Platinum(IV) Oxide Catalyzed H−D Exchange Reactions in Arylsilanes

Deuteration and Tritiation of Pharmaceuticals by Non-Directed Palladium-Catalyzed C-H Activation in Heavy and Super-Heavy Water

Deuterated and tritiated analogs of drugs are valuable compounds for pharmaceutical and medicinal chemistry. In this work, we present a novel hydrogen isotope exchange reaction of drugs using non-directed homogeneous Pd-catalysis. Aromatic C-H activation is achieved by a commercially available pyridine ligand. Using the most convenient and cheapest deuterium source, D2O, as the only solvent 39 pharmaceuticals were labelled with clean reaction profiles and high deuterium uptakes. Additionally, we describe the first application of non-directed homogeneous Pd-catalysis for H/T exchange on three different pharmaceuticals by using T2O as isotopic source, demonstrating the applicability to the synthesis of radiotracers.

Ru Supported on p-phthalic acid-Mn Derived from a Mn Metal-Organic Framework for Thermo- and Electrocatalytic Synthesis of Ethylene-D4 Glycol

Deuterium-labeled polyols are one of the most extensive applied chemicals in biochemistry and biophysics. However, the deuteriation still is insufficient, exhibiting a low deuterated ratio and indistinct reaction mechanism. Herein, Ru supported on MnBCD (MnBDC, derived from Mn p-phthalic acid metal-organic framework) as nanocatalyst with an agglomerated sheet-type structure; this allows the possibility of achieving both thermo- and electrocatalytic hydrogen isotope exchange (HIE) reaction. Furthermore, XPS characterization confirmed that the specific structural changes in the electron density of Ru outer layers were modulated through the impregnation and reduction processes. According to the change of outer electronic structure, hydrogen spillover and electron-rich flow promote the reaction of the catalyst in thermo- and electrocatalytic systems, respectively. In addition, the results indicate that a high deuterated ratio of 97 % can be obtained, hence the catalytic technology has enormous potential for the synthesis of a broad variety of deuterium-labeled compounds.

Palladium-Catalyzed Nondirected Late-Stage C-H Deuteration of Arenes

We describe a palladium-catalyzed nondirected late-stage deuteration of arenes. Key aspects include the use of D2O as a convenient and easily available deuterium source and the discovery of highly active N,N-bidentate ligands containing an N-acylsulfonamide group. The reported protocol enables high degrees of deuterium incorporation via a reversible C-H activation step and features extraordinary functional group tolerance, allowing for the deuteration of complex substrates. This is exemplified by the late-stage isotopic labeling of various pharmaceutically relevant motifs and related scaffolds. We expect that this method, among other applications, will prove useful as a tool in drug development processes and for mechanistic studies.

Continuous-Flow Hydrogenation and Reductive Deuteration of Nitriles: a Simple Access to α,α-Dideutero Amines

A simple and efficient continuous flow methodology has been developed for hydrogenation and reductive deuteration of nitriles to yield primary amines and also valuable α,α-dideutero analogues. Raney nickel proved to be a useful catalyst for the transformation of a wide range of nitriles under reasonably mild conditions with excellent deuterium incorporation (>90 %) and quantitative conversion. Among known model compounds, three new deuterated primary amines were prepared. The large-scale synthesis of deuterated tryptamine was also carried out to deliver 1.1 g product under flow conditions.

Base-Mediated Deuteration of Organic Molecules: A Mechanistic Insight

A base-promoted, step-economical, and cost-effective strategy for introducing heavy isotopes into the organic molecules has been developed. The schemes involve the selective deuteration of various electronically distinct molecules that are formed because of deuterioamination, deuteriothiolation, deuteriophenoxylation, and deuterioalkoxylation as well as tandem cyclization using dimethyl sulfoxide (DMSO)-d ₆ as a deuterium source. The reaction involves a metal-, ligand-, and additive-free route and provides a high level of deuterium incorporation in the presence of DMSO-d ₆ as an inflammable and ecological reagent. The reaction is well tolerated across the electronically varied substrates for the successful incorporation of deuterium into the product. The proposed mechanistic pathway for various transformations has been well supported by NMR studies.

Disiloxane Synthesis Based on Silicon-Hydrogen Bond Activation using Gold and Platinum on Carbon in Water or Heavy Water

Disiloxanes possessing a silicon-oxygen linkage are important as frameworks for functional materials and coupling partners for Hiyama-type cross coupling. We found that disiloxanes were effectively constructed of hydrosilanes catalyzed by gold on carbon in water as the solvent and oxidant in association with the emission of hydrogen gas at room temperature. The present oxidation could proceed via various reaction pathways, such as the hydration of hydrosilane into silanol, dehydrogenative coupling of hydrosilane into disilane, and the subsequent corresponding reactions to disiloxane. Additionally, the platinum on carbon catalyzed hydrogen-deuterium exchange reaction of arylhydrosilanes as substrates in heavy water proceeded on the aromatic nuclei at 80 °C with high deuterium efficiency and high regioselectivity at the only meta and para positions of the aromatic-silicon bond to give the deuterium-labeled disiloxanes.

Rapid, regioselective deuteration of dimethyl-2,2′-bipyridines via microwave-assistance

Isotopically pure [D₆]-dimethyl-2,2′-bipyridine derivatives were selectively and rapidly formed using microwave-assisted regioselective deuteration of the methyl moieties of the parent bipyridine in a deuterium oxide solution.

Investigation into the catalytic activity of porous platinum nanostructures

The catalytic activity of porous platinum nanostructures, viz. platinum nanonets (PtNNs) and platinum nanoballs (PtNBs), synthesized by radiolysis were studied using two model reactions (i) electron transfer reaction between hexacyanoferrate (III) and sodium thiosulfate and (ii) the reduction of p-nitrophenol by sodium borohydride to p-aminophenol. The kinetic investigations were carried out for the platinum nanostructure-catalyzed reactions at different temperatures. The pseudofirst-order rate constant for the electron transfer reaction between hexacyanoferrate (III) and sodium thiosulfate catalyzed by PtNNs and PtNBs at 293 K are (9.1 ± 0.7) × 10(-3) min(-1) and (16.9 ± 0.6) × 10(-3) min(-1), respectively. For the PtNN- and PtNB-catalyzed reduction of p-nitrophenol to p-aminophenol by sodium borohydride, the pseudofirst-order rate constant was (8.4 ± 0.3) × 10(-2) min(-1) and (12.6 ± 2.5) × 10(-2) min(-1), respectively. The accessible surface area of the PtNNs and PtNBs determined before the reaction are 99 and 110 m(2)/g, respectively. These nanostructures exhibit significantly higher catalytic activity, consistent with the largest accessible surface area reported so far for the solid platinum nanoparticles. The equilibrium of the reactants on the surface of the platinum nanostructures played an important role in the induction time (t0) observed in the reaction. A possible role of structural modifications of PtNBs catalyzed the reaction leading to change in the accessible surface area of PtNBs is being explored to explain the nonlinear behavior in the kinetic curve. The activation energy of the PtNN- and PtNB-catalyzed reduction of p-nitrophenol are 26 and 6.4 kJ/mol, respectively. These observations open up new challenges in the field of material science to design and synthesize platinum nanostructures which could withstand such reaction conditions.

Efficient and Convenient Heterogeneous Palladium-Catalyzed Regioselective Deuteration at the Benzylic Position

The Pd/C-catalyzed efficient and regioselective hydrogen-deuterium (H-D) exchange reaction on the benzylic site proceeded in D2O in the presence of a small amount of H2 gas. The use of the Pd/C-ethylenediamine complex [Pd/C(en)] as a catalyst instead of Pd/C led to the efficient deuterium incorporation into the benzylic site of O-benzyl protective groups without hydrogenolysis. These H-D exchange reactions provide a post synthetic and D(2)-gas-free deuterium-labeling method on a wide variety of benzylic sites using D2O as the deuterium source and heterogeneous Pd/C or Pd/C(en) as a reusable heterogeneous palladium catalyst under mild and neutral conditions.

The renaissance of H/D exchange

The increasing demand for stable isotopically labeled compounds has led to an increased interest in H/D-exchange reactions at carbon centers. Today deuterium-labeled compounds are used as internal standards in mass spectrometry or to help elucidate mechanistic theories. Access to these deuterated compounds takes place significantly more efficiently and more cost effectively by exchange of hydrogen by deuterium in the target molecule than by classical synthesis. This Review will concentrate on the preparative application of the H/D-exchange reaction in the preparation of deuterium-labeled compounds. Advances over the last ten years are brought together and critically evaluated.

Efficient H/D Exchange Reactions of Alkyl-Substituted Benzene Derivatives by Means of the Pd/C–H2–D2O System

A method for efficient and extensive H/D exchange of substituted benzene derivatives which is catalyzed by heterogeneous Pd/C in D(2)O as a deuterium source under hydrogen atmosphere is described. Multi-deuterium incorporation into unactivated linear or branched alkyl chains that bear a carboxyl, hydroxyl, ether, ester, or amide moiety and are connected with a benzene ring was achieved by using the Pd/C-H(2)-D(2)O system. The present method does not require expensive deuterium gas or any special equipment.