Highly Efficient Bioconversion of trans-Resveratrol to δ-Viniferin Using Conditioned Medium of Grapevine Callus Suspension Cultures

Peroxidase 4-Based Enzymatic Synthesis of Stilbene Oligomers in Methyl Jasmonate-Elicited Grapevine Cell Suspensions

Stilbenes are specialized metabolites that are particularly abundant in Vitis species. Although the biosynthetic pathways of stilbenes have been well-characterized, the role of specific peroxidases in stilbene oligomerization remains to be investigated. In this study, we used grapevine cell cultures to characterize the functional role of Vitis vinifera peroxidase 4 (VvPRX4) in the production of resveratrol oligomers after elicitation with methyl jasmonate (MeJA). We showed that MeJA triggers the accumulation of t-resveratrol, resveratrol dimers, and predicted resveratrol trimers in culture medium. This accumulation was correlated with upregulation of the PRX4 gene in grapevine cells. Using bacterial crude extracts containing VvPRX4, we demonstrated that VvPRX4 converts t-resveratrol into dimers, t-ε-viniferin into tetramers, and both combined substrates into resveratrol trimers. Additionally, VvPRX4 mediates the formation of glycosylated dimers using t-piceid and t-resveratrol as substrates. These results highlight the functional role of VvPRX4 in stilbene oligomerization in MeJA-elicited grapevine cell cultures.

Study of phenoxy radical couplings using the enzymatic secretome of Botrytis cinerea

Phenoxy radical coupling reactions are widely used in nature for the synthesis of complex molecules such as lignin. Their use in the laboratory has great potential for the production of high value compounds from the polyphenol family. While the enzymes responsible for the generation of the radicals are well known, the behavior of the latter is still enigmatic and difficult to control in a reaction flask. Previous work in our laboratory using the enzymatic secretome of B. cinerea containing laccases has shown that incubation of stilbenes leads to dimers, while incubation of phenylpropanoids leads to dimers as well as larger coupling products. Building on these previous studies, this paper investigates the role of different structural features in phenoxy radical couplings. We first demonstrate that the presence of an exocyclic conjugated double bond plays a role in the generation of efficient reactions. In addition, we show that the formation of phenylpropanoid trimers and tetramers can proceed via a decarboxylation reaction that regenerates this reactive moiety. Lastly, this study investigates the reactivity of other phenolic compounds: stilbene dimers, a dihydro-stilbene, a 4-O-methyl-stilbene and a simple phenol with the enzymatic secretome of B. cinerea. The observed efficient dimerization reactions consistently correlate with the presence of a para-phenol conjugated to an exocyclic double bond. The absence of this structural feature leads to variable results, with some compounds showing low conversion or no reaction at all. This research has allowed the development of a controlled method for the synthesis of specific dimers and tetramers of phenylpropanoid derivatives and novel stilbene derivatives, as well as an understanding of features that can promote efficient radical coupling reactions.

Linkage and Stereochemistry Characters of Phenolic Antioxidant Product Formation

The present study developed a smart and novel strategy to elucidate the linkage and stereochemistry characters during phenolic antioxidant product formation. A series of phenolic isomers or analogues were treated with 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide radical, to create 16 antioxidant dimerization reactions in aqueous solution. The products were rapidly identified by ultraperformance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight tandem mass-spectrometry. Through a systematic function-structure relationship analysis of these reactions and theoretical calculations, it is concluded that the phenolic antioxidant product is formed via linear linkage or furanocyclic linkage. The linear linkage is fulfilled via a radical coupling and controlled by the O-O linkage exclusion, meta-linkage exclusion, and catechol-activated principles. However, when an exocyclic π-bond conjugates with the phenolic core and is affixed at the -OH para-position, the furanocyclic linkage may occur via a subsequent intramolecular Michael addition. The intramolecular addition always lacks Re-attack to show "α,β diastereoselectivity." The α,β diastereoselectivity is the stereochemistry character of furanocyclic linkage during phenolic antioxidant product formation. All these novel findings can benefit not only the field food science but also other fields as well.