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1.
Mar Pollut Bull ; 204: 116565, 2024 Jul.
Article in English | MEDLINE | ID: mdl-38843704

ABSTRACT

Increasing shipping pressure (SP) deteriorates offshore habitats of large mobile species (LMS) and invalidates marine conservation systems, while the threat of SP to the survival of LMS is not well understood. Here, for the 16 endangered LMS in the western Yellow Sea, we quantified their habitat quality in specific sea areas and conservation capacity of marine protected areas (MPAs) under SP, based on AIS (Automatic Identification System) data and an overlay analysis method for SP surfaces and LMS habitats. Results indicate that three specific sea areas have partially lost habitat function, and their MPA networks have also lost 66.7 %, 59.1 %, and 9.2 % of conservation capacity, respectively. To prevent the continued degradation and extinction of endangered LMS, urgent rescue efforts are needed. This study highlights the importance of monitoring offshore shipping pressure and LMS habitat quality, and the findings contribute to the adjustment of marine spatial planning and LMS protection strategies.


Subject(s)
Conservation of Natural Resources , Ecosystem , Endangered Species , Ships , Animals , Environmental Monitoring/methods , Oceans and Seas , China
2.
Biosens Bioelectron ; 256: 116283, 2024 Jul 15.
Article in English | MEDLINE | ID: mdl-38608495

ABSTRACT

Due to the toxicity of mercury and its harmful effects on human health, it is essential to establish a low-cost, highly sensitive and highly specific monitoring method with a wide detection range, ideally with a simple visual readout. In this study, a whole-cell biosensor with adjustable detection limits was developed for the detection of mercury ions in water samples, allowing controllable threshold detection with an expanded detection range. Gene circuits were constructed by combining the toehold switch system with lactose operon, mercury-ion-specific operon, and inducible red fluorescent protein gene. Using MATLAB for design and selection, a total of eleven dual-input single-output sensing logic circuits were obtained based on the basic logic of gene circuit construction. Then, biosensor DTS-3 was selected based on its fluorescence response at different isopropyl ß-D-Thiogalactoside (IPTG) concentrations, exhibiting the controllable detection threshold. At 5-20 µM IPTG, DTS-3 can achieve variable threshold detection in the range of 0.005-0.0075, 0.06-0.08, 1-2, and 4-6 µM mercury ion concentrations, respectively. Specificity experiments demonstrated that DTS-3 exhibits good specificity, not showing fluorescence response changes compared with other metal ions. Furthermore spiked sample experiments demonstrated its good resistance to interference, allowing it to distinguish mercury ion concentrations as low as 7.5 nM by the naked eye and 5 nM using a microplate reader. This study confirms the feasibility and performance of biosensor with controllable detection threshold, providing a new detection method and new ideas for expanding the detection range of biosensors while ensuring rapid and convenient measurements without compromising sensitivity.


Subject(s)
Biosensing Techniques , Mercury , Biosensing Techniques/methods , Biosensing Techniques/instrumentation , Mercury/analysis , Limit of Detection , Water Pollutants, Chemical/analysis , Equipment Design , Gene Regulatory Networks , Humans , Escherichia coli/genetics , Escherichia coli/isolation & purification
3.
Acc Chem Res ; 2024 Jan 31.
Article in English | MEDLINE | ID: mdl-38295513

ABSTRACT

ConspectusTransition-metal-catalyzed coupling reactions of dienes (such as 1,3-dienes, alkoxyallenes, and aminoallenes) with carbon nucleophiles have proven to be a highly effective method for creating Csp3-Csp3 bonds. These reactions have perfect atom economy and typically occur under mild reaction conditions. By using chiral metal complexes as catalysts, it is possible to create enantioenriched molecules bearing allylic stereocenters with high enantioselectivities. However, challenges arise when Csp3-Csp3 bonds bearing two vicinal stereocenters are constructed through this type of coupling reaction. Due to the inherent diastereoselectivities, only the kinetically favored diastereoisomers (either the syn- or anti-product) are usually obtained through the transition-metal catalyst system. Achieving complementary stereoisomers with high selectivity, which require complete control of both absolute and relative configurations of multiple chiral centers in a single chemical transformation, is usually impossible.Over the past decade, significant advancements have been made in stereodivergent synthesis. Notably, iridium-related synergistic catalysis has been rapidly developed for stereodivergent allylic alkylation reactions. However, these systems were limited to using allylic alcohol derivatives as electrophilic partners. Finding ways to extend the use of synergistic catalysis to other types of stereodivergent reactions is a crucial issue that needs to be addressed.In 2019, we reported the first palladium-mediated synergistic system for the stereodivergent Csp3-Csp3 coupling between 1,3-dienes and aldimine esters. Lately, this strategy has proven successful in accessing stereodivergent coupling with diverse substrate patterns. In this Account, we will summarize our laboratory's efforts in developing a range of palladium-involved synergistic catalysis systems for the stereodivergent Csp3-Csp3 coupling reactions of dienes. We discovered several synergistic catalysis systems, including Pd/Cu(Ag), Pd/amine, Pd/Lewis base, and Pd/PTC. Additionally, we developed diverse dienes, such as 1,3-dienes, alkoxyallenes, and aminoallenes, to serve as suitable coupling partners for stereodivergent coupling. These processes provide an efficient method for constructing a range of chiral scaffolds bearing vicinal stereocenters. Density functional theory (DFT) calculations have been performed to elucidate the reaction mechanism and to rationalize the origins of the stereochemistry for some of the synergistic catalyst systems. Finally, the synthetic application of these methods has been demonstrated in the concise total synthesis of a number of natural products and bioactive molecules. It is anticipated that an increasing number of chemists will join in the research on stereodivergent Csp3-Csp3 coupling reactions and contribute to more elegant examples in this area. We believe future development will further push the boundary of asymmetric catalysis and find more innovative applications soon for synthesizing complex chiral molecules.

4.
Eur J Prev Cardiol ; 31(5): 507-518, 2024 Mar 27.
Article in English | MEDLINE | ID: mdl-37651722

ABSTRACT

AIMS: Isolated sinus node dysfunction (ISND) is a sinus node dysfunction without atrial fibrillation. A high risk of ischaemic stroke (IS) has been reported in ISND populations. However, current guidelines do not recommend anticoagulation in ISND management. P-wave indicates ISND-related atrial remodelling. P-wave indices and the CHA2DS2-VASc score may contribute to risk stratification for ISND-related IS. METHODS AND RESULTS: In this multi-centre longitudinal cohort, ISND patients were divided into development (n = 1185) and external validation (n = 988) cohorts. Ischaemic stroke prediction capacity of the P-combined score was assessed with regard to discrimination, calibration, and clinical effectiveness. The cut-off value of the score was confirmed by using a restricted cubic spline curve. One hundred and twenty-four (10.46%) ISND patients developed IS [1.63%/year; 95% confidence interval (CI): 1.49-1.78%/year] after a median 3.02-year follow-up in the development cohort. The P-wave terminal force in electrocardiogram-lead V1 (PTFV1) was the only significantly abnormal P-wave index (adjusted hazard ratio: 2.56; 95% CI: 1.72-3.80). Therefore, we incorporated the PTFV1 with the CHA2DS2-VASc score to generate a P-combined score. For a 5-year IS risk, the P-combined score improved Harrell's C-statistic (95% CI) from 0.678 (0.618-0.738) to 0.716 (0.657-0.774) and 0.747 (0.677-0.816) to 0.808 (0.747-0.868) in the development and validation cohorts, respectively, along with calibration and decision curve analyses. The cut-off value of the score was 3 in the development cohort and well-discriminated in the validation cohort. CONCLUSION: Chinese ISND patients have a higher IS risk than the general population. Compared with the CHA2DS2-VASc score, the PTFV1-combined CHA2DS2-VASc score shows a better risk-stratification capacity for ISND-related IS.


By screening the risk factors of ischaemic stroke for isolated sinus node dysfunction (sinus node dysfunction without atrial fibrillation), we developed and validated a new scoring system­P-combined score, which is a combination of an abnormal P-wave terminal force in electrocardiogram-lead V1 (PTFV1) and the CHA2DS2-VASc score. We constructed the P-combined score in the following way: abnormal PTFV1 (2 points), age (1 point for 65­74 years and 2 points for ≥75 years), sex (1 point for female), congestive heart failure (1 point), hypertension (1 point), diabetes mellitus (1 point), vascular disease (1 point), and thrombotic event (2 points). Based on our analysis, we found that the P-combined score showed a strong performance (with a C-statistic of 0.716 for 5 years), which was better than the CHA2DS2-VASc score (C-statistic of 0.678 for 5 years). We also found that the performance of the P-combined score was rigorous in an independent cohort from two external centres (with a C-statistic of 0.808 for 5 years) and outperformed the CHA2DS2-VASc score (C-statistic of 0.747 for 5 years).


Subject(s)
Atrial Fibrillation , Brain Ischemia , Ischemic Stroke , Stroke , Humans , Atrial Fibrillation/diagnosis , Atrial Fibrillation/epidemiology , Stroke/diagnosis , Stroke/epidemiology , Stroke/etiology , Brain Ischemia/diagnosis , Brain Ischemia/epidemiology , Brain Ischemia/etiology , Sick Sinus Syndrome , Risk Factors , Risk Assessment
5.
Org Lett ; 25(47): 8397-8401, 2023 Dec 01.
Article in English | MEDLINE | ID: mdl-37983182

ABSTRACT

We presented a method for synthesizing allylic chiral hydrazones from 1,4-disubstituted 1,3-dienes and hydrazones through a (R)-DTBM-Segphos-Pd(0)-catalyzed hydrohydrazonation reaction. This transformation has a wide range of substrates and good functional group tolerance. The desired products were obtained in medium to high yield and good regio- and enantioselectivity. Synthetic transformation of the products into various nitrogen-containing chiral compounds was demonstrated.

6.
Sci Rep ; 13(1): 16064, 2023 Sep 25.
Article in English | MEDLINE | ID: mdl-37749141

ABSTRACT

The damage variation of a masonry structure during shield tunneling has been investigated. Furthermore, the damage degree of the masonry building has been investigated by combining the field measurement, finite element method results, and theoretical method. The results show that compared with the theoretical calculation method LSTM, the method provide by this paper can give the detail damage location of the masonry structure caused by shield construction. Due to the existence of door and window openings, the result of JMM is larger than LSTM result, the differences can be modified by concept of "characteristic tensile strain". The wall of the masonry building encounter the shield face first suffers more damage than the later ones. At the beginning of tunnlling, the damage were generated from a small area at the bottom for wall 1, but a larger area at the top of the building for wall 2. The damage area increase more at the top of the building as tunneling advanced, but the maximum damage occurred at the bottom of the building.

7.
Sci Total Environ ; 864: 161216, 2023 Mar 15.
Article in English | MEDLINE | ID: mdl-36584948

ABSTRACT

Globally, tidal flats are increasingly narrowing due to continuous reclamation and sea level rise. Nonetheless, the impact of tidal flat narrowing (TFN) on tidal creek systems that play a crucial role in the formation and shaping of tidal flats is not well understood, despite a cognition that the tidal flat-creek system is integrated and coevolved. In this study, based on the quantification and mapping of tidal creek ecosystem vitality (TCEV), we detected the state evolution of tidal creek systems in response to TFN process on the central Jiangsu coast (CJC), China. The results showed that two thirds of the original tidal flat width was lost from 1984 to 2020, with a narrowing rate of 210.9 m/yr. The seaward movement of seawall lines and the landward movement of low tide lines contributed 82.5 % and 17.5 % to this serious TFN process, respectively. Across the study period, the overall TCEV lost 82.3 % with a substantial transformation from high level to low level. In terms of three dimensions of structural complexity, functional integrity and spatial occupancy, the tidal creek system of CJC has greatly deviated from the high-quality state in 1984, which was significantly associated with TFN. For a natural mature tidal flat, the loss of its initial width seems acceptable when <1/3, but unacceptable when >1/2, which are two important thresholds corresponding to the lower and higher loss of TCEV, respectively. It is worried that the CJC tidal flat-creek system would fall into a vicious circle of state evolution. Therefore, efforts should be made to control irrational reclamation and perform ecological restoration based on an insight into the relationship between TCEV and TFN.

8.
Sci Rep ; 12(1): 18459, 2022 Nov 02.
Article in English | MEDLINE | ID: mdl-36323873

ABSTRACT

The crack propagation behavior of rock during compression involves complex mechanisms. Describing the growth behavior of a large number of cracks with conventional mechanical models is a major challenge. Therefore, in this work, we propose a new method to describe crack growth behavior by considering crack bodies as free voxels that can expand and coalesce within a rock sample according to certain rules. Specifically, we first propose a crack growth model that quantitatively describes the crack growth ratio and crack growth rate, which are integrally related to the loading rate, internal friction angle, cohesion, initial porosity, and confining stress. Second, to avoid the complex analytical process of the traditional mechanical model in solving the propagation directions of multiple cracks, we introduce a method for determining the crack growth directions of shearing failure based on the colony growth assumption. This method defines the crack propagation direction as a synthetic vector of the inertial direction, the attractive direction, the Coulomb direction, and the edge direction. Moreover, a new mathematical description method of fracture energy and plastic energy is proposed to calculate the crack growth at each time step. The simulation results show that our crack growth model for shearing failure agrees well with the experimental results and explains the fracture behavior and transformation law of cracks to some extent.

9.
Front Public Health ; 10: 936275, 2022.
Article in English | MEDLINE | ID: mdl-35899157

ABSTRACT

Background: The national essential public health service (NEPHS) has been in operation for more than a decade. Numerous studies examined the utilization of NEPHS by migrants and the factors that influence it, but few examined the effect of NEPHS awareness and utilization on the health of inhabitants, particularly migrants. The purpose of this study is to ascertain the level of awareness and utilization of NEPHS, as well as to examine their health-improving effects on migrants. Methods: Based on the data from the 2017 China Migrants Dynamic Survey, linear probability model, ordered logit model and the propensity score matching methods were employed to investigate impact of awareness and utilization of NEPHS on the health among Chinese migrants. Mediating effect model were used to identify the mechanism of the impact of NEPHS on health. Results: The findings indicated that migrants' awareness and utilization of NEPHS are still insufficient. After adjusting for other factors, the study discovered that increased awareness and use of NEPHS had a beneficial influence on migrants' self-rated health. Further heterogeneity analysis revealed significant disparities in the health consequences of NEPHS awareness and utilization across subgroups. The effect of increased awareness and usage of NEPHS on health is stronger for middle-aged and elderly people, women, and low-educated migrants with urban household registration. The estimated results of the mediating effect model supported the mechanism that increased NEPHS awareness among the floating population could encourage its utilization and further improve the floating population's health. Conclusions: Given that migrants' NEPHS utilization is still low and that NEPHS utilization has a positive effect on health, some targeted strategies, such as a variety of new media communication methods, health education related to occupational disease and tuberculosis prevention, and targeted NEPHS projects for specific groups, such as men, young and middle-aged groups, those with a high level of education, and rural migrants, should be conducted to improve the health of migrants.


Subject(s)
Transients and Migrants , Tuberculosis , Aged , China/epidemiology , Female , Health Services , Humans , Male , Middle Aged , Outcome Assessment, Health Care
10.
Angew Chem Int Ed Engl ; 61(40): e202208411, 2022 10 04.
Article in English | MEDLINE | ID: mdl-35759311

ABSTRACT

Catalysis by excited-state palladium has emerged as an active area of research, but controlling the enantioselectivity remains a challenge. Herein, we report the use of synergistic Pd/Cu catalysis to accomplish the first three-component photochemical 1,4-bisalkylation reactions of 1,3-butadiene. Consequently, α-amino acid esters bearing quaternary stereocenters were expeditiously synthesized from three simple starting materials: an alkyl bromide, butadiene, and an aldimine ester. Experimental and computational investigation of the reaction mechanism confirmed a radical pathway involving catalysis by an excited-state palladium species. The stereochemistry is mainly controlled by the chiral Cu catalyst.


Subject(s)
Butadienes , Palladium , Amino Acids/chemistry , Bromides , Catalysis , Esters , Palladium/chemistry , Stereoisomerism
11.
Angew Chem Int Ed Engl ; 61(33): e202207621, 2022 Aug 15.
Article in English | MEDLINE | ID: mdl-35713176

ABSTRACT

As a fundamental and synthetically useful C-C bond formation reaction, the aldol reaction is one of the most versatile transformations in organic synthesis. However, despite extensive research on asymmetric versions of the reaction, a unified method for stereoselective access to the complementary syn and anti diastereomeric products remains to be developed. In this study, we developed a synergistic palladium/chiral Lewis base system that overcomes the inherent diastereoselectivity bias of aldol reactions and, as a result, allowed us to achieve the first diastereodivergent coupling reactions of alkoxyallenes with pentafluorophenol esters. Computational studies suggest a mechanism involving an intermolecular protonative hydropalladation pathway rather than a palladium-hydride migratory insertion pathway. The origin of the stereochemistry for this synergistic catalysis system is rationalized by DFT calculations.

12.
Nat Commun ; 13(1): 2470, 2022 05 05.
Article in English | MEDLINE | ID: mdl-35513394

ABSTRACT

Due to high bond dissociation energies of Csp2-F bonds, using fluorinated compounds in Csp2-Csp3 cross-coupling is difficult. Here the authors report a protocol for enantioselective Csp2-Csp3 coupling of dienyl fluorides with aldimine esters, enabled by synergistic copper and palladium catalysis. This reaction represents the first example of asymmetric Csp2-Csp3 cross-coupling involving an inert Csp2-F bond and provides expeditious access to chiral α-alkenyl α-amino acids with high enantioselectivity. Control experiments suggest that the Csp2-F bond activation occurs through a pathway involving PdH migratory insertion and subsequent allylic defluorination, rather than by direct oxidative addition of the Csp2-F bond to Pd(0). The detailed mechanism is further investigated by DFT calculation and the enantioselectivity is rationalized.


Subject(s)
Esters , Fluorides , Alkylation , Amino Acids/chemistry , Catalysis , Molecular Structure , Polyenes , Stereoisomerism
13.
Materials (Basel) ; 15(7)2022 Apr 01.
Article in English | MEDLINE | ID: mdl-35407942

ABSTRACT

Successful quality control and quality assurance (QC/QA) of earthwork compaction is critical to the long-term performance of roads, railways, airports, dams, and embankments. The purpose of this paper is to provide insights into the current practice, existing problems, challenges, and future development trends of QC/QA methods from the perspective of bibliometrics and the development stage. A bibliometric analysis is presented. Through quantitative analysis of literature and qualitative analysis of the development stage, insights into the current research practices and future directions of QC/QA methods have been derived from the perspectives of literature, cluster analysis, classification, different types of QC/QA methods, conclusions, and recommendations. It is found that the current QC/QA methods can be roughly divided into conventional compaction, digital rolling compaction, automatic rolling compaction, and intelligent control compaction. Currently, QC/QA methods are mainly confronted with the issues of accurate detection of compaction quality, autonomous optimization and intelligent decision-making of compaction process, multi-machine coordination, QC/QA-related specification formulation, and process standardization. To address these issues, several critical potential research directions are further identified: comprehensive CCI measurement system; simple and realistic mathematical representation of the complex compaction dynamics; parallel computing and distributed management of multi-source heterogeneous data; standardized application workflow and the cost-benefit assessment in the context of the full life cycle; intelligent control theories, methods, and technologies of earthwork compaction based on multidisciplinary integration. The paper enables researchers to obtain a comprehensive understanding of QC/QA methods for earthwork compaction as well as the suggested solutions for future work.

14.
Brief Bioinform ; 23(3)2022 05 13.
Article in English | MEDLINE | ID: mdl-35352098

ABSTRACT

Synthetic lethality (SL) occurs between two genes when the inactivation of either gene alone has no effect on cell survival but the inactivation of both genes results in cell death. SL-based therapy has become one of the most promising targeted cancer therapies in the last decade as PARP inhibitors achieve great success in the clinic. The key point to exploiting SL-based cancer therapy is the identification of robust SL pairs. Although many wet-lab-based methods have been developed to screen SL pairs, known SL pairs are less than 0.1% of all potential pairs due to large number of human gene combinations. Computational prediction methods complement wet-lab-based methods to effectively reduce the search space of SL pairs. In this paper, we review the recent applications of computational methods and commonly used databases for SL prediction. First, we introduce the concept of SL and its screening methods. Second, various SL-related data resources are summarized. Then, computational methods including statistical-based methods, network-based methods, classical machine learning methods and deep learning methods for SL prediction are summarized. In particular, we elaborate on the negative sampling methods applied in these models. Next, representative tools for SL prediction are introduced. Finally, the challenges and future work for SL prediction are discussed.


Subject(s)
Neoplasms , Synthetic Lethal Mutations , Databases, Factual , Humans , Machine Learning , Neoplasms/genetics
15.
Pak J Pharm Sci ; 35(6(Special)): 1787-1791, 2022 Nov.
Article in English | MEDLINE | ID: mdl-36861244

ABSTRACT

The present preliminary investigation was designed to identify biomarkers in the progression of pancreatitis in Chinese patients with acute pancreatitis. Chinese patients aged <60 years with a confirmed diagnosis of acute pancreatitis were enrolled. A saliva sample was collected using salimetrics oral swab in precooled polypropylene tubes to prevent degradation of sensitive peptides. All samples were then centrifuged at 700 × g for 15 min at 4°C to remove debris. The supernatant of each sample was fractionated into 100µL aliquots and frozen at -70°C until analyses using affymetrix HG U133 Plus 2.0 array technique. Bedside index for severity acute pancreatitis (BISAP) score and CT severity index were recorded for each enrolled patient to assess the progression and severity of acute pancreatitis. Data from a total of 210 patients (105 patients in each group) were analyzed. Among identified biomarkers, acrosomal vesicle protein 1 was significantly higher in patients with disease progression as compared to patient without disease progression. Logistic regression model showed that acrosomal vesicle protein 1 (ACRV1) were positively correlated with the progression of diseases. The present reports showed that a mRNA salivary biomarker (ACRV1) are associated with progression of pancreatitis in patients with early stage of pancreatitis. This study suggest that mRNA salivary biomarker (ACRV1) is a predictor of pancreatitis progression.


Subject(s)
Pancreatitis , Humans , Acute Disease , East Asian People , RNA, Messenger , Disease Progression
16.
Brief Bioinform ; 23(1)2022 01 17.
Article in English | MEDLINE | ID: mdl-34477201

ABSTRACT

Combination therapy has shown an obvious efficacy on complex diseases and can greatly reduce the development of drug resistance. However, even with high-throughput screens, experimental methods are insufficient to explore novel drug combinations. In order to reduce the search space of drug combinations, there is an urgent need to develop more efficient computational methods to predict novel drug combinations. In recent decades, more and more machine learning (ML) algorithms have been applied to improve the predictive performance. The object of this study is to introduce and discuss the recent applications of ML methods and the widely used databases in drug combination prediction. In this study, we first describe the concept and controversy of synergism between drug combinations. Then, we investigate various publicly available data resources and tools for prediction tasks. Next, ML methods including classic ML and deep learning methods applied in drug combination prediction are introduced. Finally, we summarize the challenges to ML methods in prediction tasks and provide a discussion on future work.


Subject(s)
Algorithms , Machine Learning , Databases, Factual , Drug Combinations , Drug Interactions
17.
Ultrasonics ; 119: 106634, 2022 Feb.
Article in English | MEDLINE | ID: mdl-34781117

ABSTRACT

Ultrasonic shot peening(USP) is an advanced surface treatment technology for obtaining excellent surface properties or manufacturing a three-dimensional curved surface of the metal sheets. The impact of the medium driven by ultrasonic vibration is significant to parameter optimization and excellent performance of the USP technology. However, the impact characteristics of the medium lack careful study, which is a complex dynamic analysis involving many factors, such as collision, plastic deformation, air pressure, etc. In this paper, a detection system is successfully developed to investigate the needle impact force and frequency against the material surface, consisting of a piezoelectric load sensor, oscilloscope, and a single needle USP device. Moreover, the FE model of the needle impact is developed simultaneously to study the characteristics of residual stress implantation induced by needle impact. Based on the experiment and FE simulation results, it is discovered that the impacts with high speed primarily determine the thickness of the modified layer implanted with residual stress during multiple impacts at different rates. According to residual stress implantation characteristics, the low-speed impact whose speed does not reach 50% of the maximum impact speed was defined as the ineffective impact. Besides, increasing the amplitude of ultrasonic vibration results in a significant increase in the maximum impact force and the effective impact frequency. The travel distance of needle impact has a considerable effect on the effective impact frequency, but it has little effect on the maximum impact force. Finally, it was concluded that the low air pressure plays a positive role in the needle impact. Furthermore, excessive air pressure hinders the needle impact and results in a decline in the effective impact frequency and the maximum impact force.

18.
J Am Chem Soc ; 143(29): 10948-10962, 2021 07 28.
Article in English | MEDLINE | ID: mdl-34264662

ABSTRACT

Metal-hydride-catalyzed hydroalkylation of 1,3-dienes with enolizable carbonyl compounds is an atom- and step-economical method for preparing chiral molecules with allylic stereocenters. Although high diastereo- and enantioselectivities have been achieved for many coupling partners, aldehydes have not yet been used for this purpose because they are less stable than other carbonyl compounds under basic conditions and they have the potential to rapidly epimerize at the α-position. Moreover, stereodivergent hydroalkylation reactions of 1,3-dienes to access complementary diastereomers with vicinal stereocenters is challenging. Herein, we describe a synergistic palladium/amine catalyst system that allowed us to achieve the first stereodivergent hydroalkylation reactions of 1,3-dienes with aldehydes. By choosing an appropriate combination of chiral palladium and amine catalysts, we could obtain either syn or anti coupling products, and this method therefore provides highly diastereo- and enantioselective access to complementary diastereomers of chiral aldehydes with α,ß-vicinal stereocenters. Density functional theory calculations revealed a mechanism involving PdH formation and migratory insertion into the alkene, followed by C-C bond formation. The origin of the stereoselectivities was investigated by means of distortion/interaction analysis.

19.
Angew Chem Int Ed Engl ; 60(12): 6545-6552, 2021 03 15.
Article in English | MEDLINE | ID: mdl-33274595

ABSTRACT

Both syn- and anti-ß-amino alcohols are common structural motifs in natural products, drug molecules, chiral ligands and catalysts. However, the currently available methods for synthesizing these motifs are limited to generate only one diastereoisomer. Therefore, development of a unified method for stereoselective access to complementary diastereomers would be highly desirable. Herein, we report a method for dual-metal-catalyzed diastereodivergent coupling of alkoxyallenes with aldimine esters. By carefully selecting the two metals and appropriate chiral ligands, we could synthesize both syn- and anti-ß-amino alcohol motifs with high enantioselectivity and diastereoselectivity from the same set of starting materials. Furthermore, stereodivergent syntheses of all four stereoisomers of ß-amino alcohols could be achieved. We demonstrated the synthetic utility of this method by concisely synthesizing two ß-amino alcohol natural products, mycestericins F and G.

20.
J Am Chem Soc ; 142(37): 15860-15869, 2020 09 16.
Article in English | MEDLINE | ID: mdl-32813509

ABSTRACT

Chiral sulfones are important structural motifs in organic synthesis because of their widespread use in pharmaceutical chemistry. In particular, chiral allylic sulfones have drawn particular interest because of their synthetic utility. However, enantioselective synthesis of 1,3-disubstituted unsymmetrical chiral allylic sulfones remains a challenge. In this article, we report a protocol for (R)-DTBM-Segphos/Pd-catalyzed regio- and enantioselective hydrosulfonylation of 1,3-dienes with sulfinic acids, which provides atom- and step-economical access to 1,3-disubstituted chiral allylic sulfones. The reaction occurs under mild conditions and has a broad substrate scope. Combined experimental and computational studies suggest that the reaction is initiated by a ligand-to-ligand hydrogen transfer followed by a C-S bond reductive elimination via a six-membered transition state. Steric repulsion between the olefinic C-H of the substrate and the tert-butyl group of (R)-DTBM-Segphos was found to be a key factor in the enantiocontrol.

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