Chiral salts

An extremely important aspect in pharmaceutical research is the determination of drug optical purity. The most frequently applied technique for chiral separations in CZE remains the so-called dynamic mode where resolution of enantiomers is carried out by adding a chiral selector directly into the BGE for in situ formation of diastereomeric derivatives. Various additives, such as cyclodextrins (CD), chiral crown ethers, proteins, antibiotics, bile salts, chiral micelles, and ergot alkaloids, are reported as chiral selectors in the literature, but CDs are by far the selectors most widely used in chiral CE. 

Keywords Asymmetric epoxidation Chiral iminium salt Chiral ketone... 

Many organosulfur compounds can be resolved into optically active forms (enantiomers) owing to the presence of a chiral (asymmetric) sulfur atom 5 important examples include sulfoxides and sulfonium salts. Chiral sulfoxides containing amino or carboxylic acid groups have been resolved by formation of the diastereoisomeric salts with d-camphor-10-sulfonic acid or d-brucine. The salts can then be separated by fractional crystallisation and the free optically isomeric sulfoxides liberated by acid hydrolysis. However, a more convenient synthetic procedure for the preparation of chiral sulfoxides of high optical purity is Andersen s method (see p. 30). 

Various chiral selector additives, such as chiral crown ethers, proteins, antibiotics, bile salts, chiral micelles and ergot alkaloids, have been reported in the literature [15-17]. An extensive review of the numerous selectors of CE is outside the scope of the present chapter. Nevertheless, CDs are by far the most widely used selectors in chiral CE. CD are nonionic cychc oligosaccharides consisting of six, seven or eight glucose units and are called a-, [i-, and y-CD, respectively. 

The reaction of amine (91) with methyltriphenoxyphosphonium iodide (92) or (92) + I2, gave the two phosphoranes (93) and (94) respectively. X-ray crystallography revealed weak P-N interactions in both molecules, the first examples of phosphatranes containing all six-membered rings. Variable temperature NMR of (93) indicated fluxional behaviour whereby enantiomeric forms of the phos-phonium salt (chiral by virtue of clockwise and anticlockwise orientations of the propeller-shaped molecule when viewed along the C-P-N axis) interconverted rapidly at room temperature. The free energy of activation for the enantiomeric interconversion was reported to be 11.2 kcal mol compared to the isoelectronic silatrane (95) at 10.3 kcal mol. ... 

Chiral metal salt Chiral metal salt Polymerization Carbene addition... 

Prod, in vivo by hydrol. of phosphatidylinositol 4,5-diphosphate. Present in mammalian brain tissue. Important cellular second messenger. Controls Ca release from intracellular stores. Cryst. (MeOH aq.) (as tri-Na salt), [a] -11.1 (c, 0.9 in H2O) (tri-Na salt). Mp >270° (as tri-Na salt). Chiral, D-form. 

In addition, Snyder demonstrated that the use of a lipophilic quaternary proUne-derived ammonium salt chiral selector to transfer the nucleophile (a hydroxide ion) from the aqueous layer to the organic layer containing an electron-deficient arene allows the spectroscopic characterization... 

On the other hand, the use of the suitable combination of a metal salt, chiral ligand, and base promotes at low temperature the formation in situ of chiral A-metalated azomethine ylides from the corresponding iminoester and the subsequent selective cycloaddition onto the fullerene cage. Thus, the P,S chiral ligand Fesulphos along with copper(II) acetate directs the addition toward the formation of the stereoisomer (25, 55)-2-alkoxycarbonyl-5-arylpyrrolidino[3,4 l,2][60]fullerene with complete cis diasteroselectivity and enantiomeric excesses up to 93% (Scheme 34.9). 

By using polymeric onium salts chiral epoxides have been prepared by either epoxidation of olefinic substra-tes or carbenation of prochiral and chiral carbonyl compounds. ... 

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