Self-assembly of dipeptidyl ureas: a new class of hydrogen-bonded molecular duplexes.

The dipeptidyl urea 1 composed of two dipeptide chains bearing the C-terminal pyridyl moiety (-L-Ala-L-Pro-NHPy) was prepared. Two molecules of 1 are revealed to be held together by six intermolecular hydrogen bonds to form a hydrogen-bonded duplex by the single-crystal X-ray structure determination. Proton magnetic resonance nuclear Overhauser effect (NOE) study indicates the hydrogen-bonded duplex even in solution. Furthermore, a shuttle-like molecular dynamics based on recombination of the hydrogen bonds was observed. The dipeptidyl urea composed of two dipeptide chains bearing the C-terminal pyrenyl moiety (-L-Ala-L-Pro-NHCH(2)Pyr) exhibited both monomer and eximer emissions in the fluorescence spectra, supporting the formation of a duplex. A combination of the C-terminal amide NH function in each side and the designed sequence of hydrogen-bonding sites are considered to be a crucial factor for the duplex formation.