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Anew halimane diterpene was isolated from Vellozia kolbekii Alves (Velloziaceae) and identified as (5R,8R,9S,13R)-halim-1,10-ene-15,16-diol (1). It showed cytotoxicityagainst three human cancer cell lines, SF-295 (glioblastoma), MDA-MB-435 (melanoma), and HCT-8 (colon adenocarcinoma). In the mechanismofcytotoxic action, halimane 1 interferes in two major phases of the cell cycle: in Sphase,in which DNAsynthesisoccurs and where it is very sensitive to damage,and G2M phase which is the phase of preparation for mitosis and mitosis itself,s howinga poptosis-inducingp roperties.A ntimicrobial activity towards Gram-positive and Gram-negative bacteria was studied and, against Bacilluscereus, B. subtilis, Escherichia coli,a nd Pseudomonas aeruginosa,aMIC value of 0.025 mm was observedf or halimane 1,w hich is more active than the positive control chloramphenicol.