P450 enzymes-catalyzed aromatic hydroxylation plays an important role in detoxification,biosynthesis,and potential carcinogenic effect of aromatic compounds.Though it has been explored for decades,the actual process o...P450 enzymes-catalyzed aromatic hydroxylation plays an important role in detoxification,biosynthesis,and potential carcinogenic effect of aromatic compounds.Though it has been explored for decades,the actual process of aromatic hydroxylation and mechanism of regioselectivity catalyzed by cytochrome P450 monooxygenases remained ambiguous.Here,we have resolved these issues.With a stable chiral organofluorine probe,and especially with X-ray data of two isolated arene oxides derivatives,we demonstrate that an arene oxide pathway is definitely involved in P450-catalyzed aromatic hydroxylation.By the capture,isolation,identification and reactivity exploration of the arene 1,2-oxide and arene 2,3-oxide intermediates,together with advanced QM calculations,the mechanism of how two intermediates go to the same product has been elucidated.In addition to the model substrate,we also confirmed that an arene oxide intermediate is involved in the P450-catalyzed hydroxylation pathway of a natural product derivative methyl cinnamate,which indicates that this intermediate appears to be universal in P450-catalyzed aromatic hydroxylation.Our work not only provides the most direct evidence for the arene oxide pathway and new insights into the regioselectivity involved in P450-catalyzed aromatic hydroxylation,but also supplies a new synthetic approach to achieve the dearomatization of aromatic compounds.展开更多
Two series, totalizing twelve, of new compounds, ethyl 1-aroyl/aroylmethyl-5-methyl-3- methylthiopyrazole-4-carboxylates 5/6, have been synthesized via highly regioselective acylation and alkylation of ethyl 3-methyl-...Two series, totalizing twelve, of new compounds, ethyl 1-aroyl/aroylmethyl-5-methyl-3- methylthiopyrazole-4-carboxylates 5/6, have been synthesized via highly regioselective acylation and alkylation of ethyl 3-methyl-5-methylthio-1H- pyrazole-4-carboxylate 2a with aroyl chloride 3 and alpha-tosyloxysubstitutedacetophenones 4. Unexpected structures of the product have been unambiguously determined by both X-ray crystallographic analysis and 2D NMR.展开更多
The benzyl-substituted flavone compounds are rare in nature, while some of which have interesting biological activities. The total synthesis of benzyl-substituted flavone derivatives via the acidic rearrangement of be...The benzyl-substituted flavone compounds are rare in nature, while some of which have interesting biological activities. The total synthesis of benzyl-substituted flavone derivatives via the acidic rearrangement of benzyl groups in flavone benzyl ethers, and the complicated regioselectivity of the rearrangement were reported. The regioselectivity was proposed to be determined by the steric hindrance as well as the ease of electrophilic substitution reaction for benzyl cations at different positions of corresponding debenzylated fiavone compounds.展开更多
Several novel cobalt dichloride complexes with amino-phosphine bidentate ligands were synthesized and characterized.For some of them single crystals were obtained and their molecular structure was determined by X-ray ...Several novel cobalt dichloride complexes with amino-phosphine bidentate ligands were synthesized and characterized.For some of them single crystals were obtained and their molecular structure was determined by X-ray diffraction method.All the complexes were then used in combination with MAO for the polymerization of 1,3-butadiene,obtaining polymers with different structures(i.e.,predominantly 1,2 or cis-1,4)mainly depending on the type of ligand and on the MAO/Co molar ratio.The behavior of these novel catalysts was compared with that exhibited,in the polymerization of the same monomer,by the systems CoCl_(2)(PR3)2-MAO and CoCl_(2)(PRPh2)2-MAO(R=alkyl or cycloalkyl group),and by the systems based on cobalt dichloride complexes with various bi-and tridentate ligands(e.g.,diphosphines,bis-imines,pyridyl-imines,bis-iminopyridines).The comparison between the different systems allowed us to make some clarity about the actual and effective role played by the various types of ligands in the polymerization of conjugated dienes with catalytic systems CoCl_(2)(L)-MAO,in which L=mono-,bi-,or tri-dentate ligand.展开更多
Density functional theory（DFT） method was used to explore the origin of the regioselectivity of Cocatalyzed hydroacylation of 1,3-dienes.The reaction of 2-methyl-1,3-butadiene and benzaldehyde with1,3-bis（diphenylp...Density functional theory（DFT） method was used to explore the origin of the regioselectivity of Cocatalyzed hydroacylation of 1,3-dienes.The reaction of 2-methyl-1,3-butadiene and benzaldehyde with1,3-bis（diphenylphosphino）propane ligand was chosen as the model reaction.The energies of the intermediates and transition states in the stages of oxidative cyclization,β-H elimination and C-H reductive elimination were investigated.Computational results show that β-H elimination is the ratedetermining step for the whole catalytic cycle.C1-Selective oxidative cyclization is favored over C4-selective oxidative cyclization.Besides.C4-selective oxidative cyclization is kinetically disfavored than all the steps in C1-hydroacylation mechanisms,consistent with the experimentally obtained C1-selective hydroacylation products.Analyzing the reason for such observation,we suggest that both electronic and steric effects contribute to the C1-selectivity.On the electronic aspect,C1 is more electron rich than C4 due to the methyl group on C2,which makes the electrophilic attack of aldehyde carbon on C1 more favorable.On the steric aspect,the methyl group locates farther from the ligands in the transition state of C1-selective oxidative cyclization than in that of C4-selective oxidative cyclization.展开更多
This paper reports the primary results of the study. on the regioselectivity of the cyclization reaction of 5-amino-1, 2, 4-triazole and its analogues until asym-1, 3-dicarbonyl compounds. The mechanistic explanation ...This paper reports the primary results of the study. on the regioselectivity of the cyclization reaction of 5-amino-1, 2, 4-triazole and its analogues until asym-1, 3-dicarbonyl compounds. The mechanistic explanation for the regioselectivity is presented.展开更多
Many attempts have been made to control the regioselectivity for olefin poly- merization by varying the structures of ligands in catalysts. The regioselectivity of propylene polymerization was investigated by replacin...Many attempts have been made to control the regioselectivity for olefin poly- merization by varying the structures of ligands in catalysts. The regioselectivity of propylene polymerization was investigated by replacing a nitrogen atom in the Pd(II) diimine catalyst with an oxygen atom from density functional theory method at the B3LYP/LANL2DZ level. The results show that the 1,2-insertion becomes a rival mechanism to the 2,1-insertion when the nitrogen atom is replaced by the oxygen atom leading to an asymmetric environment in the catalyst, and that the steric effect in the asymmetrical catalyst plays an important part in the polymerization. The insertion barrier from 2-O is much higher than that from 2-N. A pyramid transition state was characterized for the catalyst to convert 2-O back to 2-N through internal rotation. The propylene prefers to coordinate at the opposite side of O in the catalyst. This is the driving force for the internal rotation. The results are significant for isotactic and syndiotactic polymerization.展开更多
Accepted theories predict that substitution reactions are controlled by the electronic nature of the attacked site for electrophilic aromatic substitution. Here it is shown that in addition the bond strength of the br...Accepted theories predict that substitution reactions are controlled by the electronic nature of the attacked site for electrophilic aromatic substitution. Here it is shown that in addition the bond strength of the broken bond may also influence the regioselectivity of the substitution reaction, and that the Dpb is a good indicator of the strength of a chemical bond. The Dpb denotes the depth of the potential acting on one electron in a molecule at the bond center （bc）. In this letter, the values of Dpb along the C-H and N-H bonds have been investigated, and it is demonstrated that for aromatic compounds, the regioselectivity of the electrophilic substitution can well be rationalized in terms of Dpb values.展开更多
The mechanism and regioselectivity of 1,3-dipolar cycloaddition of N-[methyl]-C-[5-nitro-2-furyl] nitrilimine with dimethyl 7-oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylate were investigated using activation energ...The mechanism and regioselectivity of 1,3-dipolar cycloaddition of N-[methyl]-C-[5-nitro-2-furyl] nitrilimine with dimethyl 7-oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylate were investigated using activation energy calculations and density functional theory-based reactivity indexes. The reaction proceeds by an asynchronous concerted mechanism. The calculations are performed at the B3LYP/6-31G（d） level of theory and the obtained results are in agreement with experimental outcome.展开更多
Chondroitin sulfate(CS) B and T are rare subtypes of CS,which are scare in nature.There are also limited synthetic methods to prepare them.Here we report an ingenious semisynthetic approach to prepare a library of dis...Chondroitin sulfate(CS) B and T are rare subtypes of CS,which are scare in nature.There are also limited synthetic methods to prepare them.Here we report an ingenious semisynthetic approach to prepare a library of disaccharides,tetrasaccharides and hexasaccharides of CS-B and CS-T based on the acid or enzymatic degradation of natural CS polysaccharide in 9 or 10 steps.Our approach is the shortest synthetic route toward size-defined CS-B and CS-T oligosaccharides reported to date.In addition,a regioselective protection method of hydroxyls is highlighted,which has achieved the regioselective protection of 4 hydroxyl groups among 7 equatorial hydroxyl groups.By preparing size-defined rare CS oligosaccharides from commercially available natural CS polysaccharides,this strategy has the potential to meet the need of rare natural oligosaccharides.展开更多
A new oxidative N-heterocyclic carbene(NHC)-catalyzed high-order[7+3]annulation reaction ofγ-indolyl phenols as 1,7-dinucleophiles andα,β-alkynals with the aid of Sc(OTf)_(3)is reported,enabling the highly regiosel...A new oxidative N-heterocyclic carbene(NHC)-catalyzed high-order[7+3]annulation reaction ofγ-indolyl phenols as 1,7-dinucleophiles andα,β-alkynals with the aid of Sc(OTf)_(3)is reported,enabling the highly regioselective access to unprecedented polyarene-fused ten-membered lactams bearing a bridged aryl-aryl-indole scaffold in moderate to good yields.This protocol demonstrates a broad substrate scope,good compatibility with substituents and complete regioselectivity,providing an organocatalytic modular synthetic strategy for creating medium-sized lactams.展开更多
Regioselevtive functionalization of perylene diimides(PDIs)at bay area often requires multistep synthesis and strenuous recrystallization.Direct bromination of perylene diimides only afford the 1,6 and 1,7-regioisomer...Regioselevtive functionalization of perylene diimides(PDIs)at bay area often requires multistep synthesis and strenuous recrystallization.Direct bromination of perylene diimides only afford the 1,6 and 1,7-regioisomers.More importantly,the 1,6-dibromo regioisomers could only be separated by preparative HPLC.Herein,we report a promising strategy for constructing Janus backbone of BN-doped perylene diimide derivatives.This Janus-type configuration results in the unique regioselective functionalization of BN-JPDIs,which yields exclusively the 1,6-regioisomers.Further investigation shows that the Janus-type configuration leads to a net dipole moment of 1.94 D and intramolecular charge transfer,which causes substantial changes on the optoelectronic properties.Moreover,the single crystal organic field-effect transistors based on BN-JPDIs exhibit electron mobilities up to 0.57 cm^(2)V^(-1)s^(-1),showcasing their potential as versatile building block towards high-performance n-type organic semiconductors.展开更多
文摘P450 enzymes-catalyzed aromatic hydroxylation plays an important role in detoxification,biosynthesis,and potential carcinogenic effect of aromatic compounds.Though it has been explored for decades,the actual process of aromatic hydroxylation and mechanism of regioselectivity catalyzed by cytochrome P450 monooxygenases remained ambiguous.Here,we have resolved these issues.With a stable chiral organofluorine probe,and especially with X-ray data of two isolated arene oxides derivatives,we demonstrate that an arene oxide pathway is definitely involved in P450-catalyzed aromatic hydroxylation.By the capture,isolation,identification and reactivity exploration of the arene 1,2-oxide and arene 2,3-oxide intermediates,together with advanced QM calculations,the mechanism of how two intermediates go to the same product has been elucidated.In addition to the model substrate,we also confirmed that an arene oxide intermediate is involved in the P450-catalyzed hydroxylation pathway of a natural product derivative methyl cinnamate,which indicates that this intermediate appears to be universal in P450-catalyzed aromatic hydroxylation.Our work not only provides the most direct evidence for the arene oxide pathway and new insights into the regioselectivity involved in P450-catalyzed aromatic hydroxylation,but also supplies a new synthetic approach to achieve the dearomatization of aromatic compounds.
基金The project was supported by the Natural Science Foundation of Shandong Province(No.Y2003B01)NNSFC(No.20172031.
文摘Two series, totalizing twelve, of new compounds, ethyl 1-aroyl/aroylmethyl-5-methyl-3- methylthiopyrazole-4-carboxylates 5/6, have been synthesized via highly regioselective acylation and alkylation of ethyl 3-methyl-5-methylthio-1H- pyrazole-4-carboxylate 2a with aroyl chloride 3 and alpha-tosyloxysubstitutedacetophenones 4. Unexpected structures of the product have been unambiguously determined by both X-ray crystallographic analysis and 2D NMR.
基金supported by the National Natural Science Foundation of China (Nos.21172260 and 30901859)Shanghai Natural Science Foundation (No.09ZR1438800)‘‘Chen Guang’’ project supported by Shanghai Municipal Education Commission and Shanghai Education Development Foundation (12CG42)
文摘The benzyl-substituted flavone compounds are rare in nature, while some of which have interesting biological activities. The total synthesis of benzyl-substituted flavone derivatives via the acidic rearrangement of benzyl groups in flavone benzyl ethers, and the complicated regioselectivity of the rearrangement were reported. The regioselectivity was proposed to be determined by the steric hindrance as well as the ease of electrophilic substitution reaction for benzyl cations at different positions of corresponding debenzylated fiavone compounds.
文摘Several novel cobalt dichloride complexes with amino-phosphine bidentate ligands were synthesized and characterized.For some of them single crystals were obtained and their molecular structure was determined by X-ray diffraction method.All the complexes were then used in combination with MAO for the polymerization of 1,3-butadiene,obtaining polymers with different structures(i.e.,predominantly 1,2 or cis-1,4)mainly depending on the type of ligand and on the MAO/Co molar ratio.The behavior of these novel catalysts was compared with that exhibited,in the polymerization of the same monomer,by the systems CoCl_(2)(PR3)2-MAO and CoCl_(2)(PRPh2)2-MAO(R=alkyl or cycloalkyl group),and by the systems based on cobalt dichloride complexes with various bi-and tridentate ligands(e.g.,diphosphines,bis-imines,pyridyl-imines,bis-iminopyridines).The comparison between the different systems allowed us to make some clarity about the actual and effective role played by the various types of ligands in the polymerization of conjugated dienes with catalytic systems CoCl_(2)(L)-MAO,in which L=mono-,bi-,or tri-dentate ligand.
基金the NSFC(Nos.21325208,21172209,21361140372,21202006)SRFDP(No.20123402110051)+4 种基金FRFCU(No.WK2060190025)CAS(No.KJCX2-EW-J02)Fok Ying Tung Education Foundation,Anhui Provincial Natural Science Foundation(No.1308085QB38)China National Grid Project funded by MOE of Chinathe supercomputer center of Shanghai and USTC
文摘Density functional theory（DFT） method was used to explore the origin of the regioselectivity of Cocatalyzed hydroacylation of 1,3-dienes.The reaction of 2-methyl-1,3-butadiene and benzaldehyde with1,3-bis（diphenylphosphino）propane ligand was chosen as the model reaction.The energies of the intermediates and transition states in the stages of oxidative cyclization,β-H elimination and C-H reductive elimination were investigated.Computational results show that β-H elimination is the ratedetermining step for the whole catalytic cycle.C1-Selective oxidative cyclization is favored over C4-selective oxidative cyclization.Besides.C4-selective oxidative cyclization is kinetically disfavored than all the steps in C1-hydroacylation mechanisms,consistent with the experimentally obtained C1-selective hydroacylation products.Analyzing the reason for such observation,we suggest that both electronic and steric effects contribute to the C1-selectivity.On the electronic aspect,C1 is more electron rich than C4 due to the methyl group on C2,which makes the electrophilic attack of aldehyde carbon on C1 more favorable.On the steric aspect,the methyl group locates farther from the ligands in the transition state of C1-selective oxidative cyclization than in that of C4-selective oxidative cyclization.
文摘This paper reports the primary results of the study. on the regioselectivity of the cyclization reaction of 5-amino-1, 2, 4-triazole and its analogues until asym-1, 3-dicarbonyl compounds. The mechanistic explanation for the regioselectivity is presented.
基金This work was supported by the Natural Science Foundation of Heilongjiang Province (No. B0313) and Research Foundation of China University of Mining and Technology
文摘Many attempts have been made to control the regioselectivity for olefin poly- merization by varying the structures of ligands in catalysts. The regioselectivity of propylene polymerization was investigated by replacing a nitrogen atom in the Pd(II) diimine catalyst with an oxygen atom from density functional theory method at the B3LYP/LANL2DZ level. The results show that the 1,2-insertion becomes a rival mechanism to the 2,1-insertion when the nitrogen atom is replaced by the oxygen atom leading to an asymmetric environment in the catalyst, and that the steric effect in the asymmetrical catalyst plays an important part in the polymerization. The insertion barrier from 2-O is much higher than that from 2-N. A pyramid transition state was characterized for the catalyst to convert 2-O back to 2-N through internal rotation. The propylene prefers to coordinate at the opposite side of O in the catalyst. This is the driving force for the internal rotation. The results are significant for isotactic and syndiotactic polymerization.
基金support of the National Natural Science Foundation of China (Nos.21133005 and 21473083)program for Liaoning Excellent Talents in University LNET(No.LJQ2013111)Natural Science Foundation of Liaoning Province(No. 2014020150)
文摘Accepted theories predict that substitution reactions are controlled by the electronic nature of the attacked site for electrophilic aromatic substitution. Here it is shown that in addition the bond strength of the broken bond may also influence the regioselectivity of the substitution reaction, and that the Dpb is a good indicator of the strength of a chemical bond. The Dpb denotes the depth of the potential acting on one electron in a molecule at the bond center （bc）. In this letter, the values of Dpb along the C-H and N-H bonds have been investigated, and it is demonstrated that for aromatic compounds, the regioselectivity of the electrophilic substitution can well be rationalized in terms of Dpb values.
文摘The mechanism and regioselectivity of 1,3-dipolar cycloaddition of N-[methyl]-C-[5-nitro-2-furyl] nitrilimine with dimethyl 7-oxabicyclo[2,2,1]hepta-2,5-diene-2,3-dicarboxylate were investigated using activation energy calculations and density functional theory-based reactivity indexes. The reaction proceeds by an asynchronous concerted mechanism. The calculations are performed at the B3LYP/6-31G（d） level of theory and the obtained results are in agreement with experimental outcome.
基金supported by the National Natural Science Foundation of China(Nos.81930097,82151223)the National Key R&D Program of China(Nos.2022YFF1203005,2022YFC2303700)。
文摘Chondroitin sulfate(CS) B and T are rare subtypes of CS,which are scare in nature.There are also limited synthetic methods to prepare them.Here we report an ingenious semisynthetic approach to prepare a library of disaccharides,tetrasaccharides and hexasaccharides of CS-B and CS-T based on the acid or enzymatic degradation of natural CS polysaccharide in 9 or 10 steps.Our approach is the shortest synthetic route toward size-defined CS-B and CS-T oligosaccharides reported to date.In addition,a regioselective protection method of hydroxyls is highlighted,which has achieved the regioselective protection of 4 hydroxyl groups among 7 equatorial hydroxyl groups.By preparing size-defined rare CS oligosaccharides from commercially available natural CS polysaccharides,this strategy has the potential to meet the need of rare natural oligosaccharides.
基金National Natural Science Foundation of China(Nos.21971090 and 22271123)the NSF of Jiangsu Province(No.BK20230201)+1 种基金the Natural Science Foundation of Jiangsu Education Committee(No.22KJB150024)the Natural Science Foundation of Jiangsu Normal University(No.21XSRX010)。
文摘A new oxidative N-heterocyclic carbene(NHC)-catalyzed high-order[7+3]annulation reaction ofγ-indolyl phenols as 1,7-dinucleophiles andα,β-alkynals with the aid of Sc(OTf)_(3)is reported,enabling the highly regioselective access to unprecedented polyarene-fused ten-membered lactams bearing a bridged aryl-aryl-indole scaffold in moderate to good yields.This protocol demonstrates a broad substrate scope,good compatibility with substituents and complete regioselectivity,providing an organocatalytic modular synthetic strategy for creating medium-sized lactams.
基金support from the National Natural Science Foundation of China(Nos.22071007,22020102001,22335002)the National Key R&D Program of China(No.2022YFB3602802)+3 种基金Beijing Natural Science Foundation(No.Z220025)the National Facility for Protein Science in Shanghai,Shanghai Advanced Research Institute,CAS,for providing technical support in X-ray diffraction data collectionthe High-Performance Computing Platform of Peking University for supporting the computational workthe support of BMS Junior Fellow program。
文摘Regioselevtive functionalization of perylene diimides(PDIs)at bay area often requires multistep synthesis and strenuous recrystallization.Direct bromination of perylene diimides only afford the 1,6 and 1,7-regioisomers.More importantly,the 1,6-dibromo regioisomers could only be separated by preparative HPLC.Herein,we report a promising strategy for constructing Janus backbone of BN-doped perylene diimide derivatives.This Janus-type configuration results in the unique regioselective functionalization of BN-JPDIs,which yields exclusively the 1,6-regioisomers.Further investigation shows that the Janus-type configuration leads to a net dipole moment of 1.94 D and intramolecular charge transfer,which causes substantial changes on the optoelectronic properties.Moreover,the single crystal organic field-effect transistors based on BN-JPDIs exhibit electron mobilities up to 0.57 cm^(2)V^(-1)s^(-1),showcasing their potential as versatile building block towards high-performance n-type organic semiconductors.
