A flurry of recent research has centered on harnessing the power of nickel catalysis in organic synthesis. These efforts have been bolstered by contemporaneous development of well‐defined nickel ...(pre)catalysts with diverse structure and reactivity. In this report, we present ten different bench‐stable, 18‐electron, formally zero‐valent nickel–olefin complexes that are competent pre‐catalysts in various reactions. Our investigation includes preparations of novel, bench‐stable Ni(COD)(L) complexes (COD=1,5‐cyclooctadiene), in which L=quinone, cyclopentadienone, thiophene‐S‐oxide, and fulvene. Characterization by NMR, IR, single‐crystal X‐ray diffraction, cyclic voltammetry, thermogravimetric analysis, and natural bond orbital analysis sheds light on the structure, bonding, and properties of these complexes. Applications in an assortment of nickel‐catalyzed reactions underscore the complementary nature of the different pre‐catalysts within this toolkit.
A series of air‐stable Ni0 pre‐catalysts of the general type Ni (COD) (L) are described, where L=thiophene oxide, quinone, cyclopentadienone, or fulvene. The properties of the complexes are analyzed through computational and experimental techniques. The precatalysts are competent in a variety of nickel‐catalyzed reactions and together constitute a toolkit that overcomes the limitations of both Ni (COD)2 and Ni (COD) (DQ).
Bioactivity-directed fractionation of the organic extracts of two filamentous fungi of the Bionectriaceae, strains MSX 64546 and MSX 59553 from the Mycosynthetix library, led to the isolation of a ...new dimeric epipolythiodioxopiperazine alkaloid, verticillin H (1), along with six related analogs, Sch 52900 (2), verticillin A (3), gliocladicillin C (4), Sch 52901 (5), 11'-deoxyverticillin A (6) and gliocladicillin A (7). The structures of compounds 1-7 were determined by extensive NMR and HRMS analyses, as well as by comparisons to the literature. All compounds (1-7) were evaluated for cytotoxicity against a panel of human cancer cell lines, displaying IC(50) values ranging from 1.2 μM to 10 nM. Compounds 1-5 were examined for activity in the NF-κB assay, where compounds 2 and 3 revealed activity in the sub-micromolar range. Additionally, compounds 1, 3 and 4 were tested for EGFR inhibition using an enzymatic assay, while compound 3 was examined against an overexpressing EGFR(+ve) cancer cell line.
Two new xanthone-anthraquinone heterodimers, acremoxanthone C (5) and acremoxanthone D (2), have been isolated from an extract of an unidentified fungus of the order Hypocreales (MSX 17022) by ...bioactivity-directed fractionation as part of a search for anticancer leads from filamentous fungi. Two known related compounds, acremonidin A (4) and acremonidin C (3) were also isolated, as was a known benzophenone, moniliphenone (1). The structures of these isolates were determined via extensive use of spectroscopic and spectrometric tools in conjunction with comparisons to the literature. All compounds (1-5) were evaluated against a suite of biological assays, including those for cytotoxicity, inhibition of the 20S proteasome, mitochondrial transmembrane potential and nuclear factor-κB.
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•Identification of an unknown byproduct generated in Curtius rearrangement reaction in the synthesis of BMS-986020.•Impurity was isolated by reverse phase semi-preparative HPLC and ...identified by a combination of high resolution mass spectrometry and NMR.
BMS-986020 was developed as an antagonist of the LPA1 receptor for the treatment of lung fibrosis (Idiopathic Pulmonary Fibrosis (IPF)). During the development of BMS-986020, a high percentage byproduct was observed in the mother liquor of a Curtius rearrangement reaction. The structure identification and formation mechanism of this unknown byproduct was deemed necessary to understand for further the reaction optimization and knowledge generation for the project. The characterization process required a multifaceted approach utilizing LC-HRMS, VT-NMR, and HPLC isolation. The investigation’s final result implicated the reaction base as the root cause of the byproduct formation and indicated a nitrene-iminium reaction pathway to form the byproduct.
Five diastereomeric polyketide glycosides, roselipins 3A-3E (1-5), have been isolated from the acetone extract of Clonostachys candelabrum on the basis of their positive anthelmintic activity. The ...structures of these compounds were elucidated by comparison of their NMR and MS data to those of previously reported roselipins and related structures, and were confirmed by 2D-NMR spectral analysis. Known compounds linoleic acid (6) and aurantiogliocladin (7) were also isolated as active anthelmintic components, although much less potent than the roselipins.
Having robust and reliable methods for monitoring catalyst activation processes is an important part of ensuring the reproducibility of a catalytic reaction. For asymmetric Diels–Alder reactions, ...chiral oxazaborolidine or oxazaborolidinium catalysts are powerful reagents that promote these reactions in high yield and selectivity. Supported by mechanistic findings, several modern analytical methods are compared for quantitating the oxazaborolidine catalyst formation from amino alcohol and boroxine to arrive at useful monitoring methods for this important transformation.
A new macrolactam, fluvirucin B0 (1), and two known macrolactams, Sch 38516/fluvirucin B1 (2) and Sch 39185/fluvirucin B3 (3), have been isolated from an acetone extract of a strain of Nonomuraea ...turkmeniaca. These compounds were isolated by bioassay-guided fractionation as part of our search for new anthelmintics. The structures of these compounds were elucidated by comparison of their NMR and MS data to those of previously reported fluvirucins, and confirmed by 2D-NMR. 1approximately 3 exhibited in vitro activity (EC90 <1.0 approximately 1.7 microg/ml) against Haemonchus contortus larvae, but were ineffective in reducing worm counts in vivo against Heligmosomoides polygyrus in mice at 50 mg/kg dosed intramuscularly.
As sp2–sp3 disconnections gain acceptance in the medicinal chemist’s toolbox, an increasing number of potential drug candidates containing this motif are moving into the pharmaceutical development ...pipeline. This raises a new set of questions and challenges around the novel, direct methodologies available for forging these bonds. These questions gain further importance in the context of process chemistry, where the focus is the development of scalable processes that enable the large-scale delivery of clinical supplies. In this paper, we describe our efforts to apply a wide variety of standard, photo-, and electrochemical sp2–sp3 cross-coupling methods to a pharmaceutically relevant intermediate and optimize each through a combination of high throughput and mechanistically guided experimentation. With data regarding the performance, benefits, and limitations of these novel methods, we evaluate them against a more traditional two-step palladium-catalyzed process. This work reveals trends and similarities between these sp2–sp3 bond-forming methods and suggests a path forward for further refinements.
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