Supramolecular polymer chemistry:: Self-assembling dendrimers using the DDA•AAD (GC-like) hydrogen bonding motif

Heterocyclic unit 2 containing complementary donor-donor-acceptor (DDA) and acceptor-acceptor-donor (AAD) hydrogen bonding arrays at an angle of about 601 Was designed to self-assemble into a hexamer. To investigate whether this unit could self-assemble dendrimers, the 2,8-diamino-2-N-ethylpyrimido-(4,5-b)(1, 8)naphthyridine-3H-4-one subunit was synthesized with a first (2a), second (2b), and third generation (2c) Frechet-type dendron attached to the 8-amino group. The synthesis of 2a-c was accomplished in 11 steps beginning with 2,6-diaminopyridine and the corresponding dendron bromide. Studies using H-1 NMR, size exclusion chromatography (SEC), and dynamic light scattering (DLS) support the cooperative formation of cyclic hexamers in apolar solvents. The stability of the self-assembled dendrimers is dependent on the size of the attached dendron, and mixing studies with 2a-c indicate their usefulness in constructing dynamic combinatorial libraries.