Novel stationary phases for high-performance liquid chromatography analysis of cyclodextrin derivatives

Novel stationary phases were prepared for separation of cyclodextrins and cyclodextrin derivatives by bonding substituted aromatic groups (phenyl and naphthyl) to the silica gel matrix. Both the electron-withdrawing (nitro) and the hydrogen-donor/acceptor (amide or carbamide) substituents of the phenyl group play essential role in the separation of cyclodextrins and cyclodextrin derivatives. On the basis of the comparison of experimental data obtained on different columns the N-(4-nitrophenyl)-carbamide group bonded silica gel stationary phase was selected as the most effective one for analysis of cyclodextrin derivatives. Improved separation potency was observed for hydroxypropylated, methylated and several other cyclodextrin derivatives compared with the previously and presently used stationary phases. Owing to the strong retention of cyclodextrins and its derivatives on the selected column, detection of their decomposition products was easily achieved. Determination of unsubstituted, natural cyclodextrin as an impurity in the cyclodextrin derivatives was implemented. Identification and characterization of cyclodextrin derivatives in industrial products could also be performed.     

Photocontrolled release and uptake of a porphyrin guest by dithienylethene-tethered beta-cyclodextrin host dimers

Two photoswitchable dithienylethene-tethered beta-cyclodextrin dimers were synthesized to function as host molecules with an externally controllable binding affinity. The cyclodextrin cavities of these dimers are linked through their secondary sides by a photochromic dithienylethene unit that is connected to the secondary rim either directly (4) or through propyl spacers (9). Irradiation with light switches these dimers between a relatively flexible (open) and a rigid (closed) form. The binding properties of the dimers depend on the configuration of the dithienylethene spacer, as is shown by microcalorimetry performed with tetrakis-sulfonatophenyl porphyrin (TSPP) as a guest molecule. The differences in binding properties are most pronounced for the more rigid dimer 4, which binds TSPP 35 times more strongly in the open form (4 a) than in the closed form (4 b). The values found for the enthalpy of binding (deltaH degrees ) indicate that this difference in binding is due to the loss of cooperativity between the two beta-cyclodextrin cavities in the closed form. Molecular modeling shows that 4 b is not able to bind TSPP effectively in both cyclodextrin cavities. The open and closed forms of the more flexible dimer 9 show no substantial difference in their binding of TSPP. Thermodynamic values indicative of strong binding of TSPP by two beta-cyclodextrin cavities were measured for both forms of the dimer, and molecular modeling confirms that both are flexible enough to tightly bind TSPP. The binding differences between the forms of dimer 4 allow the photocontrolled release and uptake of TSPP, which renders control of the ratio of complexed to free TSPP in solution possible.     

Aliphatic Poly(ether amide)s by Polycondensation of Activated Sebacic Acid Derivatives

Poly(ether amide)s were prepared by polycondensation of 1,13‐diamino‐4,7,11‐trioxatridecane (DTT) with the bisimidazolide or with the bis N‐hydroxysuccinimide ester of sebacic acid. Four different solvents and three different temperatures were compared. The highest molecular weights were obtained with the bisimidazolide in dimethylsulfoxide (DMSO) at 60°C. MALDI‐TOF mass spectra revealed the existence of cyclic oligoamides and polyamides in all samples. The molar fraction of cycles considerably increased with higher molecular weights of the entire sample. The polycondensations were repeated under optimum conditions in the presence of α‐cyclodextrin to prepare polydisperse catenanes consisting of α‐cyclodextrin threaded on cyclic polyamides. Yet, despite broad variation of the reaction conditions, only cylic polyamides free of cyclodextrin were isolated. Furthermore, a pseudorotaxane was prepared from DTT and α‐cyclodetrin and polycondensed with bis‐(4‐chlorophenyl)sebacate. Again, only cyclic polyamides free of cyclodextrin were detectable.     

Use of Chemically Bonded β‐Cyclodextrin Silica Stationary Phase for Liquid Chromatographic Separation of Structural Isomers

The retention behavior of five disubstituted benzene derivatives and two naphthalene derivatives is examined by using a chemically bonded β‐cyclodextrin silica stationary phase with the moiety containing the s‐triazine. The chromatographic results of five disubstituted benzene derivatives and two naphthalene derivatives show that effective separation is achieved on this stationary phase by high‐performance liquid chromatography. The results of the present investigation indicate that the formation of inclusion complexes plays a dominant role in the separation mechanism. However, the selectivity can be significantly enhanced by the n‐n interactions between the s‐triazine ring of the chemically bonded β‐cyclodextrin silica stationary phase and the aromatic ring of solutes. For example, the effective separation of the o‐, m‐, and p‐toluidine isomers on this stationary phase with the moiety containing the s‐triazine ring was better than on that of some β‐cyclodextrin bonded stationary phases without the moiety containing s‐triazine ring.     

Use of various β‐cyclodextrin derivatives as chiral selectors for the enantiomeric separation of ofloxacin and its five related substances by capillary electrophoresis

A capillary electrophoretic method for the enantioseparation of ofloxacin and its five related substances (potential impurities, indicated as impurities B–F) was developed using β‐cyclodextrin derivatives as chiral selectors. To our knowledge, there are no previous studies about using capillary electrophoresis for the separation of impurities B–D. Six β‐cyclodextrin derivatives including cationic (piperidine‐ and cyclohexylamine‐), neutral (dimethyl‐ and hydroxypropyl‐), and anionic (carboxymethyl‐ and sulfated‐) β‐cyclodextrin derivatives were tested and operational parameters such as buffer pH and concentration of β‐cyclodextrin derivatives were investigated. The best resolutions were all obtained with anionic β‐cyclodextrin derivatives: ofloxacin, impurities C–F could be best resolved with carboxymethyl‐β‐cyclodextrin at satisfactory resolutions of 8.27, 9.98, 5.92, 8.49 and 6.78, respectively, while for impurity B, a particularly impressive resolution value, up to 21.38, was observed using sulfated‐β‐cyclodextrin. The enhancement of enantioseparation observed for the tested analytes using anionic β‐cyclodextrin derivatives might be due to some favorable interaction between selectors and analytes. Given the fact that the selection of chiral selector depends on the structures of analytes, with the help of structural similarities and differences of the analytes, the structure–separation relationship was further discussed.     

Chiral separation of cathinone derivatives using β‐cyclodextrin‐assisted capillary electrophoresis–Comparison of four different β‐cyclodextrin derivatives used as chiral selectors

In the past decade, more than 100 different cathinone derivatives slopped over entire Europe due to their enormous popularity. Generally, these novel psychoactive substances are easily available via the internet. This fact leads to various social problems, since cathinones are substances with consciousness‐changing effects and are mainly misused for recreational matters by their consumers. Cathinones possess a chiral center including two enantiomeric forms with potentially different pharmacological behavior. This fact makes analytical method development regarding their chiral separation indispensable. In this study, a chiral capillary zone electrophoresis method for the enantioseparation of 61 cathinone and pyrovalerone derivatives was developed by means of four different β‐cyclodextrin derivatives. As chiral selectors, native β‐cyclodextrin as well as three of its derivatives namely acetyl‐β‐cyclodextrin, 2‐hydroxypropyl‐β‐cyclodextrin, and carboxymethyl‐β‐cyclodextrin were used. The cathinone and pyrovalerone derivatives were either purchased in internet stores or seized by police. As a result, overall 58 of 61 studied substances were partially or baseline separated by at least one of the four chiral selectors using 10 mM of β‐cyclodextrin derivative in a 10 mM sodium phosphate buffer (pH 2.5). Furthermore, the method was found to be suitable for simultaneous enantioseparations, for enantiomeric purity checks and to differentiate between positional isomers. Moreover, an intra‐ and an interday validation was performed successfully for each chiral selector to prove the robustness of the method.     

New cyclodextrin derivatives as chiral selectors in capillary electrophoresis

The separation of three pairs of enantiomeric herbicides has been successfully achieved by capillary electrophoresis at two different pH values in the presence of cyclodextrin derivatives previously synthesized in our laboratory. Two of these derivatives constitute a new class of receptor, the hemispherodextrins, in which a trehalose capping moiety is bonded to beta-cyclodextrin. Because of their peculiar structure hemispherodextrins have very promising characteristics and the low receptor concentration required to achieve separation deserves particular interest.     

New cyclodextrin derivatives as chiral selectors in capillary electrophoresis

The separation of three pairs of enantiomeric herbicides has been successfully achieved by capillary electrophoresis at two different pH values in the presence of cyclodextrin derivatives previously synthesized in our laboratory. Two of these derivatives constitute a new class of receptor, the hemispherodextrins, in which a trehalose capping moiety is bonded to β-cyclodextrin. Because of their peculiar structure hemispherodextrins have very promising characteristics and the low receptor concentration required to achieve separation deserves particular interest.     

荧光标识的环糊精二聚体与小肽衍生物之间的包合行为研究

报道了利用荧光偏振方法研究导硫氰酸盐荧光素（FITC）标识,并由天冬氨酸 、谷氨酸、(1R, 3R)-1-氨基-1,3-二羟基环丁烷和（1R, 3R）-1-氨基-1,3-二 羟基环戊烷衍生物桥联的环糊精二聚体（1～4,作为主体）,在pH = 7.4的水溶液 中与几个低分子量的多肽衍生物:Adm-Lys(Adm)-Arg-Arg 5; Adm-Lys(Adm)-D-Arg- D-Arg 6; Adm-Cha-Arg-Arg 7; Adm-Cha-D-Arg-D-Arg 8（作为客体,其中Arg, Lys, Cha和Adm分别为精氨酸,赖氨酸,β-环已烷丙氨酸和1-羟基金刚烷）之间 的键合常数（K_b)和包合反应的热力学参数（△G°,△H°,△S°）。从主-客体 键合常数的比较、客体嵌入基团的结构与周边环境的考察发现,主、客体之间的键 合能力因客体非进入基团（Arg)空间构型上的变化而有所不同。通过比较主体包结 一对手性异构体的自由能变化增量（-△△G_(DL)°）以及一对手性异构体（L-与 D-）与同一主体的键合常数之比（K_L/K_D),讨论了环糊精二聚体对D-型或L-型多 肽衍生物的手性识别能力。根据各体系T△S°与△H°之间较好的线性关系,探讨 了环糊精二聚体与多肽衍生物之间相互作用的焓-熵补偿行为。     

Crystal Structures of β‐Cyclodextrin Inclusion Complexes with 7‐Hydroxycoumarin and 4‐Hydroxycoumarin and Substituent Effects on Inclusion Geometry

Two inclusion complexes of β‐cyclodextrin‐7‐hydroxycoumarin ( 1 ) and β‐cyclodextrin‐4‐hydroxycoumarin ( 2 ) were prepared and their crystal structures were investigated by single crystal X‐ray crystallography under cryogenic condition. Both structures consist of stacks of face‐to‐face cyclodextrin dimers arranged in brickwork‐like pattern along the crystallographic a‐axis. For complex 1 , each of the two dimeric β‐cyclodextrins includes one 7‐hydroxycoumarin molecule that penetrates deeply into the cyclodextrin dimer and locates its lactonering at the center of the dimer cavity. For complex 2 , each cyclodextrin dimer accommodates three 4‐hydroxycoumarin molecules. One of them is sandwiched between two units of the cyclodextrin dimer, the other two are shallowly included in the cavities of the dimeric cyclodextrins respectively and protrude their lactone rings from the primary end of the cyclodextrin. The substituent effects of guest molecules on inclusion geometry of various coumarin molecules in β‐cyclodextrin were examined.     

Synthesis of Terpyridine Derivatives Containing β—Cyclodextrin

A novel β-cyclodextrin-based terpyridine derivatives has been prepared by the coupling of 4‘‘‘‘‘‘‘‘-(4“-bromomethyl phenyl)-2,2‘‘‘‘‘‘‘‘:6‘‘‘‘‘‘‘‘,2“-terpyridine with mono-6-hydroxy permethylated β-cyclodextrin.The cyclodextrin dimmer appending a 4‘‘‘‘‘‘‘‘-phenyl-2,2‘‘‘‘‘‘‘‘:6‘‘‘‘‘‘‘‘,2“-terpyridine spacer on the primary faces was synthesized by reaction of 4‘‘‘‘‘‘‘‘-phenyl-2,2‘‘‘‘‘‘‘‘:6‘‘‘‘‘‘‘‘,2“-terpyridine-6,6‘‘‘‘‘‘‘‘-dicarbonitrile with an excess of 6-deoxy-6-O-tosyl-β-cyclodextrin.     

Synthesis of a novel cyclodextrin dimer linked by a macrocyclic polyamine

The first example of cyclodextrin dimer appending a macrocyclic polyamine spacer on the primary faces was synthesized via two approaches: 1,a direct reaction of l,7-bis(2'-aminoethyl)-4,10-dimethyl-l,4,7,10-tetraazacyclododecane (1) with an excess of 6-deoxy-6-O-tosyl-β-cyclodextrin; 2,a condensation of 1 with two equivalents of 6-deoxy-6-formyl-β-cyclodextrin,which was followed by a reduction with NaBH4.     

Retention behavior of bile acid derivatives using cyclodextrin in the mobile phase in high-performance liquid chromatography

The retention behavior of 3-(1-anthroyl)bile acids together with bile acid glucuronides, sulfates, and 12-dehydro derivatives is examined by the addition of cyclodextrin to the mobile phase in reversed-phase high-performance liquid chromatography. The data suggest that the functional group at the 12 position of the steroid moiety may be the important factor for the formation of the inclusion complex from the solute and cyclodextrin. The separation of these bile acid derivatives is much improved by this inclusion chromatography.     

Chiral separation of brompheniramine enantiomers by recycling high‐speed countercurrent chromatography using carboxymethyl‐β‐cyclodextrin as a chiral selector

A recycling high‐speed countercurrent chromatography protocol was proposed for the enantioseparation of brompheniramine by employing β‐cyclodextrin derivatives as a chiral selector. The two‐phase solvent system of n‐hexane/isobutyl acetate/0.10 mol/L phosphate buffer solution with a volume ratio of 2:4:6 was selected by a series of extraction experiments. Factors that affected the distribution of the enantiomers over the two‐phase system (e.g., the type and concentration of β‐cyclodextrin derivatives = pH value of the aqueous solution, and the separation temperature) were also investigated. In addition, the theory of thermodynamics is applied to verify the feasibility of the enantioseparation process and the corresponding results demonstrate that this separation process is feasible. The optimized conditions include carboxymethyl‐β‐cyclodextrin concentration of 0.010 mol/L, pH of 7.5, and temperature of 5°C. Under the optimal conditions, the purities of both monomer molecules were over 99%, and the recovery yields were 88% for (+)‐brompheniramine and 85% for (–)‐brompheniramine, respectively.     

Study on clarithromycin lactobionate based dual selector systems for the enantioseparation of basic drugs in capillary electrophoresis

In this paper, the use of clarithromycin lactobionate, a kind of antibiotic chiral selector, in combination with four neutral cyclodextrin derivatives (glucose‐β‐cyclodextrin, hydroxyethyl‐β‐cyclodextrin, methyl‐β‐cyclodextrin and hydroxypropyl‐β‐cyclodextrin) was reported for the first time. As a result, these dual systems gave much better resolution of nefopam (the Rs increased to 3.58, 2.72, 1.49 and 1.42, respectively) compared to the single systems. The effects of buffer pH and selector concentration on the separation of nefopam were also investigated. Additionally, some other basic drugs including metoprolol, atenolol, propranolol, bisoprolol, esmolol and ritodrine were tested for the investigation and evaluation of the enantiorecognition capability of the four dual systems. As expected, the synergistic effect was observed in four systems. Different results of these dual systems were also summarized.     

Comparison of Different Di‐tert‐butyldimethyl‐Silylated Cyclodextrins as Chiral Stationary Phases in Capillary Gas Chromatography

Separation factors and thermodynamic data for the separation of various chiral analytes on different di‐O‐tert‐butyldimethyl‐silylated cyclodextrin derivatives are collected and described. Modifying the substitution pattern of the tert‐butyldimethylsilyl group in position 2 and 3 or changing from β‐ to γ‐cyclodextrin significantly affects the separation properties of the cyclodextrin derivatives.     

Bonded Cyclodextrin Stationary Phase Columns for the Separation of Cis/Trans Cyclohexane Derivatives

Abstract

Cyclohexane derivatives are important in the manufacture of monomers for the preparation of polyester polymers. The separation of cis/trans isomers of these derivatives has been investigated by using a bonded cyclodextrin column. This stationary phase offers excellent selectivity for the separation of these compounds. Although the efficiency of this column with the cyclohexane derivatives is less than the efficiency with nitroanalines, its excellent selectivity enabled adequate separation of the isomers of all but one of the compounds studied. A strategy for enhancing the efficiency and selectivity of this stationary phase is presented.     

Retention behavior of cardiac steroids using cyclodextrin in the mobile phase in high-performance liquid chromatography

The retention behaviour of twenty cardiac steroids and four fluorescent derivatives was examined by the addition of cyclodextrin to the mobile phase in reversed-phase high-performance liquid chromatography. The addition of a suitable cyclodextrin improved the separation of isomeric cardiac steroids. The steroid A/B ring junction is the most important factor in the choice of the optimum cyclodextrin to be added; the C/D ring junction is less important. The hydroxyl group at the 3- or 12-position of the steroid enhanced the changes in retention times of these compounds. The effect of an unsaturated lactone ring at the 17 beta-position on the retention in the presence of cyclodextrin was also determined with cardenolide (five-membered ring) and bufadienolide (six-membered ring) but little difference was observed. Isomeric cardiac steroids, whose separation has not been done by the conventional method, were clearly separated by this method. The fluorescence intensity of 3-(1-anthroyl)-cardiac steroid was enhanced by the addition of cyclodextrin to the mobile phase.     

A facile synthesis of novel types of cyclodextrin derivatives by insertion of an aromatic dicarbonyl spacer into a permethylated alpha-cyclodextrin skeleton

Novel types of cyclodextrin derivatives are easily synthesized by the insertion of an aromatic dicarbonyl spacer into the skeleton of permethylated alpha-cyclodextrin, and the isophthaloyl-inserted one shows almost the same complexing ability toward p-nitrophenol as permethylated beta-cyclodextrin.     

Taxol Inclusion Complexes with a Cyclodextrin Dimer: Possibilities to Detoxify Chemotherapeutics and to Target Drugs Specifically to Tumors?

The natural drug, paclitaxel (taxol), is highly effectiveas a tumor chemotherapeuticwith a low probability of inducing chemoresistance,but shows severe toxic side effectsat the therapeutic dose. How can this toxicitybe overcome? Here we report the synthesisof cyclodextrin dimers connected at thesecondary face by amide-bonded aliphatic spacers. The spacer length of one of the dimers referred to asdiβCD(2N-A4C5A4) or dimer 7cmatches the distance between the twobenzoic acid residues of paclitaxel. We investigated the physical inclusion of taxol into this dimer using the TNS-label competition method. Affinity constants with the dimer in comparison to free β-cyclodextrin are found to be of the order of 10⁷ l/mole.When included into the cyclodextrin dimer, the drug shows a considerable time delay of incorporation into human tumor cell cultures (OAT SCLC cells) or a total exclusion from the cells. This is the prerequisite to avoid intoxication of other organs of a patient. Possibilities are discussed to detoxify chemotherapeutics and to target their inclusioncomplexes specifically to tumors using specific biological signals.