Optical isomer separation of flavanones and flavanone glycosides by nano-liquid chromatography using a phenyl-carbamate-propyl-beta-cyclodextrin chiral stationary phase

Chiral Determination of Naringenin by Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry and Application in Citrus Peel and Pulp

A chiral separation method of naringenin in citrus pulp and peel was established using ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) in this study. The liquid-phase conditions for separation were Chiralpak IG-3 column at 40°C, mobile phase of methanol, and 0.1% formic acid solution (85/15; v/v). Isovolumetric elution can complete the detection within 5 min. Considering the matrix effect, the matrix standard calibration curve was used for sample quantification. Quantitation was achieved by fitting a calibration curve using a standard matrix. The mean overall recoveries of the two enantiomers from orange pulp were 91.0–110.0% and orange peel were 85.3–110.3%, with relative standard deviations of 1.5–3.8 and 0.9–3.6% at the 0.5, 2.5, 50, and 250 μg/kg levels, respectively. The limit of quantification for all enantiomers in the citrus matrix did not exceed 0.5 μg/kg. Furthermore, the absolute configuration of the naringenin enantiomer was determined by combining experimental and predicted electron circular dichroism spectroscopy, and it was confirmed on a Chiralpak IG-3 column that the first eluting enantiomer was (S)-naringenin. The determination of chiral naringenin content in actual citrus samples showed that the naringenin content in hybrid citrus and citrus pulp was significantly higher than that in pomelo. The method established in this study can be used for the determination of naringenin enantiomers in citrus, which is beneficial to variety selection.

Enantioseparation on a new synthetic β-cyclodextrin chemically bonded chiral stationary phase and molecular docking study

A novel β-cyclodextrin derivative chemically bonded chiral stationary phase (EDACD) was synthesized by the reaction of mono-6-ethylenediamine-β-cyclodextrin with the active alkyl isocyanate, anchoring to silica gel. After the successful analysis and characterization using scanning electron microscopy, Fourier transform infrared spectra, solid-state nuclear magnetic resonance spectra, elemental analysis, and thermogravimetric analysis techniques, the enantioselective performance of the as-prepared EDACD column was evaluated by non-steroidal antiinflammatory drugs and flavonoids under the reversed-phase HPLC condition. The factors that affected enantioseparation including mobile phase compositions and buffers were investigated in more detail. As a result, EDACD showed a satisfactory enantioselectivity for the tested drugs. With the mobile phase of acetonitrile and 20-mM ammonium formate adjusted to pH 4.0 using formic acid (85:15, v/v) at the flow rate of 0.6 mL min^-1, the enantiomers of ibuprofen, carprofen, naproxen, indoprofen, ketoprofen, eriocitrin, naringin, and narirutin were separated with the best resolutions of 1.53, 1.64, 3.72, 2.40, 0.50, 0.61, 0.58, and 0.52. To adjust the proportion of acetonitrile to 80% (by volume), the enantiomers of pranoprofen and flurbiprofen were completely resolved with the best resolutions of 1.60 and 1.59. Additionally, by the study of the molecular docking, hydrogen bonding and inclusion complexation were believed to play an important role in chiral recognition. As a new material, EDACD will have a wider application in the analysis of chiral compounds.

Stereoisomer separation of flavanones and flavanone-7-O-glycosides by means of nanoliquid chromatography employing derivatized β-cyclodextrins as mobile-phase additive

A nanoliquid chromatographic method for the stereoisomer separation of some flavanone aglycones and 7-O-glycosides has been proposed employing a C18 capillary column and a chiral mobile-phase additive such as cyclodextrin. The chiral separation of eriodictyol, naringenin, and hesperitin was obtained by addition of carboxymethyl-β-cyclodextrin to the mobile phase, whereas eriocitrin, naringin, narirutin, and hesperidin diastereoisomers were resolved by using sulfobutyl ether-β-cyclodextrin. The influence of the composition of the mobile phase, the length of the capillary column, and the flow rate on the chiral recognition were investigated. At optimum conditions, baseline separation for the selected aglycones and glycosylated forms were achieved with a mobile phase consisting of 50 mM sodium acetate buffer pH 3 and 30% methanol containing 20 mM of carboxymethyl-β-cyclodextrin and 10 mM of sulfobutyl ether-β-cyclodextrin, respectively. Precision, linearity, and sensitivity of the method were tested. Limits of detection and quantification for the studied flavanone glycosides were in the range 1.3-2.5 and 7.5-12.5 µg/mL, respectively. The method was used for the determination of the diastereomeric composition of the flavanone-7-O-glycosides in Citrus juices after solid-phase extraction procedure.

Advances in Chiral Separations at Nano Level

Background::

Nano level chiral separation is necessary and demanding in the development of the drug, genomic, proteomic, and other chemical and the environmental sciences. Few drugs exist in human body cells for some days at nano level concentrations, that are out of the jurisdiction of the detection by standard separation techniques. Likewise, the separation and identification of xenobiotics and other environmental contaminants (at nano or low levels) are necessary for our healthiness.

Discussion:

Conclusion:

This article will be beneficial for chiral chromatographers, academicians, pharmaceutical industries, environmental researchers and Government regulation authorities.

Site-specific oxidation of flavanone and flavone by cytochrome P450 2A6 in human liver microsomes

The roles of human cytochrome P450 (P450 or CYP) 2A6 in the oxidation of flavanone [(2R)- and (2S)-enantiomers] and flavone were studied in human liver microsomes and recombinant human P450 enzymes. CYP2A6 was highly active in oxidizing flavanone to form flavone, 2'-hydroxy-, 4'-, and 6-hydroxyflavanones and in oxidizing flavone to form mono- and di-hydroxylated products, such as mono-hydroxy flavones M6, M7, and M11 and di-hydroxy flavones M3, M4, and M5. Liver microsomes prepared from human sample HH2, defective in coumarin 7-hydroxylation activity, were very inefficient in forming 2'-hydroxyflavanone from flavanone and a mono-hydroxylated product, M6, from flavone. Coumarin and anti-CYP2A6 antibodies strongly inhibited the formation of these metabolites in microsomes prepared from liver samples HH47 and 54, which were active in coumarin oxidation activities. Molecular docking analysis showed that the C2'-position of (2R)-flavanone (3.8 Å) was closer to the iron center of CYP2A6 than the C6-position (10 Å), while distances from C2' and C6 of (2S)-flavanone to the CYP2A6 were 6.91 Å and 5.42 Å, respectively. These results suggest that CYP2A6 catalyzes site-specific oxidation of (racemic) flavanone and also flavone in human liver microsomes. CYP1A2 and CYP2B6 were also found to play significant roles in some of the oxidations of these flavonoids by human liver microsomes.

Comprehensive investigation into the interconversion of C-2 diastereomers of naringin

Naringin is a flavanone that widely presents on daily diet and traditional medicinal materials. The ratios of naringin C-2 diastereomers are found different in reported samples, thus suspiciously leading to various functions. In this study, we measured the interconversion of C-2 diastereomers intensively with ultimate high-performance liquid chromatography and circular dichroism spectra. We examined the diastereomeric naringins in fresh citrus fruit, Huajuhong decoction pieces, and naringin tablet; evaluated the impact of tablet production procedures in factory; and monitored the rapid racemization in incubation. The results not only confirmed that enzyme, temperature, and pH condition could influence the interconversion but also demonstrated that diverse ratios of diastereomers showed limited influence on metabolic behaviors of naringin in the blood, which consequently cause comparable bioactivities. This study could provide comprehensive understanding of diastereomeric interconversion and provide useful reference for drug development.

Chiral separation of terbutaline and non-steroidal anti-inflammatory drugs by using a new lysine-bridged hemispherodextrin in capillary electrophoresis

A method for the separation of a mixture of terbutaline and non-steroidal anti-inflammatory drugs was developed using capillary electrophoresis with a new hemispherodextrin, ad hoc designed, the lysine - bridged hemispherodextrin (THLYSH). The use of lysine residues to bridge the trehalose capping unit moiety to the cyclodextrin cavity gives rise to a receptor with two long chains with amine nitrogen atoms, whose charge can be easily tuned as a function of the solution pH. The new hemispherodextrin was accurately characterised by ESI-MS and NMR spectroscopy, also highlighting its protonation behaviour. Circular dichroism and ESR spectroscopy measurements were also carried out to test its inclusion ability towards anthraquinone-3-sulfonate and its metal coordination ability towards copper(II) ion, respectively. Analogously to the other hemispherodextrins, the main skill of this new derivative lies in its chiral selector properties, as shown by the separation of the enantiomeric pairs of terbutaline and ibuprofen, flurbiprofen, suprofen and tiaprofenic acid by capillary electrophoresis. The focused use of the solution equilibria involved in the separations made it possible to understand the phenomena occurring in solution, and to finely tune the charge status of the receptor. In this way the chiral separation of the racemic mixture was successfully obtained, even if the receptor was individually used, differently by the other hemispherodextrins previously studied whose chiral separation capabilities are present only if used as binary mixtures.

Facile one-pot preparation of chiral monoliths with a well-defined framework based on the thiol–ene click reaction for capillary liquid chromatography

A novel chiral cyclodextrin (CD) monolith was easily prepared via a one-pot process based on the thiol–ene click reaction of allyl-β-CD with pentaerythritol tetra-(3-mercaptopropionate) in a fused-silica capillary.

A Review on Pharmacological and Analytical Aspects of Naringenin

Flavonoids are a widely distributed group of phytochemicals having benzo-pyrone nucleus, and more than 4,000 different flavonoids have been described and categorized into flavonols, flavones, flavanones, isoflavones, catechins and anthocyanidins. Flavonoids occurs naturally in fruits, vegetables, nuts, and beverages such as coffee, tea, and red wine, as well as in medical herbs. Flavonoids are responsible for the different colors of plant parts and are important constituents of the human diet. Flavanoids have different pharmacological activities, such as antioxidant, anti-allergic, antibacterial, anti-inflammatory, antimutagenic and anticancer activity. Naringenin belongs to the flavanones and is mainly found in fruits (grapefruit and oranges) and vegetables. Pharmacologically, it has anticancer, antimutagenic, anti-inflammatory, antioxidant, antiproliferative and antiatherogenic activities. Naringenin is used for the treatments of osteoporosis, cancer and cardiovascular diseases, and showed lipid-lowering and insulin-like properties. In the present review, detailed pharmacological and analytical aspects of naringenin have been presented, which revealed the impressive pharmacological profile and the possible usefulness in the treatment of different types of diseases in the future. The information provided in this communication will act as an important source for development of effective medicines for the treatment of various disorders.

Evaluation of perphenylcarbamated cyclodextrin clicked chiral stationary phase for enantioseparations in reversed phase high performance liquid chromatography

In this study, perphenylcarbamated cyclodextrin clicked chiral stationary phase (CSP) was developed with high column efficiency. The characteristics of the column were evaluated in terms of linearity, limit of detection and limit of quantification. The enantioselectivity of the as-prepared clicked CSP was explored with 26 recemates including aryl alcohols, flavanoids and adrenergic drugs in reversed phase high-performance liquid chromatography. The effect of separation parameters including flow rate, column temperature, organic modifier and buffer on the enantioselectivity of the clicked CSP was investigated in detail. The correlation study of the analytes structure and their chiral resolution revealed the great influence of analytes' structure on the enantioseparations with cyclodextrin CSP. Methanol with 1% of triethylammonium acetate buffer (pH 4) was proved to be the best choice for the chiral separation of basic enantiomers.

Cationic cyclodextrins chemically-bonded chiral stationary phases for high-performance liquid chromatography

Two covalently bonded cationic β-CD chiral stationary phases (CSPs) prepared by graft polymerization of 6(A)-(3-vinylimidazolium)-6-deoxyperphenylcarbamate-β-cyclodextrin chloride or 6(A)-(N,N-allylmethylammonium)-6-deoxyperphenylcarbamoyl-β-cyclodextrin chloride onto silica gel were successfully applied in high-performance liquid chromatography (HPLC). Their enantioseparation capability was examined with 12 racemic pharmaceuticals and 6 carboxylic acids. The results indicated that imidazolium-containing β-CD CSP afforded more favorable enantioseparations than that containing ammonium moiety under normal-phase HPLC. The cationic moiety on β-CD CSPs could form strong hydrogen bonding with analytes in normal-phase liquid chromatography (NPLC) to enhance the analytes' retention and enantioseparations. In reversed-phase liquid chromatography (RPLC), the analytes exhibited their maximum retention when the pH of mobile phase was close to their pK(a) value. Inclusion complexation with CD cavity and columbic/ionic interactions with cationic substituent on the CD rim would afford accentuated retention and enantioseparations of the analytes.

Extraction and isolation of phenolic compounds

Phenolic compounds constitute a major class of plant secondary metabolites that are widely distributed in the plant kingdom and show a large structural diversity. These compounds occur as aglycones or glycosides, as monomers or constituting highly polymerized structures, or as free or matrix-bound compounds. Furthermore, they are not uniformly distributed in the plant and their stability varies significantly. This greatly complicates their extraction and isolation processes, which means that a single standardized procedure cannot be recommended for all phenolics and/or plant materials; procedures have to be optimized depending on the nature of the sample and the target analytes, and also on the object of the study. In this chapter, the main techniques for sample preparation, and extraction and isolation of phenolic compounds have been reviewed-from classical solvent extraction procedures to more modern approaches, such as the use of molecularly imprinted polymers or counter-current chromatography.

Stereoisomeric separation of some flavanones using highly succinate-substituted α-cyclosophoro-octadecaoses as chiral additives in capillary electrophoresis

α-Cyclosophoro-octadecaoses (α-C18), produced by Rhodobacter sphaeroides, are mostly homogeneous in size with 18 glucose units per ring as the predominant form. α-C18s are linked by β-(1→4)-linkages and one α-(1→6)-linkage and are also known to be highly substituted by acetyl (0-2 per mol) and/or succinoyl groups (1-7 per mol). We isolated and purified α-C18 and successfully used it in capillary electrophoresis (CE) as a chiral additive for the separation of five flavanones and flavanone-7-O-glycosides, including naringenin, hesperetin, eriodictyol, homoeriodictyol, isosakuranetin, and hesperidin. Throughout the CE experiment with unsubstituted α-C18 (uα-C18) obtained after alkaline treatment of the isolated α-C18, we found that successful chiral separation critically depends on the presence of succinate substituents attached to α-C18 in CE, suggesting that succinoylation of α-C18 is decisive for effective stereoisomeric separation.

Production of hesperetin glycosides by Xanthomonas campestris and cyclodextrin glucanotransferase and their anti-allergic activities

The production of hesperetin glycosides was investigated using glycosylation with Xanthomonas campestris and cyclodextrin glucanotransferase (CGTase). X. campestris glucosylated hesperetin to its 3'-, 5-, and 7-O-glucosides, and CGTase converted hesperetin glucosides into the corresponding maltosides. The resulting 7-O-glucoside and 7-O-maltoside of hesperetin showed inhibitory effects on IgE antibody production and on O2- generation from rat neutrophils.