pharmaceuticals and natural products capitalizing on the presence of carboxylic acid moiety. Extensive mechanistic and DFT studies provide key insight into the reaction mechanism and high decarbonylative cross-coupling selectivity.

Succinate induces skeletal muscle fiber remodeling via SUNCR1 signaling

The conversion of skeletal muscle fiber from fast twitch to slow‐twitch is important for sustained and tonic contractile events, maintenance of energy homeostasis, and the alleviation of fatigue. Skeletal muscle remodeling is effectively induced by endurance or aerobic exercise, which also generates several tricarboxylic acid (TCA) cycle intermediates, including succinate. However, whether succinate regulates muscle fiber‐type transitions remains unclear. Here, we found that dietary succinate supplementation increased endurance exercise ability, myosin heavy chain I expression, aerobic enzyme activity, oxygen consumption, and mitochondrial biogenesis in mouse skeletal muscle. By contrast, succinate decreased lactate dehydrogenase activity, lactate production, and myosin heavy chain IIb expression. Further, by using pharmacological or genetic loss‐of‐function models generated by phospholipase Cβ antagonists, SUNCR1 global knockout, or SUNCR1 gastrocnemius‐specific knockdown, we found that the effects of succinate on skeletal muscle fiber‐type remodeling are mediated by SUNCR1 and its downstream calcium/NFAT signaling pathway. In summary, our results demonstrate succinate induces transition of skeletal muscle fiber via SUNCR1 signaling pathway. These findings suggest the potential beneficial use of succinate‐based compounds in both athletic and sedentary populations.

Computational Study of Mechanism and Thermodynamics of Ni/IPr-Catalyzed Amidation of Esters

Nickel catalysis has shown remarkable potential in amide C⁻N bond activation and functionalization. Particularly for the transformation between ester and amide, nickel catalysis has realized both the forward (ester to amide) and reverse (amide to ester) reactions, allowing a powerful approach for the ester and amide synthesis. Based on density functional theory (DFT) calculations, we explored the mechanism and thermodynamics of Ni/IPr-catalyzed amidation with both aromatic and aliphatic esters. The reaction follows the general cross-coupling mechanism, involving sequential oxidative addition, proton transfer, and reductive elimination. The calculations indicated the reversible nature of amidation, which highlights the importance of reaction thermodynamics in related reaction designs. To shed light on the control of thermodynamics, we also investigated the thermodynamic free energy changes of amidation with a series of esters and amides.

Measurement of the total cross section for hadronic production by e(+)e(-) annihilation at energies between 2.6-5 GeV

Using the upgraded Beijing Spectrometer, we have measured the total cross section for e(+)e(-) annihilation into hadronic final states at center-of-mass energies of 2.6, 3.2, 3.4, 3.55, 4.6, and 5.0 GeV. Values of R, sigma(e(+)e(-)-->hadrons)/sigma(e(+)e(-)-->&mgr;(+)&mgr;(-)), are determined.