Abstract:

The syntheses of the cyclic peptides [I, II, and III (X = NMe, O, S)], 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 I reveal a mol. 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 II and III (X = O) display distorted mol. square conformations with the heterocycles (II) and the aCH groups [III (X = O)] placed at the corners of the rectangle, resp.