Synthesis, Characterization And Properties Of Helical Foldamers Based On 8-fluoro-quinoline Amide Skeletons

Design and synthesis of new foldamers is one of intensively studying fields in supramolecular chemistry.In nature,most biomolecules,such as DNA,peptides and proteins,have folded or helical structures.Therefore,it will facilitate one to understand structure and function of biomolecules by studying folded or helical structures of non-natural one.In this thesis,we describe the synthesis,characterization and helical properties of a new series of foldamers based on 8-fluoro-quinoline amide backbone.The main results are as follows:1 Using convergent method,we have successfully synthesized a new series of 8-fluoro-quinoline based oligoamides,.The structure for all these new compounds were fully characterized by ¹H NMR,¹³C NMR,¹⁹F NMR and Mass Spectroscopy.In particular,crystal structures of tetramer 1 and octamer 2 have been analyzed by X-ray diffraction.2 These oligomers could fold into well defined helical structures through intramoleclar F…H-N and N…H-N hydrogen bonds,which has been characterized by single crystal X-ray diffractions in solid state and by NMR in solution.Furthermore,¹H NMR,¹⁹F NMR,NOE,¹H DOSY,variable-temperature NMR,X-ray measurements reaveals that these helical oligomers could self-assemble into double and/or quadruple helices through intermoleclar noncovalent forces.We find that single-helical conformers must increase their helical pitch and undergo a springlike extension to accommodate a complementary strand and wind into a double helix.This process is very similar with the self-assemble mechanism of gramicidin D.This result provide a new model system for us to mimic the structures and functions of biological substance.