Cyclodextrin phase

Rizzi, A. M. and Plank, C., Coupled column chromatography in chiral separations systems employing P-cyclodextrin phases for chiral separation, /. Chromatogr., 557, 199, 1991. 

In an attempt to change and broaden the capabilities of the vancomycin CSP, the glycopeptide was derivatized with (R)- and (S )-(l-naphthylethyl) isocyanate (NEIC) and then bonded to a silica-gel support [48]. A variety of chiral compounds was tested on the two composite stationary phases and the results were compared with the ones obtained using the underivatized vancomycin CSP. The advantages of the NEIC derivatization were not as obvious or substantial as they were in the case of cyclodextrin phases [49]. Moreover, the exact chemical structures of the synthesized NEIC derivatives of vancomycin were not reported. 

Enantiomer separation on modified macrocyclic cyclodextrin phases via inclusion into chiral cavities. ... 

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. 

The presence of three hydroxyl groups of different reactivity offers an enormous number of possible cyclodextrin (a, /3, 7) derivatives. Unfortunately, there is at present no universally applicable cyclodextrin phase available, and selection is still a matter of trial and error134,181. 

The precision of enantiomeric purity determinations by gas chromatography is high123 124-1 >s. This statement holds not only for small enantiomeric purities ( 0% ee), e.g., in the differentiation of a true racemate from enantiomerically slightly enriched mixtures (in reactions devoted to the amplification of optical activity under prebiotic conditions), but also for very high enantiomeric purities (— 100% ee), with detection of 1.0 to 0.1% (and less) of enantiomeric impurities (see Section 3.1.5.8). It is always advantageous if the enantiomer present as an impurity is eluted as the first peak from the gas chromatographic column (Section 3.1.5.3.). This is achieved by the proper selection of the chirality of the nonracemic stationary phase147-188 which, unfortunately, is not possible for the cyclodextrin phases. 

From our own experience, it should be emphasised that the enantioselectivity of modified cyclodextrin phases is considerably influenced by the polarity of the (non-chiral) polysiloxane solvents used. 

Kreis P, Dietrich A, Mosandl A (1996) Elution order of the furanoid linalool oxides on common gas chromatographic phases and modified cyclodextrin phases. J Essent Oil Res 8 339 Weinert B, Wiist M, Mosandl A Hanssum H (1998) Stereoisomeric flavour compounds LXX-Vlff. Separation and structure elucidation of the pyranoid linalool oxide stereoisomers using common gas chromatographic phases, modified cyclodextrin phases and nuclear magnetic resonance spectroscopy. Phytochem Anal 9.T0... 

The extracts contained almost pure pheromone, with only minor amounts of other components. By comparison with synthetic samples, derivatization, and gas chromatography on a chiral cyclodextrin phase, the pheromone was identified as a 95 5 mixture of (5)- and (/ )-enantiomers of dimethyl citrate (cupilure (3), Fig. 4.2). Only the (5)-enantiomer was active (Tichy et al., 2001). Cupilure is probably present in ionized form on the silk (pK 3.5), because solvent extracts were neutral. The ionized carboxyl group may be conjugated to basic amino acids of the silk proteins. This would also explain why the pheromone is not volatile, despite its relatively low molecular weight, and is easily washed from the silk by water, including rain. In the tropical habitat of C. salei this would ensure the presence of cupilure only on freshly laid silk. 

In addition to the parameters already discussed, other factors contribute the chiral resolution on these cyclodextrin phases. These include injection amount, silica gel particle size, spacers between the CD and the silica gel, and column dimensions. In 1985 Feitsma et al. [26] studied variations in chiral resolution by varying... 

The extent of stereoselectivity in the chiral synthesis can be checked by determining the enantiomeric excess of the optically active olefins in the products. The optical purity was determined by gas chromatographic resolution of enantiomers by means of an optically active column. Thermostable substituted cyclodextrins are well suited as asymmetric phases (206). The trimer, 2,4-dimethyl-l-heptene, was resolved into its enantiomers by capillary gas chromatography with an octakis(6-0-methyl-2,3-r/-0-pentyl-)-7-cyclodextrine phase. 

Zukowski J., Pawlowska M., Nagatkina M. Armstrong D. W., High-performance Liquid Chromatographic Enantioseparation of Glycyl dipeptides and tripeptides on Native Cyclodextrin Phases, Mechanistic Considerations, Journal of Chromatograpf. 629(1993), 169-179. 

A. Mosandl, K. Rettinger, K. Fischer, V. Schubert, H.-G. Schmarr and B. Maas. Stereoisomeiic Flavor Compounds XLI New applications of permethylated 3-cyclodextrin phase in chiral CGC analysis. J. High Resolut. Chromatogr., 12, 382-385 (1990). 

A bimolecular photoreaction between different reagents in a solid cyclodextrin phase occurred upon photolysis of crystalline ternary P-CD com[flexes (1 1 2 nitro/amine/p-CD) (Scheme 29) [56a]. Study by diffuse reflectance laser flash photolysis was performed and an observed transient was assigned to the radical anion of 4-nitroveratrole (X = Y = OMe) generated via photoiriduced... 

Hydridopentacyanocobaltate(II), [HCo(CN)5]3, is a catalyst of choice for selective hydrogenation of conjugated dienes and polyenes to monoenes unactivated alkenes are totally unreactive [12, 62, 63]. In general, hydrogenation proceeds with 1,4-addition of H2 (Eq. 28). Because of the insolubility of dienes in water, such reactions are carried out in aqueous/organic biphasic systems. The possibilities for modification of the catalyst by ligand alteration are very restricted but various additives, such as KCN, KOH, lanthanide salts, cyclodextrins, phase-transfer, and micellar agents, are known to influence the selectivity of [HCo(CN)r, 3 -catalyzed reactions. 

FIGURE 40.22 Solubility of geranial as a function of P CD in ethanol water (25 75 v/v) solution at 30°C. Each data point is the mean of three measurements. (From Nur Ain, A.H. et al., Encapsulation of Lemongrass (Cymbopogon citratus) oleoresin with P-cyclodextrin phase solubility study and its characterization. Second International Conference on Biotechnology and Food Science IPCBEE, vol. 7, Singapore, 2011.)... 

---