Chelating agents, chiral

Renn, O., and Meares, C.F. (1992) Large scale synthesis of the bifunctional chelating agent 2-p-nitroben-zyl-l,4,7,10-tetraazacyclododecane-N,N, N"N" -tetraacetic acid and the determination of its enantiomeric purity by chiral chromatography. Bioconjugate Chem. 3, 563-569. 

The use of chiral chelating agents in reactions of organometallic reagents with carbonyl compounds has been intensively investigated (134-138). However, the influence of such chiral addends in the aldol process has not met with much success. In the presence of the... 

The use of CDs for chiral separations has, to date, been the most common approach when using CE or MEKC, so it would be difficult to discuss and detail every aspect relating to their chemistry, effects on separation, and application in this held. The emphasis will, thus, be placed on a short description of the principle and mechanism of chiral separation, typical method development procedures, and an outline of the influential experimental parameters using CE and MEKC. References to recent published review and research literature will enable the reader to explore this vast area further. It is also beyond the scope of this short introductory review to actually outline the actual CE or MEKC separation principles in detail, but an in-depth discussion can be found in this encyclopedia and references to recent textbooks and can be readily found elsewhere. It must, of course, be pointed out that CDs are not the only useful chiral selectors that can be employed using electrophoretic techniques. The use of chiral surfactants (bile salts), crown ethers, metal-chelation agents, carbohydrates, proteins, and glycopeptides have all been used effectively [2]. 

Chelating agent in antitumor activity, 17 Chiral aminodiols, 59, 65 Chiral bis(monoaza-crown)s, 183 Chiral cyclam, 141, 541 Chiral diamino ethers, 41, 43 Chiral 1,2-3,4-diepoxybutane, 183 Chiral l,4-diiodo-2,3-butanediol, 183... 

While this work was in progress an alternate method of asymmetric synthesis via hydride transfer was reported, in which the asymmetric center of the chiral moiety is not sacrificed (3, p. 204). This method uses the reaction product of LiAlH4 and varying amounts of optically active amino carbinols, such as ( — )-quinine, (-f)-cinchonidine, and ( — )-ephedrine, to reduce prochiral substrates. In this system the hydride anion species is sigma bonded to the optically active residue, and a maximum of three hydrides are available for further reaction. The aminocarbinols could sometimes be recovered for reuse. In the instant system the chiral chelating agent forms coordinate bonds to the lithium cation, and four hydrides are available for subsequent reaction. 

An interesting development in asymmetric additions to azomethines employs chiral ligands (chelating agents) on the organometallic. Tomioka has shown that the same ligand used for addition of aryllithiums to unsaturated esters cf. Scheme 4.10) also works for unsaturated imines, as illustrated in Scheme 4.15 [154]. The... 

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