Molekulare Pinzetten mit unterschiedlichem Biß – Erhöhung der Affinität synthetischer Rezeptoren durch Variation der Gelenkgruppe

Complexation of phenolic guests by endo- and exo-hydrogen-bonded receptors

This article describes the complexation of phenol derivatives by hydrogen-bonded receptors. These phenol receptors are formed by self-assembly of calix[4]arene dimelamine or tetramelamine derivatives with 5,5-diethylbarbiturate (DEB) or cyanurate derivatives (CYA). The double rosette assemblies 3(3).(DEB)6/(CYA)6 have their phenol-binding functionalities (ureido groups) at the top and at the bottom of the double rosette (exo-receptors). The tetrarosette assemblies 4(3).(DEB)12/(CYA)12 form a cavity with binding sites between the two double rosettes for guest encapsulation (endo-receptors). An intrinsic binding constant Ka of 202 M-1 and 286 M-1 for the binding of 4-nitrophenol to the ureido functionalized exo- and endo-receptors, respectively, was observed. For the exo-receptor a 1:6 stoichiometry was observed while for the endo-receptor 1:4 binding stoichiometry was determined by Job plot and MALDI-TOF MS. The important role that the hydroxy group's acidity plays in the complexation of 4-nitrophenol is clarified by binding studies with different phenol derivatives. The hydrogen-bonded receptors showed a much smaller response towards less acidic phenol derivatives.

Synthesis of guanidinium-derived receptor libraries and screening for selective peptide receptors in water

A library of "tweezer" receptors, incorporating a guanidinium "head group" and two peptide derived side arms has been prepared on the solid-phase using an orthogonally protected guanidinium scaffold 12. The library was screened with various tripeptide derivatives in an aqueous solvent system. A tweezer receptor 25 for the side chain protected tripeptide 19 was identified from the screening experiments. Receptor 25 was resynthesised and solution binding studies were carried out, which revealed that 25 binds to tripeptide 19 with K(a)=8.2 x 10(4) +/- 2.5 x 10(4) (15 % DMSO/H(2)O, pH 8.75) and with appreciable selectivity over the tripeptide enantiomer 22 and the side chain deprotected tripeptide 20.

Diketopiperazine receptors: a novel class of highly selective receptors for binding small peptides

A novel class of receptors consisting of a rigid diketopiperazine backbone and peptidic side chains has been developed with the use of combinatorial chemistry. These diketopiperazine receptors interact with peptidic substrates with high specificity as shown in combinatorial on-bead assays. The central diketopiperazine moiety can be easily obtained from natural 4-hydroxyproline and serves as a rigidifying template for the peptidic modules which allow for structural as well as functional variations. Screenings of several dye-marked receptor prototypes against an encoded tripeptide library demonstrated not only the high binding specificities of the diketopiperazine receptors towards peptides but also revealed that small structural changes induce significant changes in their binding properties.

Bio-inspired synthetic receptor molecules towards mimicry of vancomycin

A 512-member library of bio-inspired synthetic receptor molecules was prepared featuring a triazacyclophane scaffold. The purpose of this scaffold was to orient three (identical) peptide 'binding arms' in order to mimic an antibiotic binding cavity as is present in the vancomycin antibiotics. The library was screened with D-Ala-D-Ala and D-Ala-D-Lac containing ligands, which are present in the cell wall precursors of pathogenic bacteria. Screening and validation led to identification of a synthetic receptor capable of binding these ligands.

Identification of sequence selective receptors for peptides with a carboxylic acid terminus

Split-and-mix libraries of resin-bound "tweezer" receptors have been prepared and screened to identify receptors for dye-labelled tripeptides. The receptors incorporate a diamidopyridine unit to serve as a specific recognition site for the CO2H group, leading to strong and selective receptors for peptide guests with a CO2H terminus. The role of the dye-label, attached to the peptide guest to allow visualisation of selective recognition events in the screening experiments, has also been examined and was found to have a significant influence on the binding selectivities.

Synthesis of pseudopeptides with sulfoximines as chiral backbone modifying elements

The synthesis of pseudopeptides with a chiral alpha-sulfonimidoylcarboxy moiety in the backbone is described. Starting from readily available (Ss)-S-methyl S-phenyl sulfoximine and various cyclic and acyclic alpha-amino acids the desired products are obtained in good yields with peptide coupling methodology. Specific secondary structures caused by intramolecular hydrogen bonds may be adopted. Results of NMR studies to reveal conformational preferences will be discussed.