Peptide-based anion receptors

In recent years anion receptors based on peptides (oligomers of amino acids) have become of increasing interest, not least because of their resemblance to biological receptors. The archetypal example is the antibiotic vancomycin illustrated in Section 1.5. Vancomycin binds to the L-Lys-D-Ala-D-Ala... 

Kubik and co-workers have developed a series of highly effective anion receptors based upon cyclic peptides. Cyclic hexapeptide receptors such as 17 consist of alternately linked L-proline and 6-aminopicolinic acid subunits [25]. A 1 1 binding stoichiometry for 17 and the sodium salt of ben-zenesulfonate was confirmed by a Job plot but in the case of the halide and sulfate sodium salts 2 1 host/guest complexes were found. This was confirmed by electrospray mass spectrometry and in the case of iodide a crystal structure of the 2 1 complex was obtained where the iodide was sandwiched between two cyclic hexapeptide receptors. 

DCLs where this type of reversible bond-formation is used to generate the virtual library of receptors. One of these examples has been reported by Otto and Kubic who developed a DCL of anion receptors [54]. The library is based on disulfide exchange reactions between a dimeric cyclic peptide (35) - where the two peptidic cycles are linked by a disulfide group - and a range of different thiol-substituted spacers a-f (see Scheme 17). Mixing of all these components yields a range of dimeric cyclic peptides in different proportions. 

Peptide-based receptors can be distinguished according to the type of snbstrate recognized (cationic, anionic, and... 

Although the works concerning amide-based receptors for anions are rather rare, several very interesting publications dealing with this topic can be found. One review on peptide and glycocalixarenes has recently appeared [63]. 

Another way of avoiding the problems of pH range and counterion competition is to use a neutral hydrogen-bonding receptor based on amide functionalities. Peptide groups from the protein backbone are, of course, well known to be involved in enzyme anion binding as discussed earlier. Amide involve-... 

Kubik et al. have used DCC for the optimization of a synthetic receptor for anions. Kubik had previously designed the cyclic peptide 54 which binds to anions in aqueous solvents [125] (Figure 3.13). Based on the observation that 54 forms a... 

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