Synthesis and characterization of benzyl β-cyclodextrins used as GC stationary phases

Summary Heptakis(2,6-di-O-benzyl)-β-CD(I), heptakis(2,6-di-O-benzyl-3-O-pentyl)-β-CD(II), heptakis(2,6-di-O-benzyl-3-O-methyl)-β-CD(III) and heptakis(2,6-di-O-benzyl-3-O-acetyl)-β-CD(IV) derivatives were synthesized and identified. Their thermal stabilities were tested using PyGC. These CD derivatives are stable up to 300°C and suitable for use as gas chromatographic stationary phases. The fused silica capillary columns coated with heptakis(2,6-di-O-benzyl-3-O-methyl)-β-CD and heptakis(2,6-di-O-benzyl-3-O-pentyl)-β-CD showed excellent chromatographic properties in separating positional isomers.     

Synergistic effect of resorcarene and cyclodextrin mixed stationary phase in gas chromatography

Summary A new resorcarene derivatives, ethylhexylresorcarene, was synthesized and used as stationary phase in opentubular (capillary) columns. It was combined with heptakis(2,6-di-O-pentyl-3-O-trifluoroacetyl)-β-CD and coated on fused-silica capillary tubes. By studying the chromatographic properties of the mixed stationary phase and its selectivity for different isomers, as well as comparing with the resorcarene and the CD used as individual stationary phases, a synergistic effect was observed on the mixed stationary phase.     

3-位烯丙基及甲基衍生的β-环糊精固定相的合成及气相色谱性能研究

制备了一种新的β-环糊精衍生物固定相2,6-二-O-戊基-3-O-[(甲基)5(烯丙基)2]-β-CD,并对其气相色谱分离性能进行研究。实验显示,该固定相具有良好的柱表面性能和较强的色谱分离能力,对一些芳香族位置异构体的分离能力优于2,6-二-O-戊基-3-O-烯丙基-β-CD衍生物,对10余种手性物质显示出较好的选择性能,且对α-位取代的丙酸酯类手性分离效果明显优于杂环类β-CD衍生物。与2,6-二-O-戊基-3-O-烯丙基-β-CD固定相的分离性能比较表明,β-CD 3位羟基部分甲基基团的引入能增强对芳香族位置异构体的选择能力,但不能明显改变烯丙基衍生物的手性分离能力。     

Separation of the enantiomers of four chiral drugs by neutral cyclodextrin-mediated capillary zone electrophoresis

Summary Neutral cyclodextrin (CD)-modified capillary zone electrophoresis (CZE) has been applied to the chiral separation of four basic drugs— clorprenaline, benzhexol, esmolol and terazosin. Selector screening and concentration optimization experiments were performed. The resolution was 3.9 for clorprenaline, 2.3 for benzhexol, 3.1 for esmolol and 1.2 for terazosin when the running electrolyte was 60 mM hydroxypropyl-β-CD, 15 mM heptakis (2,3,6-Tri-O-methyl)-β-CD, 60 mM γ-CD and 60 mM heptakis (2,6-di-O-methyl)-β-CD, respectively, in 50 mM, pH 2.5 sodium phosphate buffer.     

Correlation between the chromatographic poperties of silica phenyl packing materials and the retention behaviour of methylated β-cyclodextrins

Summary The chromatographic properties of five columns packed with phenyl-bonded phases were characterized by an approach based on Tanaka's method for column to column comparisons in order to develop an LC analysis of partially methylated β-cyclodextrins. The retention behaviour of β-cyclodextrin, heptakis(2,6-di-O-methyl)-β-cyclodextrin and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin was examined in order to evaluate the different interactions between phenyl stationary phase and this family of compound. Chromatograms show that the residual silanol activity of the packing materials plays a beneficial role in the partially methylated β-cyclodextrins separation process. It is concluded that knowledge of the interactions involved allows one to make a reasoned choice of the stationary phase in order to obtain the best possible analysis of three different commercial samples of partially methylated β-cyclodextrins.     

Synergistic effects in mixed gas chromatographic stationary phases containing hepatkis(2.3.6-tri-O-pentyl)-β-cyclodextrin and AgNO3 or TINO3 in the separation of xylene isomers

Summary The gas chromatographic separation of xylene isomers using special mixed stationary phases consisting of heptakis(2.3.6-tri-O-pentyl)-β-CD-AgNO₃, heptakis (2.3.6-tri-O-pentyl)-β-CD-TINO₃ or bentone-34-AgNO₃ is investigated. The first two have positive synergistic effects for the separation of m, and p-xylene isomers, but negative synergistic effects for the m, and oisomers. The separation effects depend on temperature, mixing ratio and how mixing is accomplished.     

Enantiomeric separation of racemic sulphoxides on chiral stationary phases by gas and liquid chromatography

Summary The enantiomeric resolution of seven racemic sulphoxides on chiral stationary phases has been investigated by gas and liquid chromatography. In gas chromatography the separations were performed on octakis-(2,6-di-O-pentyl-3-O-butyryl)-γ-cyclodextrin (FS Lipodex-E) and heptakis-(2,6-di-O-methyl-3-O-pentyl)-β-cyclodextrin (DMP-β-CD). Both stationary phases were suitable for separation of the enantiomers of the sulphoxides. With one exception for each series all racemetes could be resolved on both stationary phases; FS Lipodex-E was more enantioselective than DMP-β-CD, whereas the latter seemed more generally applicable. Liquid chromatographic separations with Chiralcel-OB as stationary phase were significantly improved by optimization of mobile phase composition and temperature. Resolution factors up to R_s=6 were achieved indicating that the improved separations could now be easily used for preparative purposes.     

溶胶-凝胶法制备四种环糊精衍生物毛细管气相色谱柱

采用溶胶-凝胶法制备了七(2,3,6-三-O-乙基)-β-环糊精(全乙基-β-CD)、七(2,3,6-三-O-丙基)-β-环糊精(全丙基-β-CD)、七(2,3,6-三-O-辛基)-β-环糊精(全辛基-β-CD)和2,6-二-O-苄基-β-CD 4种环糊精衍生物毛细管气相色谱柱。在制备方法上,仿照一般动态法,大大简化了制备过程,缩短了制备时间。所得色谱柱的理论塔板数在3000/m左右,能够很好地分离苯衍生物的位置异构体,尤其对难分离的二甲苯、甲酚等取得了理想效果(α＞1),其中溶胶-凝胶法制备的全烷基(乙基、丙基、辛基)化环糊精衍生物柱的分离能力优于2,6位苄基衍生化的环糊精柱。 同一根柱不同次进样和不同柱之间表现出良好的重复性,保留时间的相对标准偏差小于8.5%;对使用大约40次后的溶胶-凝胶柱重新进行测试,柱效下降不明显,说明该类色谱柱的稳定性良好。     

Binary Systems of Nifedipine And Various Cyclodextrins in The Solid State. Thermal,FTIR, XRD studies

Nifedipine complexes with β-cyclodextrin (β-CD), γ-cyclodextrin (γ-CD), 2-hydroxypropyl-β-cyclodextrin (2HP-β-CD), randomly methylated-β-cyclodextrin (RM-β-CD) and heptakis(2,6-O-dimethyl)-β-cyclodextrin (DM-β-CD) have been prepared by both kneading and heating methods and their behaviour studied by differential scanning calorimetry (DSC), diffuse reflectance mid-infrared spectroscopy (FTIR) and X-ray diffractometry (XRD). DSC revealed the nifedipine melting endotherm with onset at approximately 171°C for the kneaded mixtures with β-CD, γ-CD and 2HP-β-CD, thus confirming the presence of nifedipine in the crystalline state, while some decrease in crystallinity was observed in the DM-β-CD kneaded mixture. With RM-β-CD, however, broadening and shifting of the nifedipine endotherm and reduction in its intensity suggested that the kneading could have produced an amorphous inclusion complex. These differing extents of interaction of nifedipine with the cyclodextrins were confirmed by FTIR and XRD studies. This revised version was published online in August 2006 with corrections to the Cover Date.     

一种苄基取代的环糊精衍生物的合成及其气相色谱性能研究

合成了一种苄基取代的环糊精衍生物2,6-二-O-戊基-3-O-苄基-β-CD,研究了其气相色谱分离性能,发现此固定相涂渍性好,极性适中,是一种良好的气相色谱固定相,对甲酚、二甲苯等难分离的二取代苯的位置异构体具有良好的分离能力.2,6-二-O-戊基-3-O-苄基-β-CD因其特有的空腔结构,具有比OV-225更好的分离性能.     

A novel compound from <Emphasis Type="Italic">Flos carthami</Emphasis> and its bioactivity

A novel compound, 4-{1′-hydroxy-1′-mercapto-1′-[1′′-2′′(N→O)-isoquinolyl]}yl-1-benzoic acid (1), together with six known compounds, 6-hydroxykaempferol-3-O-β-D-glucopyranoside (2), rutin (3), quercetin-3-O-β-D-glucopyranoside (4), kaempferol-3-O-β-D-glucopyranoside (5), cartormin (6), hydroxysafflor yellow A (7), were isolated by chromatography from the n-BuOH fraction of 50% ethanol extraction of Flos carthami. Their structures were elucidated on the basis of spectral analysis and comparison with published data. Among them, compound 1 was shown to possess a weak protective effect against cerebral ischemic damage in rats. Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 339–341, May–June, 2009.     

A new cerebrogalactoside from <Emphasis Type="Italic">Juglans mandshurica</Emphasis>

A new cerebrogalactoside, Juglans cerebroside A (1), together with five known compounds, quercetin-3-O-β-D-galactopyranoside (2), myricetin-3-O-β-D-galactopyranoside (3), 2″E-quercetin-3-O-β-D-(6″″-O-[3″(4′″-hydroxyphenyl) propylene acyl]) glucopyranoside (4), gallic acid (5), and 2-methyl-1-hexadecanol (6) were isolated from the leaves of Juglans mandshurica Maxim. The structures of these compounds were determined by 1D, 2D NMR, and MS techniques.     

The role of β-cyclodextrin and hydroxypropyl β-cyclodextrin in the secondary chemical equilibria associated to the separation of β-carbolines by HPLC

The use of cyclodextrins (CDs) in HPLC as mobile phase additives provides a flexible alternative for the separation of chemically related compounds because these separations can be performed on conventional columns and are economically advantageous over the use of chiral stationary phases. The present paper describes the influence of the presence of β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HPβ-CD) on the separation of the β-carboline alkaloids norharmane, harmane and harmine. The nature of the stationary phase (reverse phases C₁ and C₁₈) affects the chromatographic separations and also the stability of the inclusion complexes that are developed. The changes in the proportion of the organic solvents at constant concentration of CDs (3 mM for β-CD and 15 mM for HPβ-CD) modify the retention factors (k′) for all alkaloids studied. The nature of the organic solvent in the mobile phase also changes the chromatographic parameters. The logarithm of the capacity factor (k′) is linearly increased with the proportion of water in the hydro-organic mobile phase (ethanolic or methanolic) but the slopes obtained vary depending on the CD added to the mobile phase. The role of competitive equilibria, i.e., chromatographic distribution and inclusion complexes formation is discussed. This paper was presented at XIIIth International Cyclodextrin Symposium. Torino, Italy, May, 14–17, 2006     

A host-guest optical sensor for aliphatic amines based on lipophilic cyclodextrin

A host-guest optical sensor for the determination of aliphatic amines as exemplified by octylamine is proposed. It is based on the reversible fluorescence enhancement of heptakis(2,6-di-O-isobutyl)-β-cyclodextrin(DOB-β-CD) hosting tetraphenylporphyrin (TPP) immobilized in poly(vinyl chloride) (PVC) membrane by aliphatic amine extracted from aqueous phase into membrane phase. The optimum membrane contained 1.15 wt % TPP, 6.15 wt % DOB-β-CD as sensing reagent and other membrane materials. The fluorescence enhancement of the membrane resulted from the formation of a stable three-component complex among DOB-β-CD, TPP, and aliphatic amines. With the optimum conditions described, the fluorescence response of the sensor to octylamine shows a good correlation with the theoretically derived equation in the range 1.0 × 10^–6 to 8.0 × 10^–4 mol/L. The response characteristics including reversibility, response time, reproducibility and lifetime and selectivity of this optical device are also discussed in detail. This sensor has also been applied for the determination of octylamine in water samples containing interferents with satisfactory recovery. Received: 21 November 1999 / Revised: 10 January 2000 / Accepted: 15 January 2000     

New steroidal glycosides from the stem bark of <Emphasis Type="Italic">Mimusops elengi</Emphasis>

Two new steroidal glycosides (1 and 2) have been isolated from the ethanolic extract of the stem bark of Mimusops elengi L. and characterized as stigmasta-5,22-dien-3β-ol-3β-D-glucuropyranosyl-(6′β→1″)-D-glucopyranoside (1) and β-sitosterol-3β-(3″′,6″′,7″′-trihydroxynaphthyl-2″′-carboxyl)-4″-glucopyranosyl-(1″→4′)-glucopyranoside (2) along with the known compounds stigmasta-5-en-3β-ol, lup-20(29)-en-3β-ol, and stigmasta-5-en-3β-D-glucopyranoside. Their structures have been elucidated on the basis of spectral data analysis and chemical reactions.     

Mechanistic studies on cationic ring-opening polymerisation of cyclodextrin derivatives using various Lewis acids

In order to investigate the potential of cyclodextrins for the preparation of block-like substituted polysaccharides, we submitted mixtures of heptakis[2,3,6-tri-O-methyl]-β-cyclodextrin (Me₂₁-β-CD, 1) and heptakis[2,3,6-tri-O-methyl-d ₃]-β-cyclodextrin ((Me-d ₃)₂₁-β-CD, 2) to cationic ring-opening polymerisation (CROP). Reactions were performed with BF₃·OEt₂, methyl triflate (MeOTf), and Et₃OSbCl₆. Products were compared with respect to their degree of polymerisation (DP) and the average block length (BL). Highest DP was observed with BF₃·OEt₂, while Et₃OSbCl₆ was the most active initiator. Average block length decreased from 14 in the early stage of product formation to about 2 due to competing chain transfer reaction. ¹H NMR spectroscopy, GLC, GLC–MS, ESI-MS and MALDI-TOF-MS were applied for detailed investigations of side reactions. During incubation with BF₃·OEt₂, a stereroisomeric β-CD with one β-glucosidic linkage (Me₂₁-β-CD_6α1β, 3a (Me-d ₃)₂₁-β-CD_{6α 1β}, 3b) is formed as an intermediate, while linear Me₂₁- and (Me-d ₃)₂₁-maltoheptaose (4a/b) was detected in the early stage of the reaction promoted by MeOTf. In the case of Et₃OSbCl₆, both intermediates (3a/b, 4a/b) can be observed during the lag phase of polymerisation, but to a very low degree. End group analysis by GLC reveals that some alkyl exchange occurs at position 3 and 6 in the presence of Et₃OSbCl₆, and that polymerisation is also initiated by protons. Copolymerisation of heptakis[2,3,6-tri-O-benzyl]-β-cyclodextrin (Bn₂₁-β-CD, 5) and Me₂₁-β-CD (1) and subsequent debenzylation yielded a polymer of only 1,4-glcp-Me₃- and 1,4-glcp-residues. Reactivity of Bn₂₁-β-CD was significantly lower than of Me₂₁-β-CD, resulting in higher average block length of 1,4-glcp-Me₃-units.     

Ethylenediaminetetraacetic acid (EDTA) as an auxiliary tool in the electrospray ionization mass spectrometry analysis of native and derivatized β-cyclodextrins,maltoses, and fructans contaminated with Ca and/or Mg

The effect of Ca²⁺ (and Mg²⁺) and the disodium salt of ethylenediaminetetraacetic acid (EDTA), a well known Ca²⁺ (and Mg²⁺) chelating agent, on the volatilization/ionization of carbohydrates by using electrospray ionization mass spectrometry has been studied. Model compounds such as maltoses (maltose to maltoheptaose), β-cyclodextrins (β-cyclodextrin, methyl-β-cyclodextrin, heptakis(2,6-di-O-methyl)-β-cyclodextrin, heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin, and 2-hydroxypropyl-β-cyclodextrin) and fructans (sucrose, 1-ketose, nystose, and 1F-fructofuranosylnystose) were used.     

Complexation of Ketoconazole by Native and Modified Cyclodextrins

Complexation of ketoconazole (KET), a broad-spectrum antifungal drug, with β- and γ-cyclodextrins (CDs), heptakis (2,6-di-O-methyl)-β-CD (2,6-DM-β-CD), heptakis (2,3,6-tri-O-methyl)-β-CD (TM-β-CD), 2-hydroxypropyl-β-CD (2HP-β-CD) and carboxymethyl-β-CD (CM-β-CD) was studied. The stability constants were determined by the solubility method at pH = 6 and for 2,6-DM-β-CD and CM-β-CD at pH = 5. At pH = 6, the stability constants increased in the order: TM-β-D < γ-CD < 2HP-β-CD < β-CD < CM-β-CD < 2,6-DM-β-CD. At pH = 5, due to the increased ionization of KET, the stability constant with CM-β-CD increased and with 2,6-DM-β-CD decreased. For complexes of KET with 2HP-β-CD and 2,6-DM-β-CD, the thermodynamic parameters of complexation were determined from the temperature dependence of the corresponding stability constants. For β–γ and TM-β-CD complexes, calculations using HyperChem 6 software by the Amber force field were carried out to gain some insight into the host–guest geometry.     

Inclusion complexes of 2-phenoxyethanol and alkoxyethanols in cyclodextrins: an 1H NMR study

The association in aqueous solutions of small amphiphilic molecules [2-phenoxyethanol, PhE₁, and some α-n-alkyl-ω-hydroxyoligo(oxiethylenes], C₄E₁, C₄E₂ and C₆E₂) with β-cyclodextrin (βCD), heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TRIMEB) was investigated by ¹H NMR spectroscopy. The upfield shifts observed for the H3 and H5 NMR signals due to anisotropic shielding confirm that the host–guest associations are of inclusion type. The stoichiometries and the apparent inclusion constants, K _app, were determined by ¹H NMR spectroscopy using the H5 and H3 signals. The relative differences in the K _app values for βCD inclusion complexes seem to reflect the hydrophobic/hydrophilic balance of the guests. The K _app values for the PhE₁ inclusion complexes can be related to the degree of methylation and hydrophobicity variation within the considered hosts. In addition, a comparative study between βCD and TRIMEB inclusion complexes using 2D ROESY (Rotating-frame Overhauser Enhancement SpectroscopY) NMR spectra provides structural features for these complexes which are inaccessible by other experimental methods.     

A new gas chromatographic stationary phase: Polysiloxane with β-cyclodextrin side chain for the separation of chiral and positional isomers

Summary A new stationary phase [bikis(2,6-di-O-pentyl-3-O-hex-6-enyl)-pentakis(2,6-di-O-pentyl-3-O-methyl)-β-CD-polysiloxane] was synthesized and successfully applied in GC for the separation of chiral and achiral isomers. It possesses high column efficiency and exhibits excellent separation ability for disubstituted benzenes. Some typical enantiomers and optical isomers are well separated. The separation behavior of this new phase is characterized and discussed.