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.