Chiral polysiloxane peptide

Under reducing conditions with zine/HCl - -iminodipro-pionic acid (IDP) was isolated. IDP was already described in the literature by Karrer and Appenzeller (ref. 8), and occurs as RR and SS enantiomer and meso form. All forms were synthesized, and compared with the IDP obtained by degradation of amavadin. Since the amount of material was restricted a micromethod had to be devised for this purpose. Therefore capillary gas chromatography on Chirasil-Val (ref. 9, 10), a chiral polysiloxane peptide stationary phase was chosen. Very well resolved are the chiral forms of IDP as derivatization products with isopropyl isocyanate on Chirasil-L-Val, as is shown in Fig. 3. The IDP degradation product of amavadin is identical with SS-IDP. 

Another elegant example of the imitation of the properties of biopolymers by synthetic polymers comes from the school of E. Bayer of Tubingen (172). They have prepared chiral polysiloxane polymers for resolution of optical antipodes. The prochiral polymeric backbone was a copolymer of poly [(2-carboxypropyl)methylsiloxane], octamethylcyclotetrasiloxane, and hexa-methyldisiloxane. Amino acids or small peptides were covalently linked to this polymer in order to introduce a chiral surface. For this, the free carboxyl function of the polymer was reacted with the L-amino acid in the presence of DCC (see Chapter 2). The individual chiral centers (amino acids) on the polymer surface were separated by siloxane chains of specified length in order to achieve optimum interaction with the substrate and polymer viscosity. An example of great value for optical resolution is the polymer designated chirasil-Val, containing 0.86 mmole of iV-tert-butyl-L-valin-amide per gram of polymer (Fig. 5.14). 

There have been many reported chiral stationary phases for use in both packed and capillary gas chromatography. Most of these phases are of the carbonyl-bis-L-valine isopropyl ester, diamide, and peptide phase types. The most common phase is Chirasil-Val from Alltech Applied Science Laboratories (State College, PA). This phase is ideal for the separation of a variety of enantiomers including amino acids, sugars, amines, and peptides. The phase is composed of L-valine-tert-butylamide linked through a car-oxamide group to a polysiloxane backbone every seven dimethylsiloxane units apart. 

The Amino Acid-Peptide Polysiloxane Stationary Phases Peptide-Dimethylpolysiloxane Chiral Stationary Phases Peptide-Phenylpolysiloxane Chiral Stationary Phases Cyanopolysiloxane Peptide Chiral Stationary Phases The Polysiloxane-Cyclodextrin Based Stationary Phases Chiral Liquid Chromatography... 

Despite the early successes with the polysiloxane based stationary phases carrying peptide chiral selection agents, the chiral selectors used in contemporary chiral GC are largely cyclodextrin based. 

There are two commonly used chiral GC stationary phases from which the analyst can choose. Firstly, there are the polysiloxane based stationary phases that contain amino acids or peptides included in the polymer or reacted with the polymer matrix, secondly, there are those that contain one of the cyclodextrins, or deiivatized cyclodextrins... 

Although the polysiloxane phases carrying chiral peptides are still used in contemporary chiral GC, the presently popular phases are based on cyclodextrins. These materials are formed by the partial degradation of starch followed by the enzymatic coupling of the glucose units into... 

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