Neodymium chloride isopropanol complex （NdCl3.3＇prOH） activated by modified methylaluminoxane （MMAO） was examined in isoprene polymerization in hexane, with regards to Nd compounds, aluminum （Al） compounds, [Al...Neodymium chloride isopropanol complex （NdCl3.3＇prOH） activated by modified methylaluminoxane （MMAO） was examined in isoprene polymerization in hexane, with regards to Nd compounds, aluminum （Al） compounds, [Al]/[Nd] ratio, polymerization temperature and time. NdCl3＇3iprOH exhibited high activity producing polymers feasting high cis-l,4 stereospecificity （〉 96%）, very high molecular weight （Mn 〉 1.0 × 10^6） and fairly narrow molecular weight distribution （MWD, Mw/Mn 〈 2.0） simultaneously. In comparison, neodymium isopropoxide also showed high activity providing polymers with narrow MWD （Mw/Mn = 2.07）, but somewhat low cis-1,4 content （ca. 92%）, while neodymium chloride had no activity under present polymerization conditions. The Al compounds affected the polymer yield in the order of Al（i-Bu）3 〉 MMAO 〉 Al（i-Bu）2H. MMAO as cocatalyst afforded polyisoprene with high Mn over 1.0 × 10^6, whereas as stronger chain transfer agent than MMAO, AI（i-Bu）3 and AI（i-Bu）EH yielded polymers with low Mn （1.0 × 10^5-8.0 × 10^5）. NdCl3·3＇PrOH/MMAO catalyst showed a fairly good catalytic activity even at relatively low [Al]/[Nd] ratio of 30, and the produced polymer remained high cis-1,4 content of 95.8% along with high Mn over 1.0× 10^6 even at elevated temperatures up to 70℃. The polymerization rate is of the first order with respect to the concentration of isoprene. The mechanism of active species formation was discussed preliminarily.展开更多
TiCl4/MgCl2/clay compound catalyst was prepared by chemical reaction. Exfoliated polypropylene （PP）/clay nanocomposites were synthesized by in situ polymerization with this compound catalyst. Effects of polymerizati...TiCl4/MgCl2/clay compound catalyst was prepared by chemical reaction. Exfoliated polypropylene （PP）/clay nanocomposites were synthesized by in situ polymerization with this compound catalyst. Effects of polymerization temperature, polymerization time, propylene pressure, solvent consumption and pre-treat time of catalyst on catalyst activity and catalytic stereospecificity were studied. Under optimal conditions, activity of the nano-compound catalyst is about 88.3 kg/（mol Ti-h）. Isotacticity of PP obtained in the nanocomposites is in the range of 89%-99%, and its melting temperature is about 159℃. The weight-average molecular weight of PP can reach 6.7 × 10^5 - 7.8 × 10^5, and the molecular weight distribution is between 7.7 and 7.9.展开更多
The present paper covers the stereoselective syntheses of four 1 thiogalactopyranosides 1—4 and three thio disaccharides 5—7 through the PTC methods and their structures confirmed by means of elementary analysis, ...The present paper covers the stereoselective syntheses of four 1 thiogalactopyranosides 1—4 and three thio disaccharides 5—7 through the PTC methods and their structures confirmed by means of elementary analysis, IR and NMR spectral data.展开更多
Introduction The cyano branched carbohydrates are useful, versatil intermediaries for the synthesis of branched sugars having biological activity in nature. Owing to the good yield, mild reaction conditions and high s...Introduction The cyano branched carbohydrates are useful, versatil intermediaries for the synthesis of branched sugars having biological activity in nature. Owing to the good yield, mild reaction conditions and high stereospecificity, the phase transition catalysis(PTC)method has been widely used to the syntheses of C-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
The stereospecific carbocupration of terminal alkynes via higher order cuprates to give 1,1'-disubstituted olefins with 99% configuration purity is described. Its synthetic utility as a general method for the prep...The stereospecific carbocupration of terminal alkynes via higher order cuprates to give 1,1'-disubstituted olefins with 99% configuration purity is described. Its synthetic utility as a general method for the preparation of substituted olefins is further illustrated by the direct synthesis of (±)-ipsenol and (E)-β-farnesene with highly geometric purity of the carbon-carbon double bond.展开更多
The stereospecific hydrolysis of mandelate can be effectively catalyzed by hyperthermophilic acylpeptide esterase APE 1547（Aeropyrum pernix esterase 1547）. APE 1547 used in this reaction showed a remarkable stereodi...The stereospecific hydrolysis of mandelate can be effectively catalyzed by hyperthermophilic acylpeptide esterase APE 1547（Aeropyrum pernix esterase 1547）. APE 1547 used in this reaction showed a remarkable stereodi-scrimination in favour of R-mandelic acid（99% e.e.） with an enantiomeric ratio E〉200. The results of computer simulation are consistent with the experimental results. It can be inferred that the R-substrate adopted a binding mode productive of the reaction due to the formation of the hydrogen bond at the active site of APE 1547.展开更多
1, 5-Benzothiazepines 1 react with phenylacetyl chloride to give the title compounds.The structures of these new compounds were confirmed by elemental analysis, ~1H NMR, ^(13)C NMRand MS spectroscopy, and their config...1, 5-Benzothiazepines 1 react with phenylacetyl chloride to give the title compounds.The structures of these new compounds were confirmed by elemental analysis, ~1H NMR, ^(13)C NMRand MS spectroscopy, and their configuration (the mutual positions of the substituents relative to theβ-lactam ring) and conformation of the compounds were determined by X-ray crystal analysis.展开更多
Reaction of 1,5-benzothiazepine with N-protected glycine gives new a-amino-β-lactamderivatives of 1.5-benzothiazepine. The configuration and conformation of the products wereconfirmed by x-ray diffraction. The resu...Reaction of 1,5-benzothiazepine with N-protected glycine gives new a-amino-β-lactamderivatives of 1.5-benzothiazepine. The configuration and conformation of the products wereconfirmed by x-ray diffraction. The result further reveals that the reaction of 1.5-benzothiazepineswith derivatives of carboxylic acid stereospecific.展开更多
Structural analysis of Candida antarctica lipase B (CALB) indicates that side chain of leucine at 278 site lies above the entrance of the catalytic pocket, which prognosticates its potential role on substrate specific...Structural analysis of Candida antarctica lipase B (CALB) indicates that side chain of leucine at 278 site lies above the entrance of the catalytic pocket, which prognosticates its potential role on substrate specificity of the enzyme. To verify this presumption, shortened side chain of glycine or proline was rational designed and mutants were constructed by site-directed mutagenesis method. The colorimetric assay using p-nitrophenyl esters of fatty acids with various chain-lengths was used to study the substrate preference of lipases. Results indicated that L278G or L278P mutations both induced the drift of substrate specificity of CALB from p-nitrophenyl caprylate (pNP-C8) to longer carbon chain length of p-nitrophenyl caprate (pNP-C10). Meanwhile, Vmax value of two mutants to pNP-C10 was both higher than that of wild-type. Docking results also indicated that shortened side chain of glycine or proline residues substitution at this site could get rid of the space block present above the catalytic pocket, and made longer chain substrate (pNP-C10) enter into the catalytic pocket easier. The modulation of specificity observed allowed for building substrate binding model and opened new possibilities for designing ligand specific lipases.展开更多
In recent years,milk fat has garnered significant attention.over 98%of milk fat is composed of triglycerides,with fatty acids being one of the main components that play important physiological roles.the distribution o...In recent years,milk fat has garnered significant attention.over 98%of milk fat is composed of triglycerides,with fatty acids being one of the main components that play important physiological roles.the distribution of fatty acids on the glycerol backbone of triglycerides is closely related to the digestion and absorption of milk fat.However,there is a lack of research comparing the stereospecific distribution of fatty acids in human milk and different ruminant milks.this review summarizes the extraction techniques and analytical methods of fatty acids from milk fat,analyzes and compares the composition and content of total fatty acids in human,yak,camel,cow,buffalo,and goat milks,overviews the stereospecific location of fatty acids on triglycerides and digestion and absorption of fatty acids in different milk sources,and evaluates the nutritional value of different milk sources using seven fatty acid nutritional evaluation indices to evaluate the nutritional value of different milk sources,providing guidance for promoting human health,and exploring the potential importance of the fatty acid composition of ruminant milk for infant or special dairy development,providing a basis for further development and utilization of dairy products.展开更多
Archimedean solids were first proposed by the ancient Greek philosopher Archimedes.Unfortunately,this aspect of his work was not well-documented.It was not until 1619 that the mathematician Johannes Kepler reconstruct...Archimedean solids were first proposed by the ancient Greek philosopher Archimedes.Unfortunately,this aspect of his work was not well-documented.It was not until 1619 that the mathematician Johannes Kepler reconstructed the complete set of 13 Archimedean solids[1].Among these solids,only the snub cube and snub dodecahedron are chiral.展开更多
Most of the electrophilic additions on carbon-carbon multiply bond can be summarized as: where Y are certain atoms on the fight of the periodic table; Z may be null, atom or group. Regardless of the rate law of Ad_E2 ...Most of the electrophilic additions on carbon-carbon multiply bond can be summarized as: where Y are certain atoms on the fight of the periodic table; Z may be null, atom or group. Regardless of the rate law of Ad_E2 Ad_E3 or the more complex kinetics, the micromechanisms of transition state of electrophilic addition can be divided into two sorts, i.e. open ion and bridged ion mechanisms. The former one allows free rotation of展开更多
Grain phytate,a mixed metal ion salt of inositol hexakisphosphate,accounts for 60%–80%of stored phosphorus in plants and is a potent antinutrient of non-ruminant animals including humans.Through neofunctionalization ...Grain phytate,a mixed metal ion salt of inositol hexakisphosphate,accounts for 60%–80%of stored phosphorus in plants and is a potent antinutrient of non-ruminant animals including humans.Through neofunctionalization of purple acid phytases(PAPhy),some cereals such as wheat and rye have acquired particularly high mature grain phytase activity.As PAPhy activity supplies phosphate,liberates metal ions necessary for seedling emergence,and obviates antinutrient effects of phytate,its manipulation and control are targeted crop traits.Here we show the X-ray crystal structure of the b2 isoform of wheat PAPhy induced during germination.This high-resolution crystal structure suggests a model for phytate recognition that,validated by molecular dynamics simulations,implicates elements of two sequence inserts(termed PAPhy motifs)relative to a canonical metallophosphoesterase(MPE)domain in forming phytate-specific substrate specificity pockets.These motifs are well conserved in PAPhys from monocot cereals,enzymes which are characterized by high specificity for phytate.Tested by mutagenesis,residues His229 in PAPhy motif 4 and Lys410 in the MPE domain,both conserved in PAPhys,are found to strongly influence phytase activity.These results explain the observed phytase activity of cereal PAPhys and open the way to the rational engineering of phytase activity in planta.展开更多
An unprecedented deammoniative condensation reaction of primary allylic amines with nonallylic amines has been developed through C-N bond cleavage.In the presence of 5 mol%palladium diacetate,10 mol%1,4-bis(diphenylph...An unprecedented deammoniative condensation reaction of primary allylic amines with nonallylic amines has been developed through C-N bond cleavage.In the presence of 5 mol%palladium diacetate,10 mol%1,4-bis(diphenylphosphino)butane(dppb),and 5 mol%p-toluenesulfonic acid(TsOH),a range of α-unbranched primary allylic amines smoothly underwent deammoniative condensation with nonallylic amines in an α-selective fashion to give structurally diverse secondary and tertiary amines in good to excellent yields and E selectivity.Replacing dppb with racemic 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl(BINAP)permitted the deammoniative condensation of enantioenriched α-chiral primary allylic amines with nonallylic amines to proceed with complete retention of configuration.Electrospray ionization(ESI)mass spectrometric analysis of the reaction mixture permitted the identification of some π-allylpalladium intermediates,and plausible mechanisms have been proposed to account for the regioselectivity and stereospecificity of the deammoniative condensation reaction.展开更多
Nonclassical C-glycosides,distinguished by their unique glycosidic bond connection mode,represent a promising avenue for the development of carbohydrate-based drugs.However,the accessibility of nonclassical C-glycosid...Nonclassical C-glycosides,distinguished by their unique glycosidic bond connection mode,represent a promising avenue for the development of carbohydrate-based drugs.However,the accessibility of nonclassical C-glycosides hinders broader investigations into their structural features and modes of action.Herein,we present the first example of Pd-catalyzed stereospecific glycosylation of nonclassical anomeric stannanes with aryl or vinyl halides.This method furnishes desired nonclassical aryl and vinyl C-glycosides in good to excellent yields,while allowing for exclusive control of nonclassical anomeric configuration.Of significant note is the demonstration of the generality and practicality of this nonclassical C-glycosylation approach across more than 50 examples,encompassing various protected and unprotected saccharides,deoxy sugars,oligopeptides,and complex molecules.Furthermore,biological evaluation indicates that nonclassical C-glycosylation modifications of drug molecules can positively impact their biological activity.Additionally,extensive computational studies are conducted to elucidate the rationale behind differences in reaction reactivity,unveiling a transmetalation transition state containing silver(Ag)within a six-membered ring.Given its remarkable controllability,predictability,and consistently high chemical selectivity and stereospecificity regarding nonclassical anomeric carbon and Z/E configuration,the method outlined in this study offers a unique solution to the longstanding challenge of accessing nonclassical C-glycosides with exclusive stereocontrol.展开更多
China is rich in rare earth resources. Rare earth elements, also named lanthanides, are number 58 to number 81 elements in the elemental periodic table. They have unique electronic structures and may form various coor...China is rich in rare earth resources. Rare earth elements, also named lanthanides, are number 58 to number 81 elements in the elemental periodic table. They have unique electronic structures and may form various coordination compounds. In the early 1960s, researchers at the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences (CIAC) found the catalytic activities of lanthanide compounds in stereospecific polymerization of conjugated dienes, and published the first paper on this topic in 1964. On the basis of this finding, CIAC launched extensive research activities on lanthanide compounds as diene polymerization catalysts, from a series of fundamental research to the efforts of industrializing the rare earth catalyzed cis-1,4-polybutatine rubber and cis-1,4-polyisoprene rubber. This review aims to summarize the progress in this field in the past half century.展开更多
基金supported by the Administration of Science and Technology of Jilin Province,China (No.200505254)
文摘Neodymium chloride isopropanol complex （NdCl3.3＇prOH） activated by modified methylaluminoxane （MMAO） was examined in isoprene polymerization in hexane, with regards to Nd compounds, aluminum （Al） compounds, [Al]/[Nd] ratio, polymerization temperature and time. NdCl3＇3iprOH exhibited high activity producing polymers feasting high cis-l,4 stereospecificity （〉 96%）, very high molecular weight （Mn 〉 1.0 × 10^6） and fairly narrow molecular weight distribution （MWD, Mw/Mn 〈 2.0） simultaneously. In comparison, neodymium isopropoxide also showed high activity providing polymers with narrow MWD （Mw/Mn = 2.07）, but somewhat low cis-1,4 content （ca. 92%）, while neodymium chloride had no activity under present polymerization conditions. The Al compounds affected the polymer yield in the order of Al（i-Bu）3 〉 MMAO 〉 Al（i-Bu）2H. MMAO as cocatalyst afforded polyisoprene with high Mn over 1.0 × 10^6, whereas as stronger chain transfer agent than MMAO, AI（i-Bu）3 and AI（i-Bu）EH yielded polymers with low Mn （1.0 × 10^5-8.0 × 10^5）. NdCl3·3＇PrOH/MMAO catalyst showed a fairly good catalytic activity even at relatively low [Al]/[Nd] ratio of 30, and the produced polymer remained high cis-1,4 content of 95.8% along with high Mn over 1.0× 10^6 even at elevated temperatures up to 70℃. The polymerization rate is of the first order with respect to the concentration of isoprene. The mechanism of active species formation was discussed preliminarily.
基金financially supported by the National Natural Science Foundation of China(Nos.20774098,50973123, 50503023)the Scientific Research Startup Foundation of Qingdao University of Science and Technology
文摘TiCl4/MgCl2/clay compound catalyst was prepared by chemical reaction. Exfoliated polypropylene （PP）/clay nanocomposites were synthesized by in situ polymerization with this compound catalyst. Effects of polymerization temperature, polymerization time, propylene pressure, solvent consumption and pre-treat time of catalyst on catalyst activity and catalytic stereospecificity were studied. Under optimal conditions, activity of the nano-compound catalyst is about 88.3 kg/（mol Ti-h）. Isotacticity of PP obtained in the nanocomposites is in the range of 89%-99%, and its melting temperature is about 159℃. The weight-average molecular weight of PP can reach 6.7 × 10^5 - 7.8 × 10^5, and the molecular weight distribution is between 7.7 and 7.9.
文摘The present paper covers the stereoselective syntheses of four 1 thiogalactopyranosides 1—4 and three thio disaccharides 5—7 through the PTC methods and their structures confirmed by means of elementary analysis, IR and NMR spectral data.
基金Supported by the National Natural Science Foundation of China
文摘Introduction The cyano branched carbohydrates are useful, versatil intermediaries for the synthesis of branched sugars having biological activity in nature. Owing to the good yield, mild reaction conditions and high stereospecificity, the phase transition catalysis(PTC)method has been widely used to the syntheses of C-
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Supported by the National Natural Science Foundation of China
文摘The stereospecific carbocupration of terminal alkynes via higher order cuprates to give 1,1'-disubstituted olefins with 99% configuration purity is described. Its synthetic utility as a general method for the preparation of substituted olefins is further illustrated by the direct synthesis of (±)-ipsenol and (E)-β-farnesene with highly geometric purity of the carbon-carbon double bond.
基金Supported by the National Natural Science Foundation of China(Nos.30870539, 21072075)the 38th Postdoctoral Foundation of China(No.801050321413)
文摘The stereospecific hydrolysis of mandelate can be effectively catalyzed by hyperthermophilic acylpeptide esterase APE 1547（Aeropyrum pernix esterase 1547）. APE 1547 used in this reaction showed a remarkable stereodi-scrimination in favour of R-mandelic acid（99% e.e.） with an enantiomeric ratio E〉200. The results of computer simulation are consistent with the experimental results. It can be inferred that the R-substrate adopted a binding mode productive of the reaction due to the formation of the hydrogen bond at the active site of APE 1547.
文摘1, 5-Benzothiazepines 1 react with phenylacetyl chloride to give the title compounds.The structures of these new compounds were confirmed by elemental analysis, ~1H NMR, ^(13)C NMRand MS spectroscopy, and their configuration (the mutual positions of the substituents relative to theβ-lactam ring) and conformation of the compounds were determined by X-ray crystal analysis.
文摘Reaction of 1,5-benzothiazepine with N-protected glycine gives new a-amino-β-lactamderivatives of 1.5-benzothiazepine. The configuration and conformation of the products wereconfirmed by x-ray diffraction. The result further reveals that the reaction of 1.5-benzothiazepineswith derivatives of carboxylic acid stereospecific.
文摘Structural analysis of Candida antarctica lipase B (CALB) indicates that side chain of leucine at 278 site lies above the entrance of the catalytic pocket, which prognosticates its potential role on substrate specificity of the enzyme. To verify this presumption, shortened side chain of glycine or proline was rational designed and mutants were constructed by site-directed mutagenesis method. The colorimetric assay using p-nitrophenyl esters of fatty acids with various chain-lengths was used to study the substrate preference of lipases. Results indicated that L278G or L278P mutations both induced the drift of substrate specificity of CALB from p-nitrophenyl caprylate (pNP-C8) to longer carbon chain length of p-nitrophenyl caprate (pNP-C10). Meanwhile, Vmax value of two mutants to pNP-C10 was both higher than that of wild-type. Docking results also indicated that shortened side chain of glycine or proline residues substitution at this site could get rid of the space block present above the catalytic pocket, and made longer chain substrate (pNP-C10) enter into the catalytic pocket easier. The modulation of specificity observed allowed for building substrate binding model and opened new possibilities for designing ligand specific lipases.
基金supported by the beijing Municipal University Classification Development Project,and the Ganzi Prefecture Seda County Zang Yuan Zhao Mei dairy products Co.,Ltd.(KJ200301).
文摘In recent years,milk fat has garnered significant attention.over 98%of milk fat is composed of triglycerides,with fatty acids being one of the main components that play important physiological roles.the distribution of fatty acids on the glycerol backbone of triglycerides is closely related to the digestion and absorption of milk fat.However,there is a lack of research comparing the stereospecific distribution of fatty acids in human milk and different ruminant milks.this review summarizes the extraction techniques and analytical methods of fatty acids from milk fat,analyzes and compares the composition and content of total fatty acids in human,yak,camel,cow,buffalo,and goat milks,overviews the stereospecific location of fatty acids on triglycerides and digestion and absorption of fatty acids in different milk sources,and evaluates the nutritional value of different milk sources using seven fatty acid nutritional evaluation indices to evaluate the nutritional value of different milk sources,providing guidance for promoting human health,and exploring the potential importance of the fatty acid composition of ruminant milk for infant or special dairy development,providing a basis for further development and utilization of dairy products.
文摘Archimedean solids were first proposed by the ancient Greek philosopher Archimedes.Unfortunately,this aspect of his work was not well-documented.It was not until 1619 that the mathematician Johannes Kepler reconstructed the complete set of 13 Archimedean solids[1].Among these solids,only the snub cube and snub dodecahedron are chiral.
基金Project supported by the National Natural Science Foundation of China.
文摘Most of the electrophilic additions on carbon-carbon multiply bond can be summarized as: where Y are certain atoms on the fight of the periodic table; Z may be null, atom or group. Regardless of the rate law of Ad_E2 Ad_E3 or the more complex kinetics, the micromechanisms of transition state of electrophilic addition can be divided into two sorts, i.e. open ion and bridged ion mechanisms. The former one allows free rotation of
基金This work was funded by the UK Biotechnology and Biological Sciences Research Council and AB Vista Ltd.through IPA award BB/M022978/1the Danish Ministry of Food,Agriculture and Fisheries(grant no.3304-FVFP-08-M-07-01).
文摘Grain phytate,a mixed metal ion salt of inositol hexakisphosphate,accounts for 60%–80%of stored phosphorus in plants and is a potent antinutrient of non-ruminant animals including humans.Through neofunctionalization of purple acid phytases(PAPhy),some cereals such as wheat and rye have acquired particularly high mature grain phytase activity.As PAPhy activity supplies phosphate,liberates metal ions necessary for seedling emergence,and obviates antinutrient effects of phytate,its manipulation and control are targeted crop traits.Here we show the X-ray crystal structure of the b2 isoform of wheat PAPhy induced during germination.This high-resolution crystal structure suggests a model for phytate recognition that,validated by molecular dynamics simulations,implicates elements of two sequence inserts(termed PAPhy motifs)relative to a canonical metallophosphoesterase(MPE)domain in forming phytate-specific substrate specificity pockets.These motifs are well conserved in PAPhys from monocot cereals,enzymes which are characterized by high specificity for phytate.Tested by mutagenesis,residues His229 in PAPhy motif 4 and Lys410 in the MPE domain,both conserved in PAPhys,are found to strongly influence phytase activity.These results explain the observed phytase activity of cereal PAPhys and open the way to the rational engineering of phytase activity in planta.
基金We are grateful for the financial support from the National Natural Science Foundation of China(Nos.21232007,21202154 and 21172206)the National Key Basic Research Program of China(No.2014CB931800).
文摘An unprecedented deammoniative condensation reaction of primary allylic amines with nonallylic amines has been developed through C-N bond cleavage.In the presence of 5 mol%palladium diacetate,10 mol%1,4-bis(diphenylphosphino)butane(dppb),and 5 mol%p-toluenesulfonic acid(TsOH),a range of α-unbranched primary allylic amines smoothly underwent deammoniative condensation with nonallylic amines in an α-selective fashion to give structurally diverse secondary and tertiary amines in good to excellent yields and E selectivity.Replacing dppb with racemic 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl(BINAP)permitted the deammoniative condensation of enantioenriched α-chiral primary allylic amines with nonallylic amines to proceed with complete retention of configuration.Electrospray ionization(ESI)mass spectrometric analysis of the reaction mixture permitted the identification of some π-allylpalladium intermediates,and plausible mechanisms have been proposed to account for the regioselectivity and stereospecificity of the deammoniative condensation reaction.
基金sponsored by the National Key R&D Program of China(Grant No.2023YFA1508800)National Science Foundation(Grant No.22301178)+10 种基金Shanghai Pilot Program for Basic Research-Shanghai Jiao Tong University(Grant No.21TQ1400210)Fundamental Research Funds for the Central Universities(Grant No.22X010201631)the Open Grant from the Pingyuan Laboratory(2023PY-OP-0102)Excellent Young Scientists Fund Program(Overseas),Natural Science Founda-tion of Shanghai(Grant No.21ZR1435600)Shanghai Sailing Program(Grant No 21YF1420600)start-up fundings from Shanghai Jiao Tong University(SJTU)Part of this study was supported by the National Science Foundation(Grant No.82204192 to Y.N.)National Key R&D Program of China(Grant No.2023YFC2308200 to Y.N.)Natural Science Foundation of Jiangsu Province(BK20220471 to Y.N.)Beatriu de Pinós programme from AGAUR(Grant No.2022 BP 00055 to Y.L)the China Postdoctoral Science Foundation(2022M722071 to B.Y.).
文摘Nonclassical C-glycosides,distinguished by their unique glycosidic bond connection mode,represent a promising avenue for the development of carbohydrate-based drugs.However,the accessibility of nonclassical C-glycosides hinders broader investigations into their structural features and modes of action.Herein,we present the first example of Pd-catalyzed stereospecific glycosylation of nonclassical anomeric stannanes with aryl or vinyl halides.This method furnishes desired nonclassical aryl and vinyl C-glycosides in good to excellent yields,while allowing for exclusive control of nonclassical anomeric configuration.Of significant note is the demonstration of the generality and practicality of this nonclassical C-glycosylation approach across more than 50 examples,encompassing various protected and unprotected saccharides,deoxy sugars,oligopeptides,and complex molecules.Furthermore,biological evaluation indicates that nonclassical C-glycosylation modifications of drug molecules can positively impact their biological activity.Additionally,extensive computational studies are conducted to elucidate the rationale behind differences in reaction reactivity,unveiling a transmetalation transition state containing silver(Ag)within a six-membered ring.Given its remarkable controllability,predictability,and consistently high chemical selectivity and stereospecificity regarding nonclassical anomeric carbon and Z/E configuration,the method outlined in this study offers a unique solution to the longstanding challenge of accessing nonclassical C-glycosides with exclusive stereocontrol.
文摘China is rich in rare earth resources. Rare earth elements, also named lanthanides, are number 58 to number 81 elements in the elemental periodic table. They have unique electronic structures and may form various coordination compounds. In the early 1960s, researchers at the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences (CIAC) found the catalytic activities of lanthanide compounds in stereospecific polymerization of conjugated dienes, and published the first paper on this topic in 1964. On the basis of this finding, CIAC launched extensive research activities on lanthanide compounds as diene polymerization catalysts, from a series of fundamental research to the efforts of industrializing the rare earth catalyzed cis-1,4-polybutatine rubber and cis-1,4-polyisoprene rubber. This review aims to summarize the progress in this field in the past half century.
