Maslinic acid

For sample preparation, we used LC-grade methanol, chloroform, acetone, and ethanol from Scharlab (Barcelona, Spain). As an ionization agent, we selected MS-grade formic acid. 2-Propanol and acetonitrile from Fisher Scientific (Madrid, Spain) were used for the preparation of chromatographic mobile phases. Deionized water (18 MΩ cm) was obtained from a Milli-Q water purification system.
Standards of those compounds that are commercially available were used to confirm the identification. Hydroxytyrosol, oleuropein, maslinic acid, oleanolic acid, nuzhenide, and GL3 were purchased from Extrasynthese (Genay, France). Apigenin, luteolin, luteolin-7-O-glucoside, luteolin-7-rutinoside, quercitrin, quercetin-3-glucoside, rhoifolin, rutin, oleacein, oleuropein aglycone, ligstroside aglycone, and oleocanthal were from Sigma-Aldrich (St. Louis, MO, USA). The purity of all of them was greater than 95%.

All solvents and chemicals were of analytical reagent grade. The solvents used for the extraction and for HPLC-MS/MS analysis were methanol, acetic acid (both HiPerSolv Chromanorm, VWR chemicals, Fontenay-sous-Bois, France), and ultrapure water (reverse-osmosis type water (pureAqua, Schnaitsee, Germany) coupled to a Milli-Q station (Millipore, Eschborn, Germany)). The reference substances, acetyl-α-boswellic acid (α-ABA), acetyl-β-boswellic acid (β-ABA), α-boswellic acid (α-BA), β-boswellic acid (β-BA), acetyl-11-keto-β-boswellic acid (AKBA), 11-keto-β-boswellic acid (KBA), and maslinic acid (MA) were purchased from Extrasynthese (Genay Cedex, France). Acetyl-lupeolic acid (ALA) and lupeolic acid (LA) were isolated and characterized as previously published [7 (link),8 (link),10 (link)].