Polyamine-Conjugated Nitroxides Are Efficacious Inhibitors of Oxidative Reactions Catalyzed by Endothelial-Localized Myeloperoxidase.

The heme enzyme myeloperoxidase (MPO) is a key mediator of endothelial dysfunction and a therapeutic target in cardiovascular disease. During inflammation, MPO released by circulating leukocytes is internalized by endothelial cells and transcytosed into the subendothelial extracellular matrix of diseased vessels. At this site, MPO mediates endothelial dysfunction by catalytically consuming nitric oxide (NO) and producing reactive oxidants, hypochlorous acid (HOCl) and the nitrogen dioxide radical (•NO2). Accordingly, there is interest in developing MPO inhibitors that effectively target endothelial-localized MPO. Here we studied a series of piperidine nitroxides conjugated to polyamine moieties as novel endothelial-targeted MPO inhibitors. Electron paramagnetic resonance analysis of cell lysates showed that polyamine conjugated nitroxides were efficiently internalized into endothelial cells in a heparan sulfate dependent manner. Nitroxides effectively inhibited the consumption of MPO's substrate hydrogen peroxide (H2O2) and formation of HOCl catalyzed by endothelial-localized MPO, with their efficacy dependent on both nitroxide and conjugated-polyamine structure. Nitroxides also differentially inhibited protein nitration catalyzed by both purified and endothelial-localized MPO, which was dependent on •NO2 scavenging rather than MPO inhibition. Finally, nitroxides uniformly inhibited the catalytic consumption of NO by MPO in human plasma. These studies show for the first time that nitroxides effectively inhibit local oxidative reactions catalyzed by endothelial-localized MPO. Novel polyamine-conjugated nitroxides, ethylenediamine-TEMPO and putrescine-TEMPO, emerged as efficacious nitroxides uniquely exhibiting high endothelial cell uptake and efficient inhibition of MPO-catalyzed HOCl production, protein nitration, and NO oxidation. Polyamine-conjugated nitroxides represent a versatile class of antioxidant drugs capable of targeting endothelial-localized MPO during vascular inflammation.

Total Synthesis of a Dimeric Thymol Derivative Isolated from Arnica sachalinensis.

The total synthesis of a dimeric thymol derivative (thymarnicol) isolated from Arnica sachalinensis was accomplished in 6 steps. A key biomimetic Diels-Alder dimerization was found to occur at ambient temperature and the final oxidative cyclization occurs when the substrate is exposed to air and visible light. These results indicate that this natural product is likely the result of spontaneous (non-enzyme-mediated) reactivity.

Enantioselective para-Claisen Rearrangement for the Synthesis of Illicium-Derived Prenylated Phenylpropanoids.

The development of the first enantioselective para-Claisen rearrangement has been achieved. Using a chiral aluminum Lewis acid, illicinole is rearranged to give (-)-illicinone A (er 87:13), which can then be converted into more complex Illicium-derived prenylated phenylpropanoids. The absolute configurations of the natural products (+)-cycloillicinone and (-)-illicarborene A have been determined, and our results cast doubt on the enantiopurity of the natural samples.