Synthesis of N-substituted pyrido[4,3-d]pyrimidines for the large-scale production of self-assembled rosettes and nanotubes.

N-substituted pyrido[4,3-d]pyrimidines are heterocycles which exhibit the asymmetric hydrogen bonding codes of both guanine and cytosine at 60° angles to each other, such that the molecules self-organize unambiguously into a cyclic hexamer, assembled via 18 intermolecular hydrogen bonds. The synthesis is straightforward and can be concluded in six steps from the commercially available malononitrile dimer. X-ray crystallographic analysis of the supermacrocyclic structure shows an undulating disk with a ca. 10.5 Å cavity, the centers of which do not overlap sufficiently to describe a channel in the solid state. However, AFM, SEM, and TEM imaging in solution reveals the formation of 1D nanostructures in agreement with their self-assembly into rosette supermacrocycles, which then stack linearly to form rosette nanotubes.