Oleacein

Syringaldehyde, deuterated chloroform (D, 99.8%), sodium molybdate dihydrate, hydroxytyrosol, apigenin, gallic acid, catechin, and pinoresinol were purchased from Sigma-Aldrich (Steinheim, Germany). Glacial acetic acid, acetonitrile, cyclohexane, aluminium chloride, sodium carbonate anhydrous, sodium nitrite, and methanol (HPLC grade) were obtained from Merck (Darmstadt, Germany). Folin–Ciocalteu’s reagent, tyrosol, and cinnamic acid were bought from Fluka Chemie (Buchs, Switzerland), while oleacein and oleocanthal were obtained from PhytoLab GmbH (Vestenbergsgreuth, Germany) and dacarbazine from Selleck Chemicals (München, Germany). Sodium hydroxide and n-hexane were purchased from Kemika (Zagreb, Croatia). Components for cell culture maintenance, including RPMI 1640, FBS, trypsin-EDTA, phosphate-buffered saline (PBS; Ca²⁺ and Mg²⁺ free), penicillin, and streptomycin, were from Lonza (Basel, Switzerland) and the CellTiter 96^®AQueous One Solution Cell Proliferation Assay was from Promega (Madison, WI, USA).

LC grade reagents and solvents were used in this research. Ammonium fluoride from Fisher Scientific (Hampton, NH, USA) was used as the ionizing agent. Methanol (MeOH) from Scharlab (Barcelona, Spain) and deionized water (18 mΩ • cm) from a Millipore Milli-Q water purification system (Merck Millipore, Bedford, MA, USA) were used for the preparation of chromatographic mobile phases.
Hydroxytyrosol and tyrosol were purchased from Extrasynthese (Genay, France), whereas secoiridoid derivatives oleacein and oleocanthal were acquired from Phytolab (Vestenbergsgreuth, Germany). On the other hand, oleuropein aglycone and ligstroside aglycone (both as monoaldehyde closed isomers) were purchased from TRC (Ontario, Canada). Syringaldehyde from Sigma-Aldrich (St. Louis, MO, USA) was used as an internal standard (IS) to control the LC-MS/MS performance.

High purity standards for the qualitative-quantitative determination of fatty acids (palmitic, palmitoleic, heptadecanoic, stearic, oleic, linoleic, linolenic, arachidic, eicosenoic, behenic), α-T, triterpenic acids (maslinic and oleanoic acids), hexanal, and 2-methylpropyl acetate, as well as all High-Performance Liquid Chromatography (HPLC) grade solvents, were all purchased from Sigma–Aldrich (Milan, Italy). Tyrosol, hydroxytyrosol, and verbascoside were purchased from Fluka (Milan, Italy), Cabru s.a.s. (Arcore, Milan, Italy), and Extrasynthese (Genay Cedex, France), respectively. Oleacein and oleocanthal were obtained from PhytoLab GmbH & Co. (Vestenbergsgreuth, Germany). Carotenoids (lutein and β-carotene) and β-T3 standards were purchased from CaroteNature (Lupsingen, Liestal, Switzerland) and Cayman chemicals (Ann Arbor, MI, USA), respectively.