Bicyclic organo-peptides as selective carbohydrate receptors: Design, solid-phase synthesis, and on-bead binding capability

Selective recognition of monosaccharides in polar media by conformationally restricted bicyclic peptides containing an aromatic surface to facilitate the initial interaction has been examined. Molecular modeling assisted design of these peptidic receptors has been employed to optimize guest fitting in the peptide cavity. Different solid-phase synthetic approaches to the target structures are discussed in order to develop a flexible methodology suitable for a combinatorial approach. A series of putative receptors, differing in the aromatic spacer as well as the peptide ring size, has been synthesized and characterized by HPLC and HR-MS. They have been subjected to FRET-based screening for binding to mono and disaccharides. This indicates that binding properties are strongly dependent on the size and rigidity of the receptors, detecting P-glucoside selectivity in the case of a naphthyl-bridged cyclic dodecapeptide. In addition, an ES-MS/MS-based method that allows structural elucidation of single bead samples with no need of encoding techniques has been devised, which will be useful for structure elucidation in libraries of cyclic peptides.