Manganese Catalyzed Asymmetric Transfer Hydrogenation of Ketones Using Chiral Oxamide Ligands

The asymmetric transfer hydrogenation of ketones using isopropyl alcohol (IPA) as hydrogen donor in the presence of novel manganese catalysts is explored. The selective and active systems are easily generated in situ from [MnBr(CO)5] and inexpensive C 2-symmeric bisoxalamide ligands. Under the optimized reaction conditions, the Mn-derived catalyst gave higher enantioselectivity compared with the related ruthenium catalyst

Untersuchungen zur Rolle von Ifapsoriasin-/Filaggrin-2-Peptiden in der antimikrobiellen Hautabwehr

Als Barriereorgan ist die Haut des Menschen zahlreichen Umwelteinflüssen ausgesetzt, zu denen neben physikalischen Einflüssen auch eine Vielzahl verschiedener Mikroorganismen wie Bakterien, Viren und Pilze gehört. Die erfolgreiche Abwehr dieser Umwelteinflüsse setzt ein außerordentlich effektives Abwehrsystem voraus. Wichtige Bestandteile der Immunabwehr der menschlichen Haut sind die konstitutiven und induzierbaren antimikrobiellen und antiviralen Moleküle, darunter die Ribonuklease 7, Psoriasin, Dermcidin und Lysozym. Für Fragmente der epidermalen ″S100 Fused-Type″-Proteine Profilaggrin und Hornerin konnte ebenfalls antimikrobielle Aktivität nachgewiesen werden. Ifapsoriasin wurde in unserer Arbeitsgruppe als neues Mitglied der ″S100 Fused-Type″-Proteinfamilie auf genomischer Ebene in der Region des "Epidermalen Differenzierungskomplexes" im Abschnitt 1q21 des humanen Chromosoms 1 identifiziert. Für rekombinant hergestellte Ifapsoriasin-Fragmente wurde bereits antimikrobielle Aktivität nachgewiesen. In dieser Arbeit wurden zwei weitere Peptide aus der Region der B-Repeats des Ifapsoriasins mittels rekombinanter Expression hergestellt und mithilfe des Radialdiffusionstest auf mögliche antimikrobielle Aktivität untersucht. Das innerhalb des B1-Repeats lokalisierte RGD-Motiv könnte Peptiden aus dieser Region eventuell antivirale Aktivität, z. B. gegen Herpes-Simplex-Viren-Typ 1 verleihen. Untersuchungen zur antiviralen Aktivität konnten in dieser Arbeit allerdings nicht durchgeführt werden. In der antimikrobiellen Testung konnte für das Ifapsoriasin-Fragment IFPS-1 keine antimikrobielle Aktivität nachgewiesen werden. Das Ifapsoriasin-Fragment IFPS-2 zeigte gegen Escherichia coli und Candida albicans eine sehr geringe Aktivität, während die Aktivität gegen Pseudomonas aeruginosa moderat war. Die Tatsache, dass nur eines der beiden getesteten Fragmente mit ähnlich hohen pI-Werten wirksam ist, zeigt, dass für die antimikrobielle Wirkweise eines Moleküls seine Nettoladung nicht allein entscheidend ist. Zusätzlich enthält das wirksame IFPS-2 im Gegensatz zum unwirksamen IFPS-1 fünf stark hydrophobe Aminosäuren, die dem Molekül vermutlich die Einlagerung in bakterielle Membranen ermöglichen. Mit dieser Arbeit konnte gezeigt werden, dass ein weiteres Ifapsoriasin-Fragment antimikrobiell wirksam ist und somit möglicherweise einen Beitrag zur kutanen Abwehr von Mikroorganismen leisten könnte

A General Regioselective Synthesis of Alcohols by Cobalt-Catalyzed Hydrogenation of Epoxides

A straightforward methodology for the synthesis of anti-Markovnikov-type alcohols is presented. By using a specific cobalt triphos complex in the presence of Zn(OTf)2 as an additive, the hydrogenation of epoxides proceeds with high yields and selectivities. The described protocol shows a broad substrate scope, including multi-substituted internal and terminal epoxides, as well as a good functional-group tolerance. Various natural-product derivatives, including steroids, terpenoids, and sesquiterpenoids, gave access to the corresponding alcohols in moderate-to-excellent yields. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Transport of Mars-Crossing Asteroids from the Quasi-Hilda Region

We employ set oriented methods in combination with graph partitioning algorithms to identify key dynamical regions in the Sun-Jupiter-particle three-body system. Transport rates from a region near the 3:2 Hilda resonance into the realm of orbits crossing Mars' orbit are computed. In contrast to common numerical approaches, our technique does not depend on single long term simulations of the underlying model. Thus, our statistical results are particularly reliable since they are not affected by a dynamical behavior which is almost nonergodic (i.e., dominated by strongly almost invariant sets)

Intermetallic nickel silicide nanocatalyst—A non-noble metal–based general hydrogenation catalyst

Hydrogenation reactions are essential processes in the chemical industry, giving access to a variety of valuable compounds including fine chemicals, agrochemicals, and pharmachemicals. On an industrial scale, hydrogenations are typically performed with precious metal catalysts or with base metal catalysts, such as Raney nickel, which requires special handling due to its pyrophoric nature. We report a stable and highly active intermetallic nickel silicide catalyst that can be used for hydrogenations of a wide range of unsaturated compounds. The catalyst is prepared via a straightforward procedure using SiO2 as the silicon atom source. The process involves thermal reduction of Si–O bonds in the presence of Ni nanoparticles at temperatures below 1000°C. The presence of silicon as a secondary component in the nickel metal lattice plays the key role in its properties and is of crucial importance for improved catalytic activity. This novel catalyst allows for efficient reduction of nitroarenes, carbonyls, nitriles, N-containing heterocycles, and unsaturated carbon–carbon bonds. Moreover, the reported catalyst can be used for oxidation reactions in the presence of molecular oxygen and is capable of promoting acceptorless dehydrogenation of unsaturated N-containing heterocycles, opening avenues for H2 storage in organic compounds. The generality of the nickel silicide catalyst is demonstrated in the hydrogenation of over a hundred of structurally diverse unsaturated compounds. The wide application scope and high catalytic activity of this novel catalyst make it a nice alternative to known general hydrogenation catalysts, such as Raney nickel and noble metal–based catalysts

Cascade Synthesis of Pyrroles from Nitroarenes with Benign Reductants Using a Heterogeneous Cobalt Catalyst

A bifunctional 3d-metal catalyst for the cascade synthesis of diverse pyrroles from nitroarenes is presented. The optimal catalytic system Co/NGr-C@SiO2-L is obtained by pyrolysis of a cobalt-impregnated composite followed by subsequent selective leaching. In the presence of this material, (transfer) hydrogenation of easily available nitroarenes and subsequent Paal–Knorr/Clauson-Kass condensation provides >40 pyrroles in good to high yields using dihydrogen, formic acid, or a CO/H2O mixture (WGSR conditions) as reductant. In addition to the favorable step economy, this straightforward domino process does not require any solvents or external co-catalysts. The general synthetic utility of this methodology was demonstrated on a variety of functionalized substrates including the preparation of biologically active and pharmaceutically relevant compounds, for example, (+)-Isamoltane. © 2020 The Authors. Published by Wiley-VCH Gmb

Recent Advances in Catalytic Hydrosilylations: Developments beyond Traditional Platinum Catalysts

Hydrosilylation reactions, which allow the addition of Si−H to C=C/C≡C bonds, are typically catalyzed by homogeneous noble metal catalysts (Pt, Rh, Ir, and Ru). Although excellent activity and selectivity can be obtained, the price, purification, and metal residues of these precious catalysts are problems in the silicone industry. Thus, a strong interest in more sustainable catalysts and for more economic processes exists. In this respect, recently disclosed hydrosilylations using catalysts based on earth-abundant transition metals, for example, Fe, Co, Ni, and Mn, and heterogeneous catalysts (supported nanoparticles and single-atom sites) are noteworthy. This minireview describes the recent advances in this field. © 2020 The Authors. Published by Wiley-VCH Gmb

Selective Acceptorless Dehydrogenation of Primary Amines to Imines by Core-Shell Cobalt Nanoparticles

Core–shell nanocatalysts are attractive due to their versatility and stability. Here, we describe cobalt nanoparticles encapsulated within graphitic shells prepared via the pyrolysis of a cationic poly-ionic liquid (PIL) with a cobalt(II) chloride anion. The resulting material has a core–shell structure that displays excellent activity and selectivity in the self-dehydrogenation and hetero-dehydrogenation of primary amines to their corresponding imines. Furthermore, the catalyst exhibits excellent activity in the synthesis of secondary imines from substrates with various reducible functional groups (C=C, C≡C and C≡N) and amino acid derivatives. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Efficient and selective N-alkylation of amines with alcohols catalysed by manganese pincer complexes

Borrowing hydrogen (or hydrogen autotransfer) reactions represent straightforward and sustainable C-N bond-forming processes. In general, precious metal-based catalysts are employed for this effective transformation. In recent years, the use of earth abundant and cheap non-noble metal catalysts for this process attracted considerable attention in the scientific community. Here we show that the selective N-alkylation of amines with alcohols can be catalysed by defined PNP manganese pincer complexes. A variety of substituted anilines are monoalkylated with different (hetero)aromatic and aliphatic alcohols even in the presence of other sensitive reducible functional groups. As a special highlight, we report the chemoselective monomethylation of primary amines using methanol under mild conditions

Efficient and Selective N‐Methylation of Nitroarenes under Mild Reaction Conditions

Herein, we report a straightforward protocol for the preparation of N,N‐dimethylated amines from readily available nitro starting materials using formic acid as a renewable C1 source and silanes as reducing agents. This tandem process is efficiently accomplished in the presence of a cubane‐type Mo3PtS4 catalyst. For the preparation of the novel [Mo3Pt(PPh3)S4Cl3(dmen)3]+ (3+) (dmen: N,N′‐dimethylethylenediamine) compound we have followed a [3+1] building block strategy starting from the trinuclear [Mo3S4Cl3(dmen)3]+ (1+) and Pt(PPh3)4 (2) complexes. The heterobimetallic 3+ cation preserves the main structural features of its 1+ cluster precursor. Interestingly, this catalytic protocol operates at room temperature with high chemoselectivity when the 3+ catalyst co‐exists with its trinuclear 1+ precursor. N‐heterocyclic arenes, double bonds, ketones, cyanides and ester functional groups are well retained after N‐methylation of the corresponding functionalized nitroarenes. In addition, benzylic‐type as well as aliphatic nitro compounds can also be methylated following this protocol