Template racemic

Based on chiral functional monomers such as (15), MICSPs can be prepared using a racemic template. Thus, using racemic A-(3,5-dinitrobenzoyl)-a-methylbenzy-lamine (16) as template, a polymer capable of racemic resolution of the template was obtained [67]. Another chiral monomer based on L-valine (17), was used to prepare MIPS for the separation of dipeptide diastereomers [68]. In these cases the configu-... 

Fig. 6-10. Influence of the number of basic interaction sites of the template versus the separation factor measured in chromatography for the corresponding racemate. The templates were imprinted using MAA as functional monomer by thermochemical initiation at 60/90/120 °C (24 h at each temperature) and using acetonitrile as porogen. (From Sellergren et al. [15].)...

Significantly, the acidic conditions for release of the amino acid derivatives from the chiral template gives access to arylglycines, even those carrying electron-withdrawing substituents, e.g., a chlorine atom, which arc prone to ready racemization under basic conditions. 

Fig.8A-C. Electropherograms of A a racemic mixture of propranolol B (S)-propranolol C (El-propranolol (using in all three experiments the MI-capillary prepared by using (E)-propranolol as template). Reprinted with permission from Schweitz L,Andersson LI, Nilsson S. (1997) Anal Chem 69 1179. Copyright 1997 American Chemical Society...

The year after, the same group developed a system based on the same anti-idiotypic approach and a similar template possessing a chiral centre, in order to investigate the possibility of controlling the enantioselectivity of the reaction uniquely by the direct moulding of the cavity. In this case the polymer was able to give 67% ee as opposed to the control polymer, which produced a virtually racemic mixture [32]. 

Diols such as the optically active 1,1 -binaphthyl-2-2 -diol (BINOL) have been used as versatile templates and chiral auxiliaries in catalysts employed successfully in asymmetric synthesis. The application of enzymes in the enantioselective access to axially dissymmetric compounds was first reported by Fujimoto and coworkers.83 In aqueous media, the asymmetric hydrolysis of the racemic binaphthyl dibutyrate (the ester) using whole cells from bacteria species afforded the (A)-diol with 96%ee and the unreacted substrate (A)-ester with 94% ee at 50 % conversion. Recently, in non-aqueous media, lipases from Pseudomonas cepacia and Ps. fluorescens have been employed in the enantioselective resolution and desymmetrization of racemic 6,6 -disubstituted BINOL derivatives using vinyl acetate.84 The monoacetate (K)-73 (product) was obtained in 32-44 % chemical yields and 78-96% ee depending on the derivatives used. The unreacted BINOL (S)-72 was obtained in 30-52 % chemical yield and 55-80% ee. 

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