Dibenzocyclooctadiene lignans are an interesting class of molecules because of their unique structure based on an axially chiral biaryl moiety as well as their significant biological activity. ...Herein, we describe the development of a palladium‐catalyzed atroposelective C−H alkynylation and its application in gram‐scale, stereocontrolled formal syntheses of (+)‐isoschizandrin and (+)‐steganone. tert‐Leucine was identified as an efficient, catalytic transient chiral auxiliary. A wide range of enantiomerically enriched biaryl compounds were prepared by this approach in good yields (up to 99 %) with excellent enantioselectivity (up to >99 % ee).
Locked into position with a Pd key: A palladium‐catalyzed atroposelective C−H alkynylation was developed and applied to gram‐scale, stereocontrolled formal syntheses of (+)‐isoschizandrin (see scheme) and (+)‐steganone. tert‐Leucine was identified as an efficient catalytic transient chiral auxiliary for this transformation, which enabled the preparation of a wide range of enantiomerically enriched biaryl compounds in good yields.
The discovery of proper ligands to simultaneously modulate the reactivity and effectively control the stereoselectivity is a central topic in the field of enantioselective C−H activation. Herein, we ...reported the synthesis of axially chiral biaryls by Pd‐catalyzed atroposelective C−H olefination. A novel chiral spiro phosphoric acid, STRIP, was identified as a superior ligand for this transformation. A broad range of axially chiral quinoline derivatives were synthesized in good yields with excellent enantioselectivities (up to 98 % ee). Density functional theory was used to gain a theoretical understanding of the enantioselectivities in this reaction.
The discovery of proper ligands to simultaneously modulate the reactivity and effectively control the stereoselectivity is a central topic in the field of enantioselective C−H activation. Herein, the synthesis of axially chiral biaryls by Pd‐catalyzed atroposelective C−H olefination is reported. A broad range of axially chiral quinoline derivatives were synthesized in good yields with excellent enantioselectivities (up to 98 % ee).
Chiral diarylmethylamines (DAMA) are important structural motifs widely present in pharmaceuticals, natural products, and chiral ligands. Herein, we reported a highly enantioselective synthesis of ...chiral DAMAs via cobalt‐catalyzed enantioselective C−H alkoxylation strategy. The reaction features easy operation, the use of earth‐abundant and cost‐efficient cobalt(II) catalyst, and readily available ligand. A range of chiral DAMAs were efficiently synthesized in high yields with excellent enantioselectivities (up to 90 % yield and up to 99 % ee) through desymmetrization and parallel kinetic resolution. Moreover, this protocol was also compatible with the synthesis of chiral benzylamines via kinetic resolution.
A highly enantioselective synthesis of chiral diarylmethylamines (DAMAs) via cobalt‐catalyzed enantioselective C−H alkoxylation was reported. A range of chiral DAMAs were efficiently synthesized in high yields with excellent enantioselectivities (up to 90 % yield and up to 99 % ee) through desymmetrization and parallel kinetic resolution. Moreover, this protocol was also compatible with the synthesis of chiral benzylamines via kinetic resolution.
The past decade has witnessed a rapid progress in asymmetric C−H activation. However, the enantioselective C−H alkoxylation and amination with alcohols and free amines remains elusive. Herein, we ...disclose the first enantioselective dehydrogenative C−H alkoxylation and amination enabled by a simple cobalt/salicyloxazoline (Salox) catalysis. The use of cheap and readily available cobalt(II) salts as catalysts and Saloxs as chiral ligands provides an efficient method to access P‐stereogenic compounds in excellent enantioselectivities (up to >99 % ee). The practicality of this protocol is demonstrated by gram‐scale preparation and further derivatizations of the resulting P‐stereogenic phosphinamides, which offering a flexible asymmetric alternative to access P‐stereogenic mono‐ and diphosphine chiral ligands. Preliminary mechanistic studies on the enantioselective C−H alkoxylation reaction suggest that a cobalt(III/IV/II) catalytic cycle might be involved.
An unprecedented enantioselective dehydrogenative C−H alkoxylation and amination is reported. The use of cheap and readily available cobalt(II) salts as catalysts and Saloxs as chiral ligands provides an efficient method to access P‐stereogenic compounds in excellent enantioselectivities (up to >99 % ee).
Highly efficient synthesis of axially chiral biaryl amines through cobalt‐catalyzed atroposelective C−H arylation using easily accessible cobalt(II) salt and salicyloxazoline ligand has been ...reported. This methodology provides a straightforward and sustainable access to a broad range of enantioenriched biaryl‐2‐amines in good yields (up to 99 %) with excellent enantioselectivities (up to 99 % ee). The synthetic utility of the unprecedented method is highlighted by its scalability and diverse transformations.
Cobalt‐catalyzed atroposelective C−H arylation/DKR reaction was realized. This strategy provides an efficient and sustainable method for the synthesis of axially chiral biaryl‐2‐amines in good yields (up to 99 %) with excellent enantioselectivities (up to 99 %ee).
Transition metal‐catalyzed enantioselective C−H carbonylation with carbon monoxide, an essential and easily available C1 feedstock, remains challenging. Here, we disclosed an unprecedented ...enantioselective C−H carbonylation catalyzed by inexpensive and readily available cobalt(II) salt. The reactions proceed efficiently through desymmetrization, kinetic resolution, and parallel kinetic resolution, affording a broad range of chiral isoindolinones in good yields with excellent enantioselectivities (up to 92 % yield and 99 % ee). The synthetic potential of this method was demonstrated by asymmetric synthesis of biological active compounds, such as (S)‐PD172938 and (S)‐Pazinaclone. The resulting chiral isoindolinones also serve as chiral ligands in cobalt‐catalyzed enantioselective C−H annulation with alkynes to construct phosphorus stereocenter.
A cobalt‐catalyzed enantioselective C−H carbonylation with carbon monoxide as C1 source, enabling highly efficient synthesis of chiral isoindolinones, is reported. The robustness and synthetic potential of this method is demonstrated by asymmetric synthesis of bioactive molecules, (S)‐PD172938 and (S)‐Pazinaclone. Moreover, the chiral isoindolinones also proved to be efficient chiral ligands for asymmetric C−H activation.
•A new strategy was developed for accurately identifying metabolites.•A number of significant difference metabolites were accurately identified.•Licorice from different regions could be separated ...clearly.•The quality of licorice from different regions in China was inconsistent.
Licorice is famous as a herbal medicine and food sweetener. This study provided a comprehensive strategy for investigating the quality of licorice based on untargeted metabolomics. A new strategy for identifying metabolite was developed, including fragment ion identification algorithm and ion fusion algorithm. The results showed that it can accurately integrate mass spectra from positive and negative ion modes to benefit metabolite identification. Based on the strategy, a number of significant difference metabolites were identified among licorice samples and 9 metabolites were confirmed by standards. Additionally, the geographical discrimination models of licorice samples were comprehensively investigated by chemometric methods. The results indicated that the supporting vector machine provided the best performance, with a prediction accuracy above 80%. The study results supported the conclusion that the quality of licorice from different regions in China was inconsistent.
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.
Abstract
In this paper, we will give a general introduction to the Ali CMB Polarization Telescope (AliCPT) project, which is a Sino–US joint project led by the Institute of High Energy Physics and ...involves many different institutes in China. It is the first ground-based Cosmic Microwave Background (CMB) polarization experiment in China and an integral part of China's Gravitational-wave Program. The main scientific goal of the AliCPT project is to probe the primordial gravitational waves (PGWs) originating from the very early Universe. The AliCPT project includes two stages. The first stage, referred to as AliCPT-1, is to build a telescope in the Ali region of Tibet at an altitude of 5250 meters. Once completed, it will be the highest ground-based CMB observatory in the world and will open a new window for probing PGWs in the northern hemisphere. The AliCPT-1 telescope is designed to have about 7000 transition-edge sensor detectors at 95 GHz and 150 GHz. The second stage is to have a more sensitive telescope (AliCPT-2) with more than 20 000 detectors. Our simulations show that AliCPT will improve the current constraint on the tensor-to-scalar ratio r by one order of magnitude with three years' observation. Besides the PGWs, AliCPT will also enable a precise measurement of the CMB rotation angle and provide a precise test of the CPT symmetry. We show that three years' observation will improve the current limit by two orders of magnitude.
Though therapy that promotes anti-tumor response about CD8
+
tumor-infiltrating lymphocytes (TILs) has shown great potential, clinical responses to CD8
+
TILs immunotherapy vary considerably, largely ...because of different subpopulation of CD8
+
TILs exhibiting different biological characters. To define the relationship between subpopulation of CD8
+
TILs and the outcome of antitumor reaction, the phenotype and function of CD103
+
CD8
+
TILs in esophageal squamous cell carcinoma (ESCC) were investigated. CD103
+
CD8
+
TILs were presented in ESCC, which displayed phenotype of tissue-resident memory T cells and exhibited high expression of immune checkpoints (PD-1, TIM-3). CD103
+
CD8
+
TILs were positively associated with the overall survivals of ESCC patients. This population of cells elicited potent proliferation and cytotoxic cytokine secretion potential. In addition, CD103
+
CD8
+
TILs were elicited potent anti-tumor immunity after anti-PD-1 blockade and were not affected by chemotherapy. This study emphasized the feature of CD103
+
CD8
+
TILs in immune response and identified potentially new targets in ESCC patients.
PDF
