Neoenactin B2

The structures of three neoenactin congeners, designated as neoenactins B1, B2 and M2 were elucidated by 1H and 13C NMR and mass spectroscopic studies. Another minor component, neoenactin M1, isolated from the crude mixture, was identified as lipoxamycin. All three new compounds were structurally related to neoenactin A. While B1 was proved to be a positional isomer of B2, M2 was found to be a dihydro derivative of A. All the compounds were active against yeasts and fungi and potentiated the activities of polyene antifungal antibiotics such as trichomycins A and B and amphotericin B.

Neoenactins (NEs) are L-serine-containing antifungal antibiotics produced by Streptoverticillium olivoreticuli. The effect of supplementation of individual amino acids on the production of NEs by this organism was examined from both quantitative and qualitative view points by using a nitrogen source-restricted medium. L-Alanine, L-arginine, L-glutamine, L-histidine, L-lysine and L-proline increased significantly the total productivity of NEs without changing the production ratio of the congeners. The supplementation of L-norvaline, L-isoleucine, L-leucine and L-valine to the culture medium resulted in selective enhancement of the production of NEs A, B1, B2, and M1, respectively, while significant change was not observed in terms of overall production of NEs. When L-norleucine was employed as an amino acid supplement, new NE congeners, named NEs NL1 and NL2, were preferentially produced; but the amount of NEs produced was not markedly affected.