Proton‐Coupled Reduction of an Iron Cyanide Complex to Methane and Ammonia

Nitrogenase enzymes mediate the six‐electron reductive cleavage of cyanide to CH₄ and NH₃. Herein we demonstrate for the first time the liberation of CH₄ and NH₃ from a well‐defined iron cyanide coordination complex, [SiP^iPr₃]Fe(CN) (where [SiP^iPr₃] represents a tris(phosphine)silyl ligand), on exposure to proton and electron equivalents. [SiP^iPr₃]Fe(CN) additionally serves as a useful entry point to rare examples of terminally‐bound Fe(CNH) and Fe(CNH₂) species that, in accord with preliminary mechanistic studies, are plausible intermediates of the cyanide reductive protonation to generate CH₄ and NH₃. Comparative studies with a related [SiP^iPr₃]Fe(CNMe₂) complex suggests the possibility of multiple, competing mechanisms for cyanide activation and reduction.     

Hierarchical Layer Engineering Using Supramolecular Double‐Comb Diblock Copolymers

The formation of unusual multilayered parallel lamellae‐in‐lamellae in symmetric supramolecular double‐comb diblock copolymers is presented. While keeping the concentration of surfactant fixed, the number of internal layers was found to increase with molecular weight M up to 34 for the largest block copolymer. The number of internal structures n was established to scale as M^0.67 and therefore enables easy design of such structures with great precision.     

Enantioselective Pd‐Catalyzed Allylic Alkylation Reactions of Dihydropyrido[1,2‐a]indolone Substrates: Efficient Syntheses of (−)‐Goniomitine, (+)‐Aspidospermidine,and (−)‐Quebrachamine

The successful application of dihydropyrido[1,2‐a]indolone (DHPI) substrates in Pd‐catalyzed asymmetric allylic alkylation chemistry facilitates rapid access to multiple alkaloid frameworks in an enantioselective fashion. Strategic bromination at the indole C3 position greatly improved the allylic alkylation chemistry and enabled a highly efficient Negishi cross‐coupling downstream. The first catalytic enantioselective total synthesis of (?)‐goniomitine, along with divergent formal syntheses of (+)‐aspidospermidine and (?)‐quebrachamine, are reported herein.     

Latest Advances Towards Ras Inhibition: A Medicinal Chemistry Perspective

Owing to their high occurrence rate across many human cancers and their lack of druggability so far, mutant forms of the signaling protein Ras are currently among the most attractive (and elusive) oncology targets. This strong appeal explains the sustained effort in the field, and the ensuing progress has rekindled optimism regarding the discovery of Ras inhibitors. In this Minireview, we discuss the most recent advances towards irreversible inhibitors, and highlight approaches to inhibitors of Ras–effector interactions that have been overshadowed by the current focus on direct Ras inhibition. At the same time, we provide a critical assessment from a medicinal chemistry perspective.     

Formation and Fate of Formaldehyde in Methanol-to-Hydrocarbon Reaction: In Situ Synchrotron Radiation Photoionization Mass Spectrometry Study

HCHO has been confirmed as an active intermediate in the methanol-to-hydrocarbon (MTH) reaction, and is critical for interpreting the mechanisms of coke formation. Here, HCHO was detected and quantified during the MTH process over HSAPO-34 and HZSM-5 by in situ synchrotron radiation photoionization mass spectrometry. Compared with conventional methods, excellent time-resolved profiles were obtained to study the formation and fate of HCHO, and other products during the induction, steady-state reaction, and deactivation periods. Similar formation trends of HCHO and methane, and their close correlation in yields suggest that they are derived from disproportionation of methanol at acidic sites. In the presence of Y₂O₃, the amount of HCHO changes, affecting the hydrogen-transfer processes of olefins into aromatics and aromatics into cokes. The yield of HCHO affects the aromatic-based cycle and the formation of ethylene, indicating that ethylene is mainly formed from the aromatic-based cycle.     

π-Interactions between Cyclic Carbocations and Aromatics Cause Zeolite Deactivation in Methanol-to-Hydrocarbon Conversion

The understanding of catalyst deactivation represents one of the major challenges for the methanol-to-hydrocarbon (MTH) reaction over acidic zeolites. Here we report the critical role of intermolecular π-interactions in catalyst deactivation in the MTH reaction on zeolites H-SSZ-13 and H-ZSM-5. π-interaction-induced spatial proximities between cyclopentenyl cations and aromatics in the confined channels and/or cages of zeolites are revealed by two-dimensional solid-state NMR spectroscopy. The formation of naphtalene as a precursor to coke species is favored due to the reaction of aromatics with the nearby cyclopentenyl cations and correlates with both acid density and zeolite topology.     

Target-Directed Azide-Alkyne Cycloaddition for Assembling HIV-1 TAR RNA Binding Ligands

The highly conserved HIV-1 transactivation response element (TAR) binds to the trans-activator protein Tat and facilitates viral replication in its latent state. The inhibition of Tat–TAR interactions by selectively targeting TAR RNA has been used as a strategy to develop potent antiviral agents. Therefore, HIV-1 TAR RNA represents a paradigmatic system for therapeutic intervention. Herein, we have employed biotin-tagged TAR RNA to assemble its own ligands from a pool of reactive azide and alkyne building blocks. To identify the binding sites and selectivity of the ligands, the in situ cycloaddition has been further performed using control nucleotide (TAR DNA and TAR RNA without bulge) templates. The hit triazole-linked thiazole peptidomimetic products have been isolated from the biotin-tagged target templates using streptavidin beads. The major triazole lead generated by the TAR RNA presumably binds in the bulge region, shows specificity for TAR RNA over TAR DNA, and inhibits Tat–TAR interactions.     

In Situ Pyrolysis Tracking and Real-Time Phase Evolution: From a Binary Zinc Cluster to Supercapacitive Porous Carbon

The in situ tracking of the pyrolysis of a binary molecular cluster [Zn₇(μ₃-CH₃O)₆(L)₆][ZnLCl₂]₂ is presented with one brucite disk and two mononuclear fragments (L=mmimp: 2-methoxy-6-((methylimino)-methyl)phenolate) to porous carbon using TG-MS from 30 to 900 °C. Following up the spilled gas product during the decomposed reaction of zinc cluster along the temperature rising, and in conjunction with XRD, SEM, BET and other materials characterization, where three key steps were observed: 1) cleavage of the bulky external ligand; 2) reduction of ZnO and 3) volatilization of Zn. The real-time-dependent phase-sequential evolution of the remaining products and the processing of pore forming template transformation are proposed simultaneously. The porous carbon structure featuring a uniform nano-sized pore distribution synthesized at 900 °C with the highest surface area of 1644 m² g⁻¹ and pore volume of 0.926 cm³ g⁻¹ exhibits the best known capacitance of 662 F g⁻¹ at 0.5 A g⁻¹.     

A Conjugate Addition Approach to Diazo-Containing Scaffolds with β Quaternary Centers

Structurally complex diazo-containing scaffolds are formed by conjugate addition to vinyl diazonium salts. The electrophile, a little studied α-diazonium-α,β-unsaturated carbonyl compound, is formed at low temperature under mild conditions by treating β-hydroxy-α-diazo carbonyls with Sc(OTf)₃. Conjugate addition occurs selectively at the 3-position of indole to give α-diazo-β-indole carbonyls, and enoxy silanes react to give 2-diazo-1,4-dicarbonyl products. These reactions result in the formation of tertiary and quaternary centers, and give products that would be otherwise difficult to form. Importantly, the diazo functional group is retained within the molecule for future manipulation. Treating an α-diazo ester indole addition product with Rh₂(OAc)₄ caused a rearrangement to occur to give a 2-(1H-indol-3-yl)-2-enoate. In the case of diazo ketone compounds, this shift occurred spontaneously on prolonged exposure to the Lewis acidic reaction conditions.