- One-pot preparation of chiral dinuclear vanadium(V) complex
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A convenient one-pot procedure for the preparation of dinuclear vanadium(V) complex is described. The complex exhibited high catalytic activity for oxidative coupling of 2-naphthol derivatives. In addition, coupling of 9-phenanthrol gave (S)-10,10′-dihydroxy-9,9′-biphenanthryl in quantitative yield with 93% ee. Georg Thieme Verlag Stuttgart.
- Takizawa, Shinobu,Rajesh, Doss,Katayama, Tomomi,Sasai, Hiroaki
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- Induction of Axial Dissymmetry into the 1,1'-Binaphthyl Bond via an Intramolecular Ullmann Coupling Reaction
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Intramolecular Ullmann coupling of (S)-2,2'-bis-(1-bromo-2-naphthylcarbonyloxy)-1,1'-binaphthyl induced axial dissymmetry of the S-configuration into the newly formed 1,1'-binaphthyl linkage affording (S,S)-tetranaphthodioxacyclododecene-11,16-dione with virtually complete diastereoselectivity.
- Miyano, Sotaro,Tobita, Masayuki,Nawa, Masayoshi,Sato, Shinya,Hashimoto, Harukichi
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- Enantioselective, Electrocatalytic Oxidative Coupling of Naphthol, Naphthyl Ether and Phenanthrol on a TEMPO-modified Graphite Felt Electrode in the Presence of (-)-Sparteine (TEMPO = 2,2,6,6-tetramethylpiperidin-1-yloxyl)
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Constant potential electrolysis of 2-naphthol, 2-methoxynaphthalene and 10-hydroxyphenanthrene at 0.6 V vs.Ag/AgCl on a TEMPO-modified graphite felt electrode in the presence of (-)-sparteine in acetonitrile yields, enantioselectively, (S)-binaphthyl type dimers in > 92percent isolated yield and with > 88percent current efficiency with enantiomeric excess of 98, 91 and 97percent respectively for each dimer, respectively.
- Osa, Tetsuo,Kashiwagi, Yoshitomo,Yanagisawa, Yoshinori,Bobbitt, James M.
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- A HIGHLY STEREOSELECTIVE SYNTHESIS OF S(-)--2,2'-DIOL.
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The title compound is synthesized from 2-naphthol by a S-(+)-amphetamine-copper (II) complex in high chemical yield ( 85percent ) and high optical purity ( up to 95percent ).
- Brussee, J.,Jansen, A.C.A.
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- Thermal racemization of biaryl atropisomers
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Many biaryl compounds possess atropisomerism due to the steric hindrance of substituents at the ortho-position of the two aromatic moieties. Upon heating, atropisomers may have enough energy to surpass the rotational energy barrier and racemize. The thermal stability of five atropisomers was studied using chiral chromatography by following the change in enantiomeric excess ratio at different temperatures. The first order racemization reaction rate was obtained at a given temperature as the slope of the change in enantiomeric excess ratio versus time. For each atropisomer, the racemization rates at different temperatures led to the value of the rotational energy barrier for racemization, ΔG?, and to the racemization half lifetime, t1/2, indicating the atropisomer thermal stability. Binaphthol started to racemize significantly at temperature of 190 °C and above while binaphthyldiamine was much more stable showing little or very minor racemization up to 210 °C. A chloro-substituted phenylamino-naphthol was very sensitive to thermal racemization starting at a low 40 °C.
- Patel, Darshan C.,Woods, Ross M.,Breitbach, Zachary S.,Berthod, Alain,Armstrong, Daniel W.
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- Practical method and novel mechanism for optical resolution of BINOL by molecular complexation with N-benzylcinchoninium chloride
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A highly efficient and practical resolution of racemic 1,1'-bi-2- naphthol (BINOL) has been achieved through molecular complexation with N- benzylcinchoninium chloride, which can be readily prepared in 85% yield using an improved procedure through the reaction of cinchonine with benzyl chloride in dimethylformamide (DMF). It is found that the absolute configuration of BINOL included in the molecular crystals is R, which is the same as in the case of using N-benzylcinchonidinium chloride. This result is discussed in terms of molecular recognition in the solid state. X-Ray structural analysis of molecular crystal formed between (R)-BINOL and N-benzylcinchoninium chloride indicates that the additive effect of the chiral features of the host, the interaction pattern between the functional groups of the host and guest, and the complementary molecular packing in the crystal lattice dominates the stereochemistry of the guest in the molecular crystal. (C) 2000 Elsevier Science Ltd.
- Wang, Yang,Sun, Jie,Ding, Kuiling
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- Catalytic enantioselective synthesis of atropisomeric biaryls by a cation-directed O-alkylation
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Axially chiral biaryls, as exemplified by 1,1′-bi-2-naphthol (BINOL), are key components of catalysts, natural products and medicines. These materials are synthesized conventionally in enantioenriched form through metal-mediated cross coupling, de novo construction of an aromatic ring, point-to-axial chirality transfer or an atropselective transformation of an existing biaryl. Here, we report a highly enantioselective organocatalytic method for the synthesis of atropisomeric biaryls by a cation-directed O-alkylation. Treatment of racemic 1-aryl-2-tetralones with a chiral quinidine-derived ammonium salt under basic conditions in the presence of an alkylating agent leads to atropselective O-alkylation with e.r. up to 98:2. Oxidation with DDQ gives access to C 2 -symmetric and non-symmetric BINOL derivatives without compromising e.r. We propose that the chiral ammonium counterion differentiates between rapidly equilibrating atropisomeric enolates, leading to highly atropselective O-alkylation. This dynamic kinetic resolution process offers a general approach to the synthesis of enantioenriched atropisomeric materials.
- Jolliffe, John D.,Armstrong, Roly J.,Smith, Martin D.
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- Enantioselective synthesis of ammonium cations
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Control of molecular chirality is a fundamental challenge in organic synthesis. Whereas methods to construct carbon stereocentres enantioselectively are well established, routes to synthesize enriched heteroatomic stereocentres have garnered less attention1–5. Of those atoms commonly present in organic molecules, nitrogen is the most difficult to control stereochemically. Although a limited number of resolution processes have been demonstrated6–8, no general methodology exists to enantioselectively prepare a nitrogen stereocentre. Here we show that control of the chirality of ammonium cations is easily achieved through a supramolecular recognition process. By combining enantioselective ammonium recognition mediated by 1,1′-bi-2-naphthol scaffolds with conditions that allow the nitrogen stereocentre to racemize, chiral ammonium cations can be produced in excellent yields and selectivities. Mechanistic investigations demonstrate that, through a combination of solution and solid-phase recognition, a thermodynamically driven adductive crystallization process is responsible for the observed selectivity. Distinct from processes based on dynamic and kinetic resolution, which are under kinetic control, this allows for increased selectivity over time by a self-corrective process. The importance of nitrogen stereocentres can be revealed through a stereoselective supramolecular recognition, which is not possible with naturally occurring pseudoenantiomeric Cinchona alkaloids. With practical access to the enantiomeric forms of ammonium cations, this previously ignored stereocentre is now available to be explored.
- Walsh, Mark P.,Phelps, Joseph M.,Lennon, Marc E.,Yufit, Dmitry S.,Kitching, Matthew O.
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- Chiral separation materials based on derivatives of 6-amino-6-deoxyamylose
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In order to develop new type of chiral separation materials, in this study, 6-amino-6-deoxyamylose was used as chiral starting material with which 10 derivatives were synthesized. The amino group in 6-amino-6-deoxyamylose was selectively acylated and then the hydroxyl groups were carbamoylated yielding amylose 6-amido-6-deoxy-2,3-bis(phenylcarbamate)s, which were employed as chiral selectors (CSs) for chiral stationary phases of high-performance liquid chromatography. The resulted 6-amido-6-deoxyamyloses and amylose 6-amido-6-deoxy-2,3-bis(phenylcarbamate)s were characterized by IR, 1H NMR, and elemental analysis. Enantioseparation evaluations indicated that most of the CSs demonstrated a moderate chiral recognition capability. The 6-nonphenyl (6-nonPh) CS of amylose 6-cyclohexylformamido-6-deoxy-2,3-bis(3,5-dimethylphenylcarbamate) showed the highest enantioselectivity towards the tested chiral analytes; the phenyl-heterogeneous (Ph-hetero) CS of amylose 6-(4-methylbenzamido)-6-deoxy-2,3-bis(3,5-dimethylphenylcarbamate) baseline separated the most chiral analytes; the phenyl-homogeneous (Ph-homo) CS of amylose 6-(3,5-dimethylbenzamido)-6-deoxy-2,3-bis(3,5-dimethylphenylcarbamate) also exhibited a good enantioseparation capability among the developed CSs. Regarding Ph-hetero CSs, the enantioselectivity depended on the combination of the substituent at 6-position and that at 2- and 3-positions; as for Ph-homo CSs, the enantioselectivity was related to the substituent at 2-, 3-, and 6-positions; with respect to 6-nonPh CSs, the retention factor of most analytes on the corresponding CSPs was lower than that on Ph-hetero and Ph-homo CSPs in the same mobile phases, indicating π–π interactions did occur during enantioseparation. Although the substituent at 6-position could not provide π–π interactions, the 6-nonPh CSs demonstrated an equivalent or even higher enantioselectivity compared with the Ph-homo and Ph-hetero CSs.
- Gao, Ya-Ya,Zhang, Yu-Hang,Zhang, Shan,Chen, Wei,Bai, Zheng-Wu
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supporting information
p. 899 - 914
(2021/10/07)
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- Preparation of a novel bridged bis(β-cyclodextrin) chiral stationary phase by thiol-ene click chemistry for enhanced enantioseparation in HPLC
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A bridged bis(β-cyclodextrin) ligand was firstly synthesized via a thiol-ene click chemistry reaction between allyl-ureido-β-cyclodextrin and 4-4′-thiobisthiophenol, which was then bonded onto a 5 μm spherical silica gel to obtain a novel bridged bis(β-cyclodextrin) chiral stationary phase (HTCDP). The structures of HTCDP and the bridged bis(β-cyclodextrin) ligand were characterized by the 1H nuclear magnetic resonance (1H NMR), solid state 13C nuclear magnetic resonance (13C NMR) spectra spectrum, scanning electron microscope, elemental analysis, mass spectrometry, infrared spectrometry and thermogravimetric analysis. The performance of HTCDP in enantioseparation was systematically examined by separating 21 chiral compounds, including 8 flavanones, 8 triazole pesticides and 5 other common chiral drugs (benzoin, praziquantel, 1-1′-bi-2-naphthol, Tr?ger's base and bicalutamide) in the reversed-phase chromatographic mode. By optimizing the chromatographic conditions such as formic acid content, mobile phase composition, pH values and column temperature, 19 analytes were completely separated with high resolution (1.50-4.48), in which the enantiomeric resolution of silymarin, 4-hydroxyflavanone, 2-hydroxyflavanone and flavanone were up to 4.34, 4.48, 3.89 and 3.06 within 35 min, respectively. Compared to the native β-CD chiral stationary phase (CDCSP), HTCDP had superior enantiomer separation and chiral recognition abilities. For example, HTCDP completely separated 5 other common chiral drugs, 2 flavanones and 3 triazole pesticides that CDCSP failed to separate. Unlike CDCSP, which has a small cavity (0.65 nm), the two cavities in HTCDP joined by the aryl connector could synergistically accommodate relatively bulky chiral analytes. Thus, HTCDP may have a broader prospect in enantiomeric separation, analysis and detection. This journal is
- Gong, Bolin,Guo, Siyu,Zhang, Ning
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p. 35754 - 35764
(2021/12/02)
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- Enantiodivergent Kinetic Resolution of 1,1′-Biaryl-2,2′-Diols and Amino Alcohols by Dipeptide-Phosphonium Salt Catalysis Inspired by the Atherton–Todd Reaction
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A highly enantiodivergent organocatalytic method is disclosed for the synthesis of atropisomeric biaryls via kinetic resolution inspired by a dipeptide-phosphonium salt-catalyzed Atherton–Todd (A-T) reaction. This flexible approach led to both R- and S-enantiomers by fine-tuning of bifunctional phosphonium with excellent selectivity factors (s) of up to 1057 and 525, respectively. The potential of newly synthesized O-phosphorylated biaryl diols was illustrated by the synthesis of axially chiral organophosphorus compounds. Mechanistic investigations suggest that the bifunctional phosphonium halide catalyst differentiates between the in-situ-generated P-species in the A-T process, mainly involving phosphoryl chloride and phosphoric anhydride, thus leading to highly enantiodivergent O-phosphorylation reactions. Furthermore hydrogen bonding interactions between the catalysts and phosphorus molecules were crucial in asymmetric induction.
- Chen, Yuan,Fang, Siqiang,Pan, Jianke,Ren, Xiaoyu,Tan, Jian-Ping,Wang, Tianli,Zhang, Hongkui
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supporting information
p. 14921 - 14930
(2021/05/10)
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- Photo racemization of 2,2′-dihydroxy-1,1′-binaphthyl derivatives
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Photo racemization of 2,2′-dihydroxy-1,1′-binaphthyl (BINOL) and its monomethyl ether, monobutyl ether, and dimethyl ether was studied by means of circularly dichroism spectra, chiral HPLC, and theoretical calculations of rotation energy barriers. Racemiz
- Bando, Masayoshi,Fortino, Mariagrazia,Naga, Naofumi,Nakano, Tamaki,Pietropaolo, Adriana,Song, Zhiyi,Wang, Qingyu
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- Resolution of Vaulted Biaryl Ligands via Borate Esters of Quinine and Quinidine
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Given the sudden and unexplained rise in the cost of (+)- A nd (-)-sparteine, an alternative method for the resolution of vaulted biaryls has been developed. This method involves the reaction of a racemic vaulted biaryl ligand with one equivalent of BH3·SMe2 and one equivalent of either quinine or quinidine. A precipitate then forms from the resulting mixture of diastereomeric borates as a result of differential solubilities. Hydrolysis of the precipitate then liberates the (S)-ligand in the case of quinine and the (R)-ligand in the case of quinidine, both with >99% ee. This method has been applied to 16 different vaulted biaryl ligands, including 10 whose preparation is described here for the first time. In addition, proof of principle has been demonstrated for the dynamic thermodynamic resolution of the vaulted biaryl ligands with this method in combination with a nonchiral copper(II) complex that can racemize the ligand.
- Cagnon, Brian R.,Mohammadlou, Aliakbar,Wulff, William D.,Yin, Xiaopeng,Zheng, Li
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p. 10432 - 10450
(2020/09/23)
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- Novel chiral stationary phases based on 3,5-dimethyl phenylcarbamoylated β-cyclodextrin combining cinchona alkaloid moiety
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Novel chiral selectors based on 3,5-dimethyl phenylcarbamoylated β-cyclodextrin connecting quinine (QN) or quinidine (QD) moiety were synthesized and immobilized on silica gel. Their chromatographic performances were investigated by comparing to the 3,5-dimethyl phenylcarbamoylated β-cyclodextrin (β-CD) chiral stationary phase (CSP) and 9-O-(tert-butylcarbamoyl)-QN-based CSP (QN-AX). Fmoc-protected amino acids, chiral drug cloprostenol (which has been successfully employed in veterinary medicine), and neutral chiral analytes were evaluated on CSPs, and the results showed that the novel CSPs characterized as both enantioseparation capabilities of CD-based CSP and QN/QD-based CSPs have broader application range than β-CD-based CSP or QN/QD-based CSPs. It was found that QN/QD moieties play a dominant role in the overall enantioseparation process of Fmoc-amino acids accompanied by the synergistic effect of β-CD moiety, which lead to the different enantioseparation of β-CD-QN-based CSP and β-CD-QD-based CSP. Furthermore, new CSPs retain extraordinary enantioseparation of cyclodextrin-based CSP for some neutral analytes on normal phase and even exhibit better enantioseparation than the corresponding β-CD-based CSP for certain samples.
- Zhu, Lunan,Zhu, Junchen,Sun, Xiaotong,Wu, Yaling,Wang, Huiying,Cheng, Lingping,Shen, Jiawei,Ke, Yanxiong
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p. 1080 - 1090
(2020/05/25)
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- Enantioselective iron/bisquinolyldiamine ligand‐catalyzed oxidative coupling reaction of 2‐naphthols
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An iron‐catalyzed asymmetric oxidative homo‐coupling of 2‐naphthols for the synthesis of 1,1′‐Bi‐2‐naphthol (BINOL) derivatives is reported. The coupling reaction provides enantioenriched BINOLs in good yields (up to 99%) and moderate enantioselectivities (up to 81:19 er) using an iron‐complex generated in situ from Fe(ClO4)2 and a bisquinolyldiamine ligand [(1R,2R)‐N1,N2‐di(quinolin‐8‐yl)cyclohexane‐1,2‐diamine, L1]. A number of ligands (L2–L8) and the analogs of L1, with various substituents and chiral backbones, were synthesized and examined in the oxidative coupling reactions.
- Liu, Wen-Bo,Usman, Muhammad,Wu, Lin-Yang
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- Ruthenium-Catalyzed Cross-Selective Asymmetric Oxidative Coupling of Arenols
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(Aqua)ruthenium(salen) complex 1c achieved good to high chemo- A nd enantioselective oxidative cross-coupling of arenols. The catalytic system can be used to selectively produce C1-symmetric bis(arenol)s from the combination of C3- A nd C7-substituted 2-naphthols or phenols even when there is no significant difference in oxidation potential between the cross-coupling partners. This unique cross-selectivity is dominated by steric rather than electronic effects of the arenols and can be controlled by chemoselective single-electron oxidation and oxidative carbon-carbon bond formation.
- Hayashi, Hiroki,Kim, Chungsik,Uchida, Tatsuya,Ueno, Takamasa
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supporting information
(2020/02/26)
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- Atropselective hydrolysis of chiral BiNoL-phosphate esters catalyzed by the phosphotriesterase from Sphingobium sp. TCM1
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The phosphotriesterase from Sphingobium sp. TCM1 (Sb-PTE) is notable for its ability to hydrolyze a broad spectrum of organophosphate triesters, including organophosphorus flame retardants and plasticizers such as triphenyl phosphate and tris(2-chloroethyl) phosphate that are not substrates for other enzymes. This enzyme is also capable of hydrolyzing any one of the three ester groups attached to the central phosphorus core. The enantiomeric isomers of 1,1′-bi-2-naphthol (BINOL) have become among the most widely used chiral auxiliaries for the chemical synthesis of chiral carbon centers. PTE was tested for its ability to hydrolyze a series of biaryl phosphate esters, including mono- and bis-phosphorylated BINOL derivatives and cyclic phosphate triesters. Sb-PTE was shown to be able to catalyze the hydrolysis of the chiral phosphate triesters with significant stereoselectivity. The catalytic efficiency, kcat/Km, of Sb-PTE toward the test phosphate triesters ranged from ～10 to 105 M?1 s?1. The product ratios and stereoselectivities were determined for four pairs of phosphorylated BINOL derivatives.
- Xiang, Dao Feng,Narindoshvili, Tamari,Raushel, Frank M.
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p. 4463 - 4469
(2020/11/30)
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- Continuous Flow Preparation of Enantiomerically Pure BINOL(s) by Acylative Kinetic Resolution
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A polystyrene-immobilized isothiourea has been applied to the enantioselective acylative kinetic resolution (KR) of monoacylated BINOL(s) with inexpensive isobutyric anhydride in batch and flow. High selectivity values (s=29 at 0 °C) and a remarkable stability of the catalytic system in the operation conditions have been recorded for unsubstituted BINOL. No significant loss of activity/selectivity is recorded after 10 consecutive KR cycles in batch. A continuous flow process has been implemented and operated with a 100 mmol (32.8 g) sample of racemic monoacetylated BINOL in dichloromethane solution in an 84 hours experiment with a packed bed reactor containing 1 g (f=0.37 mmol.g?1) of the functional resin (s=17–21). Residence time can be decreased to 10 min with the same reactor to achieve a conversion of 58% with a selectivity factor s=17 when a more highly functionalized catalyst (f=0.88 mmol.g?1) is used. This translates into a remarkable combined productivity of 5.5 mmolprod ? mmolcat?1 ? h?1.
- Lai, Junshan,Neyyappadath, Rifahath M.,Pericàs, Miquel A.,Smith, Andrew D.
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- Base-promoted lipase-catalyzed kinetic resolution of atropisomeric 1,1′-biaryl-2,2′-diols
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Herein we report a dramatic acceleration of the lipase-catalyzed kinetic resolution of atropisomeric 1,1′-biaryl-2,2′-diols by the addition of sodium carbonate. This result likely originates from the increased nucleophilicity of the phenolic hydroxyl group toward the acyl-enzyme intermediate. Under these conditions, various substituted C2-symmetric and non-C2-symmetric binaphthols and biphenols were efficiently resolved with ～50% conversion in only 13-30 h with excellent enantioselectivity.
- Moustafa, Gamal A. I.,Kasama, Kengo,Higashio, Koichi,Akai, Shuji
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p. 1165 - 1175
(2019/01/23)
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- Three-State Switchable Chiral Stationary Phase Based on Helicity Control of an Optically Active Poly(phenylacetylene) Derivative by Using Metal Cations in the Solid State
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An unprecedented three-state switchable chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) was developed using a helical poly(phenylacetylene) bearing a chiral (R)-α-methoxyphenylacetic acid residue as the pendant (poly-1). The left- and right-handed helical conformations were induced in poly-1-based CSP upon coordination with a catalytic amount of soluble sodium and cesium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate salts (MBArF), respectively, which are soluble in the HPLC conditions [hexane-2-propanol (95:5, v/v)]. The switch between the two different helical states of poly-1 can be easily achieved by rinsing the poly-1-based CSP with MeOH and the subsequent addition of the proper MBArF salt. Using this dynamic helical CSP, we demonstrate how changes on the orientation of the secondary structure of a chiral polymer (right-handed, left-handed, and racemic helices) can alter and even invert the elution order of the enantiomers. This study was done without adding chiral additives or changing the mobile phase, which could produce changes on the retention times and make it more difficult to determine the role of the secondary structure during the chiral recognition process.
- Hirose, Daisuke,Isobe, Asahi,Qui?oá, Emilio,Freire, Félix,Maeda, Katsuhiro
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supporting information
(2019/06/10)
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- Three-State Switchable Chiral Stationary Phase Based on Helicity Control of an Optically Active Poly(phenylacetylene) Derivative by Using Metal Cations in the Solid State
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An unprecedented three-state switchable chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC) was developed using a helical poly(phenylacetylene) bearing a chiral (R)-α-methoxyphenylacetic acid residue as the pendant (poly-1). The left- and right-handed helical conformations were induced in poly-1-based CSP upon coordination with a catalytic amount of soluble sodium and cesium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate salts (MBArF), respectively, which are soluble in the HPLC conditions [hexane-2-propanol (95:5, v/v)]. The switch between the two different helical states of poly-1 can be easily achieved by rinsing the poly-1-based CSP with MeOH and the subsequent addition of the proper MBArF salt. Using this dynamic helical CSP, we demonstrate how changes on the orientation of the secondary structure of a chiral polymer (right-handed, left-handed, and racemic helices) can alter and even invert the elution order of the enantiomers. This study was done without adding chiral additives or changing the mobile phase, which could produce changes on the retention times and make it more difficult to determine the role of the secondary structure during the chiral recognition process.
- Hirose, Daisuke,Isobe, Asahi,Qui?oá, Emilio,Freire, Félix,Maeda, Katsuhiro
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supporting information
p. 8592 - 8598
(2019/06/13)
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- An enantioselective oxidative coupling reaction of 2-naphthol derivatives catalyzed by chiral diphosphine oxide-iron(ii) complexes
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An enantioselective oxidative coupling of 2-naphthol derivatives is developed with the use of chiral Fe(ii)-diphosphine oxide complexes. Optically active 1,1-bi-2-naphthol derivatives can be synthesized in high yields when a 2?:?1 complex of (S)-xylyl-iPrO-BIPHEP-oxide and Fe(OTf)2 is used in the presence of t-butyl hydroperoxide as an oxidant. The non-linear effect, X-ray crystal structure and ESI-MS suggest that a 2?:?1 complex of (S)-xylyl-iPrO-BIPHEP-oxide and Fe(OTf)2 is a pre-catalyst for a Fe(iii)/Fe(iv) redox cycle.
- Horibe, Takahiro,Nakagawa, Keita,Hazeyama, Takashi,Takeda, Kazuki,Ishihara, Kazuaki
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supporting information
p. 13677 - 13680
(2019/11/19)
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- Cu(II) complexes derived from N-carboxymethyl and N-carboxyethyl amino acids as catalysts for asymmetric oxidative coupling of 2-naphthol
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The synthesis, characterization and catalytic performance of chiral Cu(II) complexes derived from N-carboxymethylated and N-carboxyethylated amino acids is reported. The ligand precursors are prepared by single step N-alkylation of the sodium salts of the appropriate chiral amino acid with either sodium chloroacetate or sodium 3-chloropropionate in water. The Cu(II) complexes are obtained upon reaction of Cu(CH3COO)2 with the aqueous or alcoholic suspension of the suitable ligand under vigorous stirring or ultrasound irradiation at room temperature. The Cu(II) compounds are characterised by EPR, UV–vis, circular dichroism and ESI-MS. The molecular structures of two of the prepared complexes are also obtained by single-crystal X-ray diffraction analysis. The catalytic activity of the complexes in the asymmetric oxidative coupling of 2-naphthol is described. All compounds exhibit moderate activity, selectivity and enantioselectivity in ethanol/water mixtures, under aerobic conditions and using potassium iodide as additive. The yields of 1,1′-bi-2-naphthol (BINOL) reached 50% under the optimal conditions, while enantiomeric excesses reached ca. 48%. The effect of variables such as ligand substituents, solvent, temperature and additives on the catalytic activity is also described. In the absence of a base, the complexes only show catalytic activity in the presence of alkali metal iodide such as KI. Details of the oxidative coupling mechanism are studied using spectroscopic and electrochemical methodologies.
- Ad?o,Teixeira, Carlos M.,Carvalho, M. Fernanda N.N.,Kuznetsov, Maxim L.,Gomes, Clara S.B.,Pessoa, Jo?o Costa
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- Isothiourea-Catalysed Regioselective Acylative Kinetic Resolution of Axially Chiral Biaryl Diols
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An operationally simple isothiourea-catalysed acylative kinetic resolution of unprotected 1,1′-biaryl-2,2′-diol derivatives has been developed to allow access to axially chiral compounds in highly enantioenriched form (s values up to 190). Investigation of the reaction scope and limitations provided three key observations: i) the diol motif of the substrate was essential for good conversion and high s values; ii) the use of an α,α-disubstituted mixed anhydride (2,2-diphenylacetic pivalic anhydride) was critical to minimize diacylation and give high selectivity; iii) the presence of substituents in the 3,3′-positions of the diol hindered effective acylation. This final observation was exploited for the highly regioselective acylative kinetic resolution of unsymmetrical biaryl diol substrates bearing a single 3-substituent. Based on the key observations identified, acylation transition state models have been proposed to explain the atropselectivity of this kinetic resolution.
- Qu, Shen,Greenhalgh, Mark D.,Smith, Andrew D.
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supporting information
p. 2816 - 2823
(2019/02/05)
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- Synthesis of new C3 symmetric amino acid- and aminoalcohol-containing chiral stationary phases and application to HPLC enantioseparations
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We recently reported a new C3-symmetric (R)-phenylglycinol N-1,3,5-benzenetricarboxylic acid-derived chiral high-performance liquid chromatography (HPLC) stationary phase (CSP 1) that demonstrated better results as compared to a previously described N-3,5-dintrobenzoyl (DNB) (R)-phenylglycinol-derived CSP. Over a decade ago, (S)-leucinol, (R)-phenylglycine, and (S)-leucine derivatives were used as the starting materials of 3,5-DNB-based Pirkle-type CSPs for chiral separation. In this study, three new C3-symmetric CSPs (CSP 2, 3, and 4) were prepared by combining the ideas and results mentioned above. Here we describe the synthetic procedures and applications of the new C3-symmetric CSPs (CSP 2–CSP 4).
- Yu, Jeongjae,Armstrong, Daniel W.,Ryoo, Jae Jeong
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- Chiral Organic Cages with a Triple-Stranded Helical Structure Derived from Helicene
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We report the use of helicene with an intrinsic helical molecular structure to prepare covalent organic cages via imine condensation. The organic cages revealed a [3+2]-type architecture containing a triple-stranded helical structure with three helicene units arranged in a propeller-like fashion with the framework integrally twisted. Such structural chirality was retained upon dissolution in organic solvents, as indicated by a strong diastereotopy effect in proton NMR and unique Cotton effects in circular dichroism spectra. Further study on chiral adsorption showed that the chiral organic cages possess considerable enantioselectivity toward a series of aromatic racemates.
- Malik, Abaid Ullah,Gan, Fuwei,Shen, Chengshuo,Yu, Na,Wang, Ruibin,Crassous, Jeanne,Shu, Mouhai,Qiu, Huibin
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supporting information
p. 2769 - 2772
(2018/03/08)
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- Design and Enantioresolution of Homochiral Fe(II)-Pd(II) Coordination Cages from Stereolabile Metalloligands: Stereochemical Stability and Enantioselective Separation
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The stereochemistry of chiral-at-metal complexes is much more abundant, albeit complicated, than chiral-at-carbon compounds, but how to make use of stereolabile metal-centers remains a formidable challenge due to the highly versatile coordination geometry of metal ions and racemization/epimerization problem. We demonstrate herein a stepwise assembly of configurationally stable [Pd6(FeL3)8]28+ (Δ/-MOCs-42) homochiral octahedral cages from unstable D3-symmetry tris-chelate-Fe type metalloligands via strong face-directed stereochemical coupling and facile chiral-induced resolution processes based on stereodifferentiating host-guest dynamics. Kinetic studies reveal that the dissociation rate of MOC-42 cages is 100-fold slower than that of Fe-metalloligands and the racemization is effectively inhibited, making the cages retain their chirality over extended periods of time (>5 months) at room temperature. Recyclable enantioseparation of atropisomeric compounds has been successfully achieved, giving up to 88% ee.
- Hou, Ya-Jun,Wu, Kai,Wei, Zhang-Wen,Li, Kang,Lu, Yu-Lin,Zhu, Cheng-Yi,Wang, Jing-Si,Pan, Mei,Jiang, Ji-Jun,Li, Guang-Qin,Su, Cheng-Yong
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supporting information
p. 18183 - 18191
(2019/01/09)
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- Enantioselective Vanadium-Catalyzed Oxidative Coupling: Development and Mechanistic Insights
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The evolution of a more reactive chiral vanadium catalyst for enantioselective oxidative coupling of phenols is reported, ultimately resulting in a simple monomeric vanadium species combined with a Br?nsted or Lewis acid additive. The resultant vanadium complex is found to effect the asymmetric oxidative ortho-ortho coupling of simple phenols and 2-hydroxycarbazoles with good to excellent levels of enantioselectivity. Experimental and quantum mechanical studies of the mechanism indicate that the additives aggregate the vanadium monomers. In addition, a singlet to triplet crossover is implicated prior to carbon-carbon bond formation. The two lowest energy diastereomeric transition states leading to the enantiomeric products differ substantially with the path to the minor enantiomer involving greater torsional strain between the two phenol moieties.
- Kang, Houng,Herling, Madison R.,Niederer, Kyle A.,Lee, Young Eun,Vasu Govardhana Reddy, Peddiahgari,Dey, Sangeeta,Allen, Scott E.,Sung, Paul,Hewitt, Kirsten,Torruellas, Carilyn,Kim, Gina J.,Kozlowski, Marisa C.
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p. 14362 - 14384
(2018/11/23)
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- Lipase-Catalyzed Dynamic Kinetic Resolution of C1- and C2-Symmetric Racemic Axially Chiral 2,2′-Dihydroxy-1,1′-biaryls
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We have discovered that the racemization of configurationally stable, axially chiral 2,2′-dihydroxy-1,1′-biaryls proceeds with a catalytic amount of a cyclopentadienylruthenium(II) complex at 35–50 °C. Combining this racemization procedure with lipase-catalyzed kinetic resolution led to the first lipase/metal-integrated dynamic kinetic resolution of racemic axially chiral biaryl compounds. The method was applied to the synthesis of various enantio-enriched C1- and C2-symmetric biaryl diols in yields of up to 98 % and enantiomeric excesses of up to 98 %, which paves the way for new developments in the field of asymmetric synthesis.
- Moustafa, Gamal A. I.,Oki, Yasuhiro,Akai, Shuji
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p. 10278 - 10282
(2018/05/30)
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- A surface molecularly imprinted polymer as chiral stationary phase for chiral separation of 1,1′-binaphthalene-2-naphthol racemates
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Acrylamide (AM) was copolymerized with ethylene glycol dimethacrylate (EGDMA) in the presence of (R)-1,1′-binaphthalene-2-naphthol (BINOL) as the template molecules on the surface of silica gel by a free radical polymerization to produce a chiral stationary phase based on the surface molecularly imprinted polymer (SMIP-CSP). The SMIP-CSP showed a much better separation factor (α = 4.28) than the CSP based on the molecularly imprinted polymer (MIP-CSP) without coating on the silica gel (α = 1.96) during the chiral separation of BINOL enantiomers by high-performance liquid chromatography. The influence of the pretreatment temperature and the content of the template molecule ((R)-BINOL) of the SMIP-CSP, and the mobile phase composition on the separation of the racemic BINOL were systematically investigated.
- Dong, Hongxing,Zhang, Danxia,Lin, Hailong,Wang, Yudan,Liu, Lijia,Zheng, Meixia,Li, Xiaobo,Zhang, Chunhong,Li, Junqing,Zhang, Peng,So, Juhyok
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p. 340 - 347
(2017/06/19)
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- New chiral stationary phases based on xanthone derivatives for liquid chromatography
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Six chiral derivatives of xanthones (CDXs) were covalently bonded to silica, yielding the corresponding xanthonic chiral stationary phases (XCSPs). The new XCSPs were packed into stainless-steel columns with 150 x 4.6 mm i.d. Moreover, the greening of the chromatographic analysis by reducing the internal diameter (150 x 2.1 mm i.d.) of the liquid chromatography (LC) columns was also investigated. The enantioselective capability of these phases was evaluated by LC using different chemical classes of chiral compounds, including several types of drugs. A library of CDXs was evaluated in order to explore the principle of reciprocity as well as the chiral self-recognition phenomenon. The separation of enantiomeric mixtures of CDXs was investigated under multimodal elution conditions. The XCSPs provided high specificity for the enantiomeric mixtures of CDXs evaluated mainly under normal-phase elution conditions. Furthermore, two XCSPs were prepared with both enantiomers of the same xanthonic selector in order to confirm the inversion order elution.
- Fernandes, Carla,Tiritan, Maria Elizabeth,Cravo, Sara,Phyo, Ye’ Zaw,Kijjoa, Anake,Silva, Artur M.S.,Cass, Quezia B.,Pinto, Madalena M.M.
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p. 430 - 442
(2017/07/25)
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- Tetrahydro-1,4-epoxynaphthalene-1-carboxylic acid: a chiral resolving agent for the resolution and absolute configuration assignment of 7,7'-disubstituted 1,1'-bi-2-naphthols
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Tetrahydro-1,4-epoxynaphthalene-1-carboxylic acid (THENA), was applied as a chiral derivatizing agent to resolve 7,7'-disubstituted 1,1'-bi-2-naphthol derivatives. This process is very efficient and could potentially be used as a preliminary tool to assign the absolute configuration of substituted 1,1'-bi-2-naphthols by means of a simple TLC.
- Dolsophon, Kulvadee,Ruangsupapichat, Nopporn,Soponpong, Jakapun,Sungsuwan, Suttipun,Prabpai, Samran,Kongsaeree, Palangpon,Thongpanchang, Tienthong
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p. 1113 - 1120
(2016/11/11)
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- A 3D Homochiral MOF [Cd2(d-cam)3]?2Hdma?4dma for HPLC Chromatographic Enantioseparation
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Up to now, some chiral metal-organic frameworks (MOFs) have been reported for enantioseparation in liquid chromatography. Here we report a homochiral MOF, [Cd2(d-cam)3]·2Hdma·4dma, used as a new chiral stationary phase for high-performance liquid chromatographic enantioseparation. Nine racemates of alcohol, naphthol, ketone, and base compounds were used as analytes for evaluating the separation properties of the chiral MOF packed column. Moreover, some effects such as mobile phase composition, column temperature, and analytes mass for separations on this chiral column also were investigated. The relative standard deviations for the resolution values of run-to-run and column-to-column were less than 2.1% and 3.2%, respectively. The experimental results indicate that the homochiral MOF offered good recognition ability, which promotes the application of chiral MOFs use as stationary phase for enantioseparation. Chirality 28:340-346, 2016.
- Zhang, Mei,Chen, Xinglian,Zhang, Junhui,Kong, Jiao,Yuan, Liming
-
supporting information
p. 340 - 346
(2016/03/19)
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- Reversible, short α-peptide assembly for controlled capture and selective release of enantiomers
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Although significant progress has been achieved with short peptide nanostructures, the construction of switchable membrane assemblies remains a great challenge. Here we report short α-peptide assemblies that undergo thermo-reversible switching between assembly and disassembly states, triggered by the conformational change of laterally grafted short peptides from a folded α-helix to a random coil conformation. The α-helical peptide based on two oligoether dendron side groups forms flat disks, while the peptide helix based on three dendron side groups forms hollow vesicles. The vesicular membrane can spontaneously capture a racemic mixture through the self-formation of vesicular containers upon heating and enantioselectively release the chiral guest molecule through preferential diffusion across the vesicular walls.
- Chen, Xi,He, Ying,Kim, Yongju,Lee, Myongsoo
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supporting information
p. 5773 - 5776
(2016/06/09)
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- Chiral Polymers of Intrinsic Microporosity: Selective Membrane Permeation of Enantiomers
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Following its resolution by diastereomeric complexation, 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane (TTSBI) was used to synthesize a chiral ladder polymer, (+)-PIM-CN. (+)-PIM-COOH was also synthesized by the acid hydrolysis of (+)-PIM-CN. Following characterization, both (+)-PIM-CN and (+)-PIM-COOH were solvent cast directly into semipermeable membranes and evaluated for their ability to enable the selective permeation of a range of racemates, including mandelic acid (Man), Fmoc-phenylalanine, 1,1′-bi-2-naphthol (binol), and TTSBI. High ee values were observed for a number of analytes, and both materials exhibited high permeation rates. A selective diffusion–permeation mechanism was consistent with the results obtained with these materials. Their high permeability, processability, and ease of chemical modification offer considerable potential for liquid-phase membrane separations and related separation applications.
- Weng, Xilun,Baez, José E.,Khiterer, Mariya,Hoe, Madelene Y.,Bao, Zongbi,Shea, Kenneth J.
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p. 11214 - 11218
(2016/07/06)
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- Synthesis of optically active poly(diphenylacetylene)s using polymer reactions and an evaluation of their chiral recognition abilities as chiral stationary phases for HPLC
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A series of optically active poly(diphenylacetylene) derivatives bearing a chiral substituent (poly-2S) or chiral and achiral substituents (poly-(2Sx-co-31-x)) on all of their pendant phenyl rings were synthesized by the reaction of poly(bis(4-carboxyphenyl)acetylene) with (S)-1-phenylethylamine ((S)-2) or benzylamine (3) in the presence of a condensing reagent. Their chiroptical properties and chiral recognition abilities as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) were investigated. Poly-2S and poly-(2Sx-co-31-x) (0.06 x-co-31-x)). Furthermore, h-poly-2S and h-poly-(2S0.36-co-30.64) emitted circularly polarized luminescence with opposite signs. h-Poly-2S showed higher chiral recognition abilities toward a larger number of racemates than poly-2S without a preferred-handed helicity and the previously reported preferred-handed poly(diphenylacetylene) derivative bearing the same chiral substituent on half of its pendant phenyl rings. h-Poly-(2S0.36-co-30.64) also exhibited good chiral recognition abilities toward several racemates, though the elution order of some enantiomers was reversed compared with h-poly-2S.
- Maeda, Katsuhiro,Maruta, Miyuki,Sakai, Yuki,Ikai, Tomoyuki,Kanoh, Shigeyoshi
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- Eluent tolerance and enantioseparation recovery of chiral packing materials based on chitosan bis(phenylcarbamate)-(n-octyl urea)s for high performance liquid chromatography
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The goal of the present work was to study the influence of the swelling of chitosan derivatives on the enantioseparation and the separation performance recovery of chiral stationary phases (CSPs) based on these derivatives. Therefore, six chitosan bis(phenylcarbamate)-(n-octyl urea)s were synthesized, which were coated on macroporous 3-aminopropyl silica gel affording new CSPs. Most of the CSPs demonstrated strong enantioseparation capability for the tested chiral compounds. The swelling capacity of the chitosan bis(phenylcarbamate)-(n-octyl urea)s in ethyl acetate, acetone and tetrahydrofuran (THF) was evaluated. Among the chitosan derivatives, the chitosan bis(3,5-dichlorophenylcarbamate)-(n-octyl urea) polymer showed the highest swelling capacity in ethyl acetate and THF. The polymer-based CSPs could be utilized with pure ethyl acetate and a normal phase containing 70% THF, but was damaged by pure THF. On the other hand, the separation performance of the damaged CSP could be recovered after it was allowed to stand for a period of time. The observations are important for the development and application of polysaccharide derivative-based CSPs.
- Wang, Jing,Huang, Shao-Hua,Chen, Wei,Bai, Zheng-Wu
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supporting information
(2016/12/02)
-
- Temperature-triggered switchable helix-helix inversion of poly(phenylacetylene) bearing L-valine ethyl ester pendants and its chiral recognition ability
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A phenylacetylene containing the L-valine ethyl ester pendant (PAA-Val) was synthesized and polymerized by an organorhodium catalyst (Rh(nbd)BPh4) to produce the corresponding one-handed helical cis-poly(phenylacetylene) (PPAA-Val). PPAA-Val showed a unique temperature-triggered switchable helix-sense in chloroform, while it was not observed in highly polar solvents, such as N,N′-dimethylformamide (DMF). By heating the solution of PPAA-Val in chloroform, the sign of the CD absorption became reversed, but recovered after cooling the solution to room temperature. Even after six cycles of the heating-cooling treatment, the helix sense of the PPAA-Val's backbone was still switchable without loss of the CD intensity. The PPAA-Val was then coated on silica gel particles to produce novel chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC). These novel PPAA-Val based CSPs showed a high chiral recognition ability for racemic mandelonitrile (α = 2.18) and racemic trans-N,N′-diphenylcyclohexane-1,2-dicarboxamide (α = 2.60). Additionally, the one-handed helical cis-polyene backbone of PPAA-Val was irreversibly destroyed to afford PPAA-Val-H by heating in dimethyl sulfoxide (DMSO) accompanied by the complete disappearance of the Cotton effect. Although PPAA-Val-H had the same L-valine ethyl ester pendants as its cis-isomer PPAA-Val, it showed no chiral recognition. It was concluded that the one-handed helical cis-polyene backbone of PPAA-Val plays an important role in the chiral recognition ability.
- Zhou, Yanli,Zhang, Chunhong,Qiu, Yuan,Liu, Lijia,Yang, Taotao,Dong, Hongxing,Satoh, Toshifumi,Okamoto, Yoshio
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- Enantioselective Oxidative Homocoupling and Cross-Coupling of 2-Naphthols Catalyzed by Chiral Iron Phosphate Complexes
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Novel chiral iron phosphate complexes were prepared as catalysts for asymmetric oxidative coupling reactions. These catalysts were applied for the synthesis of enantio-enriched C1- and C2-symmetric BINOLs, in which the 3 and 3′ positions are available for chemical modifications. It was proposed that the reaction takes place via an oxidative radical-anion coupling mechanism. A destructive BINOL racemization that competes with the enantioselective oxidative coupling of 2-naphthols was revealed, thereby offering new insights into this highly important reaction.
- Narute, Sachin,Parnes, Regev,Toste, F. Dean,Pappo, Doron
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p. 16553 - 16560
(2016/12/27)
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- A novel type of catalysts for asymmetric oxidative coupling of 2-naphthol
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Stereochemically inert, positively charged chiral octahedral complexes of CoIII and CrIII were used as catalysts for asymmetric oxidative coupling of 2-naphthol. The reaction product 1,1′-bi-2-naphthol was produced with a yield of up to 74% and enantiomeric excess of up to 22%. The reduction and oxidation potentials of a series of CoIII and CrIII cationic complexes were measured.
- Larionov,Peregudova,Maleev,Belokon, Yu. N.
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p. 685 - 688
(2016/12/27)
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- Effects of solvent on inclusion complexation of a chiral dipeptide toward racemic BINOL
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The effects of reaction solvent on inclusion complexation of a chiral dipeptide (3S,6S)-1 derived from (S)-proline toward racemic BINOL was investigated, discovering that the reaction solvent played a crucial role in determining the inclusion complexation behavior of dipeptide (3S,6S)-1 toward rac-BINOL. (3S,6S)-1 did not show any chiroselective or achiroselective complexation toward rac-BINOL in polar protic solvents such as methanol and ethanol, polar aprotic solvents including trichloromethane and THF, while in polar aprotic solvent ethyl acetate and apolar aprotic solvents benzene, (3S,6S)-1 displayed achiroselective complexation toward rac-BINOL. However, the resulting heterocomplex HC-2 from benzene and HC-3 from ethyl acetate have a different composition. Single crystal X-ray diffraction analysis demonstrates that the two heterocomplexes are formed via different H-bond interaction patterns, in which the reaction solvent has a dramatic effect. Furthermore, this work provides a relatively green method for quantitative enantiomeric enrichment of nonracemic BINOL, in which unacceptable and toxic benzene was replaced by ethyl acetate.
- Hu, Xiaoyun,Yang, Yuyuan,Shi, Shuai,Shan, Zixing
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p. 784 - 788
(2016/12/03)
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- Synthesis and chiral recognition of helical poly(phenylacetylene)s bearing L-phenylglycinol and its phenylcarbamates as pendants
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A series of novel stereoregular one-handed helical poly(phenylacetylene) derivatives (PPA-1 and PPA-1a-g) bearing L-phenylglycinol and its phenylcarbamate residues as pendants was synthesized for use as chiral stationary phases (CSPs) for HPLC, and their chiral recognition abilities were evaluated using 13 racemates. The phenylcarbamate residues include an unsubstituted phenyl, three chloro-substituted phenyls (3-Cl, 4-Cl, 3,5-Cl2), and three methyl-substituted phenyls (3-CH3, 4-CH3, 3,5-(CH3)2). The acidity of the phenylcarbamate N-H proton and the hydrogen bonds formed between the N-H groups of the phenylcarbamate residues were dependent on the type, position, and the number of substituents on the phenylcarbamate residues. The chiral recognition abilities of these polymers significantly depended on the dynamic helical conformation of the main chain with more or less regularly arranged pendants. The chiral recognition abilities seem to be improved by the introduction of substituents on the phenylcarbamate residues, and PPA-1d bearing the more acidic N-H groups due to the 3,5-dichloro substituents, exhibited a higher chiral recognition than the others. PPA-1d showed an efficient chiral recognition for some racemates, and baseline separation was possible for racemates 5, 11, 12, and 15.
- Zhang, Chunhong,Wang, Hailun,Yang, Taotao,Ma, Rui,Liu, Lijia,Sakai, Ryosuke,Satoh, Toshifumi,Kakuchi, Toyoji,Okamoto, Yoshio
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p. 809 - 821
(2015/03/04)
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- Synthesis and Enantioseparation Ability of Xylan Bisphenylcarbamate Derivatives as Chiral Stationary Phases in HPLC
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Ten novel xylan bisphenylcarbamate derivatives bearing meta- and para-substituents on their phenyl groups were synthesized and their chiral recognition abilities were evaluated as the chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) after coating them on macroporous silica. The chiral recognition abilities of these CSPs depended on the nature, position, and number of the substituents on the phenyl moieties. The introduction of an electron-donating group was more attractive than an electron-withdrawing group to improve the chiral recognition ability of the xylan phenylcarbamate derivatives. Among the CSPs discussed in this study, xylan bis(3,5-dimethylphenylcarbamate)-based CSP seems to possess the highest resolving power for many racemates, and the meta-substituted CSPs showed relatively better chiral recognition than the para-substituted ones. For some racemates, the xylan bis(3,5-dimethylphenylcarbamate) derivative exhibited higher enantioselectivity than the CSP based on cellulose tris(3,5-dimethylphenylcarbamate). Chirality 27:518-522, 2015
- Li, Geng,Shen, Jun,Li, Qiang,Okamoto, Yoshio
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p. 518 - 522
(2015/08/03)
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- Influence of Helical Structure on Chiral Recognition of Poly(phenylacetylene)s Bearing Phenylcarbamate Residues of L -Phenylglycinol and Amide Linage as Pendants
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Four poly(phenylacetylene)s (PPA-1, PPA-2, PPA-3, PPA-4) bearing phenylcarbamate residues of L-phenylglycinol and amide linkage as pendants were prepared to be used as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC), and the influences of coating solvents, dimethylformamide (DMF) and tetrahydrofuran (THF), which were used for coating the polymers on silica gel, on the helical structure of the polymers and their chiral recognition abilities were investigated. The structure analysis of PPA-1, PPA-2, PPA-3, PPA-4 by 1H nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), optical rotation, and circular dichroism (CD) spectra indicated that the polymers possess the cis-transoidal structure with dynamic helical conformation. The polymers in THF seem to have shorter conjugated helical main chains along with a tighter twist conformation than those in DMF. The chiral recognition abilities of PPA-1, PPA-2, PPA-3, PPA-4 with the different helical structures induced by the coating solvents were evaluated as the CSPs in HPLC. The helical structures of PPA-1, PPA-2, PPA-3, PPA-4 induced with THF are preferable for chiral recognition for some racemates compared to those induced with DMF, and higher chiral recognition abilities of PPA-1, PPA-2, PPA-3, PPA-4 were achieved using THF.
- Zhang, Chunhong,Ma, Rui,Wang, Hailun,Sakai, Ryosuke,Satoh, Toshifumi,Kakuchi, Toyoji,Liu, Lijia,Okamoto, Yoshio
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p. 500 - 506
(2015/08/03)
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- Macromolecular helicity induction and memory in a poly(biphenylylacetylene) bearing an ester group and its application to a chiral stationary phase for high-performance liquid chromatography
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An optically inactive poly(biphenylylacetylene) bearing an ester group at the 4′-position of the pendants formed a preferred-handed helical conformation and biased axial chirality in the pendants through a noncovalent interaction with a chiral alcohol, both of which were retained (memorized) even after removal of the chiral alcohol. The chiral stationary phase for high-performance liquid chromatography, prepared by coating the polymer with macromolecular helicity memory on silica gel, showed good chiral recognition ability towards various racemates.
- Ishidate, Ryoma,Shimomura, Kouhei,Ikai, Tomoyuki,Kanoh, Shigeyoshi,Maeda, Katsuhiro
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p. 946 - 948
(2015/08/24)
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- Synthesis and chiral recognition ability of a novel fullerene-functionalized cellulose derivative
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The fullerene-functionalized cellulose derivative 1 was synthesized and coated onto silica gel as chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC). The chiral recognition ability of the obtained chiral packing material (CPM) was evaluated by HPLC with ten types of racemates 2-11. This CPM could be used in the eluents including chloroform and terahydrofuran (THF), which are usually unsuitable solvents for conventional coating-type CPMs. Hence the scope of application of this CPM is wider than conventional coating CPM.
- Gao, Bo,Xu, Zeyu,Fan, Luan,Xu, Xiaodong,Bai, Jianwei,Shen, Xiande
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p. 1479 - 1481
(2015/11/24)
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- Oxidative coupling of 2-naphthol to (R)/(S)-BINOL by MCM-41 supported Mn-chiral Schiff base complexes
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Three Mn(III)-chiral Schiff base complexes supported on MCM-41 are found to be effective reusable catalysts for enantioselective oxidation of 2-naphthol to (R)- and (S)-BINOL (1,1′ bi-2-naphthol) in the presence of oxygen. The supported Mn(III)-complexes are characterized by PXRD, FTIR, solid state-NMR, BET, and cyclic voltammetry study. The homo-coupling reaction with oxygen as the oxidant is promoted by 20 mg of Mn(III) Schiff base complexes to afford binaphthols in nearly quantitative yields with high enantioselectivity of up to 91% ee. The catalytic activities of the homogeneous and heterogeneous chiral catalyst are found to be almost similar. However, the heterogeneous counterparts are found to be advantageous in terms of recyclability and storability. Oxygen partial pressure, the nature of the solvent, temperature and the amount of catalyst affect the catalytic oxidation process. High temperature and highly polar solvent are found to have adverse effects on the catalytic oxidation process.
- Bania, Kusum K.,Karunakar,Satyanarayana, Lanka
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p. 33185 - 33198
(2015/04/27)
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- Enantioselective and aerobic oxidative coupling of 2-naphthol derivatives using chiral dinuclear vanadium(V) complex in water
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Abstract The enantioselective oxidative coupling of 2-naphthols in water was established using dinuclear vanadium(V/IV) catalysis with O2 as the sole co-oxidant. In the vanadium-catalyzed reaction, the corresponding coupling products were obtained in good to excellent yields with up to 94% enantiomeric excess. In water, racemization of the coupling product was suppressed even at high temperature (70°C).
- Sako, Makoto,Takizawa, Shinobu,Yoshida, Yasushi,Sasai, Hiroaki
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p. 613 - 616
(2015/08/03)
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- Amino acid derived CuII compounds as catalysts for asymmetric oxidative coupling of 2-naphthol
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We report the synthesis and characterization of several novel aminopyridine-l-amino acid derived CuII-complexes. The ligands are prepared by a one-pot reductive alkylation of the l-amino acid scaffold and the respective aminopyridine CuII-complexes were obtained by reaction with CuCl2 or Cu(acetato)2. All compounds were characterized by spectroscopic techniques, as well as ESI-MS. Two of the CuII-complexes were characterized by single-crystal X-ray diffraction, one of them, [CuII(L)(CH3COO)] (HL = (S)-3-phenyl-2-(pyridin-2-ylmethylamino)propanoic acid), being the first ever reported aminopyridine-class CuII complex bearing a tridentate N,N,O donor set and a monodentate acetato ligand. The complexes are tested as catalysts in the oxidative coupling of 2-naphthol in organic solvent-water mixtures using dioxygen as the terminal oxidant. The effect of variables such as ligand denticity and substituents, as well as solvent, temperature and oxidant intake, on the overall performance is studied. In general, moderate to low conversions of 2-naphthol to 1,1′-bi-2-naphthol (BINOL) are obtained. The catalysts also showed moderate to low enantioselectivity. Some aspects of the reaction mechanism were elucidated by spectroscopy, electrochemical and theoretical studies. It was found that basic additives are important for activity, but these also increase the formation of secondary oxidation products. The addition of peroxide scavengers such as KI resulted in an increase of conversion, the yield of BINOL and enantioselectivity. This journal is
- Ado, Pedro,Barroso, Snia,Carvalho, M. Fernanda N. N.,Teixeira, Carlos M.,Kuznetsov, Maxim L.,Costa Pessoa, Joo
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supporting information
p. 1612 - 1626
(2015/02/19)
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- Kinetic resolution of 1,1-biaryl-2,2-diols and amino alcohols through NHC-catalyzed atroposelective acylation
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We present here a highly efficient NHC-catalyzed kinetic resolution of a wide range of 1,1-biaryl-2,2-diols and amino alcohols to provide them in uniformly ≥99% ee. This represents the first highly enantioselective catalytic acylation of axially chiral alcohols. The aldehyde backbone that is incorporated into the chiral acyl azolium intermediate was found to have a significant effect on the enantioselectivity of the process.
- Lu, Shenci,Poh, Si Bei,Zhao, Yu
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supporting information
p. 11041 - 11045
(2015/03/30)
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- Arthrobacter sp. lipase catalyzed kinetic resolution of BINOL: The effect of substrate immobilization
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(S)-1,1′-Binaphthyl-2,2′-diol was prepared in high optical purity (～98%) via Arthrobacter sp. lipase (MTCC No. 5125) catalyzed kinetic resolution. The immobilization of the substrate on a solid inert support significantly improved the enantioselectivity factor (E) by almost sixfolds, i.e. from ～27 to >180. The effect of acyl substituents and co-solvents were also studied.
- Gupta, Pankaj,Rouf, Abdul,Shah, Bhahwal Ali,Mahajan, Neha,Chaubey, Asha,Taneja, Subhash Chandra
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- Separating agent for optical isomers
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A separating agent for optical isomers that uses a polysaccharide derivative provided by replacing all or a portion of the hydrogen atoms on the hydroxyl groups present in a polysaccharide with two specific atomic groups that act on optical isomers targeted for separation in an optical resolution, wherein the sum of the average introduction ratios of specific terminal substituents in these atomic groups is greater than 3.0 per monosaccharide unit.
- -
-
Page/Page column 5-6
(2014/10/29)
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- Resolution of (RS)-Binol through co-crystal formation with 3-n-propyl-4-((R/S)-1′-phenylethylamino)butanoic acid
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A method for the optical resolution of (RS)-Binol to obtain optically pure (S)-Binol (99% ee) through co-crystal formation with (RS)-3-n-propyl-4-((S)- 1′-phenylethylamino)butanoic acid (3RS, 1′S) and similarly optically pure (R)-Binol (99% ee) through co-crystal formation with (RS)-3-n-propyl-4- ((R)-1′-phenylethylamino)butanoic acid (3RS,1′R), in high yield is reported. The individual co-crystal of optically pure (S)-3-n-propyl-4-((S)- 1′-phenylethylamino)butanoic acid (3S,1′S) (99% ee) with (S)-Binol, and (R)-3-n-propyl-4-((S)-1′-phenylethylamino)butanoic acid (3R,1′S) (90% ee) with (S)-Binol have been analyzed by single crystal X-ray diffraction to understand hydrogen bonding in the crystal structure and the chiral recognition parameters.
- Roy, Bhairab Nath,Singh, Girij Pal,Lathi, Piyush Suresh,Mitra, Rangan,Nath, Naba K.,Kalyanachakravarthi,Nangia, Ashwini
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p. 394 - 404
(2013/05/08)
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- Synthesis and chiral recognition of nickel(II) macrocyclic complex with (R)-naphthylethyleneamine pendant groups and its self-assembled framework
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A novel nickel(II) hexaaza macrocyclic complex, [Ni(LR,R)] (ClO4)2 (), containing chiral pendant groups was synthesized by an efficient one-pot template condensation and characterized (LR,R1,8-di((R)-α-methylnaphthyl)-1,3,6,8,10,13- hexaazacyclotetradecane). The crystal structure of compound was determined by single-crystal X-ray analysis. The complex was found to have a square-planar coordination environment for the nickel(II) ion. Open framework [Ni(L R,R)]3[C6H3(COO)3] 2 () was constructed from the self-assembly of compound with deprotonated 1,3,5-benzenetricarboxylic acid, BTC3-. Chiral discrimination of rac-1,1'-bi-2-naphthol and rac-2,2,2-trifluoro-1-(9-anthryl) ethanol was performed to determine the chiral recognition ability of the chiral complex () and its self-assembled framework (). Binaphthol showed a good chiral discrimination on the framework (). The optimum experimental conditions for the chiral discrimination were examined by changing the weight ratio between the macrocyclic complex or self-assembled framework and racemates. The detailed synthetic procedures, spectroscopic data including single-crystal X-ray analysis, and the results of the chiral recognition for the compounds are described. Copyright
- Min, Kil Sik,Park, Mi Jung,Ryoo, Jae Jeong
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- Chiral recognition and supramolecular photoreaction of 1,1'-binaphthol with bovine and human serum albumins
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In their pioneering study in 1991, Levi-Minzi and Zandomeneghi discovered that photoirradiation of racemic 1,1'-binaphthol (rac-1) in the presence of bovine serum albumin (BSA) in distilled water gave (R)-1 in 99 % enantiomeric excess (ee) after 77 % of the starting material had been consumed. No similar attempt was made with human serum albumin (HSA). In this study of the effects of phosphate buffer solution on the ground-state affinity and excited-state photobehavior of 1 with serum albumin we found that both BSA and HSA preferentially bind the (S) enantiomer of 1 and that photoreaction of rac-1 mediated by BSA and HSA affords (R)-1 in 98 % ee with 99 % conversion and in 46 % ee with 65 % conversion, respectively.
- Nishijima, Masaki,Chang, Jae-Won,Yang, Cheng,Fukuhara, Gaku,Mori, Tadashi,Inoue, Yoshihisa
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p. 371 - 383
(2013/03/14)
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