A practical synthesis of (S)-N-(2-ethyl-6-methylphenyl)alanine, a key intermediate for (S)-metolachlor, was completed by means of lipase-catalyzed hydrolytic kinetic resolution and chemical racemization of the r...A practical synthesis of (S)-N-(2-ethyl-6-methylphenyl)alanine, a key intermediate for (S)-metolachlor, was completed by means of lipase-catalyzed hydrolytic kinetic resolution and chemical racemization of the remaining ester. The effects of operating temperature and enzyme concentration on the activity and enantioselectivity of enzyme were initially studied, and it was found that the enantioselectivity of CAL-B towards the resolution was not high enough to obtain enantiomerically pure compound(E=12.1). When diethyl ether(15%, volume fraction) was added in the reaction medium, the lipase gave an excellent enantioselectivity(E=117.8), which is about 9.7-fold that in pure buffered aqueous solution. For overcoming the limitation of a maximum theoretical yield of 50%, the acid product was separated from the remaining ester by a simple extraction procedure and the remaining ester was racemized with aldehyde and acetic acid under microwave irradiation or conventional heating condition, The results show the microwave irradiation was more effective than the conventional heating method and gave the desired (R,S)-N-(2- ethyl-6-methylphenyl)alanine methyl ester a high yield(92%) with R/S=50/50 in 1 h.展开更多
Racemization of aspartic acid (Asp) residues in proteins plays an important role in the molecular biology of aging. In the widely accepted mechanism of the Asp racemization, a succinimide (SI) intermediate is the spec...Racemization of aspartic acid (Asp) residues in proteins plays an important role in the molecular biology of aging. In the widely accepted mechanism of the Asp racemization, a succinimide (SI) intermediate is the species which actually undergo the direct racemization. In the present study, a two-water-assisted mechanism of the SI racemization was computationally investigated using a model compound in which an aminosuccinyl (Asu) residue is capped with acetyl and NMe groups on the N-and C-termini, respectively. The two water molecules catalyze the enolization of the Hα-Cα-C=O portion in the Asu residue by mediating proton relay from the α-carbon atom to the carboxyl oxygen atom. After the enolization, migration of the water molecules and conformational change lead to the mirror image of the initially formed enol two-water complex, and the racemization is completed by the following ketonization. The overall activation barrier (28.2 kcal·mol-1) corresponds to the enolization and ketonization steps, and falls within the available experimental activation energies (21.4-29.0 kcal·mol-1). Therefore, the two-water-assisted mechanism investigated here is plausible for the in vivo and in vitro racemization reactions of the SI intermediates formed in peptides and proteins.展开更多
Chiral alcohols and amines are important structural units widely existing in pharmaceuticals,agrochemicals,and food additives.Dynamic kinetic resolution(DKR)is an efficient strategy to deliver optically active alcohol...Chiral alcohols and amines are important structural units widely existing in pharmaceuticals,agrochemicals,and food additives.Dynamic kinetic resolution(DKR)is an efficient strategy to deliver optically active alcohols and amines from their racemates.For the development of DKR method,racemization catalyst plays as a crucial element with the requirement of compatibility with the kinetic resolution(KR)system.In this paper,recent advance in the catalytic racemization of secondary alcohols and amines is summarized based on different types of racemizing intermediates,which are redox racemization via ketone/imine intermediates,racemization via radical intermediates,and racemization via carbocation intermediates.Enzymatic racemization of secondary alcohols and amines is also enclosed.展开更多
D-aspartate, a natural and endogenous amino acid, widely exists in animal tissues and can be synthesized through aspartate racemase and transformed by D-aspartate oxidase(DDO). D-aspartate mainly serves as a neurotran...D-aspartate, a natural and endogenous amino acid, widely exists in animal tissues and can be synthesized through aspartate racemase and transformed by D-aspartate oxidase(DDO). D-aspartate mainly serves as a neurotransmitter and has been demonstrated to exhibit various physiological functions,including nutritional potential, regulation on reproduction and hormone biology, and neuron protection.This article mainly reviews the synthesis, racemization, and physiological functions of D-aspartate with emphasis on the potential in diseases.展开更多
Four racemic tetrahydroisoquinolines(RS)-(±)-1-4 were prepared from homoveratrylamine via amidation,Bischler-Napieralski reaction and the subsequent reduction.The enantiomerically pure tetrahydroisoquinolines(S)-...Four racemic tetrahydroisoquinolines(RS)-(±)-1-4 were prepared from homoveratrylamine via amidation,Bischler-Napieralski reaction and the subsequent reduction.The enantiomerically pure tetrahydroisoquinolines(S)-(−)-norcryptostyline Ⅰ[(S)-(−)-1],(S)-(−)-norcryptostyline Ⅱ[(S)-(−)-2],(R)-(+)-salsolidine[(R)-(+)-3]and(S)-(−)-norlaudanosine[(S)-(−)-4]were then obtained in 45%,40%,41%and 38%yields,respectively,via resolution of the racemic compounds(RS)-(±)-1-4 with half equivalent of chiral acids.In addition,the enantiomerically enriched compounds(R)-(+)-1,(R)-(+)-2,(S)-(−)-3 and(R)-(+)-4 from the mother liquors were efficiently racemized via a one-pot redox method in almost quantitative yields.展开更多
1-Ethyl-2-fluoropyridinium tetrafluoroborate (FEP) was shown to be a very efficient coupling reagent for the synthesis of the hindered peptide with fast reaction speed, low racemization and good yields.
The crystal structure of tetrakis[(pyrrol-1-yl)methyl]methane was determined by X-ray diffraction measurement, and the result shows that it belongs to monoclinic crystal system, space group is P2 1/n, with a=0.9284(3...The crystal structure of tetrakis[(pyrrol-1-yl)methyl]methane was determined by X-ray diffraction measurement, and the result shows that it belongs to monoclinic crystal system, space group is P2 1/n, with a=0.9284(3) nm, b=1.0950(6) nm, c=1.8749(8) nm; α=γ= 90.00(4)°, β=103.63(3)°, V=1.8523(14) nm 3, Z=4, ρ calcd. =1.192 kg/m 3, μ=0.072 nm -1 , F(000)=712, R 1=0.0854, wR 2=0.1884. It has been found that the molecules exist in two enantiomeric states. Enantioselective self-assemblies such as one-dimensional molecular stacks in a single handedness, homochiral monolayers and a chiral superlattice are specified in this racemic crystal. In addition, a simple technique is advocated to distinguish chiral states from tetrahedral molecules in the solid state. The present R/S nomenclature of the tetracooradinated carbon centers is used solely for its convenience to distinguish the two enantiomeric states, but not used to determine the absolute configurations.展开更多
Introduction The formation of gelatin-containing mieroemulsionbased gels(MBGs) was first described in 1986 and the physical/structural characterization was carried out by a number of groups with a variety of techni...Introduction The formation of gelatin-containing mieroemulsionbased gels(MBGs) was first described in 1986 and the physical/structural characterization was carried out by a number of groups with a variety of techniques including tracer diffusion, electrical conductivity, NMR, X-ray and small angle neutron scattering. The MBGs were proposed to comprise an extensive, rigid, interconnected network of gelatin/water rods stabilized by a monolayer of surfactant, in coexistence with a po- pulation of conventional W/O microemulsion droplets.展开更多
L-carnitine selective polymers were prepared by molecular imprinting using methacrylic acid as the functional monomer. The acid function of the monomer is expected to form hydrogen bond and ionic interactions with th...L-carnitine selective polymers were prepared by molecular imprinting using methacrylic acid as the functional monomer. The acid function of the monomer is expected to form hydrogen bond and ionic interactions with the amine function of the target molecule L-carnitine. The imprinted polymers were used as stationary phases in high-performance liquid chromatography (HPLC). It was shown that L-carnitine imprinted polymer exhibited a higher affinity to its template molecule, while the non-imprinted polymer had no affinity to the compounds tested. Racemic carnitine hydrochloride was efficiently resolved on the L-carnitine imprinted polymer, and the separation factor is 1.9.展开更多
The new shortcut synthesis route of(±)raphidecursinol 1,a racemic 8,4′-oxyneolignan compound,can be more easily achieved by the synthesis route,starting from readily available inexpensive 3,4,5-trimethoxybenzald...The new shortcut synthesis route of(±)raphidecursinol 1,a racemic 8,4′-oxyneolignan compound,can be more easily achieved by the synthesis route,starting from readily available inexpensive 3,4,5-trimethoxybenzaldehyde and 1,2,3-trihydroxybenzene.All structures were confirmed by ~1H NMR,IR and MS.展开更多
A system of structure depiction, as an extension of the wedge and hashed wedge bonds (Natta projection), and text notation is herein suggested that embodies more explicit information—or reduced over-statement as circ...A system of structure depiction, as an extension of the wedge and hashed wedge bonds (Natta projection), and text notation is herein suggested that embodies more explicit information—or reduced over-statement as circumstances warrant—on the stereochemical nature of the system at hand, in particular, for those cases where only the relative stereochemistry of a compound is known.展开更多
A new layered zincophosphate was synthesized under solvothermal conditions by employing racemic 1,2-diaminopropane as the structure-directing agent. The structure of the compound was solved by means of single-crystal ...A new layered zincophosphate was synthesized under solvothermal conditions by employing racemic 1,2-diaminopropane as the structure-directing agent. The structure of the compound was solved by means of single-crystal X-ray diffraction analysis. It crystallized in the monoclinic space group P2_1/c (No. 14) with a= 1.047 0(3) nm, b=0.787 31(18) nm, c=0.662 68(16) nm, β=103.120(5)°, V=0.532 0(2) nm 3 and Z=4. The structure is made up of anionic zincophosphate sheets stacked in an AAAA sequence. The individual sheet contains three- and four-membered rings and the infinite Zn-O-Zn chains can also be envisaged in the sheet. The charge-balancing diprotonated racemic 1,2-diaminopropane cations are sandwiched between the layers, whereas the inorganic layers are stabilized by strong H-bonds formed between the N atoms of the amine and the O atoms in the inorganic sheets.展开更多
A one-dimensional chain aluminophosphate C1.5H7.5N1.5Al0.5PO4 containing diprotonated racemic 1, 2-diaminopropane cations was synthesized from an alcoholic system. The compound consists of infinite inorganic [AlP2O8]...A one-dimensional chain aluminophosphate C1.5H7.5N1.5Al0.5PO4 containing diprotonated racemic 1, 2-diaminopropane cations was synthesized from an alcoholic system. The compound consists of infinite inorganic [AlP2O8] chains of alternately connected AlO4 and PO2(=O)2 tetrahedral units and the racemic template molecules. The macroanionic chains contain corner-shared double four-membered rings.展开更多
Deficiencies in the terminology used to describe chiral systems exist for behaviors under various processes and thus a more general, robust terminology is considered. For example, the descriptions for characterizing m...Deficiencies in the terminology used to describe chiral systems exist for behaviors under various processes and thus a more general, robust terminology is considered. For example, the descriptions for characterizing melting point, solubility, and recrystallization behaviors were adopted well before it was realized that perturbation of the enantiomeric com-position (ec) due to self-disproportionation could be effected by processes other than recrystallization such as sublimation, chromatography over achiral substrates, and even distillation. Thus, an endeavor has been made to address the question of universally describing behaviors under processes that effect, or are dependent on, the ec. The main terms that have been defined with respect to behavior are homomate (analogous to a conglomerate), heteromate, bimate (analogous to a racemic compound), and unimate (analogous to a solid solution) and they apply to melting point, solubility, recrystallization, sublimation, distillation, and chromatographic processes. Additionally, suggestions for improving the terminology for describing the states of chiral systems are also considered and the defined terms are: holemate (hol, ec = 100%), scalemate (scl, 50% ec eqm, ec = 50%).展开更多
Deviations from chemical parity (PV) were evaluated with the search for very small enantiomeric excesses in a racemate prepared from non chiral materials and were detected by means of the circular dichroism (CD). Thus...Deviations from chemical parity (PV) were evaluated with the search for very small enantiomeric excesses in a racemate prepared from non chiral materials and were detected by means of the circular dichroism (CD). Thus, intensely light-absorbing perylenebiscarboximides were attached to axially chiral biphenyls for the amplification of CD effects by exciton interactions of the adjacent chromophores. A rapidly racemising system was applied for the exclusion of artifacts and compared with an analogous with locked chirally. A very slight enantiomeric excess was detected for the (M) enantiomer. Application of the method for other systems was suggested and relations to natural products discussed.展开更多
The present study involves the enantioselective resolution of racemic Felodipine by using free and immobilized forms of microbial cultures as well as an enzyme (Lipase AP6). Among the microbial cultures employed in th...The present study involves the enantioselective resolution of racemic Felodipine by using free and immobilized forms of microbial cultures as well as an enzyme (Lipase AP6). Among the microbial cultures employed in the present study, Aspergillus niger, Sphingomonas paucimobilis, Cunninghamella elegans, Escherichia coli, Pseudomonas putida and Cunninghamella blakesleeana were found to possess capability of enantioselective resolution of racemic Felodipine. The enantiomeric excess (ee%) of Felodipine after reaction catalyzed by whole-cell A. niger and S. paucimobilis was found as 81.59 and 71.67%, respectively. Immobilization enhanced the enantioselectivity (enantiomeric ratio (E)) of the biocatalysts and hence this led to enhanced enantiomeric purity of the drug. The ee% values were found to be enhanced in reactions catalyzed by A. niger and S. paucimobilis cultures after immobilization as 98.27 and 93.56%, respectively. Enantiomeric ratio (E) of the reactions catalyzed by all the biocatalysts has been improved after immobilization. E value of the reaction catalyzed by immobilized A. niger was found to be excellent (E > 100) and hence the drug showed high enantiomeric purity. In lipase AP6 catalyzed study, the enantioselectivity was enhanced after immobilization with excellent E value, which led to enhanced enantiomeric purity of the drug (99.21% ee%).展开更多
The construction of molecular chirality is crucial for exploring novel luminophores with chiroptical properties.Classic asymmetric synthesis of chiral center or axial is not powerful enough on through-space architectu...The construction of molecular chirality is crucial for exploring novel luminophores with chiroptical properties.Classic asymmetric synthesis of chiral center or axial is not powerful enough on through-space architecture.Accessible methodologies for breaking molecular symmetry could be promising but remain less investigated.Herein,we report a novel methodology for constructing chiral through-space luminophores via simple chlorination on bridged carbazole motifs.The chlorination breaks the molecular symmetry and thus results in molecular chirality by eliminating the mirror plane or rotating axis.Interestingly,continuous multiple chlorinations can rebuild and break the symmetry of the skeleton in succession.Several chiral and achiral isomeric analogues are synthesized and characterized with impressive chiroptical properties.Results of chiral high performance liquid chromatography(HPLC),single-crystal X-ray diffraction,kinetic racemization,and chiroptical property investigation demonstrate the effectiveness of our rational design strategy.It provides a feasible methodology for exploring novel chiral luminescent materials based on versatile though-space skeletons.展开更多
The model of right-handed α helix of peptide,in which the intrachain hydrogen bonds be-tween amino acid residues are in the direction of the axis of the helix,is used to compute the energy differ-ences between D-and ...The model of right-handed α helix of peptide,in which the intrachain hydrogen bonds be-tween amino acid residues are in the direction of the axis of the helix,is used to compute the energy differ-ences between D-and L-form residues.The dominant intramolecular interactions involved are the Coulombinteraction for the residues with charged and polarized R group and van der Waals interaction for thehydrophobic residues respectively.The results obtained show that the energy states of L-forms are lower thanthose of the corresponding D-forms.Therefore,L-form states are more stable.The racemization of the aminoacid after the residue has been dislocated from the peptide chain is interpreted as the consequence of the pari-ty conservation of the electromagnetic interaction.展开更多
基金Supported by the National Natural Science Foundation of China(No.20802025)the Hi-Tech Research and Development Program of China(No.2007AA021306)Jilin Provincial Science & Technology Sustentation Program,China(No.20070553)
文摘A practical synthesis of (S)-N-(2-ethyl-6-methylphenyl)alanine, a key intermediate for (S)-metolachlor, was completed by means of lipase-catalyzed hydrolytic kinetic resolution and chemical racemization of the remaining ester. The effects of operating temperature and enzyme concentration on the activity and enantioselectivity of enzyme were initially studied, and it was found that the enantioselectivity of CAL-B towards the resolution was not high enough to obtain enantiomerically pure compound(E=12.1). When diethyl ether(15%, volume fraction) was added in the reaction medium, the lipase gave an excellent enantioselectivity(E=117.8), which is about 9.7-fold that in pure buffered aqueous solution. For overcoming the limitation of a maximum theoretical yield of 50%, the acid product was separated from the remaining ester by a simple extraction procedure and the remaining ester was racemized with aldehyde and acetic acid under microwave irradiation or conventional heating condition, The results show the microwave irradiation was more effective than the conventional heating method and gave the desired (R,S)-N-(2- ethyl-6-methylphenyl)alanine methyl ester a high yield(92%) with R/S=50/50 in 1 h.
文摘Racemization of aspartic acid (Asp) residues in proteins plays an important role in the molecular biology of aging. In the widely accepted mechanism of the Asp racemization, a succinimide (SI) intermediate is the species which actually undergo the direct racemization. In the present study, a two-water-assisted mechanism of the SI racemization was computationally investigated using a model compound in which an aminosuccinyl (Asu) residue is capped with acetyl and NMe groups on the N-and C-termini, respectively. The two water molecules catalyze the enolization of the Hα-Cα-C=O portion in the Asu residue by mediating proton relay from the α-carbon atom to the carboxyl oxygen atom. After the enolization, migration of the water molecules and conformational change lead to the mirror image of the initially formed enol two-water complex, and the racemization is completed by the following ketonization. The overall activation barrier (28.2 kcal·mol-1) corresponds to the enolization and ketonization steps, and falls within the available experimental activation energies (21.4-29.0 kcal·mol-1). Therefore, the two-water-assisted mechanism investigated here is plausible for the in vivo and in vitro racemization reactions of the SI intermediates formed in peptides and proteins.
基金the National Natural Science Foundation of China (No. 22271054)the “1000-Youth Talents Plan”Fudan University (start-up grant) for financial support.
文摘Chiral alcohols and amines are important structural units widely existing in pharmaceuticals,agrochemicals,and food additives.Dynamic kinetic resolution(DKR)is an efficient strategy to deliver optically active alcohols and amines from their racemates.For the development of DKR method,racemization catalyst plays as a crucial element with the requirement of compatibility with the kinetic resolution(KR)system.In this paper,recent advance in the catalytic racemization of secondary alcohols and amines is summarized based on different types of racemizing intermediates,which are redox racemization via ketone/imine intermediates,racemization via radical intermediates,and racemization via carbocation intermediates.Enzymatic racemization of secondary alcohols and amines is also enclosed.
基金supported by Hunan Province key research and development projects(2017NK2321)National Basic Research Program of China(973)(2013CB127301)+1 种基金National Natural Science Foundation of China(31472106)China Agriculture Research System(CARS-35)
文摘D-aspartate, a natural and endogenous amino acid, widely exists in animal tissues and can be synthesized through aspartate racemase and transformed by D-aspartate oxidase(DDO). D-aspartate mainly serves as a neurotransmitter and has been demonstrated to exhibit various physiological functions,including nutritional potential, regulation on reproduction and hormone biology, and neuron protection.This article mainly reviews the synthesis, racemization, and physiological functions of D-aspartate with emphasis on the potential in diseases.
基金We thank the National Natural Science Foundation of China(No.20972048)for the financial support of this work.
文摘Four racemic tetrahydroisoquinolines(RS)-(±)-1-4 were prepared from homoveratrylamine via amidation,Bischler-Napieralski reaction and the subsequent reduction.The enantiomerically pure tetrahydroisoquinolines(S)-(−)-norcryptostyline Ⅰ[(S)-(−)-1],(S)-(−)-norcryptostyline Ⅱ[(S)-(−)-2],(R)-(+)-salsolidine[(R)-(+)-3]and(S)-(−)-norlaudanosine[(S)-(−)-4]were then obtained in 45%,40%,41%and 38%yields,respectively,via resolution of the racemic compounds(RS)-(±)-1-4 with half equivalent of chiral acids.In addition,the enantiomerically enriched compounds(R)-(+)-1,(R)-(+)-2,(S)-(−)-3 and(R)-(+)-4 from the mother liquors were efficiently racemized via a one-pot redox method in almost quantitative yields.
基金This work was financially supported by the National Natural Science Foundation of China!(9772045 )
文摘1-Ethyl-2-fluoropyridinium tetrafluoroborate (FEP) was shown to be a very efficient coupling reagent for the synthesis of the hindered peptide with fast reaction speed, low racemization and good yields.
基金the National Natural Science Foundation of China(No.6 0 1710 0 8) and Shanghai Science and TechnologyCom mittee(No.0 2 14 nm0 0 5 )
文摘The crystal structure of tetrakis[(pyrrol-1-yl)methyl]methane was determined by X-ray diffraction measurement, and the result shows that it belongs to monoclinic crystal system, space group is P2 1/n, with a=0.9284(3) nm, b=1.0950(6) nm, c=1.8749(8) nm; α=γ= 90.00(4)°, β=103.63(3)°, V=1.8523(14) nm 3, Z=4, ρ calcd. =1.192 kg/m 3, μ=0.072 nm -1 , F(000)=712, R 1=0.0854, wR 2=0.1884. It has been found that the molecules exist in two enantiomeric states. Enantioselective self-assemblies such as one-dimensional molecular stacks in a single handedness, homochiral monolayers and a chiral superlattice are specified in this racemic crystal. In addition, a simple technique is advocated to distinguish chiral states from tetrahedral molecules in the solid state. The present R/S nomenclature of the tetracooradinated carbon centers is used solely for its convenience to distinguish the two enantiomeric states, but not used to determine the absolute configurations.
基金Supported by the Natural Science Foundation of Shandong Province in China(No.Y2003B01).
文摘Introduction The formation of gelatin-containing mieroemulsionbased gels(MBGs) was first described in 1986 and the physical/structural characterization was carried out by a number of groups with a variety of techniques including tracer diffusion, electrical conductivity, NMR, X-ray and small angle neutron scattering. The MBGs were proposed to comprise an extensive, rigid, interconnected network of gelatin/water rods stabilized by a monolayer of surfactant, in coexistence with a po- pulation of conventional W/O microemulsion droplets.
基金Research supported by The Analysis & Test Fund of Zhejiang Province.
文摘L-carnitine selective polymers were prepared by molecular imprinting using methacrylic acid as the functional monomer. The acid function of the monomer is expected to form hydrogen bond and ionic interactions with the amine function of the target molecule L-carnitine. The imprinted polymers were used as stationary phases in high-performance liquid chromatography (HPLC). It was shown that L-carnitine imprinted polymer exhibited a higher affinity to its template molecule, while the non-imprinted polymer had no affinity to the compounds tested. Racemic carnitine hydrochloride was efficiently resolved on the L-carnitine imprinted polymer, and the separation factor is 1.9.
基金the National Natural Science Foundation of China(No.29972013)
文摘The new shortcut synthesis route of(±)raphidecursinol 1,a racemic 8,4′-oxyneolignan compound,can be more easily achieved by the synthesis route,starting from readily available inexpensive 3,4,5-trimethoxybenzaldehyde and 1,2,3-trihydroxybenzene.All structures were confirmed by ~1H NMR,IR and MS.
文摘A system of structure depiction, as an extension of the wedge and hashed wedge bonds (Natta projection), and text notation is herein suggested that embodies more explicit information—or reduced over-statement as circumstances warrant—on the stereochemical nature of the system at hand, in particular, for those cases where only the relative stereochemistry of a compound is known.
基金Supported by the National Natural Science Foundation of China( No.2 993 10 10 )
文摘A new layered zincophosphate was synthesized under solvothermal conditions by employing racemic 1,2-diaminopropane as the structure-directing agent. The structure of the compound was solved by means of single-crystal X-ray diffraction analysis. It crystallized in the monoclinic space group P2_1/c (No. 14) with a= 1.047 0(3) nm, b=0.787 31(18) nm, c=0.662 68(16) nm, β=103.120(5)°, V=0.532 0(2) nm 3 and Z=4. The structure is made up of anionic zincophosphate sheets stacked in an AAAA sequence. The individual sheet contains three- and four-membered rings and the infinite Zn-O-Zn chains can also be envisaged in the sheet. The charge-balancing diprotonated racemic 1,2-diaminopropane cations are sandwiched between the layers, whereas the inorganic layers are stabilized by strong H-bonds formed between the N atoms of the amine and the O atoms in the inorganic sheets.
基金This work was financially supported by the National Natural Science Foundation of China.
文摘A one-dimensional chain aluminophosphate C1.5H7.5N1.5Al0.5PO4 containing diprotonated racemic 1, 2-diaminopropane cations was synthesized from an alcoholic system. The compound consists of infinite inorganic [AlP2O8] chains of alternately connected AlO4 and PO2(=O)2 tetrahedral units and the racemic template molecules. The macroanionic chains contain corner-shared double four-membered rings.
文摘Deficiencies in the terminology used to describe chiral systems exist for behaviors under various processes and thus a more general, robust terminology is considered. For example, the descriptions for characterizing melting point, solubility, and recrystallization behaviors were adopted well before it was realized that perturbation of the enantiomeric com-position (ec) due to self-disproportionation could be effected by processes other than recrystallization such as sublimation, chromatography over achiral substrates, and even distillation. Thus, an endeavor has been made to address the question of universally describing behaviors under processes that effect, or are dependent on, the ec. The main terms that have been defined with respect to behavior are homomate (analogous to a conglomerate), heteromate, bimate (analogous to a racemic compound), and unimate (analogous to a solid solution) and they apply to melting point, solubility, recrystallization, sublimation, distillation, and chromatographic processes. Additionally, suggestions for improving the terminology for describing the states of chiral systems are also considered and the defined terms are: holemate (hol, ec = 100%), scalemate (scl, 50% ec eqm, ec = 50%).
文摘Deviations from chemical parity (PV) were evaluated with the search for very small enantiomeric excesses in a racemate prepared from non chiral materials and were detected by means of the circular dichroism (CD). Thus, intensely light-absorbing perylenebiscarboximides were attached to axially chiral biphenyls for the amplification of CD effects by exciton interactions of the adjacent chromophores. A rapidly racemising system was applied for the exclusion of artifacts and compared with an analogous with locked chirally. A very slight enantiomeric excess was detected for the (M) enantiomer. Application of the method for other systems was suggested and relations to natural products discussed.
文摘The present study involves the enantioselective resolution of racemic Felodipine by using free and immobilized forms of microbial cultures as well as an enzyme (Lipase AP6). Among the microbial cultures employed in the present study, Aspergillus niger, Sphingomonas paucimobilis, Cunninghamella elegans, Escherichia coli, Pseudomonas putida and Cunninghamella blakesleeana were found to possess capability of enantioselective resolution of racemic Felodipine. The enantiomeric excess (ee%) of Felodipine after reaction catalyzed by whole-cell A. niger and S. paucimobilis was found as 81.59 and 71.67%, respectively. Immobilization enhanced the enantioselectivity (enantiomeric ratio (E)) of the biocatalysts and hence this led to enhanced enantiomeric purity of the drug. The ee% values were found to be enhanced in reactions catalyzed by A. niger and S. paucimobilis cultures after immobilization as 98.27 and 93.56%, respectively. Enantiomeric ratio (E) of the reactions catalyzed by all the biocatalysts has been improved after immobilization. E value of the reaction catalyzed by immobilized A. niger was found to be excellent (E > 100) and hence the drug showed high enantiomeric purity. In lipase AP6 catalyzed study, the enantioselectivity was enhanced after immobilization with excellent E value, which led to enhanced enantiomeric purity of the drug (99.21% ee%).
基金supported by the National Natural Science Foundation of China(21975061)Shenzhen Fundamental Research Program(JCYJ20190806142403535,GXWD20201230155427003-20200728150952003)
文摘The construction of molecular chirality is crucial for exploring novel luminophores with chiroptical properties.Classic asymmetric synthesis of chiral center or axial is not powerful enough on through-space architecture.Accessible methodologies for breaking molecular symmetry could be promising but remain less investigated.Herein,we report a novel methodology for constructing chiral through-space luminophores via simple chlorination on bridged carbazole motifs.The chlorination breaks the molecular symmetry and thus results in molecular chirality by eliminating the mirror plane or rotating axis.Interestingly,continuous multiple chlorinations can rebuild and break the symmetry of the skeleton in succession.Several chiral and achiral isomeric analogues are synthesized and characterized with impressive chiroptical properties.Results of chiral high performance liquid chromatography(HPLC),single-crystal X-ray diffraction,kinetic racemization,and chiroptical property investigation demonstrate the effectiveness of our rational design strategy.It provides a feasible methodology for exploring novel chiral luminescent materials based on versatile though-space skeletons.
文摘The model of right-handed α helix of peptide,in which the intrachain hydrogen bonds be-tween amino acid residues are in the direction of the axis of the helix,is used to compute the energy differ-ences between D-and L-form residues.The dominant intramolecular interactions involved are the Coulombinteraction for the residues with charged and polarized R group and van der Waals interaction for thehydrophobic residues respectively.The results obtained show that the energy states of L-forms are lower thanthose of the corresponding D-forms.Therefore,L-form states are more stable.The racemization of the aminoacid after the residue has been dislocated from the peptide chain is interpreted as the consequence of the pari-ty conservation of the electromagnetic interaction.