A dimeric stilbene extract produced by oxidative coupling of resveratrol active against <em>Plasmopara viticola</em> and <em>Botrytis cinerea</em> for vine treatments

Abstract

a b s t r a c tAim: Stilbenes are a group of polyphenols that contribute to the defense mechanisms of grapevine under stress conditions. The main active compounds are oligomeric stilbenes. The sourcing of such compounds is limited by plant raw material availability. In order to overcome this limitation, we proceeded to hemisynthesis of oligomeric stilbenes from natural resveratrol by oxidative coupling using metals. The reaction mixture and the obtained pure compounds were tested for their antimicrobial activity in vitro against P. viticola and B. cinerea, and compared with that of resveratrol and grapevine cane extract. Methods and results: Hemisynthesis was achieved in methanol using silver acetate (AgOAc) as oxidative coupling reagent. Four main compounds were obtained in the reaction mixture: δ-viniferin, parthenostilbenin B, oxistilbenins A and B. Results demonstrate the ability of oxidative coupling reaction to produce potent inhibitors of P. viticola and B. cinerea. The reaction mixture is enriched in antimicrobial compounds with high potency as it is at least eight times more active than grapevine cane extract against P. viticola. In addition, this reaction mixture reveals a high fungitoxicity against B. cinerea in contrast to the grapevine extract. Conclusion: The present findings indicate that metals could be used for producing highly antimicrobial compounds from natural resveratrol. Significance and impact of the study: In this study, a method to produce active dimeric stilbenes to protect grapevine was developed based on botanical ingredients. The combination of natural extracts, rich in resveratrol, and metals such as copper may be used as alternatives to Bordeaux mixture and chemical fungicides to protect crops. k e y w o r d s resveratol, stillbene, hemisynthesis, grey mould, mildew

Chemical process to improve natural grapevine-cane extract effectivity against powdery mildew and grey mould

“…Based on our previously published protocol (El Khawand et al, 2020a), regioselective oxidative coupling reaction was conducted on 1 g of the purified extract. The quantity of the silver acetate (AgOAc) metallic catalyst added to perform the reaction was calculated according to the quantities of resveratrol and εviniferin in the extract, to afford a stilbene:AgOAc ratio of 1:1.5 The purified extract and AgOAc were dissolved in MeOH (100 %, 100 mL).…”

“…Several studies showed that oxidative coupling of resveratrol was possible using metals (Sako et al, 2004;Snyder et al, 2011;Velu et al, 2008) leading to the formation of effective compounds against grapevine pathogens (El Khawand et al, 2020a). These reactions could take place in different media including wine (El Khawand et al, 2020b).…”

Grapevine Cane Extracts: Raw Plant Material, Extraction Methods, Quantification, and Applications

“…Natural extracts rich in stilbenes have received increasing attention due to their antimicrobial activity against grapevine pathogens [ 103 , 104 , 105 ]. Stilbenes have exhibited significant antifungal activity in vitro and in the field on P. viticola and B. cinerea [ 16 , 106 ], even in the hemisynthesis of oligomeric stilbenes by oxidative coupling using metals such as copper [ 16 , 106 , 107 ]. In fact, plants have been found to accumulate the most toxic stilbenes at infection sites [ 108 , 109 ].…”

Optimization and Green Metrics Analysis of the AgOAc-Mediated Dimerization of Piceid: Toward a High-Yielding and More Sustainable Access to δ-Viniferin and Synthesis of New Piceid Dimers

“…[6][7][8][9] Resveratrol (1, Figure 1), the major stilbene in wine, 10 can be obtained in relatively significant amount (a few milligrams per liter) from other natural sources such as Japanese knotweed (Polygonum cuspidatum). 11 In planta, resveratrol is commonly present under its corresponding 3-O-glucoside, called piceid or polydatin (3,5,4'-trihydroxystilbene-3-O-β-Dglucopyranoside) (2, Figure 1). 12,13 It was demonstrated that piceid can be hydrolyzed by some βglucosidases during fermentation to release neat resveratrol.…”

“…for crop treatment. Some (bio)chemical oxidative coupling reactions have been studied to obtain δ-viniferin (3). First, a laccase-catalyzed or peroxidase-catalyzed dimerization of resveratrol allows the obtention of the desired compound.…”