Absolute Configuration and Antibiotic Activity of Piceamycin.

The cultivation of a sp. SD53 strain isolated from the gut of the silkworm produced two macrolactam natural products, piceamycin () and bombyxamycin C (). The planar structures of and were identified by a combination of NMR, MS, and UV spectroscopic analyses. The absolute configurations were assigned based on chemical and chromatographic methods as well as ECD calculations. A new chromatography-based experimental method for determining the configurations of stereogenic centers β to nitrogen atoms in macrolactams was established and successfully applied in this report. These compounds exhibited significant bioactivities against the silkworm entomopathogen and various human pathogens as well as human cancer cell lines. In particular, piceamycin potently inhibited and with MIC values of 0.083 μg/mL and 0.025 μg/mL, respectively. The biosynthetic pathway involved in the formation of the cyclopentenone moiety in piceamycin is discussed.