Circadian variation and <i>in vitro</i> cytotoxic activity evaluation of volatile compounds from leaves of <i>Piper regnellii</i> (Miq) C. DC. var. <i>regnellii</i> (C. DC.) Yunck (Piperaceae)

<p>Aiming detection of circadian variation in the chemical composition of volatiles from <i>Piper regnellii</i>, the leaves were collected during four different periods (8, 12, 16 and 20 h) in the same day. After extraction by hydrodistillation and GC/MS analysis, no significant variation was observed for the main compounds: germacrene D (45.6 ± 1.5–51.4 ± 3.1%), α–chamigrene (8.9 ± 1.3–11.3 ± 2.7%) and β–caryophyllene (8.2 ± 0.9–9.5 ± 0.3%). Evaluation of <i>in vitro</i> cytotoxicity against several cancer and non-tumourigenic cells indicated promising activity, especially to HeLa (human cervical carcinoma) with IC<sub>50</sub> ranging from 11 ± 3 to 17 ± 3 μg/mL. The obtained volatile oils were pooled and subjected to fractionation to afford pure β-caryophyllene, α-chamigrene and germacrene D, being this last compound the more active against HeLa cells with IC<sub>50</sub> of 7 ± 1 μg/mL (34 ± 5 μM). Therefore, the predominance of germacrene D in all analysed oils could justify, at least in part, the activity observed for the volatile compounds from <i>P. regnellii</i> leaves.</p>