Cyclodextrins modified

Figure 3.7 [continued) (b) Chromatograms of (iii) the dichloromethane extract of strawberry fruit yoghurt analysed with an apolar primary column, with the heart-cut regions indicated, and (iv) a non-racemic mixture of y-deca-(Cio) and 7-dodeca-Cj2 lactones isolated by heart-cut transfer, and separated by using a chiral selective modified cyclodextrin column. Reproduced from A. Mosandl, et al J. High Resol. Chromatogr. 1989, 12, 532 (39f. 

It is in the study of this phenomenon where two-dimensional GC offers by far the most superior method of analysis. The use of chiral selector stationary phases, in particular modified cyclodextrin types, allows apolar primary and atropisomer selective secondary separation. Reported two-dimensional methods have been successful... 

The problem of molecular recognition has attracted biologically oriented chemists since Emil Fischer s lock-and-key theory l0). Within the last two decades, many model compounds have been developed micelle-forming detergents11, modified cyclodextrins 12), many kinds of crown-type compounds13) including podands, coronands, cryptands, and spherands. Very extensive studies using these compounds have, however, not been made from a point of view of whether or not shape similarity affects the discrimination. 

Several model systems related to metalloenzymes such as carboxypeptidase and carbonic anhydrase have been reviewed. Breslow contributed a great deal to this field. He showed how to design precise geometries of bis- or trisimidazole derivatives as in natural enzymes. He was able to synthesize a modified cyclodextrin having both a catalytic metal ion moiety and a substrate binding cavity (26). Murakami prepared a novel macrocyclic bisimidazole compound which has also a substrate binding cavity and imidazole ligands for metal ion complexation. Yet the catalytic activities of these model systems are by no means enzymic. 

N. A. Konig, "Enantioselective Gas Chromatography With Modified Cyclodextrins , Huethig, Heidelberg, 1991. 

These interesting results are attributed to the formation of an alkene/ cyclodextrin inclusion complex as well as the solubility of the chemically modified cyclodextrin in both phases. Prior to this study, hydroformylation in the presence of unmodified cyclodextrins had been studied by Jackson, but the results were rather disappointing.174... 

Moriya T, Saito K, Kurita H, Matsumoto K, Otake T, Mori H, Morimoto M, Ueba N, Kunita N. A new candidate for an anti-HIV-1 agent modified cyclodextrin sulfate (mCDS71). J Med Chem 1993 36 1674-1677. 

Otake T, Schols D, Witvrouw M, Naesens L, Nakashima H, Moriya T, Kurita H, Matsumoto K, Ueba N, De Clercq E. Modified cyclodextrin sulphates (mCDSll) have potent inhibitory activity against HIV and high oral bioavailability. Antiviral Chem Chemother 1994 5 155-161. 

Custom-made column with a 1 1 mixture modified cyclodextrin and OV-1701. j Chiralcel OJ-R. 

Pun SH, Tack F, Bellocq NC, Cheng J, Grubbs BH, Jensen GS, Davis ME, Brewster M, Janicot M, Janssens B, Floren W, Bakker A (2004) Targeted delivery of RNA-cleaving DNA enzyme (DNAzyme) to tumor tissue by transferrin-modified, cyclodextrin-based particles. Cancer Biol Ther 3 641-650... 

Another chiral stationary phase is modified cyclodextrin. Cyclodextrins are cyclic chiral carbohydrates composed of six, seven, or eight glucopyranose... 

Many chiral compounds can be used as selectors, for example, chiral metal complexes, native and modified cyclodextrins, crown ethers, macrocyclic antibiotics, noncyclic oligosaccharides, and polysaccharides all have been shown to be useful for efficient separation of different types of compounds. 

Ueno A., Ikeda H. and Wang J. (1997) Signal Transduction in Chemosensors of Modified Cyclodextrins, in Desvergne J.-P. and Czarnik A. W. (Eds), Chemosensors of Ion and Molecule Recognition, NATO ASI Series, Kluwer Academic Publishers, Dordrecht, pp. 105-19. 

K. Hamasaki, H. Ikeda, A. Nakamura, A. Ueno, F. Toda, I. Suzuki, andT. Osa, Fluorescence sensors of molecular recognition. Modified cyclodextrins capable of exhibiting guest-responsive twisted intramolecular charge transfer fluorescence, /. Am. Chem. Soc. 775,5035-5040(1993). 

Investigations on the stereochemistry of chiral semiochemicals may be carried out by (gas) chromatographic separation of stereoisomers using chiral stationary phases, e.g. modified cyclodextrins [32]. Alter natively, formation of diastereomers (e.g. Mosher s ester or derivatives involving lactic acid etc.) may be followed by separation on conventional achiral stationary phases. Assignment of the absolute configuration of the natural product will again need comparison with an authentic (synthetic) reference sample. 

Based on the theory, the separation of enantiomers requires a chiral additive to the CE separation buffer, while diastereomers can also be separated without the chiral selector. The majority of chiral CE separations are based on simple or chemically modified cyclodextrins. However, also other additives such as chiral crown ethers, linear oligo- and polysaccharides, macrocyclic antibiotics, chiral calixarenes, chiral ion-pairing agents, and chiral surfactants can be used. Eew non-chiral separation examples for the separation of diastereomers can be found. 

Attachment of a catalytic unit to the cyclodextrin toms can be achieved by several modifications. One recent example is shown on Scheme 10.3 (although no catalytic application of complexes with this ligand have been disclosed yet), other modified cyclodextrins (126-128) are depicted in Chapter 2. 

Decene was hydrocarboxylated with a [PdClaj/TPPTS catalyst in acidic aqueous solutions (pH adjusted to 1.8) in the presence of various chemically modified cyclodextrins (Scheme 10.11) [18]. As in most cases, the best results were obtained with DiOMe-P-CD. In an interesting series of reactions 1-decene was hydrocarboxylated in 50 50 mixtures with other compounds. Although all additives decreased somewhat the rate of 1-decene hydroformylation, the order of this inhibitory effect was 1,3,5-trimethylbenzene < cumene < undecanoic acid, which corresponds to the order of the increasing stability of the inclusion complexes of additives with p-CD, at least for 1,3,5-trimethylbenzene (60 M ) and cumene (1200 M ). These results clearly show the possible effect of competition of the various components in the reaction mixture for the cyclodextrin. 

Cyclodextrines, modified with 2-cyanoethyl and with bis(2-cyanoethyl)amino groups were used as ligands in the [PdCy + [CuCU]-catalyzed Wacker-oxidation of 1-octene. Without the modified cyclodextrins the yield of 2-octanone was less than 1 %, which could be raised to 73 % by the addition of nitrile-modified P-cyclodextrin ligands (60 °C, 2 h). 

The advantage of biphasic systems over the more common CHJCN/H2O mixtures (see 6.5) is in the easier and cleaner product isolation. However, practically useful rates can be achieved only in the presence of such reverse phase transfer agents like the various chemically modified cyclodextrins, of which 2,6-di-OMe-P-CD proved the best. 

Easton, C. J. Lincoln, S. F. Modified Cyclodextrins Imperial College Press London, 1999. 

Capillary gas chromatography on optically active modified cyclodextrin phases is a simple, fast, accurate and highly sensitive method for the enantiomeric analysis of chiral volatile compounds. 

V Schurig, D Wistuba. Recent innovations in enantiomer separation by electrochromatography utilizing modified cyclodextrins as stationary phases. Electrophoresis 20 2313-2328, 1999. 

W. A. Konig, Enantioselective Gas Chromatography with Modified Cyclodextrins, Hiilhig, Heidelberg 1991. 

W. A. Kdnig, Gas Chromatographic Enantiomer Separation with Modified Cyclodextrins, Hiithig, Heidelberg 1992. 

Therefore, the authors have synthesized heptakis(carboxymethyl)-substituted a-cyclodextrin which was combined with hydrophobic ammonium to afford 9 (Figure 13), whereby the number of carboxylate-ammonium ion pairs was regulated to six. This compound was incorporated into BUM and subjected to singlechannel current measurements. The current-voltage plot gave a single straight line to afford a conductance level of 7.7 pS under several different experimental conditions. Then the modified cyclodextrin successfully controlled the ion channel structure and therefore the conductance. 

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