Efficient macrocyclization of U-turn preorganized peptidomimetics:: The role of intramolecular H-bond and solvophobic effects

Simple peptidomimetic molecules derived from amino acids were reacted with meta- and parabis(bromomethyl)benzene in acetonitrile to very efficiently yield macrocyclic structures. The cyclization reaction does not require high dilution techniques and seems to be insensitive to the size of the formed macrocycle. The analysis of data obtained by H-1 NMR, single-crystal X-ray diffraction, fluorescence measurements, and molecular mechanics indicate that folded conformations can preorganize the system for an efficient cyclization. The role played by intramolecular hydrogen-bonding and solvophobic effects in the presence of folded conformations is analyzed.