Crown ethers chiral recognition properties

CHIRAL RECOGNITION PROPERTIES OF CHIRAL 18-CROWN-6 ETHERS WITH AROMATIC SUBSTITUENTS... 

ABSTRACT. The chiral recognition properties of chiral 18-crown-6 ethers with phenyl, l naphthoxymethyl, l naphthylmethyl, or 2,3,5,6-tetra-methylphenylmethyl substituents for a-phenylglycine methyl ester and 1-phenylethylamine perchlorate were investigated by a standard extraction procedure. The chiral recognition factor of 1-naphthoxymethyl substi-tuted crown ether is 2.0 for the former salt but near 1.0 for the latter, whereas that of the other crown ethers is not so dependent on the structure of salts, which indicates the importance of the mutual relation of the structure of host and guest molecules. 

In the present paper, we report the synthesis of chiral 18-crown-6 ethers with aromatic substituents of various rigidity and bulkiness, and the effects of substituents on their chiral recognition properties for 1-phenylethylamine and a-phenyl glycine methyl ester perchlorate. ... 

The chiral recognition properties of crown ethers(4) for racemic Ct-phenylglycine methyl ester perchlorate(5) and 1-phenylethylamine perchlorate(6) were tested by standard extraction experiments.No appreciable amount of crown ethers was detected in aqueous layers. The relative amount of complexed salts to crown ethers in CDCl layers was determined by NMR integrations. When (5) is complexed with (4), the signal of ester methyl protons is moved and separated into two signals for each enantiomei When (6) is complexed with (4), the signal of methyl protons(doublet) is only shifted but not separated. The ratio of enantiomers of complexed salts was determined by HPLC using a chiral column for (5) or by GLC for (6) as diastereomeric isomers of (-)-(L)-N-trifluoroacetylalanine. The results are summarized in Table I and II. 

Table I. Chiral recognition properties of crown ethers for a-phenylglycine methyl ester perchlorate...

In the 1970s, Cram and co-workers developed an important concept of complexation, based on a new class of crown ethers which had properties of chiral recognition due to their atropoiso-merism [225, 294]. Futhermore, the molecules containing crown-6-ether and binaphthalene units showed the ability to distinguish... 

The property of chiral recognition shown by asymmetric crown ethers towards chiral substrates clearly mirrors the asymmetry of natural interactions and processes. This field is covered in Section 5.21.3.2.2. 

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