Piperine and piplartine ( Fig. 1) are naturally occurring amides from Piper species (Piperaceae), which have been used in folk medicine of tropical and subtropical countries for treatment of asma, bronchitis, fever, hemorrhoidal afflictions, gastrointestinal diseases, rheumatism, and as food additive.1-3) The amide piperine is the pungent principle of black pepper (P. nigrum) and can be extracted from dried fruits with a yield of 3-7%.4) Several biological activities have been associated to piperine, including inhibition of liver metabolism, antioxidant, central nervous system depressant and antitumoral activities. [4][5][6][7][8][9] Piplartine is one of the major amide isolated from the roots of P. tuberculatum (popularly known as "long pepper"), which has been largely used in the folk medicine as a sedative and antidote for snake bite. Piplartine has shown significant cytotoxicity against cell tumor lines, as well as antifungal, antimitotic and anti-platelet aggregation compound.9-13) Piplartine anticancer potential has been highlighted by the undergoing preclinical evaluation. In vivo studies using murine tumors demonstrated that in spite of a moderate anticancer activity, piplartine has weak toxicological side effects. 3,14) Additionally, it increases 5-fluorouracil anticancer efficacy, while reduces chemotherapeutical side effects, as evidenced by the prevention of 5-FUinduced leucopenia.15) These data suggests that piplartine is a promising anticancer compound to be used in combination of already known antineoplastic agents.The study of the oxidative metabolism on promising natural products is of major importance before they become medicines, since their oxidations can affect the drug's safety and efficacy, due to the formation of therapeutically active or toxic metabolites. 16) Thus, efforts have been addressed to describe the metabolic pathways of drug candidate compounds.The cytochrome P450 (CYP) enzymes are catalytic hemoproteins known for their role in the metabolism of non-polar comounds, present in all forms of life (plants, bacteria, mammals). They have played a key role in the oxidative transformation of endogenous and exogenous molecules. 17,18) The cytochrome P450 enzymes catalyze the hydroxylation of saturated carbon-hydrogen bonds, epoxidation of double bounds, oxidation of heteroatoms, dealkylation reactions, and oxidations of aromatic carbons, etc.17) The oxidative metabolism of drugs by cytochrome P450 monooxygenases has been extensively studied through biological models, such as direct experiments on animals, the use of perfused organs or isolated cells. However, there are several ethical restrictions using animals and also experimental drawnbacks associated with the isolation of some hydrophilic and reactive metabolites that could bind to biological macromolecules, preparation of liver and cells (microsomes, hepatocytes) are of variable quality with low yields. [18][19][20] Thus, alternative model systems of cytocrome P450 have been employed in studies of P450 functions, as well as in syn...