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

Chemical investigation of the ethyl acetate (EtOAc) extract from a marine-derived actinomycete, , resulted in the discovery of five new labdane-type diterpenoids: chlorolabdans A-C (-), epoxylabdans A and B ( and ), along with one known analog (). 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 displayed significant activity against Gram-positive bacteria, with minimum inhibitory concentration (MIC) values ranging from 4 to 8 µg/mL. Additionally, , , and 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; , , and exhibited cytotoxic activities against some blood cancer cell lines, with concentration causing 50% cell growth inhibition (IC) values ranging from 1.2 to 22.5 µM.