Racemic guest

A different non-classical approach to the resolution of sulphoxides was reported by Mikolajczyk and Drabowicz269-281. It is based on the fact that sulphinyl compounds very easily form inclusion complexes with /1-cyclodextrin. Since /1-cyclodextrin as the host molecule is chiral, its inclusion complexes with racemic guest substances used in an excess are mixtures of diastereoisomers that should be formed in unequal amounts. In this way a series of alkyl phenyl, alkyl p-tolyl and alkyl benzyl sulphoxides has been resolved. However, the optical purities of the partially resolved sulphoxides do not exceed 22% after... 

Chiral Recognition. The use of chiral hosts to form diastereomeric inclusion compounds was mentioned above. But in some cases it is possible for a host to form an inclusion compound with one enantiomer of a racemic guest, but not the other. This is caUed chiral recognition. One enantiomer fits into the chiral host cavity, the other does not. More often, both diastereomers are formed, but one forms more rapidly than the other, so that if the guest is removed it is already partially resolved (this is a form of kinetic resolution, see category 6). An example is use of the chiral crown ether (53) partially to resolve the racemic amine salt (54). " When an aqueous solution of 54 was... 

Within this approach, clathrates (for a definition see Chapter 1 in Vol. 140 of this series) and related lattice-type aggregates may be considered as multi-supramolecular systems where guest molecules are included in a crystal matrix. They allow a great many applications which have been specified in Vol. 140, first of all the separation of enantiomers by enantioselective recognition and inclusion of racemic guest molecules. 

Liquid-liquid chromatographic runs with RR-1284] in CHC13 in the mobile phase and racemic guest in the aqueous stationary phase ... 

The design of host compounds for optical resolution has received much attention. Toda [23,24] has reviewed the subject, and has used a number of novel techniques to effect efficient optical separation. He has demonstrated the possibility of resolving a racemic oil by stirring in a water suspension of a chiral host [25], and has applied fractional distillation techniques at different temperatures to separate a variety of racemic guests in the presence of chiral hosts [26]. An overview of the industrial applications and production of optically active materials is given in the book Chirality in Industry [27],... 

When a chiral host compound includes one enantiomer of racemic guest compound selectively, optical resolution of the guest can be accomplished. In this chapter, efficient resolutions of racemic compounds by the complexation with various artificial chiral hosts are described. All the data described in this chapter are those obtained in the author s research group. 

This chapter consists mainly of two sections, 1) preparation of artificial chiral host compounds and 2) optical resolution of various racemic guest compounds by inclusion complexation with these hosts. 

In 1986, we have found that l,l,6,6-tetraphenylhexa-2,4-diyne-l,6-diol (1) includes various guest molecules in a stoichiometrical ratio and forms crystalline inclusion complexes.1 X-ray analysis of a 1 2 inclusion complex of 1 and acetone showed that the guest molecules are accommodated in inclusion crystalline cavity by the formation of hydrogen bond with the hydroxyl groups of l.2 It was also found that inclusion complexation with 1 occurs selectively, and a mixture of isomers can be separated by the selective inclusion process.3 This suggests that racemic guest compound can be separated into enantiomers by inclusion... 

Some amide derivatives have been reported to form inclusion complex with a wide variety of organic compounds.9 Optically active amide derivatives are expected to include one enantiomer of a racemic guest selectively. According to this idea, some amide derivatives of tartaric acid (11-13) were designed as chiral hosts.10 As will be described in the following section, these amide hosts were found to be useful for resolution of binaphthol (BNO) (14) and related compounds (15,16). 

A solution of chiral host and racemic guest compounds in an appropriate solvent is kept at room temperature until inclusion complex crystallizes out. In the complexation, it is necessary to use a solvent which does not form inclusion complex with the host compound. The inclusion complex formed is filtered and purified by recrystallization from solvent, if necessary. Host guest molar ratio is... 

In the case of volatile racemic guest, optical resolution can be carried out by using distillation technique in the presence of a non-volatile chiral host compound. The resolution by distillation is summarized in the section of 5. In the section 5, optical resolution by inclusion crystallization in a suspension medium in hexane or water is also described. 

Racemic guest d.e. % Volume (A3) Racemic guest d.e. % Volume (A3)... 

Further helical structures in chemistry are formed, e.g. by urea, which in the course of the crystallization from suitable solvents builds up a hexagonal lattice. It contains long channels, surrounded by urea molecules, which either form a left- or right-handed helix. If urea is crystallized in the presence of a suitable racemic guest, the right-handed lattice preferably encloses the one enantiomer of the guest, the left-handed lattice the other one This discrimination of enantiomers can be applied for the separation of racemates. 

In addition, the alkaloids listed here, sparteine (85), brucine (9b) and quinine (97), can be used to differentiate between the enantiomers of racemic guest compounds... 

Enantioselective complexation between chiral host molecules and racemic guests was also achieved. One enantiomer of phenylethylammonium cation can be selectively complexed by optically pure i>A(binaphtho)-22-crown-6. The racemic ammonium salt, dissolved in water, and the chiral crown, dissolved in an immiscible solvent such as CHCI3, are shaken together. If one of the two diastereomeric complexes is favored, it can be detected (e.g., by NMR) or separated. When the chiral macrocycle is bound to a resin, a multi-plate, chiral organic separation is possible. 

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