The Structure of Hormaomycin and One of Its All‐Peptide Aza‐Analogues in Solution: Syntheses and Biological Activities of New Hormaomycin Analogues

Four new aza‐analogues of hormaomycin 1 , a secondary metabolite with interesting biological activities produced by Streptomyces griseoflavus , were synthesized and subjected to preliminary tests of their antibiotic activity to provide new insights into the structure–activity relationship studies of this class of compounds. The solution structures of hormaomycin 1 and its aza‐analogue 2 a were determined by NMR spectroscopy. The data exhibited a reasonably rigid conformation for both molecules, stabilized by stacking interactions between the aromatic moieties attached to the ring and the side chain. According to NMR‐spectral data the aza‐analogue epi ‐ 2 a has a rather different conformation and indeed shows no antibacterial activity whatsoever.