Radical Nitrososulfonation of Propargyl Alcohols: Thiazolidine-2,4-dione-Assisted Synthesis of 5-Alykyl-4-sulfonylisoxazoles

In this study, we discover a good NO/HNO precursor, N-hydroxypyridinesulfonamide, and the regioselective radical nitrososulfonylation reaction of propargyl alcohols. Direct and unique isoxazole synthesis afforded a good-to-high yield of 5-alkyl-3-aryl-4-pyridinesulfonylisoxazoles. Copper-catalyzed aerobic oxidation could efficiently proceed in the presence of thiazolidine-2,4-dione. This work provides a powerful method for the synthesis and functionalization of alkyl-substituted isoxazoles and explores a new investigation route for drug-drug discovery.

Synthesis and nitroxyl (HNO) donating properties of benzoxadiazole-based Piloty's acids

Developing functional nitroxyl (HNO) donors play a significant role in the further exploration of endogenous HNO in biochemistry and pharmacology. In this work, two novel Piloty's acids (SBD-D1 and SBD-D2) were proposed by incorporating benzoxadiazole-based fluorophores, in order to achieve the dual-function of releasing both HNO and a fluorophore in situ. Under physiological conditions, both SBD-D1 and SBD-D2 efficiently donated HNO (t_1/2 = 10.96 and 8.18 min, respectively). The stoichiometric generation of HNO was determined by both vitamin B₁₂ and phosphine compound traps. Interestingly, due to the different substitution groups on the aromatic ring, SBD-D1 with the chlorine showed no fluorescence emission, but SBD-D2 was strongly fluorescent due to the presence of the dimethylamine group. Specifically, the fluorescent signal would decrease during the release process of HNO. Moreover, theoretical calculations were performed to understand the emission difference. A strong radiation derived from benzoxadiazole with dimethylamine group due to the large transition dipole moment (∼4.3 Debye), while the presence of intramolecular charge transfer process in the donor with chlorine group caused a small transition dipole moment (<0.1 Debye). Finally, these studies would contribute to the future design and application of novel functional HNO donors for the exploration of HNO biochemistry and pharmacology.

Nitroprusside─Expanding the Potential Use of an Old Drug Using Nanoparticles

For more than 70 years, sodium nitroprusside (SNP) has been used to treat severe hypertension in hospital emergency settings. During this time, a few other clinical uses have also emerged such as in the treatment of acute heart failure as well as improving mitral incompetence and in the intra- and perioperative management during heart surgery. This drug functions by releasing nitric oxide (NO), which modulates several biological processes with many potential therapeutic applications. However, this small molecule has a short lifetime, and it has been administered through the use of NO donor molecules such as SNP. On the other hand, SNP also has some setbacks such as the release of cyanide ions, high water solubility, and very fast NO release kinetics. Currently, there are many drug delivery strategies that can be applied to overcome many of these limitations, providing novel opportunities for the use of old drugs, including SNP. This Perspective describes some nitroprusside properties and highlights new potential therapeutic uses arising from the use of drug delivery systems, mainly silica-based nanoparticles. There is a series of great opportunities to further explore SNP in many medical issues as reviewed, which deserves a closer look by the scientific community.

Reactivity of a nitrosyl ruthenium complex and its potential impact on the fate of DNA - An in vitro investigation

The role of metal complexes on facing DNA has been a topic of major interest. However, metallonitrosyl compounds have been poorly investigated regarding their reactivities and interaction with DNA. A nitrosyl compound, cis-[Ru(bpy)₂(SO₃)(NO)](PF₆)(A), showed a variety of promising biological activities catching our attention. Here, we carried out a series of studies involving the interaction and damage of DNA mediated by the metal complex A and its final product after NO release, cis-[Ru(bpy)₂(SO₃)(H₂O](B). The fate of DNA with these metal complexes was investigated upon light or chemical stimuli using electrophoresis, electronic absorption spectroscopy, circular dichroism, size-exclusion resin, mass spectrometry, electron spin resonance (ESR) and viscometry. Since many biological disorders involve the production of oxidizing species, it is important to evaluate the reactivity of these compounds under such conditions as well. Indeed, the metal complex B exhibited important reactivity with H₂O₂ enabling DNA degradation, with detection of an unusual oxygenated intermediate. ESR spectroscopy detected mainly the DMPO-OOH adduct, which only emerges if H₂O₂ and O₂ are present together. This result indicated HOO^• as a key radical likely involved in DNA damage as supported by agarose gel electrophoresis. Notably, the nitrosyl ruthenium complex did not show evidence of direct DNA damage. However, its aqua product should be carefully considered as potentially harmful to DNA deserving further in vivo studies to better address any genotoxicity.

Chemistry of a Nitrosyl Ligand κ:η-Bridging a Ditungsten Center: Rearrangement and N–O Bond Cleavage Reactions

The novel nitrosyl-bridged complex [W₂Cp₂(μ-P^tBu₂)(μ-κ:η-NO)(CO)(NO)](BAr₄) [Ar = 3,5-C₆H₃(CF₃)₂] was prepared in a multistep procedure starting from the hydride [W₂Cp₂(μ-H)(μ-P^tBu₂)(CO)₄] and involving the new complexes [W₂Cp₂(μ-P^tBu₂)(CO)₄](BF₄), [W₂Cp₂(μ-P^tBu₂)(CO)₂(NO)₂](BAr₄), and [W₂(μ-κ:η⁵-C₅H₄)Cp(μ-P^tBu₂)(CO)(NO)₂] as intermediates, which follow from reactions with HBF₄·OEt₂, NO, and Me₃NO·2H₂O, respectively. The nitrosyl-bridged cation easily added chloride upon reaction with [N(PPh₃)₂]Cl, with concomitant NO rearrangement into the terminal coordination mode, to give [W₂ClCp₂(μ-P^tBu₂)(CO)(NO)₂], and underwent N–O and W–W bond cleavages upon the addition of CN^tBu to give the mononuclear phosphinoimido complex [WCp(NP^tBu₂)(CN^tBu)₂](BAr₄). Another N–O bond cleavage was induced upon photochemical decarbonylation at 243 K, which gave the oxo- and phosphinito-bridged nitrido complex [W₂Cp₂(N)(μ-O)(μ-OP^tBu₂)(NO)](BAr₄), likely resulting from a N–O bond cleavage step following decarbonylation.

The π binding of the NO ligand in the cation [W₂Cp₂(μ-P^tBu₂)(μ-κ:η-NO)(CO)(NO)]⁺ facilitates the addition of ligands with concomitant rearrangement of the bridging nitrosyl into the terminal coordination mode and also facilitates cleavage of the N−O bond of that ligand at low temperature possibly in two different ways: either through the oxidative addition of this ligand to the dimetal center or through deoxygenation by another ligand.