Self-complementary purines by quadruple hydrogen bonding.

The first discrete, self-complementary, quadruply hydrogen-bonded complexes based on the 2,6-diaminopurine (DAP) scaffold have been prepared; regioselective urea formation at the C2 amino group of the heterocycle allows intermolecular dimerization (K(dim) approximately 1-1.6 x 10(3) M(-1) in CDCl3) through a DADA hydrogen bonding motif.