The methanol extract of the leafy covers of Corylus avellana, source of the Italian PGI (protected geographical indication) product "Nocciola di Giffoni", afforded two new cyclic diarylheptanoids, giffonins T and U (2 and 3), along with two known cyclic diarylheptanoids, a quinic acid, flavonoid-, and citric acid derivatives. The structures of giffonins T and U were determined as highly hydroxylated cyclic diarylheptanoids by 1D and 2D NMR experiments. Their relative configurations were assigned by a combined quantum mechanical/NMR approach, comparing the experimental C/H NMR chemical shift data and the related predicted values. The absolute configurations of carpinontriol B (1) and giffonins T and U (2 and 3) were assigned by comparison of their experimental electronic circular dichroism curves with the TDDFT-predicted curves. The ability of the compounds to inhibit the lipid peroxidation induced by HO and HO/Fe was determined by measuring the concentration of thiobarbituric acid reactive substances. Furthermore, the antimicrobial activity of the methanol extract of leafy covers of C. avellana and of the isolated compounds against the Gram-positive strains Bacillus cereus and Staphylococcus aureus and the Gram-negative strains Escherichia coli and Pseudomonas aeruginosa was evaluated. Carpinontriol B (1) and giffonin U (3) at 40 μg/disk caused the formation of zones of inhibition.

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Eight new diaryl ether heptanoids, giffonins A-H (1-8), and one diaryl heptanoid, giffonin I (9), were isolated from the methanol extract of the leaves of Corylus avellana. Its hazelnut is the PGI product of the Campania region (Italy) known as "Nocciola di Giffoni". The MeOH extract of C. avellana leaves and giffonins A-I (1-9) were evaluated for their inhibitory effects on human plasma lipid peroxidation induced by H2O2 and H2O2/Fe(2+), by measuring the concentration of TBARS (thiobarbituric acid reactive substances). Compounds 4 and 8 at 10 μM reduced both H2O2- and H2O2/Fe(2+)-induced lipid peroxidation by more than 60% and 50%, respectively, indicating higher activity than curcumin used as reference compound.

The endoplasmic reticulum (ER) is a dynamic organelle essential for intracellular homeostasis maintenance, controlling synthesis, the folding of secreted and membrane-bound proteins, and transport of Ca2+. During cellular stress, ER dysfunction leads to the activation of unfolded protein response (UPR) due to accumulated misfolded proteins in the ER. This condition is referred as ER stress. Mitochondria and ER form a site of close contact (the mitochondria-associated membrane, MAM) which is a major platform exerting important physiological roles in the regulation of intracellular Ca2+ homeostasis, lipid metabolism, mitochondrial fission, autophagosome formation, and apoptosis progression. Natural products have been receiving increasing attention for their ability to interfere with ER stress. Research works have focused on the capacity of these bioactive compounds to induce apoptosis by activating ER stress through the ER stress-mediated mitochondrial apoptotic pathway. In this review we discuss the role of natural products in the signaling communication between ER and mitochondria, focusing on the effects induced by ER stress including Ca2+ permeability transition and UPR signaling (protein kinase R-like ER kinase/mitofusin 2).

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