Cyclodextrins, diastereoisomers from

The separation of enantiomers can be effected either by transforming them into diastereoisomers using a chiral reagent and separating them on conventional phases or by separating the enantiomers on chiral phases. The utilization of chiral phases has not yet become routine, but studies of enantiomeric dipeptides have been carried out (115,116). Pirkle et al. (117) and Hyun et al. (118) separated enantiomeric di- and tripeptides (methyl esters of /V-3-5-dinitrobenzoyl derivatives) on chiral stationary phases (CSPs) derived from (R)-a-arylalkylamines, (S)-N-(2-naphthyl) valine, or (S)-1 -(6,7-dimethyl-1 -naphthyl) isobutylamine. These workers were able to separate four peaks for each dipeptide derivative, corresponding to the two enantiomeric pairs (R,R)/(S,S) and (R,S)/(S,R). Cyclodextrin-bonded stationary phases and chiral stationary immobilized a-chymotrypsin phases were used to separate enantiomeric peptides (118a,b). 

Detailed analyses of intramolecular structures are possible. Comparison of NMR and fluorescence data shows meso- and racemic diastereoisomers are found from 2,4-di(2-pyrenyl)pentane 24 jhe polarization of monomer and excimer of 4,9, disubstituted pyrenes have been measured in nematic liquid crystals 25 Quenching of pyrene fluorescence by alcohols in cyclodextrin inclusion complexes has also been studied in detail 26 Solvent effects on the photophysical properties of pyrene-3-carboxylic acid has been used to measure the pJJ, in different solvents 27 Geminate recombination in excited state proton transfer reactions has been studied with... 

The mono-6-tosylated p-cyclodextrin gave mixed diastereoisomers (33) when treated with the cesium salt of the appropriate acid (Ibuprofen), and the isomer derived from the (R)-acid was 10 times more sensitive to hydrolysis at pH 11.5. Tosylates have also given access to... 

Armstrong et al. [62] used a-cyclodextrin (R = H) and /8-cyclodextrin derivatives (R = hydroxypropyl) [63] as additives in the mobile phase for the separation of different diastereoisomers. Thus, they separated 5yn-azobenzene Rp = 0.09) from anti-azobenzene (Rp = 0.53) on polyamide or polyamide with fluorescent indicator adding a-cyclodextrin to the mobile phase (0.1 M) [62] or some steroid epimers and alkaloids on plates coated with chemically bonded octadecylsilane reversed-phase [62]. The used mobile phases obtained by adding hydroxypropyl-/8-cyclodextrin are presented in Table 8.9, beside the chromatographic results. 

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