Syntheses and Structures of Imidazole Analogues of Lissoclinum Cyclopeptides

The syntheses of the cyclic peptides 3−7, which contain imidazole units in their backbones and resemble naturally occurring marine cyclopeptides such as westiellamide and ascidiacyclamide, are described. Structural investigations on the trimer 3 reveal a molecular triangle conformation with all lone pairs of the imidazole nitrogen atoms and the hydrogen atoms of the secondary amides directed to the center of the macrocycle. The structures of the tetramers 4 and 6 display distorted molecular square conformations with the heterocycles (4) and the αCH groups (6) placed at the corners of the rectangle, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)