Chemodiversity evaluation of grape (Vitis vinifera) vegetative parts during summer and early fall

The majority of studies on grape secondary metabolism are focusing on the berry or stem and leaves phenolic composition. Although the composition of phytochemicals is known to be highly variable in different cultivars, the changes of this composition during vine growth in vegetative parts remain poorly understood. The present study was performed to profile and compare several non-colored polyphenol compounds and the antioxidant potential of Vitis vinifera leaves and stems during a part of growing season and early fall (July, August, September and October) from seventy Iranian native cultivars (white and red) using HPLC-DAD method. Leaves showed significantly higher amounts of analyzed phenolics. Considering the average amounts, the most predominant detected phenolics in the leaves were catechin and o-coumaric acid while the most abundant compound found in the stems was quercetin. Naringenin was found as the lowest detected phenolic. The phenolic potential of the samples varied in each time point. Antioxidant activity was detected higher in stems than leaves with the highest in white cultivar “Atabaki” in both leaves and stems. Leaves of the red cultivars “Angourab” and “Yaghouti shiraz” showed the highest concentrations considering the summation of analyzed phenolics. In addition to the cultivar and plant organ, the phenolic potential of the samples varied in each time point. All samples exhibited antioxidant activity using the DPPH radical and Folin-Ciocalteo Reagent, with mostly higher amounts in stems than leaves showing a strong correlation between two methods In view of both methods, white cultivars were more often higher than red ones with the highest amounts detected in stems and leaves of white cultivar “Atabaki”. PCA results confirmed the variability of phenolic composition in grapevines and during four-month development and showed no obvious discrimination among red and white cultivars. As far as we know, this is the first time that a relationship between the content of polyphenolic compounds is evaluated in leaves and stems, as well as the targeted phenolic profiling of several cultivars foliage. Targeted phenolics profiling indicated the high potential of such wastes to be used in the pharmaceutical, cosmetic and food industries.Maliheh Eftekhar, Abbas Yadollahi, Christopher M.Ford, Abdolali Shojaeiyan, Mahdi Ayyari, Hossein Hokmabad

The Thia-Michael reactivity of zerumbone and related cross-conjugated dienones: disentangling stoichiometry, regiochemistry and addition mode with an NMR-spectroscopy based cysteamine assay.

The cross-conjugated and electrophilic dienone system of the humulane sesquiterpene zerumbone (1a) was modified by E/Z photochem. isomerization and/or by removal of homoconjugation with the isolated endocyclic double bond of the medium-sized ring. The site (C-6/C-9), mode (transient or irreversible), stoichiometry (single or twofold), and comparative rates of thiol addn. were evaluated using an NMR-spectroscopy-based cysteamine assay. Dramatic effects were seen, and this highlights the subtleties of the reaction and the limitations of our predictive power in this field. For biol. endpoints sensitive to thiol trapping, a substantial sepn. between Michael reactivity and biol. activity was found for 1a and its analogs. This supports the view that shape complementarity plays a crit. role in the covalent binding of Michael acceptors to their macromol. target(s)