Determination Of Optical Purity Research Articles

Synthesis of Levofloxacin based Chiral Reagent and its Application in Determination of Optical Purity of Essential Racemic Amino Acids using RP-HPLC

In this report, the activated chiral reagents of the (S)- levofloxacin (CR-Lfx) were prepared via coupling reaction of N-hydroxysuccinimide and characterised by UV, IR, HRMS, NMR and CHNS. Three essential racemic amino acids were chosen for the chiral recognition study. The diastereomeric derivatives of the chosen amino acids were prepared under microwave heating conditions, using highly reactive activated reagents (CR-Lfx). RP-HPLC was used to separate the prepared diastereomeric derivatives. The effect of varying mobile phase concentrations and sample concentrations was optimised. The density functional theory calculations were performed using Gaussian 09 rev A.02 and hybrid density functional B3LYP with 6-31G* basis set software to create the lowest energy optimised structures of diastereomeric derivatives. LOD (0.208 ng mL−1), LOQ (0.624 ng mL−1), calibration range (0.02-2.0 mg mL−1), correlation coefficient (0.998) and recovery were the validation parameters for our method (99.54 and 99.89 percent for intra-day assay and 99.87 and 99.32 percent for inter-day assay).

Enantiomeric NMR signal separation mechanism and prediction of separation behavior for a praseodymium (III) complex with (S,S)-ethylenediamine-N,N-disuccinate.

Because choice of chiral nuclear magnetic resonance (NMR) shift reagents and concentration conditions have been made empirically by trials and errors for chiral NMR analyses, the prediction of NMR signal separation behavior is an urgent issue. In this study, the separation of enantiomeric and enantiotopic 1 H and 13 C NMR signals for α-amino acids and tartaric acid was performed by using the praseodymium(III) complex with (S,S)-ethylenediamine-N,N'-disuccinate ((S,S)-EDDS). All the present D-amino acids exhibited larger downfield shift of their α-protons and α-carbons compared with those for the corresponding L-amino acids in common. This regularity is applicable to absolute configurational assignment and determination of optical purity of amino acids. The chemical shifts of β-protons of d- and l-alanine fully bound with the Pr(III) ((S,S)-EDDS) complex (δb s) and the adduct formation constants of both enantiomers (Ks) were obtained by dependences of the observed downfield shifts of the β-protons on the total concentrations of the respective enantiomers in the presence of a constant concentration of the Pr(III) complex. The difference in the K values was found to be predominant determining factor for the enantiomeric signal separation. The chemical shifts of both enantiomers (δs) and the enantiomeric signal separations (Δδs) under given conditions could be calculated from the δb and K values. Furthermore, prediction of the signal separation behavior was enabled by using the calculated δ values and the signal broadening obtained by dependences of the half-height widths of the observed signals on the bound/free substrate concentration ratios for the respective enantiomers.

Effect of Various Parameters and Mechanism of Reversal Order of Elution in Chiral HPLC

Background: Chiral separation involves many phenomena in which the elution order of the enantiomers has its unique position. The phenomenon of elution order of the enantiomers has also been used in the determination of optical purity which is favorable to elute the major component after minor enantiomeric impurity but the main problem is that, this phenomenon is rare. Results: This review rumors the reversal order of elution of many chiral molecules in HPLC. Besides, this review pronounces the effects of pH, derivatisation of drugs, the composition of the mobile phase, and temperature on the reversal order of elution of chiral drugs. The efforts are also made to discuss the possible future perspectives of reversal order of elution. Conclusion: Various parameters such as pH, mobile phase composition, temperature, and chemical structure of the analytes play a role in the phenomena of the reversal order of elution of many chiral molecules which are discussed in the article.

Method for determination of optical purity of 2-arylpropanoic acids using urea derivatives based on a 1,1'-binaphthalene skeleton as chiral NMR solvating agents: Advantages and limitations thereof.

Five optically active urea derivatives (1-5) were used as NMR solvating agents for analysis of the optical purity of different 2-arylpropanoic acids commonly used as nonsteroidal anti-inflammatory drugs. These novel chiral solvating agents were more efficient at discriminating the respective enantiomers of targets than the chiral solvating agents known so far, without the need to add a base for achieving the signal splitting. The advantages and limits of the use of these novel chiral solvating agents were studied.

Determination of Optical Purity of Lactic Acid-Based Chiral Liquid Crystals and Corresponding Building Blocks by Chiral High-Performance Liquid Chromatography and Supercritical Fluid Chromatography.

Liquid crystals (LCs) are among the most prominent materials of the current information age, mainly due to their well-known application in liquid crystal displays (LCDs). Their unique electro-optical properties stem from their ability to form organised structures (mesophases) on the transition from solid state to isotropic liquid. Molecules of LCs in a mesophase still maintain the anisotropy of solid crystals, while simultaneously exhibiting the fluidity of liquids, which gives the system the ability to react immediately to external stimuli such as electric or magnetic fields, light, mechanical stress, pressure and, of course, temperature. For the proper function of LC-based devices, not only chemical, but also optical purity of materials is strongly desirable, since any impurity could be detrimental to the self-assembly of the molecules. Therefore, in this study we aimed to verify synthetic methods published in the literature, which are used nowadays to prepare chiral building blocks based on lactic acid, for their enantioselectivity. Moreover, we have focused on the development of an analytical chiral separation method for target liquid crystalline materials. Using a chiral polysaccharide-based column operated in liquid chromatography mode, we show that not all published methods of LC synthesis are enantioselective, which could lead to significant differences in the properties of the resulting materials. We show that high-performance liquid chromatography with UV detection and supercritical fluid chromatography with UV and mass spectrometry detection enable full control over the chemical and optical purity of the target LCs and the corresponding chiral building blocks. For the first time, we utilise supercritical fluid chromatography with mass detection for the direct chiral analysis of liquid crystalline materials and impurities formed during the synthesis.

Modeling of chiral gas chromatographic separation of alkyl and cycloalkyl 2-bromopropionates using cyclodextrin derivatives as stationary phases

Chiral 2-bromopropionates are widely used as raw materials or intermediates for synthesis of chiral pesticides and medicines with high biological activities. Enantioseparation of 2-bromopropionates is crucial for evaluating the optical purity of chiral 2-bromopropionates. In this study, the enantioseparation of 8 pairs of alkyl 2-bromopropionates and 5 pairs of cycloalkyl 2-bromopropionates were examined using 7 different cyclodextrin derivatives (CDs). For the enantiomers of methyl, ethyl, bromoethyl and prop-2-yn-1-yl 2-bromopropionates, three different kinds of enantioseparation results including baseline separation, partial separation and no separation, are obtained on the 7 different CDs. Besides the baseline enantioseparation of methyl and ethyl 2-bromopropionates on some CDs, baseline enantioseparation of 2-bromoethyl 2-bromopropionate on 2,3,6-tri-O-methyl-β-CD with resolution as 1.78, prop-2-yn-1-yl 2-bromopropionate on 2,3,6-tri-O-methyl-β-CD and 2,3-di-O-pentyl-6-O-propyl-β-CD with the resolution as 3.45 and 1.77, respectively, are also obtained, and can be used for determination of the optical purity. However, for the enantiomers of isopropyl, isobutyl, tert-butyl and 3-methylbut-2-en-1-yl 2-bromopropionates, only partial enantioseparation are obtained on 5 CDs, meaning that these methods cannot be used for determination of the optical purity. To 5 pairs of cycloalkyl 2-bromopropionates, the 7 CDs exhibit low enantioseparation abilities. While the investigated 5 cycloalkyl-2-bromopropionates don't result in baseline enantioseparation when they are analyzed on the 7 CDs, partial enantioseparation of 4 cycloalkyl 2-bromopropionates, cyclopentyl, cyclohexyl, cyclohexylmethyl and benzyl 2-bromopropionates, are obtained on some CDs, and no any enantioseparation of phenyl 2-bromopropionates are observed on the 7 CDs. The baseline enantioseparation methods for methyl, ethyl, bromoethyl, and prop-2-yn-1-yl 2-bromopropionates have been validated for the parameters linearity, limit of detection, limit of quantification, recovery, intra-day and inter-day precision. Moreover, the validated baseline enantioseparation methods for methyl 2-bromopropionate using columns coated with 4 different CDs have been successfully applied on the determination of optical purity of chiral methyl 2-bromopropionate sample. Furthermore, molecular docking study is performed to investigate the 2,3,6-tri-O-methyl-β-cyclodextrin (PM-β-CD) inclusion complexes with various 2-bromopropionates. The docking results show the contribution of differences of geometry and interaction energy between the inclusion complexes of two enantiomers with PM-β-CD to enantioseparation of some 2-bromopropionates, however the docking results cannot explain the enantioseparation mechanism of other 2-bromopropionates, especially cycloalkyl 2-bromopropionates. This study provides information on the selection of chiral stationary phase CDs for the optimal GC enantioseparation conditions of some new 2-bromopropionates. The methodology of this study can be applied to evaluate the optical purity of some chiral 2-bromopropionates.

Enantioseparation of N-acetyl-dl-cysteine as o-phtaldialdehyde derivatives obtained with various primary aliphatic amine additives on polysaccharide-based chiral stationary phases

A sensitive and rapid high-performance liquid chromatography (HPLC) method was developed to enantioseparation of N-acetyl-dl-cysteine after precolumn derivatization using o-phthaldialdehyde and primary aliphatic amines. Seven polysaccharide-based chiral columns were tested in a reversed phase mode. Under the optimal chromatographic conditions, N-acetyl-dl-cysteine derivatives were completely enantioseparated on Chiralcel OZ-3R column with the resolution more than 2.5. The impact of various primary aliphatic amine additives as co-reagents (ethyl-, 1-propyl-, 1-butyl-, 1-pentylamine, (R)-sec-butylamine, tert-butylamine, isobutylamine, cyclopropyl-, cyclobutyl-, cyclopentyl and cyclohexylamine) used in precolumn derivatization step on the retention behavior (retention factor, selectivity and column efficiency) of N-acetyl-dl-cysteine derivatives was investigated. The effect of chromatographic conditions including acetonitrile content in the mobile phase, mobile phase pH, salt concentration in the mobile phase and column temperature on the retention and selectivity was investigated. The developed method was properly validated in terms of linearity, sensitivity (limit of detection and limit of quantification), accuracy, precision, intermediate precision and selectivity according to International Council for Harmonisation (ICH) of Technical Requirements for Pharmaceuticals for Human Use guidelines using internal normalization procedure. Proposed HPLC method was successfully applied to the determination of optical purity in commercially available N-acetyl-L-cysteine samples.

Asymmetric synthesis of (S)-dihydrokavain from l-malic acid

A practical and efficient asymmetric synthesis of (S)-dihydrokavain from known ethyl (S)-2-hydroxy-4-phenylbutanoate which is, in turn, readily available from l-malic acid as a cheap chiral pool material is described using regioselective ring-opening of the 1,2-cyclic sulfate with lithium-3,3,3-triethoxypropiolate and subsequent HgO/H2SO4-mediated lactonization as the key steps. Its opposite enantiomer (R)-dihydrokavain was also synthesized from d-malic acid using the same sequences of reactions for the purpose of optical purity determination.

Chiral syntheses of methyl (R)-2-Sulfanylcarboxylic esters and acids with optical purity determination using HPLC.

Accessible chiral syntheses of 3 types of (R)-2-sulfanylcarboxylic esters and acids were performed: (R)-2-sulfanylpropanoic (thiolactic) ester (53%, 98%ee) and acid (39%, 96%ee), (R)-2-sulfanylsucciinic diester (59%, 96%ee), and (R)-2-mandelic ester (78%, 90%ee) and acid (59%, 96%ee). The present practical and robust method involves (i) clean SN 2 displacement of methanesulfonates of (S)-2-hydroxyesters by using commercially available AcSK with tris(2-[2-methoxyethoxy])ethylamine and (ii) sufficiently mild deacetylation. The optical purity was determined by the corresponding (2R,5R)-trans-thiazolidin-4-one and (2S,5R)-cis-thiazolidin-4-one derivatives based on accurate high-performance liquid chromatography analysis with high-resolution efficiency. Compared with the reported method utilizing AcSCs (generated from AcSH and CsCO3 ), the present method has several advantages, that is, the use of odorless AcCOSK reagent, reasonable reaction velocity, isolation procedure, and accurate, reliable optical purity determination. The use of accessible AcSK has advantages because of easy-to-handle odorless and hygroscopic solid that can be used in a bench-top procedure. The Ti(OiPr)4 catalyst promoted smooth trans-cyclo-condensation to afford (2R,5R)-trans-thiazolidin-4-one formation of (R)-2-sulfanylcarboxylic esters with available N-(benzylidene)methylamine under neutral conditions without any racemization, whereas (2S,5R)-cis-thiazollidin-4-ones were obtained via cis-cyclo-condensation and no catalysts. Direct high-performance liquid chromatography analysis of methyl (R)-mandelate was also performed; however, the resolution efficiency was inferior to that of the thaizolidin-4-one derivatizations.

Ring-locking strategy facilitating determination of absolute optical purity of 2-amino-1-butanol by reverse-phase high-performance liquid chromatography

A concise and efficient reverse-phase high-performance liquid chromatography (RPLC) method has been established for absolute optical purity assay of 2-amino-1-butanol, which is an important synthetic intermediate of various drugs.

Enantiomeric Separation of Chiral Amines and Amino Alcohols Using Acetylated β-Cyclodextrin Stationary Phase by High-Performance Liquid Chromatography

Enantiomeric separation ability on high-performance liquid chromatography (HPLC) was compared between native and acetylated β-cyclodextrin stationary phases. In the chiral stationary phases (CSP) used in this work, β-cyclodextrin is chemically bonded to aminopropyl silica gel via sugar chain spacer. The acetylated β-cyclodextrin phase (SUMICHIRALTM OA-7700) exhibits excellent performance for the separation of chiral amines and amino alcohols in reversed phase mode. Conventional phosphate buffer can be used in mobile phase without special modifier and the analytical method is easy to develop. OA-7700 is very useful practically for the determination of optical purity of many important chiral amines. It can separate enantiomers of 1-phenyl-2-(p-tolyl)ethylamine (PTE) which is used for industrial scale resolution of chrysanthemic acids and norephedrin (phenylpropanolamine) which is regulated as stimulant raw material.

Enantiomeric separation ofR,S-tolterodine andR,S-methoxytolterodine with negatively charged cyclodextrins by capillary electrophoresis

The methods for separation of R,S-tolterodine and R,S-methoxytolterodine enantiomers using sulfated α-, β-CD and phosphated-γ-CD by CE in acidic BGE based on Tris/phosphate pH 2.5 buffer were developed. Sulfated α- and β-CD allow anodic detection while phosphated-γ-CD allows only cathodic detection of the separated enantiomers. The influence of chiral selector (CS)'s concentration as well as the influence of composition and concentration of BGE on resolutions were studied. Reversal migration order of tolterodine and methoxytolterodine enantiomers was observed, when sulfated-α- and sulfated-β-CD were used. The developed methods with all three studied CSs, were validated and compared. All proposed methods enable determination of 0.2% of S-tolterodine as an optical impurity in pills, however the method with phosphated-γ-CD provided lower detection limit, better repeatability of peak areas and migration times, and also lower consumption of CS. Developed method employing phosphated-γ-CD that was applied for the determination of optical purity of R-tolterodine in commercial pills.

Correction to: Determination of optical purity and absolute configuration of natural 12‐hydroxystearic acid by the 1H NMR anisotropy method

The Materials and methods section contained errors in the labeling of the compounds. The corrected text and image provided by the Authors appear below. The corrected figure is reproduced in color in the online version of this correction. 2.9 Determination of absolute configuration of natural 12-hydroxy stearic acid derivatives 2.9.1 Reduction of 8b and 8a A mixture of 8b (300 mg, 0.57 mmol) and 12 mg of 5% Pd/C in MeOH (3 ml) were stirred under hydrogen atmosphere (1 atm) for 6h at room temperature. Ethyl acetate (50 mL) was added as dilute solvent, the mixture was filtered through Celite short column. The solvent was removed under reduced pressure; the residue was purified by column chromatography on silica-gel with CHCl3/EtOAc (15:1). After removed the solvent, the product was purified by using HPLC (KUSANO silica-gel column, 2.2 cmφ × 30 cmL, N = 976–11 205) to give 9a (210 mg, 70%). The same procedure used for the reduction of 8b was adopted with 8a. A mixture of 8a (300 mg, 0.57 mmol) and 12 mg of 5% Pd/C in MeOH (3 ml) were stirred under hydrogen atmosphere (1 atm) for 8 h at room temperature afforded 9b (201 mg, 67%). 3.3 Synthesis of comparing derivatives from MαNP ester of acetylenic octadecanol Comparing samples were derived from 8-a/8-b which have acetylenic MαNP esters by hydrogenation of triple bond. The reaction was carried out under hydrogen atmosphere (1 atm) on 5% Pd/C. The products are purified by HPLC with silica-gel glass column (2.2 cmφ × 30 cmL, hexane/EtyOAc□30/1). After reduction, saturated long chain ester 9-b (R,S)/9-a (R,R) with known absolute configuration were synthesized. 1H NMR spectra of (R,R)9a, (R,S)9b, and natural 11.

Preparation and determination of optical purity of γ-lysine modified peptide nucleic acid analogues

Peptide nucleic acids (PNAs) are DNA analogues in which the nucleic acid backbone is replaced by a pseudopeptide backbone and nucleobases are attached to the backbone by methylene carbonyl linkers. γ-Carbon modification of the PNA structure allows monomers, and subsequently oligomers, with improved properties to be obtained. In this study, we report the convenient synthesis of γ-lysine-modified PNA monomers for pyrimidine bases (thymine and cytosine) with high optical purity (> 99.5%) and direct enantiomer separation of γ-lysine-modified PNA analogs, using chiral HPLC to determine the optical purity.

Preparative scale isolation, purification and derivatization of mimosine, a non-proteinogenic amino acid

Focusing on drug discovery non-proteinogenic amino acids have often been used as important building blocks for construction of compound libraries in the filed of combinatorial chemistry and chemical biology. Highly homogeneous L: -mimosine, α-amino-β-(3-hydoxy-4-oxo-1,4-dihydropyridin-1-yl)-propanoic acid, a non-proteinogenic amino acid, has been successfully isolated and purified on an industrial scale from wild leaves of Leucaena (Leucaena leucocephala de Wit) which is a widely distributed legume in Okinawa, a sub-tropical island in Japan. Optical purity determinations used for quality control have been established through diastereomer formation. Physico-chemical properties and biological properties of purified mimosine have been clarified. Mimosine is sparingly soluble in water and organic solvents but can be dissolved in aqueous alkaline solution. The tyrosinase pathway is of particular interest in the cosmetic field, since mimosine is an analog of tyrosine. Thus the present purified mimosine have been tested in tyrosinase inhibitory assays. The IC50 for tyrosinase inhibitory activity of purified Mim was compared with kojic acid. Mimosine shows significant inhibition of melanin production in murine melanoma cells. The derivatization of mimosine has been investigated with a focus on its use in conventional peptide syntheses to generate mimosyl peptides. N-(9-Fluorenylmethoxycarbonyloxy)-mimosine and resin-bound mimosine for solid-phase syntheses have also been performed. Highly homogeneous Mim is a useful material for the development of functional cosmetics or active pharmaceutical ingredients.

다당 유도체를 기초로 한 키랄 컬럼에서 아미노산 에스테르의 안트르알디민 유도체의 광학분리 및 광학순도 측정

The chromatographic enantiomer separation of 9-anthraldimine derivatives of α-amino acid methyl and ethyl esters on four polysaccharide based chiral columns was performed. The 9-anthraldehyde Schiff base derivatives of α- amino acid esters were readily synthesized by stirring the α-amino acid ester hydrochloride salts with 9-anthraldehyde in the presence of 1,8-diazabicyclo [5.4.0]undec-7-ene as a base and anhydrous MgSO₄. Chiralcel OD or Chiralcel OD-H showed the greatest enantiomer resolution of 9-anthraldimine derivatives of α-amino acid methyl and ethyl esters. The L-enantiomers of all the analytes were preferentially retained on Chiralcel OD or Chiralcel OD-H. This analytical method was applied in the determination of optical purities of several commercially available D- or L-α-amino acid methyl esters.

Determination of optical purity and absolute configuration of natural 12‐hydroxystearic acid by the 1H NMR anisotropy method

AbstractThe enantiopure of (R)‐(−) MαNPA was allowed to react with racemic 18‐(tert‐butyldimethylsilyloxy)‐5‐octadecayne‐7‐ol which was derived from dodecane‐1,12‐diol, yielding diastereomeric esters mixture. These racemic esters were easily separated by HPLC on silica‐gel. The absolute configurations of the first‐eluted diastereomeric esters from the separated esters were determined using 1H NMR anisotropy method. Analysis on 1H NMR spectra and HPLC elution time of the synthesized esters and those of MαNP ester derived from natural methyl‐12‐hydroxystealate showed that the absolute configuration of natural 12‐hydroxystearic acid was R form, and the enantiomeric excess was over 99%.

Determination of optical purity of 3,5‐dimethoxybenzoyl‐leucine diethylamide by chiral chromatography and 1H and 13C NMR spectroscopy

(R)-N-3,5-dinitrobenzoyl (DNB) leucine derived chiral selector was used as an HPLC chiral stationary phase for the resolution of various racemic amino acids derivatives. In this study, determination of optical purity of an amino acid derivative was performed by chiral high performance liquid chromatography and 1H and 13C NMR spectroscopy by using the DNB leucine derived chiral selector. The accuracy and precision of each optical purity value are calculated and the data are compared to each other.

키랄 크로마토그래피와 NMR 분광법에 의한 N-acetyl-1-naphthylethylamine의 광학순도 측정

(R)-N-3,5-dinitrobenzoyl (DNB) phenylglycinol로 부터 만들어진 키랄 선택제가 라세미 Nacylnaphthylalkylamines의 분리에 HPLC 키랄 정지상으로 이용된 바 있다. 본 연구에서는 (R)-phenylglycinol 유도체 키랄 선택제를 이용하여 키랄 크로마토그래피와 NMR 분광법에 의한 광학순도를 측정하였다. NMR과 HPLC 실험결과를 참값과 비교하여 각 광학순도 측정값의 정확도와 정밀도를 계산하였다. NMR 방법의 오차는 +2.2%, 평균 RSD는 4.54% 이었고, HPLC 방법의 오차는 -3.5%, 평균 상대표준편차는 3.23% 이었다. (R)-N-3,5-dinitrobenzoyl (DNB) phenylglycinol derived chiral selector was used as a HPLC chiral stationary phase (CSP) for the resolution of racemic N-acylnaphthylalkylamines. In this study, determination of optical purity was performed by both chiral chromatography and NMR spectroscopy by using the (R)-phenylglycinol derived chiral selector. The data of accuracy and precision of each optical purity value are calculated from the results of NMR and HPLC experiments by comparing with true value. Average error of the NMR method was +2.2% with average RSD of 4.54%, while that of HPLC method was -3.5% with average RSD of 3.23%.

Novel chiral derivatizing isothiocyanate-based agent for the enantiomeric excess determination of amines

The expedient synthesis of a novel chiral (1S,2S)-N-[(2-isothiocyanato)cyclohexyl] trifluoromethanesulfonamide and its use as a derivatizing auxiliary for the straightforward determination of optical purity of chiral amines are reported.