Labdane-Type Diterpenoids from Streptomyces griseorubens and Their Antimicrobial and Cytotoxic Activities.

Chemical investigation of the ethyl acetate (EtOAc) extract from a marine-derived actinomycete, Streptomyces griseorubens , resulted in the discovery of five new labdane-type diterpenoids: chlorolabdans A-C ( 1 - 3 ), epoxylabdans A and B ( 4 and 5 ), along with one known analog ( 6 ). The structures of the new compounds were determined by spectroscopic analysis (HR-ESIMS, 1D, and 2D NMR) and by comparing their experimental data with those in the literature. The new compounds were evaluated for their antimicrobial activity, and 2 displayed significant activity against Gram-positive bacteria, with minimum inhibitory concentration (MIC) values ranging from 4 to 8 µg/mL. Additionally, 1 , 2 , and 4 were tested for their cytotoxicity against seven blood cancer cell lines by CellTiter-Glo (CTG) assay and six solid cancer cell lines by sulforhodamine B (SRB) assay; 1 , 2 , and 4 exhibited cytotoxic activities against some blood cancer cell lines, with concentration causing 50% cell growth inhibition (IC 50 ) values ranging from 1.2 to 22.5 µM.