Novel multiply hydrogen-bonded heterodimers based on heterocyclic ureas. Folding and stability

A new series of multiply hydrogen-bonded heterodimers have been self-assembled in chloroform-d, with ureidopyrimidone derivatives and and 2,7-diamino-1,6-naphthyridine diamide and ureas and as monomers. The self-associating behavior of the compounds and the binding modules of the new heterodimers have been investigated. New tri-center hydrogen bonds have been proposed to explain the stability of the new heterodimers. 2D-NOESY, COSY and temperature variable 1H NMR studies revealed that all the new heterodimers are substantially more stable than the ureidopyrimidone-based quadruply hydrogen-bonded homodimers in chloroform-d. As a result, heterodimers and were assembled quantitatively, while heterodimers , , , and were formed in 80–85% yields. It is also revealed that intramolecular hydrogen bonds formed in monomers and reduce the stability of the corresponding heterodimers.