Studies on macrocyclic lactone antibiotics. V. The structures of azalomycins F3a and F5a.

The structures of the antibiotics azalomycin F3a (1b) (C55H93N3O17) and azalomycin F5a (1c) (C57H97N3O17) were elucidated by comparison of their physicochemical properties with those of F4a (1a) (C56H95N3O17). Structural differences among these three compounds lie only in their guanidine moieties, which have no methyl group, one methyl group and two methyl groups in F3a, F4a and F5a, respectively.