Nutrient retranslocation in trees is important in nutrient budgets and energy flows in forest ecosystems. We investigated nutrient retranslocation in the fine roots of a Manchurian Ash （Fraxinus mandshurica） and a L...Nutrient retranslocation in trees is important in nutrient budgets and energy flows in forest ecosystems. We investigated nutrient retranslocation in the fine roots of a Manchurian Ash （Fraxinus mandshurica） and a Larch （Larix olgensis） plantation in northeastern China. Nutrient retranslocation in the fine roots was investigated using three methods, specifically, nutrient concentration, the ratio of Ca to other elements （Ca/other elements ratio） and nutrient content. The method based on nutrient content proved most suitable when investigating nutrient retranslocation from fine roots of the two species. The nutrient-content-based method showed that there were retranslocations of N, P, K and Mg from the fine roots of Manchurian Ash, with retranslocation efficiencies of 13, 25, 65, and 38 %, respectively, whereas there were no Ca retranslocations. There were retranslocations of N, P, K, Ca and Mg from the fine roots of Larch, with retranslocation efficiencies of 31, 40, 52, 23 and 25 %, respectively.展开更多
Sperm cryopreservation is useful in assisted reproductive technology and male fertility preservation.However,freezing and thawing significantly reduces the total and progressive motility of human spermatozoa.In the pr...Sperm cryopreservation is useful in assisted reproductive technology and male fertility preservation.However,freezing and thawing significantly reduces the total and progressive motility of human spermatozoa.In the present study,we explored the effects of peroxiredoxin 6(PRDX6)on total and progressive motility of human spermatozoa after cryopreservation.Semen samples of 20 males with normal parameters were collected and frozen in media supplemented with different concentrations of PRDX6(0 mM,10−5 mM,10−7 mM,and 10−9 mM,respectively).Postthaw total and progressive motility of sperms were measured.The results showed that in comparison with 0 mM,the concentrations of 10−5 mM,10−7 mM,and 10−9 mM of PRDX6 all significantly improved total motility and progressive motility of sperms(p<0.05).The 10−7 mM of PRDX6 showed the best performance.In conclusion,the supplementation of PRDX6 helps to maintain the total and progressive motility of human spermatozoa.展开更多
This study aims to investigate the protective effects of peroxiredoxin 6 on the total motility and progressive motility of human spermatozoa.Semen samples with normal parameters were collected from 23 males and supple...This study aims to investigate the protective effects of peroxiredoxin 6 on the total motility and progressive motility of human spermatozoa.Semen samples with normal parameters were collected from 23 males and supplemented with different concentrations of peroxiredoxin 6.All the semen samples were measured according to the WHO 5th manual,and the motile spermatozoa were extracted using IVF fertilization medium supplemented with different peroxiredoxin 6 concentrations.Total motility and progressive motility were observed at different time-points of culture at room temperature.After peroxiredoxin 6 supplementation,all groups had a significant increase in total motility and progressive motility compared to the control group.The difference in total motility and progressive motility between the 0 and 10−7 mM groups was observed at 24 and 48 h of culture at room temperature.At 24 h,the total motility increased by 30%in the control group(16.03±11.91 vs.11.51±7.84),and progressive motility increased by 21%(10.53±9.4 vs.8.31±6.04).A similar trend was observed in the 48 h group.In addition,we also found that peroxiredoxin 6 had a well protective effect on sperm kinetic parameters at 10−7 mM.The findings of this study suggest that peroxiredoxin 6 can enhance sperm total motility and progressive motility in IVF fertilization medium.Peroxiredoxin 6 may have potential benefits for sperm preparation in assisted reproductive technology.展开更多
In this paper, we conduct research on primary core factors of influencing college students＇ entrepreneurial success rate under the perspectives of the law and team management perspectives. College students＇ entrepre...In this paper, we conduct research on primary core factors of influencing college students＇ entrepreneurial success rate under the perspectives of the law and team management perspectives. College students＇ entrepreneurship education is cultivating he students innovative spirit and creative ability as the basic value tendency, in order to cultivate creative talents as the main goal of education, it is an extension of the quality-oriented education, is the comprehensive development of students＇ qualities of wisdom education is the all-round development of students＇ personality education ＇is pay more attention to the body of the human spirit, the humanist education. Carrying out entrepreneurship education, the reform and development of higher education to improve the quality of talent training levels promote national independent innovation and entrepreneurship has important significance. Our research proposes the novel perspective on the issues that is meaningful.展开更多
Pseudolaric acids are a family of diterpenoid natural products that exhibit a broad spectrum of biological activities.The main structural feature of their framework is a trans-fused perhydroazulene bearing a bridged l...Pseudolaric acids are a family of diterpenoid natural products that exhibit a broad spectrum of biological activities.The main structural feature of their framework is a trans-fused perhydroazulene bearing a bridged lactone positioned at the junction of the rings.Herein,we have developed a radical cyclization strategy that allows flexible tuning of the cyclization process through diverse silicon substitutions on the substrates.This strategy can assist in constructing a series of skeletons with structural resemblance to pseudolaric acids and expedites the construction of the bridged lactone.Finally,it facilitates the synthesis of the entire skeletal structure of the pseudolaric acidfamily of natural products,excludingthe B-ringfunctionalization.展开更多
Dysfunction of CD8^(+)T cells in the tumor microenvironment(TME)contributes to tumor immune escape and immunotherapy tolerance.The effects of hormones such as leptin,steroid hormones,and glucocorticoids on T cell func...Dysfunction of CD8^(+)T cells in the tumor microenvironment(TME)contributes to tumor immune escape and immunotherapy tolerance.The effects of hormones such as leptin,steroid hormones,and glucocorticoids on T cell function have been reported previously.However,the mechanism underlying thyroid-stimulating hormone(TSH)/thyroid-stimulating hormone receptor(TSHR)signaling in CD8^(+)T cell exhaustion and tumor immune evasion remain poorly understood.This study was aimed at investigating the effects of TSH/TSHR signaling on the function of CD8^(+)T cells and immune evasion in colorectal cancer(CRC).Methods:TSHR expression levels in CD8^(+)T cells were assessed with immunofluorescence and flow cytometry.Functional investigations involved manipulation of TSHR expression in cellular and mouse models to study its role in CD8^(+)T cells.Mechanistic insights were mainly gained through RNAsequencing,Western blotting,chromatin immunoprecipitation and luciferase activity assay.Immunofluorescence,flow cytometry and Western blotting were used to investigate the source of TSH and TSHR in CRC tissues.Results:TSHR was highly expressed in cancer cells and CD8^(+)T cells in CRC tissues.TSH/TSHR signaling was identified as the intrinsic pathway promoting CD8^(+)T cell exhaustion.Conditional deletion of TSHR in CD8^(+)tumorinfiltrating lymphocytes(TILs)improved effector differentiation and suppressed the expression of immune checkpoint receptors such as programmed cell death 1(PD-1)and hepatitis A virus cellular receptor 2(HAVCR2 or TIM3)through the protein kinase A(PKA)/cAMP-response element binding protein(CREB)signaling pathway.CRC cells secreted TSHR via exosomes to increase the TSHR level in CD8^(+)T cells,resulting in immunosuppression in the TME.Myeloid-derived suppressor cells(MDSCs)was the main source of TSH within the TME.Low expression of TSHR in CRC was a predictor of immunotherapy response.Conclusions:The present findings highlighted the role of endogenous TSH/TSHR signaling in CD8^(+)T cell exhaustion and immune evasion in CRC.TSHR may be suitable as a predictive and therapeutic biomarker in CRC immunotherapy.展开更多
A unique characteristic of piezoelectric materials is their ability of electric-mechanical transduction and converting mechanical energy to electrical energy or vice versa. This remarkable property, embedded in piezoe...A unique characteristic of piezoelectric materials is their ability of electric-mechanical transduction and converting mechanical energy to electrical energy or vice versa. This remarkable property, embedded in piezoelectric materials, has been exploited to construct a wide variety of acoustic transducers for industrial applications. These include acoustic experimental measurements [1-3], mobile and internet communications [4,5], intravascular ultrasound [6], medical imaging [7], rangefinders [8], fingerprint sensors, implantable micro-devices, nondestructive detection, mea-surement of the in-situ stresses of underground rock formation, and early warning systems for dam damage and natural hazards, among others.展开更多
We report two models of the lateral displacement of acoustic-wave scattering on a fluid-solid interface that reveal an acoustic analog of the Goos-Hainchen effect in optics. This acoustic analog is called the acoustic...We report two models of the lateral displacement of acoustic-wave scattering on a fluid-solid interface that reveal an acoustic analog of the Goos-Hainchen effect in optics. This acoustic analog is called the acoustic Goos-Hainchen effect. Using newly proposed models, we made numerical calculations for the system ofa water-Perspex interface. Specifically, in the post-critical-angle region, we observed a lateral displacement （and transition time） of the reflected P-wave with respect to the incident P-wave. The first arrival of the acoustic signal from the interface is found to be a reflected P-wave rather than the sliding-refraction P-wave usually described in traditional acoustic-logging sliding P-wave theory. For both proposed models, the effective propagation speed of the reflected P-wave along the interface depends on not only the physical properties of the interracial media but also the incident angle. These observations are intriguing and warrant further investigation.展开更多
We explore the physical phenomenon of acoustic waves induced at the interface between two different anisotropic rock media.Specifically,one medium is a transversely isotropic medium with a vertical axis of symmetry(VT...We explore the physical phenomenon of acoustic waves induced at the interface between two different anisotropic rock media.Specifically,one medium is a transversely isotropic medium with a vertical axis of symmetry(VTI medium)and the other one is a transversely isotropic medium with a tilt axis of symmetry(TTI medium).By solving the Kelvin-Christoffel equation,an eighth-order polynomial is established for reflection and refraction angles,which is confirmed from SnelFs law.Three types of analytical expressions of the polarization coefficients of the induced waves are obtained corresponding to different incident angle regions.An effective algorithm has been developed for numerical analysis of the polarization coefficients.Applying characteristic anisotropic parameters reported in the literature,the influencing factors on reflection and refraction coefficients are analyzed,e.g.,the anisotropy,the tilt-angle of rock-layer,and the incident-angle.The calculated reflection and refraction coefficients have been rechecked for energy conservation.展开更多
A full account of semisyntheses of polychlorinated marine steroids clionastatins A and B is described.We have developed a unique two-stage chlorination-oxidation strategy that enabled concise and divergent semisynthes...A full account of semisyntheses of polychlorinated marine steroids clionastatins A and B is described.We have developed a unique two-stage chlorination-oxidation strategy that enabled concise and divergent semisyntheses of clionastatins A and B in 16 steps from inexpensive testosterone.Key transformations in chlorination stage include(a)conformationally controlled,stereospecific dichlorination through an unusualβ-chloronium intermediate to install the diequatorial C1,C2-dichloride;(b)C4-OH directed C19–H oxygenation followed by challenging neopentyl chlorination to install the C19–Cl.The high oxidation level was constructed through(a)the desaturation at C6–C7 through one-pot photochemical dibromination–reductive debromination;(b)regioselective anti-Markovnikov oxidation of the C6–C7 double bond by photoredox-metal dual catalysis to forge the B ring enone;(c)late-stage desaturation with SeO_(2)to introduce C8–C9 double bond.Wharton transposition was used to forge the D-ring enone,and thermodynamically driven epimerization secured the cis-fused C/D ring system.Furthermore,we also provided a 14-step approach to clionastatin A by optimizing the construction of the D-ring enone with a dehydration-oxidation sequence.展开更多
A unified protecting group-free approach to two stemarene and two betaerene diterpenoids through a bioinspired two-phase strategy has been developed,and three of them were obtained for the first time via chemical synt...A unified protecting group-free approach to two stemarene and two betaerene diterpenoids through a bioinspired two-phase strategy has been developed,and three of them were obtained for the first time via chemical synthesis.Starting from a common intermediate,two distinct tetracyclic frameworks containing diastereoisomeric bridged bicycles were constructed by a divergent ring reorganization strategy.Late-stage C–H functionalization through a xanthylation-oxygenation protocol furnished the corresponding oxygenated stereocenters or oxo functionality in high regio-and diastereoselective fashion within a complex hydrocarbon system.The stereochemical puzzles in(–)-2-acetoxybetaer13(17)-ene and(+)-7-acetoxybetaer-13(17)-ene were first predicted by the comparison of density functional theory(DFT)-nuclear magnetic resonance(NMR)data with the reported data and then unambiguously addressed through the total syntheses of natural products and three diastereomers.展开更多
Atkamine is a complex marine pyrroloiminoquinone alkaloid that comprises a heptacyclic scaffold bearing five different heterocycles and four contiguous stereocenters,and therefore it is a highly challenging target for...Atkamine is a complex marine pyrroloiminoquinone alkaloid that comprises a heptacyclic scaffold bearing five different heterocycles and four contiguous stereocenters,and therefore it is a highly challenging target for synthetic chemists.We herein reported a modular synthetic strategy toward this alkaloid,featuring a formal [5+2] annulation and an asymmetric Michael addition.The efficient synthesis of the long-chain aliphatic aldehyde and chiral amino acetal fragments have been achieved.A simplified tetracyclic intermediate bearing the core structure of atkamine has been successfully constructed through the formal [5+2] annulation.展开更多
基金supported by the National Key Technology Research and Development Program(2012BAD21B0202-02)the Natural Science Foundation of Heilongjiang Province of China(C201340)the assisted project by Heilong Jiang Postdoctoral Funds for Scientific Research Initiation(LBH-Q13006)
文摘Nutrient retranslocation in trees is important in nutrient budgets and energy flows in forest ecosystems. We investigated nutrient retranslocation in the fine roots of a Manchurian Ash （Fraxinus mandshurica） and a Larch （Larix olgensis） plantation in northeastern China. Nutrient retranslocation in the fine roots was investigated using three methods, specifically, nutrient concentration, the ratio of Ca to other elements （Ca/other elements ratio） and nutrient content. The method based on nutrient content proved most suitable when investigating nutrient retranslocation from fine roots of the two species. The nutrient-content-based method showed that there were retranslocations of N, P, K and Mg from the fine roots of Manchurian Ash, with retranslocation efficiencies of 13, 25, 65, and 38 %, respectively, whereas there were no Ca retranslocations. There were retranslocations of N, P, K, Ca and Mg from the fine roots of Larch, with retranslocation efficiencies of 31, 40, 52, 23 and 25 %, respectively.
基金Peking Post-doctoral Research Fund(EE 2019-50)Peking University International Hospital Research Funds(No.YN2019QN13)NHC Key Laboratory of Family Planning and Healthy/key laboratory of reproductive medicine of Hebei provincial(SZ-202006).
文摘Sperm cryopreservation is useful in assisted reproductive technology and male fertility preservation.However,freezing and thawing significantly reduces the total and progressive motility of human spermatozoa.In the present study,we explored the effects of peroxiredoxin 6(PRDX6)on total and progressive motility of human spermatozoa after cryopreservation.Semen samples of 20 males with normal parameters were collected and frozen in media supplemented with different concentrations of PRDX6(0 mM,10−5 mM,10−7 mM,and 10−9 mM,respectively).Postthaw total and progressive motility of sperms were measured.The results showed that in comparison with 0 mM,the concentrations of 10−5 mM,10−7 mM,and 10−9 mM of PRDX6 all significantly improved total motility and progressive motility of sperms(p<0.05).The 10−7 mM of PRDX6 showed the best performance.In conclusion,the supplementation of PRDX6 helps to maintain the total and progressive motility of human spermatozoa.
基金supported by the Peking Post-doctoral Research Fund(EE2019-50)and Peking University International Hospital Research Funds(No.YN2019QN13).
文摘This study aims to investigate the protective effects of peroxiredoxin 6 on the total motility and progressive motility of human spermatozoa.Semen samples with normal parameters were collected from 23 males and supplemented with different concentrations of peroxiredoxin 6.All the semen samples were measured according to the WHO 5th manual,and the motile spermatozoa were extracted using IVF fertilization medium supplemented with different peroxiredoxin 6 concentrations.Total motility and progressive motility were observed at different time-points of culture at room temperature.After peroxiredoxin 6 supplementation,all groups had a significant increase in total motility and progressive motility compared to the control group.The difference in total motility and progressive motility between the 0 and 10−7 mM groups was observed at 24 and 48 h of culture at room temperature.At 24 h,the total motility increased by 30%in the control group(16.03±11.91 vs.11.51±7.84),and progressive motility increased by 21%(10.53±9.4 vs.8.31±6.04).A similar trend was observed in the 48 h group.In addition,we also found that peroxiredoxin 6 had a well protective effect on sperm kinetic parameters at 10−7 mM.The findings of this study suggest that peroxiredoxin 6 can enhance sperm total motility and progressive motility in IVF fertilization medium.Peroxiredoxin 6 may have potential benefits for sperm preparation in assisted reproductive technology.
文摘In this paper, we conduct research on primary core factors of influencing college students＇ entrepreneurial success rate under the perspectives of the law and team management perspectives. College students＇ entrepreneurship education is cultivating he students innovative spirit and creative ability as the basic value tendency, in order to cultivate creative talents as the main goal of education, it is an extension of the quality-oriented education, is the comprehensive development of students＇ qualities of wisdom education is the all-round development of students＇ personality education ＇is pay more attention to the body of the human spirit, the humanist education. Carrying out entrepreneurship education, the reform and development of higher education to improve the quality of talent training levels promote national independent innovation and entrepreneurship has important significance. Our research proposes the novel perspective on the issues that is meaningful.
基金the National Natural Science Foundation of China(Nos.22071205,22301251 and 21772164)China Postdoctoral Science Foundation(2023M732942),NFFTBS(J1310024)+1 种基金NCETFJ,and PCSIRT is acknowledgedthe financial support(No.202005)from State Key Laboratory of Elemento-Organic Chemistry,Nankai University.
文摘Pseudolaric acids are a family of diterpenoid natural products that exhibit a broad spectrum of biological activities.The main structural feature of their framework is a trans-fused perhydroazulene bearing a bridged lactone positioned at the junction of the rings.Herein,we have developed a radical cyclization strategy that allows flexible tuning of the cyclization process through diverse silicon substitutions on the substrates.This strategy can assist in constructing a series of skeletons with structural resemblance to pseudolaric acids and expedites the construction of the bridged lactone.Finally,it facilitates the synthesis of the entire skeletal structure of the pseudolaric acidfamily of natural products,excludingthe B-ringfunctionalization.
基金supported by the National Key R&D Program of China(Grant No.2021YFF1201004)the National Natural Science Foundation of China(Grant No.82273358,No.81802306,No.81903002,No.81672821,No.82071742,No.32270926)Natural Science Foundation of Guangdong Province of China(Grant No.2019A1515012196,No.2022A1515012059).
文摘Dysfunction of CD8^(+)T cells in the tumor microenvironment(TME)contributes to tumor immune escape and immunotherapy tolerance.The effects of hormones such as leptin,steroid hormones,and glucocorticoids on T cell function have been reported previously.However,the mechanism underlying thyroid-stimulating hormone(TSH)/thyroid-stimulating hormone receptor(TSHR)signaling in CD8^(+)T cell exhaustion and tumor immune evasion remain poorly understood.This study was aimed at investigating the effects of TSH/TSHR signaling on the function of CD8^(+)T cells and immune evasion in colorectal cancer(CRC).Methods:TSHR expression levels in CD8^(+)T cells were assessed with immunofluorescence and flow cytometry.Functional investigations involved manipulation of TSHR expression in cellular and mouse models to study its role in CD8^(+)T cells.Mechanistic insights were mainly gained through RNAsequencing,Western blotting,chromatin immunoprecipitation and luciferase activity assay.Immunofluorescence,flow cytometry and Western blotting were used to investigate the source of TSH and TSHR in CRC tissues.Results:TSHR was highly expressed in cancer cells and CD8^(+)T cells in CRC tissues.TSH/TSHR signaling was identified as the intrinsic pathway promoting CD8^(+)T cell exhaustion.Conditional deletion of TSHR in CD8^(+)tumorinfiltrating lymphocytes(TILs)improved effector differentiation and suppressed the expression of immune checkpoint receptors such as programmed cell death 1(PD-1)and hepatitis A virus cellular receptor 2(HAVCR2 or TIM3)through the protein kinase A(PKA)/cAMP-response element binding protein(CREB)signaling pathway.CRC cells secreted TSHR via exosomes to increase the TSHR level in CD8^(+)T cells,resulting in immunosuppression in the TME.Myeloid-derived suppressor cells(MDSCs)was the main source of TSH within the TME.Low expression of TSHR in CRC was a predictor of immunotherapy response.Conclusions:The present findings highlighted the role of endogenous TSH/TSHR signaling in CD8^(+)T cell exhaustion and immune evasion in CRC.TSHR may be suitable as a predictive and therapeutic biomarker in CRC immunotherapy.
基金supported by Xi’an University of Posts and Telecommunicationsthe Physical Sciences Division at The University of Chicago
文摘A unique characteristic of piezoelectric materials is their ability of electric-mechanical transduction and converting mechanical energy to electrical energy or vice versa. This remarkable property, embedded in piezoelectric materials, has been exploited to construct a wide variety of acoustic transducers for industrial applications. These include acoustic experimental measurements [1-3], mobile and internet communications [4,5], intravascular ultrasound [6], medical imaging [7], rangefinders [8], fingerprint sensors, implantable micro-devices, nondestructive detection, mea-surement of the in-situ stresses of underground rock formation, and early warning systems for dam damage and natural hazards, among others.
基金the Xi’an University of Posts and Telecommunicationsthe Physical Sciences Division at the University of Chicagothe Scientific Research Program(Grant No.15JK1685)of the Shaanxi Provincial Education Department
文摘We report two models of the lateral displacement of acoustic-wave scattering on a fluid-solid interface that reveal an acoustic analog of the Goos-Hainchen effect in optics. This acoustic analog is called the acoustic Goos-Hainchen effect. Using newly proposed models, we made numerical calculations for the system ofa water-Perspex interface. Specifically, in the post-critical-angle region, we observed a lateral displacement （and transition time） of the reflected P-wave with respect to the incident P-wave. The first arrival of the acoustic signal from the interface is found to be a reflected P-wave rather than the sliding-refraction P-wave usually described in traditional acoustic-logging sliding P-wave theory. For both proposed models, the effective propagation speed of the reflected P-wave along the interface depends on not only the physical properties of the interracial media but also the incident angle. These observations are intriguing and warrant further investigation.
基金the Na-tional Natural Science Foundation of China(Grant No.41974130)the Physical Sciences Division at The University of Chicago.
文摘We explore the physical phenomenon of acoustic waves induced at the interface between two different anisotropic rock media.Specifically,one medium is a transversely isotropic medium with a vertical axis of symmetry(VTI medium)and the other one is a transversely isotropic medium with a tilt axis of symmetry(TTI medium).By solving the Kelvin-Christoffel equation,an eighth-order polynomial is established for reflection and refraction angles,which is confirmed from SnelFs law.Three types of analytical expressions of the polarization coefficients of the induced waves are obtained corresponding to different incident angle regions.An effective algorithm has been developed for numerical analysis of the polarization coefficients.Applying characteristic anisotropic parameters reported in the literature,the influencing factors on reflection and refraction coefficients are analyzed,e.g.,the anisotropy,the tilt-angle of rock-layer,and the incident-angle.The calculated reflection and refraction coefficients have been rechecked for energy conservation.
基金Financial support from the National Natural Science Foundation of China(Nos.22071205 and 21772164)NFFTBS(J1310024)+1 种基金NCETFJ,and PCSIRT is acknowledged.The authors are also grateful for the financial support(LMDBKF-2019-03)the Laboratory for Marine Drugs and Bioproducts,Pilot National Laboratory for Marine Science and Technology.
文摘A full account of semisyntheses of polychlorinated marine steroids clionastatins A and B is described.We have developed a unique two-stage chlorination-oxidation strategy that enabled concise and divergent semisyntheses of clionastatins A and B in 16 steps from inexpensive testosterone.Key transformations in chlorination stage include(a)conformationally controlled,stereospecific dichlorination through an unusualβ-chloronium intermediate to install the diequatorial C1,C2-dichloride;(b)C4-OH directed C19–H oxygenation followed by challenging neopentyl chlorination to install the C19–Cl.The high oxidation level was constructed through(a)the desaturation at C6–C7 through one-pot photochemical dibromination–reductive debromination;(b)regioselective anti-Markovnikov oxidation of the C6–C7 double bond by photoredox-metal dual catalysis to forge the B ring enone;(c)late-stage desaturation with SeO_(2)to introduce C8–C9 double bond.Wharton transposition was used to forge the D-ring enone,and thermodynamically driven epimerization secured the cis-fused C/D ring system.Furthermore,we also provided a 14-step approach to clionastatin A by optimizing the construction of the D-ring enone with a dehydration-oxidation sequence.
基金Financial support from the National Natural Science Foundation of China(nos.22071205,21772164,and 21572187)NFFTBS(no.J1310024),and PCSIRT is acknowledged.
文摘A unified protecting group-free approach to two stemarene and two betaerene diterpenoids through a bioinspired two-phase strategy has been developed,and three of them were obtained for the first time via chemical synthesis.Starting from a common intermediate,two distinct tetracyclic frameworks containing diastereoisomeric bridged bicycles were constructed by a divergent ring reorganization strategy.Late-stage C–H functionalization through a xanthylation-oxygenation protocol furnished the corresponding oxygenated stereocenters or oxo functionality in high regio-and diastereoselective fashion within a complex hydrocarbon system.The stereochemical puzzles in(–)-2-acetoxybetaer13(17)-ene and(+)-7-acetoxybetaer-13(17)-ene were first predicted by the comparison of density functional theory(DFT)-nuclear magnetic resonance(NMR)data with the reported data and then unambiguously addressed through the total syntheses of natural products and three diastereomers.
基金the National Natural Science Foundation of China for financial support of this work by grants (Nos.21772164 and 21572187)the National Found for Fostering Talents of Basic Science (NFFTBS,No.J1310024)+1 种基金New Century Excellent Talents in University of Fujian Province (NECTFJ)Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT) for support。
文摘Atkamine is a complex marine pyrroloiminoquinone alkaloid that comprises a heptacyclic scaffold bearing five different heterocycles and four contiguous stereocenters,and therefore it is a highly challenging target for synthetic chemists.We herein reported a modular synthetic strategy toward this alkaloid,featuring a formal [5+2] annulation and an asymmetric Michael addition.The efficient synthesis of the long-chain aliphatic aldehyde and chiral amino acetal fragments have been achieved.A simplified tetracyclic intermediate bearing the core structure of atkamine has been successfully constructed through the formal [5+2] annulation.
