Trans caftaric acid

The solvents used were of chromatographic grade (>99%) and the chemical standards were of analytical grade (>95%). During the experiments, ultrapure water was used (Milli-Q system). The chemical standards malvidin (mv) 3-glucoside (3-glc), mv 3,5-diglucoside (3,5-glc), peonidin (pn) 3,5-glc, p-coumaric acid, trans-piceid acid, trans-caftaric acid, (-)-epigallocatechin (EGC) and (-)-gallocatechin (GC) were obtained from Phytolab (Vestenbergsgreuth, Germany). Cyanidin (cy) 3-glc, cy 3,5-diglc, procyanidins B1 (PB1) and B2 (PB2), kaempferol (K), quercetin (Q), isorhamnetin (I), myricetin (M), syringetin (S) and the 3-glc of K, Q, I and S and the 3-galactosides (gal) of M, K, Q and I, GC, EGC, (-)-catechin 3-gallate (CG) were obtained from Extrasynthese (Genay, France); meanwhile, trans-resveratrol (resv), caffeic acid, gallic acid, (+)-catechin (C), (-)-epicatechin (EC), (-)-epicatechin 3-gallate (ECG) and (-)-gallocatechin 3-gallate (GCG) were obtained from Sigma Aldrich (Tres Cantos, Madrid, Spain). The commercially unavailable standards procyanidin B4 (PB4), M 3-glc, Q 3-glcU and laricitrin (L) 3-glc had previously been isolated from Petit Verdot grape skins [22 (link)]. The cis-isomers of resv and its 3-glc (piceid) were obtained according to the methodology previously described [23 (link)].

Formic acid and HPLC grade methanol were purchased from VWR Prolabo (Fontenay-sous-Bois, France). Deionized water was obtained from a Milli-Q purification system (Millipore, Molsheim, France). Standard of trans-piceid was purchased from Selleckchem (Houston, TX, USA). Standards of caffeic acid, vanillic acid, gallic acid and ferulic acid were purchased from Fluka (Buchs, Switzerland). Standards of syringic acid, p-coumaric acid, protocatechuic acid, ethyl protocatechuate, tyrosol, tryptophol, tryptophan, trans-resveratrol, quercetin, catechin, epicatechin, epicatechin 3-gallate, taxifolin, oxidized and reduced glutathione were purchased from Sigma-Aldrich (St. Louis, MO, USA), as well as hydrochloric acid, phloroglucinol, L-ascorbic acid, and ammonium formiate. Standards of ethyl gallate, ethyl caffeate, tyrosine, hydroxytyrosol, epigallocatechin, malvidin 3-O-glucoside chloride, and malvidin 3,5-diglucoside chloride were purchased from Extrasynthese (Geney, France). Standards of trans-caftaric acid, quercetin glucoside and procyanidin dimers B1, B2, B3, B4, and trimer C1 were purchased from Phytolab (Vestenbergsgreuth, Germany).

Syringaldazine (purity ≥ 98%), polyvinylpolypyrrolidone (PVPP) (purity ≥ 98%) and FeSO₄·7H₂O (purity ≥ 99%) were purchased from Sigma-Aldrich (Madrid, Spain). L-(·+)-tartaric acid (purity ≥ 99.5%), sodium hydroxide (purity ≥ 98%), sodium acetate (purity ≥ 99%), acetonitrile (purity ≥ 99%), methanol (purity ≥ 99%) and CuSO₄·5H₂O (purity ≥ 99%) were purchased from Panreac (Barcelona, Spain). Ethanol (96% vol.) was supplied by Fisher Scientific (Madrid, Spain). L-glutathione reduced (purity ≥ 98%) was purchased from Sigma-Aldrich (Madrid, Spain). trans-Caftaric acid (purity ≥ 95%) was purchased from Phytolab (Vestenbergsgreuth, Germany). Cellulose membranes of 3.5 KDa (6.4 mL/cm) were supplied by Spectrum Laboratories, Inc. (Rancho Dominguez, CA, USA). The equipment used was as follows: an Hpand and Entris II Series Analytical Balance (Sartorius, Goettingen, Germany), a UV-Vis Helios Alpha ™ spectrophotometer (Thermo Fisher Scientific Inc., Waltham, MA, USA), a Heraeus™ Primo™ centrifuge (Thermo Fisher Scientific Inc., Waltham, MA, USA), and an Agilent Series 1200 liquid chromatograph (Agilent, Germany) equipped with a photodiode array detector (G1315D) and a Zorbax Eclipse XDB C18 column (4.6 × 150 mm).