Mechanism of isomers and analogues of resveratrol dimers selectively quenching singlet oxygen by UHPLC-ESI-MS2

Food Chemistry 237 (2017) 1101–1111

Contents lists available at ScienceDirect

Food Chemistry journal homepage: www.elsevier.com/locate/foodchem

Mechanism of isomers and analogues of resveratrol dimers selectively quenching singlet oxygen by UHPLC-ESI-MS2 Xuefeng Yin a,b, Jia Yu a, Qingjun Kong a,b,⇑, Xueyan Ren a,⇑ a b

College of Food Engineering and Nutritional Science, Shaanxi Normal University, Xi’an 710062, China Shaanxi Engineering Laboratory for Food Green Processing and Safety Control, Xi’an 710062, China

a r t i c l e

i n f o

Article history: Received 8 March 2017 Received in revised form 3 June 2017 Accepted 5 June 2017

Chemical compounds studied in the article: Scirpusin A (PubChem CID: 5458896) Trans-e-viniferin (PubChem CID: 5315232) Trans-r-viniferin (PubChem CID: 10095474) Keywords: Singlet oxygen Resveratrol dimers Isomers Ultra-high performance liquid chromatography-electrospray ionizationtandem mass spectrometry Compounds structure

a b s t r a c t Stilbenoids, in particular, resveratrol and its dimers are abundantly present in Vitis vinifera and proved to be quenchers with selective singlet oxygen. However, only a few mechanisms are reported for their complex molecular architectures. Hence, UHPLC combined with accurate MS is employed to investigate the photo-radiation mechanism of resveratrol dimers systematically. Ⅰ: Resorcinol ring exists in Scirpusin A 1, Trans-e-viniferin 2 and Trans-r-viniferin 3. The photochemical products were 14 Da or 16 Da higher than reagents and underwent an endoperoxide intermediate to quinones; Ⅱ: [2+2] cyclization of intramolecular trans-double bond. The products were 18 Da greater than substrates thereby cycloaddited to oxygen heterocyclic; Ⅲ : [4+1], [4+2] cyclization of oxetane formed products were 28 Da and 44 Da higher than 3, 2 and 1. Ⅳ : 5-phenol-2,3-dihydrobenzofuran ring exists in 2 been oxidized, causing the products at 16 Da, 32 Da higher than 2. This is the first to reveal the generally regular mechanism of stilbenoids quenching singlet oxygen. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction Resveratrol and its dimers are biological secondary metabolites which often referred as stilbenoids or phytoalexins. They are widely present in assorted plants, especially the species of Vitis vinifera known as wine grapes. In recent years, they have attracted numerous interest in the field of disease prevention and in curbing down the aging process. The Zhang (Zhang, Li, Xu, Wang, & Wang, 2016) has demonstrated the positive effect of resveratrol on highfat diet intake, which induced renal pathological damage and cell senescence; Lygin et al. (2014) has investigated inhibitory effects of resveratrol and its dimers on the growth of soybean pathogens; In vitro studies also point out the anti-proliferative effects of Transresveratrol on tumor cells (Aluyen et al., 2012) and its antioxidant outcomes (Escote, Miranda, Menoyo, Rodriguez-Porrata, & Madeo, ⇑ Corresponding authors at: College of Food Engineering and Nutritional Science, Shaanxi Normal University, Xi’an 710062, China (K. Qingjun). E-mail addresses: [email protected] (Q. Kong), [email protected] (X. Ren). http://dx.doi.org/10.1016/j.foodchem.2017.06.021 0308-8146/Ó 2017 Elsevier Ltd. All rights reserved.

2012). These studies have indicated that either resveratrol or its dimers have a significantly beneficial effect on human life and food. The scavenging of ROS is particular interest in medicine and biological chemistry, since the strong evidence that ROS is involved in the pathogenesis of many degenerative diseases, like autoimmune diseases, multiple sclerosis diseases and aging in humans (Sohal & Weindruch, 1996). Therefore, recently published papers provide a variety of reasons why resveratrol and its dimers exert biological activity against aging and oxidative stress disorder, basic mechanisms are scavenging reactive oxygen species (ROS) (Mazzone, Alberto, Russo, & Sicilia, 2014; Shang et al., 2009). Singlet oxygen (1O2), a classical form of ROS, is the first excited state 1Dg of molecular oxygen, which is one of the most active classes involved in chemical and biochemical reactions. The reason is that it can react with a large number and importance of biological molecules, such as DNA, proteins and lipids (Kim et al., 2013; To et al., 2016) thereby inducing diseases that cannot be repaired. It is generated from biologically relevant processes in vivo and also from photosensitized oxidations in vitro (Xia, Yin, Fu, & Boudreau, 2007). Our focus is on extinguishing 1O2 by two ways in general;

1102

X. Yin et al. / Food Chemistry 237 (2017) 1101–1111

inhibition of the singlet oxygen formation and reactions with selective quenchers to produce special compounds. Recently, many studies confirmed that selective quenchers including resveratrol or its dimers could effectively scavenge the singlet oxygen. Previous work revealed that parthenocissin A, quadrangul-arin A and pallidol showed strong selective singlet oxygen scavengers (IC50 = 4.90, 1.05 and 5.50 lM, respectively) (Li, Xu, Tao, Wang, & Pan, 2015). Vitisin A, Laetevirenols F and G are potent and selective singlet oxygen quenchers investigated by He, Jiang, Wu, Zhou, and Pan (2009a), He et al. (2009b). Hence, what is the mechanism using which they can quench singlet oxygen? To the best of our knowledge, Celaje proposed the idea that resveratrol reacts with 1O2 by two major pathways: [2+2] cycloaddition and [4+2] cycloaddition, forming Moracin M by NMR analysis. The author believes that the quenching reaction is related to the carbon-carbon double bonds in resveratrol (Trans-5-(parahydroxystyryl)-resorcinol) (Celaje, Zhang, Guerrero, & Selke, 2011). Whereas, Jiang reported that the resorcinol ring in resveratrol and its oligomers was oxidized by the singlet oxygen then generated its corresponding endoperoxide, followed by reorganization to the quinones by HPLC-MSn (Jiang, He, Jiang, & Pan, 2010). However, both of the reports fail to demonstrate how the dimers of resveratrol go through selectively quenching 1O2. The dimers of resveratrol contained many isomers and derivatives, such as Pallidol, Amurensin A, Parthenocissin A, Viniferin and so on. Kong has reported the scirpusin A as a selective quencher, effectively, quenched 1O2 at very low concentrations (Kong, Ren, Jiang, Pan, & Sun, 2010). Trans-e-viniferin and Scirpusin A are analogues. They only difference is the number of hydroxyl groups (-OH) in the structure. Researchers have reported that Trans-eviniferin exhibit clearly effects in anti-obesity, anti-inflammatory and antidepressant in vivo or in vitro (Ohara et al., 2015; Yanez, Fraiz, Cano, & Orallo, 2006). Trans-r-viniferin as Trans-e-viniferin isomers showed efficaciously moderating antioxidant properties and protective activity from hemoglobin oxidation in vitro (Ficarra et al., 2016), further instructions included maintaining mitochondrial function in high glucose-treated in vivo (Zhao et al., 2016). Therefore, Scirpusin A 1, Trans-e-viniferin 2 and Trans-r-viniferin 3 have a symbolic significance in studying the mechanism of resveratrol dimers quenching 1O2. In this study, UHPLC-ESI-MSn analysis is done to further explain the idea that isomers and analogues of resveratrol as selective quenchers when reacted with 1O2. Furthermore, how would they selectively quenching 1O2 are explained by their distinctively structural similarities and differences. Hence, the aim of the paper is to make the quenching mechanism clearly and while also provide a more detailed description than is given in researches that have already been published.

2. Materials and methods 2.1. Materials and samples Rose Bengal (RB), Deionized water for UHPLC-ESI-MSn was obtained from a Milli-Q water purification system (Millipore, Bedford, MA). MeOH for accurate UHPLC-ESI-MSn analysis was the chromatographic grade and purchased from Fisher Scientific. Three types of resveratrol dimers were isolated and purified from the red wine grapes (Vitis vinifera) by organic solvent (MeOH, EtOAc) extraction then purified with silica gel CC or countercurrent chromatography (CCC) in our laboratory, Kong has provided a detailed description (Kong et al., 2010; Kong et al., 2016). Additionally, detailed NMR analyses (including 1H, 13C) were confirmed by comparison with the NMR data published in the litera-

tures (Pezet et al., 2003; Shao et al., 2007; Zhang et al., 2004). The three types are Scirpusin A 1, Trans-e-viniferin 2 and Transr-viniferin 3 (Fig. 1). 2.2. Experiment and UHPLC-ESI-MS2 analysis Three samples for UHPLC-ESI-MS2 experiments were taken, which were composed of 500 lL 72 lM RB, and 100 lL 0.1 mM Scirpusin A, 0.37 mM Trans-e-viniferin, 0.44 mM Trans-rviniferin, respectively. The samples were freshly dissolved in MeOH (only MeOH present was the blank control). Then the reaction mixtures were irradiated by a mercury lamp (20 W, k > 200 nm) for 2 min at 23 °C ± 2 °C. Before irradiation, the UV lamp was turned on for at least 15 min to reach an equilibrium status. 5 lL of the reaction mixture was withdrawn immediately and analyzed by accurate UHPLC-ESI-MS2 assays carried out on a Thermo Scientific Dionex UltiMate 3000 system, which coupled with a Bruker micrOTOF-Q III mass spectrometer (Bruker-Franzen Analytik GmbH, Bremen, Germany). The Thermo Scientific Dionex UltiMate 3000 system includes a WPS-3000 Pump, a TCC-3000 Column Thermostat, a WPS-3000 Auto sampler and a SRD-3000 Solvent Rack. The mass spectrometer was equipped with an ESI interface. Samples were analyzed on a Thermo Scientific AcclaimTM RSLC 120 C18 reversed-phase column (3.0  100 nm, 2.2 lm, 120 Å), using a gradient elution comprising MeOH and water with a flow rate of 0.2 mL/min at 20 °C, Multi-Step Gradient: 5% MeOH held for 15 min; 90% MeOH held for 11 min; 5% MeOH held for 6 min and the total runtime being 32 min. UHPLC effluent was induced into the ESI source by a Solvent line (analytical, softron P/N 5040.8117), and UHPLC connected with MS by HyStar3.2 (Bruker Hyphenation Star Application, Germany). The negative ion mode of ESI was performed for providing extensive information easily. Nitrogen was used as the nebulizing and drying gas at 1.2 Bar and a flow rate of 3.0 L/min, dry temperature was set as 200 °C. The scan modes of fragmentation amplitude and collision energy were set at Auto MS/MS with the mass scan range being 50– 1000 m/z. 2.3. Data analysis All of the precursor ions and product ions are supported by accurate mass measurements. Compass 1.7 analysis software from (Bruker-Franzen Analytik, Bremen, Germany) for OTOF data, automatically. Selective ions chromatograms and MS2 spectrum chromatograms were extracted using a mass window of 10 ppm around the [M H] ion of each compound, which is changed from Rodriguez-Cabo (Rodriguez-Cabo, Rodriguez, Ramil, & Cela, 2015). MetFrag is an online chemical structure database that is in fragmented for computer assisted identification of mass spectra. Our data source and patents information from UHPLC-ESI-MS2 via PubChem web services of MetFrag to reduce candidates redundancy due to stereoisomerism (Christoph, Emma, Sebastian, Juliane, & Steffen, 2016). 3. Results and discussion 3.1. Mechanism discussion for resorcinol ring oxidized by singlet oxygen In order to provide convincing evidence of the process, simple reaction systems including RB and three types of resveratrol dimers were irradiated with a mercury lamp (20 W, k > 200 nm) for 2 min at 23 °C ± 2 °C. According to the MS2 spectrum Figs. 2 (B1, C1, D1), the results found that two photochemical products:

X. Yin et al. / Food Chemistry 237 (2017) 1101–1111

1103

Fig. 1. Chemical structure of three types of resveratrol dimers.

(Mw = 468) and (Mw = 486) were gained by the attack of 1O2 to the symmetrical resorcinol ring. As show in Fig. 2(A), the resorcinol ring against with 1O2 the first step was 1,4-cycloaddition, producing the endoperoxide intermediate, thereafter, the subsequent reaction contained two pathways: pathway A underwent intra-molecular rearrangement to generate the quinones (Mw = 468), directly; pathway B abided by intra-molecular rearrangement and then continuous oxidation to

generate the quinones (Mw = 486), indirectly. Mechanism of 2 and 3 quenching 1O2 was elaborated by pathway A and lead directly to the formation of the quinones as showed in Figs. 2 (B2) and (C2), which inset them that the Extract Ion Chromatography (EIC) and the peak with the retention time at about 18.5 and 15.9 min represent (Mw = 468) of the reacted mixture contained 2 and 3 with 1O2, respectively. Another mechanism of 1 quenching 1 O2 was expounded by pathway B, indirectly lead to the formation

Fig. 2A. Proposed mechanism for resorcinol ring against 1O2.

Fig. 2B1. (Mw = 468) mass spectrum, Resorcinol ring of trans-epsilon-viniferin was oxidized by singlet oxygen. (The reaction mixtures contained samples : RB equal to 1 : 5, were irradiated by amercury lamp (20 W, k > 200 nm) for 2 min at 23 °C ± 2 °C. Instantly, 5 lL of the reaction mixture was withdrawn and analyzed by accurate UHPLC-ESIMS2).

1104

X. Yin et al. / Food Chemistry 237 (2017) 1101–1111

Fig. 2B2. Proposed mechanism for resorcinol ring of trans-e-viniferin against 1O2, (Mw = 468). Inset them that shows the EIC.

Fig. 2C1. (Mw = 468) mass spectrum, Resorcinol ring of trans-delta-viniferin was oxidized by singlet oxygen. (The reaction mixtures contained samples : RB equal to 1 : 5, were irradiated by amercury lamp (20 W, k > 200 nm) for 2 min at 23 °C ± 2 °C. Instantly, 5 lL of the reaction mixture was withdrawn and analyzed by accurate UHPLC-ESIMS2).

Fig. 2C2. Proposed mechanism for resorcinol ring of trans-r-viniferin against 1O2, (Mw = 468), Inset them that shows the EIC.

of the quinones that showed in Fig. 2(D2), inset it that shows the EIC and the peak with the retention time of about 15.7 min that represents (Mw = 486) of the reacted mixture of 1 with 1O2.

In Figs. 2 (B1, C1) mass spectrum, the precursor ions at 467.1100 ± 0.001 ([M H] ) produced the same neutral losses of C2O3 (72 Da), resulting in a fragment ion at 395.1285 ± 0.005

X. Yin et al. / Food Chemistry 237 (2017) 1101–1111

([M H] ), hence, Mw = 468 of the reacted mixture of 2 and 3 with 1 O2 has a similar fragmentation mechanism, resulting in a series of neutral losses of resorcinol ring and para phenol, which corresponds to Figs. 2 (B2) and (C2). With respect to 1, the precursor ions of 485.1228 ([M H] ) produced 467.1107 ([M H] ), we found that 1 and 2 have the same types of chemical structure (Fig. 2 (D2)). Thus, quinones, (Mw = 486) and (Mw = 468) have sim-

1105

ilarly fragmentation mechanism. Figs. 2 (B2), (C2) and (D2) has been well elucidated that lost basic neutral fragment at 18 Da, 28 Da were rather specific for the resorcinol ring in the samples. It is precisely due to the loss of similar neutral fragment ions, we believe that compounds which existed resorcinol ring reacted with singlet oxygen to produce quinone structure is correct and reasonable. According to the finding reported in the mentioned literature

Fig. 2D1. (Mw = 468) mass spectrum, Resorcinol ring of Scirpusin A was oxidized by singlet oxygen. (The reaction mixtures contained samples : RB equal to 1 : 5, were irradiated by amercury lamp (20 W, k > 200 nm) for 2 min at 23 °C ± 2 °C. Instantly, 5 lL of the reaction mixture was withdrawn and analyzed by accurate UHPLC-ESI-MS2).

Fig. 2D2. Proposed mechanism for resorcinol ring of Scirpusin A against 1O2, (Mw = 486), Inset them that shows the EIC.

Fig. 3A. Proposed mechanism for trans-double bond against 1O2 by [2+2] addition cyclizing.

1106

X. Yin et al. / Food Chemistry 237 (2017) 1101–1111

Fig. 3B. Proposed mechanism for oxetane against 1O2 by [4+1]/[4+2] addition cyclizing.

Fig. 3C1. (Mw = 500) mass spectrum, trans-double bond and oxetane of trans-epsilon-viniferin was cyclized with singlet oxygen. (The reaction mixtures contained samples : RB equal to 1 : 5, were irradiated by amercury lamp (20 W, k > 200 nm) for 2 min at 23 °C ± 2 °C. Instantly, 5 lL of the reaction mixture was withdrawn and analyzed by accurate UHPLC-ESI-MS2).

Fig. 3C2. Proposed mechanism for [2+2] addition of trans-double bond and [4+1] addition of oxetane of trans-e-viniferin against 1O2, (Mw = 500).

X. Yin et al. / Food Chemistry 237 (2017) 1101–1111

(Jiang et al., 2010) that the resorcinol ring in resveratrol changed into quinones during the oxidation processes by 1O2. In spite of the diversity in the structural complexity of the three samples, their reaction pathways are definitive.

1107

3.2. Process discussion of the trans-double bond and oxetane cyclized with singlet oxygen According to the mass spectrum Figs. 3 (C1, D1, E1), the paper found that two photochemical products were created: (Mw = 500)

Fig. 3D1. (Mw = 500) mass spectrum, trans-double bond and oxetane of trans-delta-viniferin was cyclized with singlet oxygen. (The reaction mixtures contained samples : RB equal to 1 : 5, were irradiated by amercury lamp (20 W, k > 200 nm) for 2 min at 23 °C ± 2 °C. Instantly, 5 lL of the reaction mixture was withdrawn and analyzed by accurate UHPLC-ESI-MS2).

Fig. 3D2. Proposed mechanism for [2+2] addition of trans-double bond and [4+1] addition of oxetane of trans-r-viniferin against 1O2, (Mw = 500).

Fig. 3E1. (Mw = 532) mass spectrum, trans-double bond and oxetane of Scirpusin A was cyclized with singlet oxygen. (The reaction mixtures contained samples : RB equal to 1 : 5, were irradiated by amercury lamp (20 W, k > 200 nm) for 2 min at 23 °C ± 2 °C. Instantly, 5 lL of the reaction mixture was withdrawn and analyzed by accurate UHPLCESI-MS2).

1108

X. Yin et al. / Food Chemistry 237 (2017) 1101–1111

Fig. 3E2. Proposed mechanism for [2+2] addition of trans-double bond and [4+2] addition of oxetane of Scirpusin A against 1O2, (Mw = 532).

Fig. 4A. Proposed mechanism for 5-phenol-2,3-dihydrobenzofuran ring of trans-e-viniferin against 1O2.

Fig. 4B. (Mw = 485) and (Mw = 469) mass spectrum, 5-phenol-2,3-dihydrobenzofuran ring of trans-e-viniferin was cyclized with singlet oxygen.(The reaction mixtures contained samples : RB equal to 1 : 5, were irradiated by amercury lamp (20 W, k > 200 nm) for 2 min 23 °C ± 2 °C. Instantly, 5 lL of the reaction mixture was withdrawn and analyzed by accurate UHPLC-ESI-MS2).

X. Yin et al. / Food Chemistry 237 (2017) 1101–1111

and (Mw = 532) and assumed to be a result of the attack of 1O2 on intra-molecular trans-double bonds and oxetane. As shown in Fig. 3(A), singlet oxygen oxidized trans-double bond divided into two categories, which determined by the number of hydroxyl

1109

groups on the benzene ring that was connected with the transdouble bond. The [2+2] cycloaddition forming different endoperoxides, 1 and 2 have one hydroxyl group on the benzene ring which led them to have the same type of cycloaddition (Fig. 3(A(a2))).

Fig. 4C. Proposed mechanism for 5-phenol-2,3-dihydrobenzofuran ring of trans-e-viniferin against 1O2, (Mw = 486).

Fig. 4D. Proposed mechanism for 5-phenol-2,3-dihydrobenzofuran ring of trans-e-viniferin against 1O2, (Mw = 470).

1110

X. Yin et al. / Food Chemistry 237 (2017) 1101–1111

Whereas [2+2] cycloaddition of 3 is used to form the other structure because of the two hydroxyl groups that shown by Fig. 3(A (a1)). According to the above explanation, calculations were carried out as a subsequent step between the oxetane and hydroxyl groups of phenol moieties, which connected with oxetane and cyclized for the formation of the (Mw = 500) and (Mw = 532). The product ions supply the reaction with rationality and integrity (Fig. 3(B)). Similar to the above chemical addition, on account of 2 and 3 having the same structure at phenol moieties that connected with one hydroxyl group, the [4+1] cycloaddition formation that results in monoxetane is shown in Fig. 3(B(b2 & b3)). Also, the [4+2] cycloaddition of the formation to dioxetane is shown in Fig. 3(B(b1)), elaborating 1 of intra-molecular catechol group. Therefore, we believe that the difference between [4+1] cycloaddition and [4+2] cycloaddition that in the number of hydroxyl groups on phenol moieties. As seen in Fig. 3 (C2) and (D2), 2 and 3 against with 1O2 formation 499.1371 ± 0.001 ([M H] ), are producing the same neutral losses of O3 (46 Da), C2O (42 Da) and CO (26 Da), resulting in fragmented ions at 453.1310 ± 0.001 ([M H] ), 411.1270 ± 0.001 ([M H] ) and 385.1348 ± 0.006 ([M H] ). Hence, (Mw = 500) of the reacted mixtures of 2 and 3 with 1O2 have a similar fragmentation mechanism. Inset it that shows the EIC and the peak with the retention time of about 17.9 and 18.0 min, respectively. However, in consideration of the results in Fig. 3(E1), it was differ from above mechanism that trans-double bond and o-dihydroxybenzene were oxidized by singlet oxygen. We suspected that 1 with 1O2 reaction was another one of the mechanisms because of precursor ion 532.1211 ([M H] ) produced neutral losses of O4 (63 Da) and C13H8O4 (228 Da) to generate 469.1295 ([M H] ) and 241.0409 ([M H] ) as shown by Fig. 3(E2). Interestingly, it was noted that the cycloaddition of trans-double bond and oxetane results matched with the literature (Celaje et al., 2011). It was generated in each case for oxygen heterocyclic structures of resveratrol derivatives, owing to the different chemical quenching of these various quenchers. In above all, we propsed that compounds contained trans-double bond and hydroxyl groups on phenol moieties feasiblely occurred [2+2] and [4+1]/[4+2] cycloaddition. 3.3. Mechanism discussion for 5-phenol-2,3-dihydrobenzofuran ring oxidized by singlet oxygen 500 lL 72 lM RB, and 100 lL 0.37 mM Trans-e-viniferin for UHPLC-ESI-MS2 experiments exhibited an exciting results. Through Fig. 1 the paper found that 2 and 1 are resveratrol dimer analogues and that they only differed by one hydroxyl group in the structure, indicating that a relationship exists between the chemical syntheses. According to the studies, the resveratrol by hydroxylase 1B1 (HsCYP1B1) led to pterostilbene or piceatannol (Martinez-Marquez et al., 2016), so generation of 1 would be expected by 2 under the effect of hydroxy transferase. Thereafter, by the UHPLC-ESI-MSn analysis the reacted mixture of 2 against 1 O2 showed the mass spectrum of two precursor ions at 469.1309 ([M H] ) and 485.1248 ([M H] ) in Fig. 4(B). However, it was seen that the fragment ions information of 485.1248 ([M H] ) was different from the fragment ions evidence of resorcinol ring of 1 oxidized by the singlet oxygen to generate the quinones 485.1228 ([M H] ). The results prove that there are no hydroxy transferase in the reaction mixture liquid and that we cannot directly make 2 plus one hydroxyl group generated 1. The paper speculated that the formations of the two precursor ions have a correlation between the similar chemical structures (5phenol-2,3-dihydrobenzofuran ring) of 2 and 1. 5-phenol-2,3dihydrobenzofuran ring was researched against with 1O2 by adding oxygen to generate the stability of the conjugate electrophilic structure that is showed in Fig. 4(A). Furthermore, the results

showed that the fragmental mechanism of two precursor ions in Fig. 4 (C & D), 2 react with 1O2 formation 485.1243 ([M H] ) and 469.1293 ([M H] ) produce a series of neutral losses of O (16 Da), two O (16 Da), C7H6O (104 Da), C6H6 (78 Da) and C6H6O (94 Da) to generate dominant fragment ions at 453.1343 ([M H] ), 347.0925 ([M H] ), 242.0506 ([M H] ), 375.0873 ([M H] ) and 281.0455 ([M H] ), inset it that shows the EIC and the peak with the retention time of about 15.6 and 14.7 min represents (Mw = 486) and (Mw = 470) of the reacted mixture of 2 with 1O2, respectively. 4. Conclusion As mentioned above, Scirpusin A 1, Trans-e-viniferin 2 and Trans-r-viniferin 3 are analogues and isomers of resveratrol dimers. The mechanism of quenching singlet oxygen was investigated by using similar and diverse groups in the three compounds. Results performed by the UHPLC combined with accurate MS with the reaction conditions. One reaction mode of the three stilbenes dimers quenching singlet oxygen namely the oxidation of resorcinol ring, which changes into the quinones with 14 Da or 16 Da higher than three resveratrol dimers; another one is [2+2] addition of trans-double bond combined with the [4+1]/[4+2] cyclization of oxetane, generating photo-chemical products with molecular weights higher than Trans-r-viniferin 3, Trans-e-viniferin 2 and Scirpusin A 1 at 46 Da, 46 Da and 63 Da respectively. Additionally, the 5-phenol-2,3-dihydrobenzofuran ring of Trans-e-viniferin 2 was oxidized by the construction stability conjugate electrophilic structure. Accordingly, we propose several mechanisms of stilbenoids quenching the singlet oxygen: compounds contained resorcinol ring reacted with singlet oxygen to produce quinone structure; trans-double bond and hydroxyl groups on phenol moieties feasiblely occurred [2+2] and [4+1]/[4+2] cycloaddition, as well as special isomers quenching singlet oxygen in different ways due to the number of hydroxyl groups. To the best of our knowledge, this is the most recent and detailed report on the mechanism discussion of isomers and the analogues of resveratrol dimers by selective quenching singlet oxygen. Acknowledgments This work was supported by National Natural Sciences Foundation of China (grant numbers 21362028, 31260402, 31460411 and 31671904); the Fundamental Research Funds for the Central Universities (grant numbers GK201603095, 2016CSZ009); Agricultural Science and Technology Innovation and Research (grant numbers 2016NY-184, 2016NY-195); One Hundred Person Project of Shaanxi Province and Oversea Scholarship Program of Shaanxi Normal University. References Aluyen, J. K., Ton, K. N., Tran, T., Yang, A. E., Gottlieb, H. B., & Bellanger, R. A. (2012). Resveratrol: Potential as anticancer agent. Journal of Dietary Supplements, 9, 45–56. Celaje, J. A., Zhang, D., Guerrero, A. M., & Selke, M. (2011). Chemistry of transresveratrol with singlet oxygen: [2+2] addition, [4+2] addition, and formation of the Phytoalexin Moracin M. American Chemical Society, 13, 4846–4849. Christoph, R., Emma, L. S., Sebastian, W., Juliane, H., & Steffen, N. (2016). MetFrag relaunched: Incorporating strategies beyond in silico fragmentation. Journal of Cheminformatics, 8, 1–16. Escote, X., Miranda, M., Menoyo, S., Rodriguez-Porrata, B., & Madeo, F. (2012). Resveratrol induces antioxidant defence via transcription factor Yap1p. Yeast, 29, 251–263. Ficarra, S., Tellone, E., Pirolli, D., Russo, A., Barreca, D., Galtieri, A., ... Rosa, M. (2016). Insights into the properties of the two enantiomers of trans-r-viniferin, a resveratrol derivative: Antioxidant activity, biochemical and molecular modeling studies of its interactions with hemoglobin. Molecular BioSystems, 12, 1276–1286.

X. Yin et al. / Food Chemistry 237 (2017) 1101–1111 He, S., Jiang, L. Y., Wu, B., Zhou, J., & Pan, Y. J. (2009a). Two novel antioxidative stilbene tetramers from Parthenocissus laetevirens. Helvetica Chimica Acta, 92, 1260–1267. He, S., Lu, Y. B., Jiang, L. Y., Wu, B., Zhang, F. Y., & Pan, Y. J. (2009b). Preparative isolation and purification of antioxidative stilbene oligomers fromVitis chunganeniss using high-speed counter-current chromatography in stepwise elutionmode. Journal of Separation Science, 32, 2339–2345. Jiang, L. Y., He, S., Jiang, K. Z., & Pan, Y. J. (2010). Resveratrol and its oligomers from wine grapes are selective 1O2 Quenchers: mechanistic implication by highperformance liquid chromatography-electrospray ionization-tandem mass spectrometry and theoretical calculation. Journal of Agricultural and Food Chemistry, 58, 9020–9027. Kim, S., Ghafoor, K., Lee, J., Feng, M., Hong, J., Lee, D. U., & Park, J. (2013). Bacterial inactivation in water, DNA strand breaking, and membrane damage induced by ultraviolet-assisted titanium dioxide photocatalysis. Water Research, 47, 4403–4411. Kong, Q. J., Ren, X. Y., Hu, R. L., Yin, X. F., Jiang, G. S., & Pan, Y. J. (2016). Isolation and purification of two antioxidant isomers of resveratrol dimer from the wine grape by counter-current chromatography. Journal of Separation Science, 39, 2374–2379. Kong, Q. J., Ren, X. Y., Jiang, L. Y., Pan, Y. J., & Sun, C. R. (2010). Scirpusin A, a hydroxystilbene dimer from Xinjiang wine grape, acts as an effective singlet oxygen quencher and DNA damage protector. Journal of The Science of Food and Technology, 90, 823–828. Li, C., Xu, X. F., Tao, Z. H., Wang, X. J., & Pan, Y. J. (2015). Resveratrol dimers, nutritional components in grape wine, are selective ROS scavengers and weak Nrf2 activators. Food Chemistry, 173, 218–223. Lygin, A. V., Hill, C. B., Pawlowski, M., Zernova, O. V., Widholm, J. M., Hartman, G. L., & Lozovaya, V. V. (2014). Inhibitory effects of stilbenes on the growth of three soybean pathogens in culture. Phytopathology, 104, 843–850. Martinez-Marquez, A., Morante-Carriel, J. A., Ramirez-Estrada, K., Cusido, R. M., Palazon, J., & Bru-Martinez, R. (2016). Production of highly bioactive resveratrol analogues pterostilbene and piceatannol in metabolically engineered grapevine cell cultures. Plant Biotechnology Journal, 14, 1813–1825. Mazzone, G., Alberto, M. E., Russo, N., & Sicilia, E. (2014). Ab initio calculations on the 1O2 quenching mechanism by trans-resveratrol. Physical Chemistry Chemical Physics, 16, 12773–12781. Ohara, K., Kusano, K., Kitao, S., Yanai, T., Takata, R., & Kanauchi, O. (2015). EpsilonViniferin, a resveratrol dimer, prevents diet-induced obesity in mice. Biochemical and Biophysical Research Communications, 468, 877–882.

1111

Pezet, R., Perret, C., Jean-Denis, J. B., Tabacchi, R., Gindro, K., & Viret, O. (2003). rViniferin, a resveratrol dehydrodimer: One of the major stilbenes synthesized by stressed grapevine leaves. Journal of Agricultural and Food Chemistry, 51, 5488–5492. Rodriguez-Cabo, T., Rodriguez, I., Ramil, M., & Cela, R. (2015). Comprehensive evaluation of the photo-transformation routes of trans-resveratrol. Journal of Chromatography A, 1410, 129–139. Shang, Y. J., Qian, Y. P., Liu, X. D., Dai, F., Shang, X. L., & Jia, W. Q. (2009). Radicalscavenging activity and mechanism of resveratrol-oriented analogues: Influence of the solvent, radical, and substitution. Journal of Organic Chemistry, 74, 5025–5030. Shao, B., Guo, H. Z., Cui, Y. J., Liu, A. H., Yu, H. L., & Guo, H. (2007). Simultaneous determination of six major stilbenes and flavonoids in Smilax china by high performance liquid chromatography. Journal of Pharmaceutical and Biomedical Analysis, 44, 737–742. Sohal, R. S., & Weindruch, R. (1996). Oxidative stress, caloric restriction, and aging. Science, 273, 59–63. To, T. L., Medzihradszky, K. F., Burlingame, A. L., DeGrado, W. F., Jo, H., & Shu, X. K. (2016). Photoactivatable protein labeling by singlet oxygen mediated reactions. Bioorganic & Medicinal Chemistry Letters, 26, 3359–3363. Xia, Q., Yin, J. J., Fu, P. P., & Boudreau, M. D. (2007). Photo-irradiation of Aloe vera by UVA - Formation of free radicals, singlet oxygen, superoxide, and induction of lipid peroxidation. Toxicology Letters, 168, 165–175. Yanez, M., Fraiz, N., Cano, E., & Orallo, F. (2006). ( )-Trans-e-viniferin, a polyphenol present in wines, is an inhibitor of noradrenaline and 5-hydroxytryptamine uptake and of monoamine oxidase activity. European Journal of Pharmacology, 542, 54–60. Zhang, Y. J., Jayaprakasam, B., Seeram, N. P., Olson, L. B., DeWitt, D., & Nair, M. D. (2004). Insulin secretion and cyclooxygenase enzyme inhibition by cabernet sauvignon grape skin compounds. Journal of the Science of Food and Agriculture, 52, 228–233. Zhang, N. N., Li, Z. C., Xu, K., Wang, Y. Y., & Wang, Z. (2016). Resveratrol protects against high-fat diet induced renal pathological damage and cell senescence by activating SIRT1. Biological & Pharmaceutical Bulletin, 39, 1448–1454. Zhao, H. J., Ma, T., Fan, B. Y., Yang, L., Han, C., Luo, J. G., & Kong, L. Y. (2016). Protective effect of trans-r-viniferin against high glucose-induced oxidative stress in human umbilical vein endothelial cells through the SIRT1 pathway. Free Radical Research, 50, 68–83.