Casearia sylvestris (Salicaceae), popularly known as "guaçatonga", is a plant widely used in folk medicine to treat various diseases, including cancer. The present work deals with the chemical composition as well as the cytotoxic evaluation of its essential oil, its main constituent and derivatives. Thus, the crude essential oil from leaves of C. sylvestris was obtained using a Clevenger type apparatus and analyzed by GC/MS. This analysis afforded the identification of 23 substances, 13 of which corresponded to 98.73% of the total oil composition, with sesquiterpene α-zingiberene accounting for 50% of the oil. The essential oil was evaluated for cytotoxic activity against several tumor cell lines, giving IC 50 values ranging from 12 to 153 μg/mL. Pure α-zingiberene, isolated from essential oil, was also evaluated against the tumor cell lines showing activity for HeLa, U-87, Siha and HL60 cell lines, but with IC 50 values higher than those determined for the crude essential oil. Aiming to evaluate the effect of the double bonds of α-zingiberene on the cytotoxic activity, partially hydrogenated α-zingiberene (PHZ) and fully hydrogenated α-zingiberene (THZ) derivatives were obtained. For the partially hydrogenated derivative only cytotoxic activity to the B16F10-Nex2 cell line (IC 50 65μg/mL) was detected, while totally hydrogenated derivative showed cytotoxic activity for almost all cell lines, with B16F10-Nex2 and MCF-7 as exceptions and with IC 50 values ranging from 34 to OPEN ACCESSMolecules 2013, 18 9478 65 μg/mL. These results indicate that cytotoxic activity is related with the state of oxidation of compound.

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A new clerodane-type diterpene, named dinor casearin X, and four known casearins (A, B, G and J) were isolated from leaves of Casearia sylvestris (Salicaceae). These compounds were evaluated for cytotoxic activity against five human cancer cell lines (A2058, HL-60, HCT, MCF-7 and HeLa) as well as against a murine melanoma cell line (B16F10-Nex2). Among these compounds, dinor casearin X exhibited the highest cytotoxic activity against HL-60 cells with IC 50 of 0.51 ± 0.11 µg mL -1 , whereas casearin A exhibited the highest cytotoxic activity against HCT cells (IC 50 1.84 ± 0.14 µg mL -1 ). ]]>