Oridamycins A and B, anti-Saprolegnia parasitica indolosesquiterpenes isolated from Streptomyces sp. KS84.

Oridamycins A (1) and B (2) were isolated from the fermentation broth of Streptomyces sp. strain KS84 as selective anti-Saprolegnia parasitica antibiotics. Their structures were elucidated as pentacyclic indolosesquiterpenes by the combination of NMR and spectroscopic analyses. The absolute configuration of 1 was determined by ROESY analyses after the advanced Mosher analysis. Compound 1 exhibited anti-S. parasitica activity with an MIC value of 3.0 microg/mL, but was much less active against the phytopathogenic fungus Phoma sp. and the yeast Saccharomyces cerevisiae.