Preparation and application of a new doubly tethered chiral stationary phase containing N-CH3 amide linkage based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid

A new doubly tethered chiral stationary phase (CSP 5) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was developed by attaching the second tethering group to silica gel through a carbon atom of the first tethering group of the corresponding singly tethered CSP (CSP 2) containing an N-CH3 tertiary amide linkage, which was previously developed in our laboratory, in order to enhance the CSP stability without the loss of chiral recognition efficiency. The new CSP was quite effective in the resolution of various racemic alpha-amino acids, amines, and amino alcohols, and the chiral recognition efficiency of the new CSP was even greater than that of the corresponding singly tethered CSP especially in terms of the resolution factors (RS). The stability of the new CSP was greater than that of the corresponding singly tethered CSP. The chromatographic resolution behaviors of the new CSP were generally consistent with those of the corresponding singly tethered CSP.     

Resolution and synthesis of optically active alcohols with immobilized water-soluble proteins from green pea, soybean and buckwheat as new bio-catalysts

Kinetic resolution of racemic alcohols, (+/-)-1-(4-substituted phenyl)ethanol and (+/-)-1-(2-naphthyl)ethanol, was done with immobilized green pea, soybean, or buckwheat proteins. The resolution was done stereoselectively by oxidizing only one enantiomer of a racemic alcohol to leave an optically active alcohol with a high purity. In addition, each protein could be reused consecutively at least three times without any decrease of yield or optical purity.     

Direct resolution of ergot alkaloid enantiomers on a novel chiral silica-based stationary phase

A new covalently-bonded, silica-based stationary phase, using as the chiral selector the 1-(3-aminopropyl) derivative of (+)-(5R,8S,10R)-terguride, has been developed to resolve optically active isomers by HPLC. Good resolution of structurally related racemic ergot alkaloids were obtained using water-methanol mixtures as the eluent. Analysis of the influence of the type and concentration of the organic modifier, and the pH of the buffer in the mobile phase allowed the enantioseparation of these compounds to be optimized. Determination of the optical purity of a lisuride-containig drug is reported. © 1994 Wiley-Liss, Inc.     

Liquid chromatographic direct resolution of tocainide and its analogs on a (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6-based chiral stationary phase containing residual silanol protecting n-octyl groups

Optically active (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6-based chiral stationary phase (CSP) containing residual silanol protecting n-octyl groups on silica surface was applied to the liquid chromatographic direct resolution of tocainide and its analogs. The chiral recognition ability of the CSP was excellent, the separation (alpha) and the resolution factors (R(S)) for 15 analytes including tocainide being in the range of 3.02-22.92 and 3.94-20.41, respectively. In addition, the chiral recognition ability of the CSP was much greater than that of (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6-based CSP containing residual silanol groups on the silica surface. The chromatographic behaviors for the resolution of tocainide and its analogs were found to be dependent on the content and the type of organic and acidic modifiers and the ammonium acetate concentration in aqueous mobile phase.     

Liquid chromatographic direct resolution of beta-amino acids on a doubly tethered chiral stationary phase containing N--H amide linkage based on (+)-(18-crown-6)- 2,3,11,12-tetracarboxylic acid

A doubly tethered chiral stationary phase (CSP) prepared by bonding (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to doubly tethered primary aminoalkyl silica gel was used for the resolution of various beta-amino acids. All the beta-amino acids tested were resolved quite well, the separation (alpha) and the resolution factors (RS) being in the ranges 1.34-2.09 and 2.52-7.45, respectively, with a mobile phase of methanol-water (50:50, v/v) containing 10 mM acetic acid. The chiral recognition efficiency of the doubly-tethered CSP was found to be generally superior to that of the corresponding singly-tethered CSP in the resolution of beta-amino acids. The chiral recognition behaviors for the resolution of beta-amino acids on the doubly tethered CSP were examined by varying the type and content of organic and acidic modifiers in the aqueous mobile phase and the column temperature.     

Successive optical resolution by replacing crystallization of DL-threonine

DL -Threonine [DL -Thr; (2RS,3SR)-2-amino-3-hydroxybutanoic acid] was optically resolved by replacing crystallization using L -serine (L -Ser) and 4-hydroxy-L -proline (L -Hyp) as optically active cosolutes. D -Thr was allowed to crystallize preferentially from racemic aqueous solutions in the presence of these L -α-amino acids. The optical resolution of DL -Thr was more successfully achieved by using L -Ser, whose structure is more similar to that of DL -Thr than L -Hyp, and successively gave D - and L -Thr of 87—92% optical purities. The D - and L -Thr obtained were then recrystallized from water to give optically pure D - and L -Thr. © 1994 Wiley-Liss, Inc.     

Liquid chromatographic resolution of 3-amino-1,4-benzodiazepin-2-ones on crown ether-based chiral stationary phases

3-Amino-5-phenyl (or 5-methyl)-1,4-benzodiazepin-2-ones, which are chiral precursors of anti-respiratory syncytial virus active agents, were resolved on three different chiral stationary phases (CSPs) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid or (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6. Among the three CSPs, the CSP that is based on (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6 and containing residual silanol group-protecting n-octyl groups on the silica surface was found to be most effective with the use of 80% ethanol in water containing perchloric acid (10 mM) and ammonium acetate (1.0 mM) as a mobile phase. The separation factors (α) and resolutions (R(S) ) were in the range of 1.90-3.21 and 2.79-5.96, respectively. From the relationship between the analyte structure and the chromatographic resolution behavior, the chiral recognition mechanism on the CSP based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was proposed to be different from that on the CSP based on (3,3'-diphenyl-1,1'-binaphthyl)-20-crown-6. In addition, the chromatographic resolution behavior of the most effective CSP was investigated as a function of the composition of aqueous mobile phase containing organic and acidic modifier and ammonium acetate.     

HPLC resolution of atropoisomeric compounds on a csp derived from (1R;2R)-diaminocyclohexane: Thermodynamic data from variable temperature chromatography

The preparation and a preliminary chromatographic evaluation of a novel polymeric chiral stationary phase (CSP) derived from (1R;2R)-diaminocyclohexane (DACH) are presented. A radical copolymerization process has been employed to generate a silica-based chiral sorbent, showing considerable high chemical and thermal stability and stereoselectivity toward racemic compounds capable of H-bonding (3-hydroxy-benzodiazepin-2-ones, chlorthalidone, atropoisomeric sulfur compounds, etc.); in the present paper we present the investigation on the resolution of racemic dihydroxy biarylic atropoisomers; the effects of eluent composition and of temperature on the separation ability of the CSP have been studied in order to elucidate the recognition mechanism operating in these chiral separations. © 1992 Wiley-Liss, Inc.     

On the kinetics of the enzyme-catalyzed hydrolysis of axial chiral alkyl allenecarboxylates: preparation of optically active R-(−)-2-ethyl-4-phenyl-2,3-hexadiene-carboxylic acid and its optically pure S-(+)-methylester

Pig liver esterase (PLE) was used for the preparation of optically active alkyl allenecarboxylates with axial chirality. Free and immobilized enzymes were used as biocatalysts for the kinetic resolution of racemic ester substrates. Whereas the biotransformations using the free biocatalyst resulted in moderately to high enantiomeric ratios, the immobilization significantly decreased the E-value. The reaction conditions were optimized with respect to the enantiomeric ratio and scaled up. The enantiomeric ratio (E-value) was thereby enhanced by a factor of four to E=60. Under optimized conditions (free enzyme, addition of acetone as a cosolvent and Triton X-100 as an emulgator) in a preparative scale biotransformation, 282 mg of optically pure S-(+)-2-ethyl-4-phenyl-2,3-hexadiene-carboxylic acid methylester (96% ee, 82% yield) and 257 mg of R-(−)-2-ethyl-4-phenyl-2,3-hexadiene-carboxylic acid (83% ee, 80% yield) could be synthesized from the racemic substrate.     

Performance of brush-type HPLC chiral stationary phases with tertiary amide in the connecting tether

The replacement of the N-H hydrogen of the secondary amide-tethered Pirkle-concept N-(3,5-dinitrobenzoyl)-L-leucine derived chiral stationary phase with various pi-basic or aliphatic groups improved the chiral discrimination ability of new chiral stationary phases, based on the leucine- or alanine-derived chiral selector, for the enantiomers of various racemic neutral analytes with amide functional groups. Retention times decreased while separation and resolution factors increased, thus proving the role of pi-donor aromatic unit as an electron-rich shield in the front of a silica surface. In general, chiral stationary phase (CSP) 5 with the 3,5-dimethylphenyl unit showed best performance, while CSP 3, with phenyl unit, and CSP 7, with 1-naphthyl unit in the tertiary amide connecting tether, were less efficient.     

A scalable synthesis of (+)-coronafacic acid

A facile, efficient, and scalable synthesis of optically pure coronafacic acid by resolution of racemic coronafacic acid obtained using an improved version of Watson's method has been developed. By optimizing the boron-mediated aldol reaction of Watson, we were able to prepare 2.1 g of racemic coronafacic acid. This was coupled with (S)-4-isopropyl-2-oxazolidinone to give a mixture of diastereomeric coronafacyl oxazolidinones, which were readily separable by silica-gel column chromatography to give 630 mg of optically pure (+)-coronafacic acid.     

Optical Rotatory Dispersion of Rotundifolone

Microbial (enzymatic) hydrolysis of (±)-O-acetyl allethrolone gave (?)-(R)-allethrolone with (+)-(S)-O-acetyl allethrolone. And microbial hydrolysis of (±)-cis and trans-2-allylcyclopentyl acetates gave the low optically active cis and trans-2-allylcyclopentanols with the acetates of their antipodes. Also, the acetates of (±)-primary alcohols with cyclopropane and cyclohexene rings: (±)-chrysanthemyl alcohol, α-cyclogeraniol, were hydrolyzed by microorganisms to give the optically active alcohols in low optical purities Further, synthesis and microbial resolution of racemic hydroxy-trimethylcyclohexanones, useful intermediate for synthesis of compounds related to carotenoids, were tried.     

Preparation of an optically pure secondary alcohol of synthetic pyrethroids using microbial lipases

Summary Enzyme-catalysed hydrolysis of esters of 4-hydroxy-3-methyl-2-(2-propynyl)-cyclopent-2-enone (HMPC) was examined for the preparation of the optically pure alcohol moiety of synthetic pyrethroids. Among microorganisms and lipases tested, some bacterial lipases hydrolysed the ester of HMPC with high enantioselectivity and high reaction rate. Arthrobacter lipase gave the optically pure (R)-HMPC at 50% hydrolysis in a two-liquid phase reaction system of water and the insoluble substrate. The hydrolysis proceeded even at a substrate concentration of 80w/v%. The enantioselectivity was not changed with the chain length of the acid moiety of the esters. By combination of the enzymatic resolution with a chemical inversion of the (R)-alcohol, an efficient proess was developed for the total conversion of racemic HMPC to (S)-HMPC, which is an important alcohol for preparation of an insecticidallyactive synthetic pyrethroid.Biological preparation of an optically active alcohol. Part I     

First synthesis of the two enantiomers of alpha-methyldiphenylalanine [(alphaMe)Dip] by HPLC resolution.

A strategy for the preparation of enantiomerically pure (R)- and (S)-alpha-methyldiphenylalanine, constrained phenylalanine analogs, is described. A racemic precursor was prepared in high yield from easily available starting products and subjected to HPLC resolution on a noncommercial chiral stationary phase. More than 600 mg of each enantiomer was isolated in optically pure form by using a 150 x 20 mm ID column containing mixed 10-undecenoate/3,5-dimethylphenylcarbamate of cellulose covalently bonded to allylsilica gel and a mixture of n-hexane/2-propanol/acetone as the mobile phase.     

Separation of praziquantel enantiomers using simulated moving bed chromatographic unit with performance designed for semipreparative applications

Praziquantel (PZQ) composes a regular medicine available in a tablet form to fight schistosomiasis and just half of its mass is composed by the active principle (L‐PZQ), the other half, D‐PZQ, is frequently associated to a strong bitter taste. Moreover, optically pure L‐PZQ derivatives could be used in studies about adult and juvenile worms' resistance. Nowadays, these studies use racemic PZQ (rac‐PZQ) as starting point. The D‐PZQ, which would be discarded, could be racemized, coming back as feed concentration in the process. The present work aims to get L‐PZQ and D‐PZQ with high optical purities (more than 97%) and productivity (more than 253 g kg_ads^?1 day^?1) towards semipreparative scale for researches involving L‐PZQ, L‐PZQ derivatives, and D‐PZQ racemization. In order to achieve this goal, a built‐in‐house simulated moving bed chromatographic unit with the cellulose tris (3‐chloro‐4‐methylphenylcarbamate) (Chiralcel OZ) as chiral stationary phase (CSP) was used to investigate different scenarios of separation according to a well‐known design method called triangle theory. In all scenarios investigated, at least one of the outlet streams presented high optically purity for one of the enantiomers. Comparison with literature showed superior performance of our unit even at racemic mixture concentrations that were 10 times lower than the racemic concentrations found in literature.     

Optical resolution of some biologically active compounds by chiral liquid chromatography on BSA-silica (resolvosil) columns

Optical resolution on the analytical scale of a number of racemic pharmaceuticals and some other biologically active compounds has been studied using immobilized bovine serum albumin (BSA) as the stationary phase. For some of the compounds the elution order was determined by the use of optically enriched fractions obtained from a preceding passage of a sample through a preparative column containing microcrystalline triacetylcellulose (MCTA). The reversal in the sign of optical rotation shown in the polarimetric elution profile from the latter, combined with the integrated peak area ratio obtained on resolution on the analytical column, gave directly the order of elution. For one of the benzothiadiazines studied (bendroflumethiazide), increasing the pH of the mobile phase produced opposite effects on the retention of the two enantiomers, leading to a large effect on the separation factor. For many of the compounds studied, high separation factors (α > 2) could be achieved.     

HPLC resolution of thioridazine enantiomers from pharmaceutical dosage form using cyclodextrin-based chiral stationary phase

Resolution of racemic thioridazine obtained from Thioril tablets (Cipla Ltd., Goa, India) into its enantiomers has been achieved by HPLC using a beta-cyclodextrin (CD)-bonded stationary phase. Thioridazine was isolated from commercial formulations and was purified using preparative TLC. The purity was ascertained by RP-HPLC. For the resolution of rac-thioridazine using cyclodextrin based CSP and mobile phase of 0.05 M phosphate buffer (pH 6.5)-acetonitrile (50:50) was found to be successful. The optimum conditions of resolution were established by systematically studying the effect of organic modifier, concentration of buffer, pH and flow rate of mobile phase. The detection limit was found to be 10 microg (5 microg of each enantiomer). The enantiomeric purity of each of the resolved isomers was verified by optical rotation.     

环氧丙醇酯立体专-性水解酶产生菌的筛选

从土壤中筛选出一株能拆分（Ｒ,Ｓ）－环氧丙醇丁酸酯的根霉（Ｒｈｉｚｏｐｕｓｓｐ．Ｂｃ０－０９）,该菌株所产胞外脂肪酶在水解环氧丙醇丁酸酯的反应中具有良好的立体专一性。在ｐＨ恒定７．０的条件下,以其发酵液水解底物,当转化率为５８％时,残留的（Ｒ）－环氧丙醇丁酸酯的光学纯度（对映体过量值）达９６．１％。     

Spacer length effect of a chiral stationary phase based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid

A new chiral stationary phase (CSP) containing 11 methylene-unit spacer was prepared by bonding (+)-(18-crown-6)-2,3,11,12-carboxylic acid to aminoundecylsilica gel. The new CSP was superior to the one containing three methylene-unit spacer in the resolution of alpha-amino acids, beta-amino acids, amines, and amino alcohols in terms of both the separation (alpha) and the resolution factors (R(S)). In the resolution of alpha-amino acids on the new CSP containing a long spacer, the retention factors (k(1)) were quite small compared to those on the CSP containing a short spacer. However, in the resolution of relatively more lipophilic beta-amino acids, amines, and amino alcohols, the retention factors (k(1)) were generally greater on the CSP containing a long spacer than on the CSP containing a short spacer. All of these resolution behaviors have been rationalized by the effective competition of the ammonium ions (R-NH(3)(+)) generated by the residual undecylamino groups of the new CSP under acidic condition with the ammonium ions (R-NH(3)(+)) of analytes for the complexation inside the cavity of the crown ether ring of the CSP and the effective lipophilic interaction between the CSP and the relatively more lipophilic analytes.     

Direct separation of albuterol enantiomers in biological fluids and pharmaceutical formulations using α1-acid glycoprotein and pirkle urea type columns

A direct, isocratic, and simple chromatographic method is described for the resolution of racemic albuterol using the α₁-acid glycoprotein chiral stationary phase (AGP-CSP) under reverse phase conditions. The effect of various organic modifiers, temperature, and phosphate buffer ionic strength on the separation factor (α) and stereochemical resolution factor (R_s) has been studied. The enantiomeric separation of albuterol was also achieved using a urea-type CSP of (S)-indoline-2-carboxylic acid and (R)-1-(α-naphthyl)ethylamine, known as Chirex 3022, running in the normal phase mode. The effect of different organic acids added to the mobile phase was examined and the chiral recognition mechanism(s) is discussed. Solid phase extraction with C₁₈ Sep-Pak cartridges was applied as a clean-up step to determine the enantiomeric ratio between (?)-R and (+)-S-albuterol in pharmaceutical formulations and in human plasma. © 1995 Wiley-Liss, Inc.