Hydrogen-Bonding-Mediated Anthranilamide Homoduplexes. Increasing Stability through Preorganization and Iterative Arrangement of a Simple Amide Binding Site

This paper describes the assembly of two new series of self-complementary duplexes by making use of amide units, the simplest assembling units of hydrogen bonding, as binding sites. All the new monomers possess a rigidified anthranilamide skeleton, which is stabilized by intramolecular hydrogen bonding. Amide units are iteratively introduced to one side of the preorganized skeletons to facilitate the formation of intermolecular hydrogen bonding. Compounds 2 and 3 bear two and three CONH₂ units, respectively, while 4, 6, and 7 are incorporated with two, three, and four AcNH units, respectively. For comparison, compound 5, which is similar to 4 but contains one AcNH and one CF₃CONH unit, is also prepared. X-ray diffraction analysis of 2, 4, and 5 revealed homodimeric motifs in the solid state which are stabilized by two or more intermolecular hydrogen bonds. ¹H NMR investigations in CDCl₃ indicated that all the compounds form hydrogen-bonded homoduplexes. Duplexes 3·3, 6·6, and 7·7 are highly stable in CDCl₃, with a lower K_assoc limit of 2.3 × 10⁵ M^-1. The K_assoc values of the three duplexes in more polar CDCl₃/CD₃CN (9:1, v/v) were determined with the ¹H NMR dilution method. The result opens the way for the development of new polymeric duplexes of well-ordered structures.