The synthesis of westiellamide analogues, wherein the oxazoline units are replaced by oxazole or thiazole units, is presented. The structures of these analogues, and also of an imidazole-based analogue, were investigated using X-ray diffraction and DFT-based molecular modelling calculations. We could show that the oxazole-based peptide is almost planar, whereas the thiazole and the imidazole cyclic