Target-specific aptamers

The chirality of DNA was applied to selective separation. A DNA aptamer as a new target-specific chiral selector for HPLC was investigated by Michaud et al. [119,120]. They showed that a tailor-made chiral stationary phase based on a DNA aptamer with known stereospecific binding for the D-enantiomer of the oligopeptide, arginine-vasopressin, exhibits enantioselectivity between the d- and L-peptides. This DNA-based target-specific aptamer chiral stationary phase provides a powerful tool for the resolution of small (bioactive) molecule enantiomers. 

The SELEX process for the selection of target-specific aptamers is a universal process characterized by the repetition of five main steps binding, partition, elution, amplification, and conditioning however, for each aptamer selection, the protocol has to be adapted to the current requirements. The SELEX design and the specific selection conditions depend, for example, on the target, the oligonucleotide hbrary, or the desired features and application of the aptamers to be selected. Therefore, a multitude of SELEX variants have been developed since the first description of this technology in 1990 (Table 2.1). 

Figure 2.1 In vitro selection of target-specific aptamers using SELEX technology. See text for full description.)...

In vitro selection generates RNA and DNA sequences that can bind to target molecules with extremely high affinity and specificity. Aptamers are considered as a promising class of compounds with a wide range of application in therapeutics (Famulok et al., 2000 Toulme, 2000 White et al., 2000), diagnostics (Brody et... 

E. Immobilized DNA aptamers as target-specific chiral stationary phases for resolution of nucleoside and amino acid derivative enantiomers, Anal. Chem., 2004, 76, 1015-1020. 

Michaud, M., Jourdan, E., Ravelet, C., Villet, A., Ravel, A., Grosset, C., Peyrin, E. (2004). Immobilized DNA aptamers as target-specific chiral stationary phases for resolution of nucleoside and amino acid derivative enantiomers. Anal Chem 76, 1015-1020. 

Nncleic acid aptamers were first exploited by our group for use in target-specific chiral separations by EC. Immobilized DNA, RNA and l-RNA (spiegelmer) oligonucleotides have been nsed snccessfnlly for the separation of enantiomers of various compounds. Table 10.1 snmmarizes the aptamer-based CSPs reported to date. 

TABLE 10.1 Aptamers Used as Target-Specific Chiral Stationary Phases for LC Enantiomeric Separation... 

The first example of aptamer-based target-specific chromatographic chiral separation has been reported using an antioligopeptide DNA aptamer. The enantiomers of arginine-vasopressin were separated using an inunobilized 55-base DNA aptamer (Michaud et al., 2003) known to bind the D-enantiomer of the oligopeptide stereopecifically (Williams et al., 1997). The influence of... 

Another major drawback of aptamers is related to the too-high target specificity obtained when using the SELEX procedure. For a broad application in the chiral separation field, such a high specificity is assumed to be of poor practical interest. 

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