Chiral stationary phases poly derivatives

The mixture of deprotected amino acid derivatives in solution was then immobilized onto a polymeric solid support, typically activated 5-)xm macroporous poly(hydroxyethyl methacrylate-co-ethylene dimethacrylate) beads, to afford the chiral stationary phases with a multiplicity of selectors. Although the use of columns... 

A few synthetic helical polymers are known to act as chiral selectors.7a,918d l8k i9d i9h ancj are widely used as chiral stationary phases (CSP) in gas or liquid chromatography.73,53 Recently, it has been reported that the preference of one helical sense in isotropic solution can be induced by some interaction between optically inactive polymers and chiral solvents/additives. Examples of this include poly(n-hexyl isocyanate)18d l8k and poly(phenylacetylene)s bearing functional group.19d 19h The polysilane derivatives also show chiral recognition ability in solution at room temperature. Poly(methyl-ft-pinanylsilane) includes two chiral centers per bulky hydrophobic pinanyl side group28 and... 

As pointed out above, no selectivity guarantee can be given for the separation on a certain chiral stationary phase. Therefore, screening routines have to be followed to obtain the appropriate adsorbent. The first possibility is the knowledge-based approach. Some CSP exhibit a certain group-specificity, e.g. the quinine-based CSPs for N-derivatized amino acids or the poly-(N-acryloyl amide derivatives) for five-membered... 

Figure 10.4. Structures of immobilized poly(siloxane) chiral stationary phases containing (A) a cyclodextrin derivative (Chirasil-Dex) and (B) a metal complex (Chirasil-Nickel).

The ester and carbamate derivatives of cellulose and amylose are among the most successful and versatile chiral stationary phases for liquid and supercritical fluid chromatography [1,4,28,107-109]. These phases are prepared by reaction of the poly(saccharide) with an acid chloride (ester derivative) or phenylisocyanate (carbamate... 

Chiral stationary phases prepared from silica-based coated poly(saccharide) derivatives... 

The popularity of the poly(saccharide) derivatives as chiral stationary phases is explained by the high success rate in resolving low molecular mass enantiomers. It has been estimated that more than 85% of all diversely structured enantiomers can be separated on poly(saccharide) chiral stationary phases, and of these, about 80% can be separated on just four stationary phases. These are cellulose tris(3,5-dimethylphenyl carbamate), cellulose tris(4-methylbenzoate), amylose tris(3,5-dimethylphenyl carbamate), and amylose tris(l-phenylethyl carbamate). Typically, n-hexane and propan-2-ol or ethanol mixtures are used as the mobile phase [111]. Both the type and concentration of aliphatic alcohols can affect enantioselectivity. Further mobile phase optimization is restricted to solvents compatible with the stationary phase, such as ethers and acetonitrile, as binary or ternary solvent mixtures, but generally not chloroform, dichloromethane, ethyl acetate, or tetrahydrofuran. Small volumes of acidic (e.g. tri-fluoroacetic acid) or basic (n-butylamine, diethylamine) additives may be added to the mobile phase to minimize band broadening and peak tailing [112]. These additives, however, may be difficult to remove from the column by solvent rinsing to restore it to its original condition. 

Schulte, M., Devant, R., Grosser, R. (2002) Enantioseparation of Gantofiban precursors on chiral stationary phases of the poly-(N-acryloyl amino acid derivative)-type./. Pharm. Biomed. Anal., 27, 627-637. 

Zhang C, Liu F, Li Y, Shen X, Xu X, Sakai R, Satoh T, Kakuchi T, Okamoto Y (2013) Influence of stereoregularity and linkage groups on chiral recognition of poly-(phenylacetylene) derivatives bearing L-leucine ethyl ester pendants as chiral stationary phases for HPLC. J Polym Sci A Polym Chem 51 2271-2278... 

Chiral polymers can be obtained in two different ways. The use of a chiral catalyst during polymerization can lead to helical structures, as observed in polysaccharides. The other synthesis path uses chiral monomers, which are polymerized to give a chiral polymer capable of folding to a supramolecular stmcture [20]. For application in HPLC, all of these polymers must be coated onto silica, since they are imable to withstand the high pressures encountered in HPLC. Currently, chiral stationary phases based on polyacrylates or polymethacrylates play only a minor role. Chirasphere (Merck) is derived from a silica material coated with poly(N-acryloyl-(S)-phenylalanine ethyl ester) and can be used for the separation of P-blockers in the normal-phase mode. The chiral polymethacrylates Chiralpak OP and Chiralpak OT (Daicel) are able to separate aromatic compounds into their enantiomers. 

The helical polytriphenylmethyl methacrylate was the first synthetic chiral polymer able to separate a very limited number of enantiomers [28]. Recently a fully synthetic chiral stationary phase based on polymerized diacryloyl derivative of fra s-l,2-diaminocyclohexane [either (R, R) or (S, S)] bonded to silica gel in the form of a very thin layer was proposed as a new LC CSP [29]. This CSP could not resolve many enantiomeric pairs. However, when it could resolve a racemate, it was shown that the amount that could be loaded was much larger than that on most other CSPs. It means that the number of active sites is large. Hydrogen bonds were found to be pivotal in the chiral recognition mechanism of this CSP. The enan-tioselectivity was adjusted by the methanol content in the organic mobile phase. Polysodium A-undecanoyl-L-leucyl-leucinate (poly-SULL) and —L-leucyl-valinate... 

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