A New Class of Intramolecularly Hydrogen-Bonded Dendrons Based on a 2-Methoxyisophthalamide Repeat Unit

The synthesis and conformational properties of folded dendrons based on a 2-methoxyisophthalamide
(2-OMe-IPA) repeat unit are described. The hydrodynamic properties of dendrons preorganized via the
syn-syn conformational preference of 2-methoxyisophthalamide are compared with 2,6-pyridinedicarboxamide (2,6-pydic) analogues. The effect of subtle differences in the nature of the conformational
equilibria that exist within the 2-OMe-IPA and 2,6-pydic repeat units on the global structural properties
of the corresponding dendrons was explored computationally, by 1H-DOSY NMR spectroscopy and
time-resolved fluorescence anisotropy (TRFA) measurements. Whereas the syn-syn preference of the
2-OMe-IPA branched repeat unit is stabilized entirely by intramolecular hydrogen-bonding interactions,
this preference in the 2,6-pydic system is a consequence of both intramolecular hydrogen-bonding and
dipole minimization effects. However, nonspecific solvophobic compression is more important in
determining hydrodynamic properties than solvent-dependent shifts in the conformational equilibria of
the repeat unit for both dendron series.