Protein S-nitrosylation modulates important cellular processes, including neurotransmission, vasodilation, proliferation, and apoptosis in various cell types. We have previously reported that protein disulfide isomerase (PDI) is S-nitrosylated in brains of patients with sporadic neurodegenerative diseases. This modification inhibits PDI enzymatic activity and consequently leads to the accumulation of unfolded/misfolded proteins in the endoplasmic reticulum (ER) lumen. Here, we describe S-nitrosylation of additional ER pathways that affect the unfolded protein response (UPR) in cell-based models of Parkinson’s disease (PD). We demonstrate that nitric oxide (NO) can S-nitrosylate the ER stress sensors IRE1α and PERK. While S-nitrosylation of IRE1α inhibited its ribonuclease activity, S-nitrosylation of PERK activated its kinase activity and downstream phosphorylation/inactivation or eIF2α. Site-directed mutagenesis of IRE1α(Cys931) prevented S-nitrosylation and inhibition of its ribonuclease activity, indicating that Cys931 is the predominant site of S-nitrosylation. Importantly, cells overexpressing mutant IRE1α(C931S) were resistant to NO-induced damage. Our findings show that nitrosative stress leads to dysfunctional ER stress signaling, thus contributing to neuronal cell death.
Cobalt-catalyzed Markovnikov-selective hydroamination of nonactivated olefins was developed. Hydrogen atom transfer from a catalytically generated cobalt(III)−hydride complex to the olefins proceeded regioselectively, and the nucleophilic addition of benzotriazoles occurred selectively at their N 2 -positions. The synthetic utility of the obtained N 2 -alkylated benzotriazoles as stable amine protecting groups under various reaction conditions was demonstrated, and the products were also transformed into primary amines by zinc-mediated reduction.
This paper describes a total synthesis of (-)-strictinin, an ellagitannin that is 1-O-galloyl-4,6-O-(S)-hexahydroxydiphenoyl (HHDP)-β-D-glucose. In the study, total efficiency of the synthesis was improved to produce a 78% overall yield in 13 steps from D-glucose. In the synthesis, formation of the 4,6-(S)-HHDP bridge including the 11-membered bislactone ring was a key step, in which intramolecular aryl-aryl coupling was adopted. The coupling was oxidatively induced by CuCl2-n-BuNH2 with perfect control of the axial chirality, and the reaction conditions of this coupling were optimized thoroughly to achieve the quantitative formation of the bridge.
Herein, we describe
the generation of an organochromium-type carbanion
species from a non-activated C–H bond and its nucleophilic
addition to aldehydes. The catalytic carbanion generation occurred
through formal deprotonation of a non-activated C–H bond under
mild conditions and did not need the prefunctionalization or anion
stabilizing group. Carbon radical intermediates generated by decatungstate
photocatalyst-mediated hydrogen abstraction were captured by a chromium
salt with the reductive radical-polar crossover reaction to produce
organochromium carbanions.
High S(N)2' selectivity in the allylic substitution of cyclohexylidene ethyl picolinates with copper reagents prepared from RMgBr and CuBr.Me(2)S was realized by addition of ZnX(2) (X = I, Br, Cl). Furthermore, ZnX(2) accelerated the reaction with the bulky iPr reagent.
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