Tormentic acid

Triterpenoids isolated from E. japonica leaves for biological activities were obtained as follow: Ursolic acid (1) was obtained from Wako Pure Chemical Industries (Osaka, Japan); Oleanolic acid (2) was from Cayman Chemicals (Ann Arbor, MI, USA); Uvaol (3) was obtained from Extrasynthese (Genay Cedex, France); Betulinic acid (4) was obtained from Focus Biomolecules (Plymouth Meeting, PA, USA); Maslinic acid (7) was obtained from Cayman Chemicals; Pomolic acid (10) was obtained from Quality Phytochemicals (East Brunswick, NJ, USA); Corosolic acid (8), 3-epicorosolic acid (9), tormentic acid (11), euscaphic acid (12), 3-oxours-12-en-28-oic acid (13), 6β,19-dihydroxyurs-12-en-3-oxo-28-oic acid (14), hyptadienic acid (16), 3-O-trans-p-coumaroyl tormentic acid (17) and 3-O-cis-p-coumaroyl tormentic acid (18) were obtained from Chemfaces (Wuhan, China). Methyl maslinate (5), methyl corosolate (6) and 2α, 19α-dihydroxy-3-oxo-12-ursen-28-oic acid (15) were previously isolated from E. japonica leaves. The purity of all tested compounds was above 95% as verified by analytical high-performance liquid chromatography (HPLC).

All chemicals and reagents used in this study were of analytical or HPLC grade. 2,2-Diphenyl-1-picryhydrazyl hydrate stable radical (DPPH^•, 95%), 2,2-azino-bis(3-ethyl- benzothiazoline-6-sulfonic acid) diammonium salt (ABTS, 98%), 2.0 M Folin–Ciocalteu phenol reagent, KCl, Na₂HPO₄, K₂S₂O₈, NaCl, Na₂CO₃, and HPLC grade acetonitrile were purchased from Merck (Darmstadt, Germany); KH₂PO₄ from Jansen Chimica (Beerse, Belgium); 2,4,6-tripyridyl-s-triazine (TPTZ) from Fluka Chemicals (Steinheim, Switzerland). Acetone, methanol (MeOH), n-hexane and acetic acid were obtained from StanLab (Lublin, Poland); agricultural origin ethanol (96.6%) from Stumbras (Kaunas, Lithuania). Dimethyl sulfoxide (DMSO), n-butanol and ethyl acetate were purchased from Sigma-Aldrich (Saint-Quentin-Fallavier, France). Reference compounds, mangiferin and hydroxytormentic acid were purchased from Sigma Aldrich (Steinheim, Germany), and tormentic acid from ChemFaces (Wuhan, Hubei, China).