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The participation of both ligand and the metal center in the redox events has been recognized as one of the ways to attain the formal high valent complexes for the late 3d metals, such as Ni and Cu. Such an approach has been employed successfully to stabilize a Ni(III) bisphenoxyl diradical species in which there exist an equilibrium between the ligand and the Ni localized resultant spin. The present work, however, broadens the scope of the previously reported three oxidized equivalent species by conveying the approaches that tend to affect the reported equilibrium in CH3CN at 233 K. Various spectroscopic characterization revealed that employing exogenous N‐donor ligands like 1‐methyl imidazole and pyridine favors the formation of the Ni centered localized spin though axial binding. In contrast, due to its steric hinderance, quinoline favors an exclusive ligand localized radical species. DFT studies shed light on the novel intermediates′ complex electronic structure. Further, the three oxidized equivalent species with the Ni centered spin was examined for its hydrogen atom abstraction ability stressing their key role in alike reactions. [ABSTRACT FROM AUTHOR]

Intramolecular [super 13]C kinetic isotope effects are determined for the dimerization of cyclopentadiene. Trajectory studies have shown that the isotope effects are unrelated to zero-point energy or the geometrical and momentum properties of the transition state.

A new methodology is described and evaluated for measuring specific interatomic distances from a combination of theoretical calculations and experimentally measured [super 13]C kinetic isotope effects. The complexities present in the epoxidation of alkenes by oxaziridines have provided a diverse array of structures that come from varying substitutions, conformations and orientations of the oxaziridine.

The first example of an organic compound having racemic crystals which sublime substantially faster than the corresponding enantiomerically pure crystals is presented.

The study explains the mechanism of N-methyltryptophan oxidase and its relationship with the flavoprotein-catalyzed amine oxidation from nitrogen isotopes. Despite of being highly inconsistent, the kinetic isotope effects for sacrosine oxidation are found to be highly pH dependent.

A rapid entry into polycyclic structures, are provided by Diels-Alder reactions employing vinylcycloalkenes and related dienes. In order to take full advantage of these reactions, synthetic chemist must be able to predict or control their stereoselectivity.

Pharmacological strategies that boost intracellular NAD+ are highly coveted for their therapeutic potential. One approach is activation of nicotinamide phosphoribosyltransferase (NAMPT) to increase production of nicotinamide mononucleotide (NMN), the predominant NAD+ precursor in mammalian cells. A high-throughput screen for NAMPT activators and hit-to-lead campaign yielded SBI-797812, a compound that is structurally similar to active-site directed NAMPT inhibitors and blocks binding of these inhibitors to NAMPT. SBI-797812 shifts the NAMPT reaction equilibrium towards NMN formation, increases NAMPT affinity for ATP, stabilizes phosphorylated NAMPT at His247, promotes consumption of the pyrophosphate by-product, and blunts feedback inhibition by NAD+. These effects of SBI-797812 turn NAMPT into a "super catalyst" that more efficiently generates NMN. Treatment of cultured cells with SBI-797812 increases intracellular NMN and NAD+. Dosing of mice with SBI-797812 elevates liver NAD+. Small molecule NAMPT activators such as SBI-797812 are a pioneering approach to raise intracellular NAD+ and realize its associated salutary effects. Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate determining step for NAD+ synthesis and is of interest as a drug target. Here the authors identify and characterize a small molecule NAMPT activator SBI-797812, elucidate its mode of action and show that it increases intracellular NMN and NAD+ levels in cultured cells and elevates liver NAD+ in mice. [ABSTRACT FROM AUTHOR]

Abstract: A combination of experimental 13C kinetic isotope effects (KIEs) and high‐level density functional theory (DFT) calculations is used to distinguish between “enamine” and “enol” mechanisms in the Michael addition of acetone to trans‐β‐nitrostyrene catalyzed by Jacobsen's primary amine thiourea catalyst. In light of the recent findings that the widely used 18O‐incorporation probe for these mechanisms is flawed, the results described in this communication demonstrate an alternative probe to distinguish between these pathways. A key advantage of this probe is that quantitative mechanistic information is obtained without modifying experimental conditions. This approach is expected to find application in resolving mechanistic debates, while providing valuable information about the key transition state of organocatalyzed reactions involving the α‐functionalization of carbonyls. [ABSTRACT FROM AUTHOR]

Purine nucleoside phosphorylase (PNP) catalyzes the reversible phosphorolysis of 6-oxypurine (2′-deoxy)ribonucleosides, generating (2-deoxy)ribose 1-phosphate and the purine base. Transition-state models for inosine cleavage have been proposed with bovine, human, and malarial PNPs using arsenate as the nucleophile, since kinetic isotope effects (KIEs) are obscured on phosphorolysis due to high commitment factors. The Phe200Gly mutant of human PNP has low forward and reverse commitment factors in the phosphorolytic reaction, permitting the measurement of competitive intrinsic KIEs on both arsenolysis and phosphorolysis of inosine. The intrinsic 1′-14C, 1′-3H, 2′-2H, 9-15N, and 5′-3H2 KIEs for inosine were measured for arsenolysis and phosphorolysis. Except for the remote 5′-3H2, and some slight difference between the 2′-2H KIEs, all isotope effects originating in the reaction coordinate are the same within experimental error. Hence, arsenolysis and phosphorolysis proceed through closely related transition states. Although electrostatically similar, the volume of arsenate is greater than phosphate and supports a steric influence to explain the differences in the 5′-3H2 KIEs. Density functional theory calculations provide quantitative models of the transition states for Phe200Gly human PNP-catalyzed arsenolysis and phosphorolysis, selected upon matching calculated and experimental KIEs. The models confirm the striking resemblance between the transition states for the two reactions. [ABSTRACT FROM AUTHOR]