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Suraj Adhikari,Kwang Joon Kim,Wonjae Lee 대한약학회 2019 약학회지 Vol.63 No.2
Normal phase high-performance liquid chromatographic enantiomeric separation of chiral amines as naphthaldimine derivatives was performed on amylose and cellulose-derived chiral stationary phases (CSPs) using three naphthaldehyde derivatizing agents. The effect of the structural characteristics of both derivatizing agent types of naphthaldehydes and CSP types on enantiodiscrimination of chiral amines was investigated. The enantioselectivities and resolutions obtained on amylose-derived CSPs were greater than those on cellulose-derived CSPs, except for 2-hydroxynaphthaldimine derivatives on cellulose-derived CSPs. In particular, the most conformationally rigid and flexible, 2-hydroxynaphthaldimine and 2-naphthaldimine derivatives, among three kinds of naphthaldehyde-derived analytes afforded the greatest enantioseparation on conformationally rigid cellulose-derived and conformationally flexible amylose-derived CSPs, respectively. The developed analytical method was applied to the determination of enantiomeric purity for its broad applicability where the enantiomeric impurities of (R)- and (S)-α-methylbenzylamine reagents were found to be 0.63 and 0.55%, respectively. The described method would be useful for evaluating the enantiomers of various chiral amines.
Suraj Adhikari,Jing Yu Jin,Hyungbum Kim,Wonjae Lee 대한약학회 2018 약학회지 Vol.62 No.2
The liquid chromatographic enantiomer separation of N-fluorenylmethoxycarbonyl (FMOC) α-amino acids was performed using a covalently immobilized CSP (Chiralpak IB) with cellulose tris(3,5-dimethylphenylcarbamate) as a chiral selector under fluorescence detection. Several mobile phases with acid additives were used to show the effect of the reversed mobile phase on the chromatographic parameters of the separation and resolution factors. In this study, we observed that the enantioseparation of investigated FMOC α-amino acids on Chiralpak IB using 90% MeOH/water with 10 mM methanesulfonic acid as an additive in the reversed mobile phase (α = 1.18 - 2.31; Rs = 1.20 - 9.08) was significantly greater than that using other mobile phases including the conventional normal mobile condition. Owing to higher sensitivity and selectivity in fluorescence detection than in UV detection, this analytical method using the reversed phase mode is expected to enlarge their application of enantiomer resolution.
Chiral separation using chiral crown ethers as chiral selectors in chirotechnology
Suraj Adhikari,이원재 한국약제학회 2018 Journal of Pharmaceutical Investigation Vol.48 No.3
This article reviews the enantiomer separation using two typical chiral crown ethers as chiral selectors in chirotechnology. The coated chiral crown ether type chiral stationary phase (CSP) derived from bis-(1,1′-binaphthyl)- 22-crown-6 and the covalently bonded chiral crown ether type CSP derived from (18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TA) in the term of their suitability and applicability are discussed and compared in chiral HPLC. It was shown that the covalently bonded type CSP using 18-C-6-TA as a chiral selector has been widely applied for resolving various chiral primary amines in chiral HPLC. Furthermore, this article focuses on the enantiomer separation and their applications using (+)- and/or (−)-18-C-6-TA as chiral selectors for capillary electrophoresis as well as a chiral solvating agent for nuclear magnetic resonance spectroscopy.
Suraj Adhikari,Kyoung-Ran Moon,Wonjae Lee 한국생물공학회 2021 KSBB Journal Vol.36 No.1
The present study aimed to evaluate the antidiarrheal and superoxide scavenging activities of ethanolic extract of Stenochlaena palustris, an edible fern from Blechnaceae family. The antidiarrheal activity was determined against castor oil induced diarrhea model, gastrointestinal transit and enteropooling tests in Swiss albino mice. The test groups received various doses (100, 200, and 400 mg/kg, body weight) of the extract, whereas positive control received loperamide (3 mg/kg, b.w.) and negative control was supplied with 1% tween-80 in distilled water (10 mL/kg, b.w.). At three test doses (100, 200 and 400 mg/kg), the extract showed significant (p < 0.001) and dose dependent antidiarrheal activity in all models. The delay and reduction in the onset, frequency, and weight of diarrheic feces as well as inhibition of the gastrointestinal transit and intraluminal fluid accumulation were observed in all models and highly comparable to the standard loperamide. The extract also exhibited high inhibitory ability to scavenge superoxide anion (O₂<SUP>• –</SUP>). The highest percentage inhibition of superoxide anion was found to be 84.32 ± 0.15% at the concentration 800 μg/mL.
Suraj Adhikari,Alisha Bhandari,Wonjae Lee 대한약학회 2021 약학회지 Vol.65 No.3
We have developed an efficient chiral HPLC method for enantiomeric resolution of some chiral amines and α- amino acid esters as nitrobenzoxadiazole (NBD) derivatives on amylose and cellulose phenylcarbamates derived chiral stationary phases (CSPs) under simultaneous ultraviolet (UV) and fluorescence (FL) detection. The observed enantioselectivities were affected by the type of the analyte (amines or α-amino acid esters), backbone structure (cellulose or amylose) of the CSP used, and substituents of phenyl moiety on the chiral selector of CSP. Further, for same chiral selectors, coated type CSPs showed better enantiomeric separation than those observed for the covalently bonded type CSPs. In general, for the enantiomeric resolution of chiral amines, Chiralpak IE and Chiralcel OD-H columns showed the highest enantioselectivities. However, for resolution of α-amino acid esters, the performances of Chiralpak IA and Chiralpak AD-H (or Lux Amylose-1) columns were superior to those of other CSPs used. In general, the degrees of enantioselectivity for α-amino acid ethyl esters are greater than those for chiral amines. The developed analytical method was applied to determine the enantiomeric purity of two commercially available chiral amine and α-amino acid ester; the enantiomeric impurities were observed to be 0.35 and 0.05% for (S)-α-methylbenzylamine and (S)-leucine ethyl ester, respectively. The validation data obtained from intra- and inter-day accuracy assays for (S)-3,3-dimethyl-2-butylamine and (S)-leucine ethyl ester were 99.92-101.46 and 100.61-101.78%; and 100.05-102.12 and 101.25-102.73%, respectively; the intra- and interday precision assays in terms of relative standard deviation (% RSD) were found to be 0.96-1.57 and 0.81- 1.91%; and 0.24-1.01% and 0.65-1.35%, respectively. Owing to the high accuracy and precision results, the developed analytical method can prove to be useful for the enantiomeric separation of various chiral amines and amino acid esters as NBD derivatives using polysaccharide derived CSPs.
Suraj Adhikari,Kwang Joon Kim,Wonjae Lee 대한약학회 2019 약학회지 Vol.63 No.6
Fluorene-2-carboxaldehyde was used as a new derivatizing agent for the first time to separate the enantiomers of chiral aliphatic amines including amino alcohols by normal phase HPLC under ultraviolet detection. The enantiomer separation of four chiral amines as fluorene-2-carboxaldimine derivatives was performed on six covalently bonded and four coated type polysaccharide-derived chiral stationary phases (CSPs) of amylose or cellulose-based chiral sorbents and the obtained chromatographic results were compared. The nature of the employed CSP (chiral selector or CSP type) and the used analyte type (aliphatic amines and amino alcohols) have significant impact on chromatographic parameters of enantioseparation and retention factor. In general, Chiralpak IE and Chiralpak IF showed good enantioseparation for all the analytes. In particular, the cellulose-derived CSPs showed the greatest enantiomer separation especially for amino alcohol analytes. Among the cellulose-derived CSPs, the coated type CSPs (Chiralcel OD-H and Lux Cellulose-1) showed better enantioselectivity and resolution for these analytes than the covalently bonded Chiralpak IB.