Enantiomeric recognition

Enantiomeric recognition of amino compounds by chiral macrocyclic receptors including pyridine or triazole subunits 97CRV3313. 

Zhang, X.X., Bradshaw, J.S. and Izatt, R.M. (1997) Enantiomeric recognition of amine compounds by chiral macrocyclic receptors. Chemical Reviews, 97, 3313-3361. 

Enantiomeric recognition was clearly displayed in films spread from solution and films in equilibrium with their crystals, and was sharply dependent on the acidity of the subphase. Protonation of the amide group appeared to be necessary for spreading to stable monolayers. For example, the crystals of the racemate deposited on a 10n H2S04 solution at 25°C spread quickly to yield a film with an ESP of 7.7 dyn cm"1, while the single enantiomers spread only to a surface pressure of 3.9 dyn cm-1 (Table 1). Similar effects are observed at 15 and 35°C. The effect of stereochemistry on equilibrium spreading is even more pronounced at lower subphase acidities. On 6n sulfuric acid, the racemate spread to an equilibrium surface pressure of 4.9 dyn cm-1, while the enantiomeric systems spread to less than 1 dyn cm-1. 

The environment of a cell membrane is often modeled by a monolayer of phospholipid on the air-water interface. Our attempts to detect enantiomeric recognition in such films has largely involved dipalmitoylphosphatidyl choline (DPPC), which has a chiral headgroup situated at the junction of two 16-carbon unit chains. 

Chiral crown ethers have been employed extensively (48-53, 56-60, 86, 90, 93-95, 107, no, 116, 117, 128, 143, 144, 152-155, 158-161, 163, 164, 212-227) for enantiomeric recognition of racemic primary alkyl ammonium cations including those associated with amino acid ester salts. Resolutions have been effected employing both bulk and chromatographic procedures. 

Badis, M. Tomaszkiewicz, I. Joly, J.-P. Rogalska, E., (2004) Enantiomeric recognition of amino acids by amphiphilic crown ethers in langmuir monolayers Langmuir 20, 6259-6267. 

TABLE 1. Enantiomeric Recognition of a-Hydroxy Esters by the Dipeptide (2). 

Akazome, M., Noguchi, M., Tanaka, O., Sumikawa, A., Uchida, T., and Ogura, K. (1997) Enantiomeric recognition of alkyl phenyl sulfoxides by crystalline (ft)-phenylglycyl-(//)-phcnylglycinc, Tetrahedron 53, 8315-8322. 

Cavitands III having chiral bridges, X, were studied in Langmuir monolayers and some pH-dependent enantiomeric recognition of amino acids in the subphase was reported.56... 

Similarly, the pinacols of p-ionone could be obtained in 75% yield by carrying out the electrolysis in the presence of chromium(III) chloride. Touboul and Dana observed a unique case of enantiomeric recognition when they reduced a series of racemic l,9,10,10a-tetrahydro-3(2/ -phenanthrones (13). Pina-colization occurred with formation of a new carbon-carbon bond preferentially between identical enantiomers, as shown in equation (7).. ... 

Catalysis by cyclodextrins often shows specificity which is characteristic of enzymatic catalysis. Here, the specificities are divided into 3 categories (1) substrate specificity, in which subtle changes in the structure of the substrates have large effects on the catalysis (2) product specificity, in which the products of the catalyzed reactions are highly selective and (3) d,l specificity, in which enantiomeric recognition is made by a-cyclodextiin. 

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