Chemical investigation of a marine-derived Streptomyces sp. KCB-132, cultivated in liquid ISP2 medium, had led to the discovery of three C-ring cleavage angucyclinone N-heterocycles, pratensilins A-C, with a novel spiro indolinone-naphthofuran skeleton. Addition of 50 μM LaCl3 to the same medium and subsequent chemical analysis of this strain returned a new member of this rare class, pratensilin D (1), along with two new angucyclinone derivatives, featuring ether-bridged (2) and A-ring cleavage (3) structural properties. Their structures and absolute configurations were assigned by spectroscopic analysis, single-crystal X-ray diffractions, and equivalent circulating density (ECD) calculations. (+)- and (-)-1, a pair of enantiomeric nitrogen-containing angucyclinones, exhibited different strengths of antibacterial and cytotoxic activities.
Keywords: Streptomyces pratensis; angucyclinones; antibacterial activity; cytotoxicity; oxygen bridge; ring cleavage; structure elucidation.
Copyright © 2020 Guo, Zhang, Yang, Xu, Fu, Liu, Li, Zhang and Xie.