Sesquiterpenes from Streptomyces qinglanensis and Their Cytotoxic Activity

Nine sesquiterpenes, including eight pentalenenes (1–8) and one bolinane derivative (9), were isolated from the culture broth of a marine-derived actinobacterium Streptomyces qinglanensis 213DD-006. Among them, 1, 4, 7, and 9 were new compounds. Their planar structures were determined by spectroscopic methods (HRMS, 1D, and 2D NMR), and the absolute configuration was established by biosynthesis consideration and electronic-circular-dichroism (ECD) calculations. All the isolated compounds were screened for their cytotoxicity against six solid and seven blood cancer cell lines. Compounds 4–6 and 8 showed a moderate activity against all of the tested solid cell lines, with GI(50) values ranging from 1.97 to 3.46 µM.