The identification, optimization, and evaluation of a new catalytic protocol for sp3 C–H hydroxylation is described. Reactions are performed in aqueous acid using a bis(bipyridine)Ru catalyst to ...enable oxidation of substrates possessing basic amine functional groups. Tertiary and benzylic C–H hydroxylation is strongly favored over N-oxidation for numerous amine derivatives. With terpene-derived substrates, similar trends in reactivity toward tertiary and benzylic C–H bonds are observed. Hydroxylation of chiral tertiary centers is enantiospecific in spite of the ionizing strength of the reaction medium. Preliminary kinetics experiments show a marked difference in reactivity between isomeric cis- and trans-Ru catalysts suggesting that the catalyst is configurationally stable under the reaction conditions.
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A general and operationally convenient method for intermolecular amination of C(sp3)−H bonds is described. This technology allows for efficient functionalization of complex molecules, including ...numerous pharmaceutical targets. The combination of pivalonitrile as a solvent, Al2O3 as an additive, and phenyl sulfamate as a nitrogen source affords differential reaction performance and substrate scope. Mechanistic data strongly implicate a pathway for catalyst decomposition that initiates with solvent oxidation, thus providing rationale for the marked influence of pivalonitrile on this reaction process.
Introducing N: A general and operationally convenient method for intermolecular amination of C(sp3)−H bonds allows for efficient functionalization of complex molecules, including numerous pharmaceutical targets. The combination of pivalonitrile as a solvent, Al2O3 as an additive, and phenyl sulfamate as a nitrogen source affords differential reaction performance and substrate scope.
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Despite progress based on multilocus, phylogenetic studies of the palms (order Arecales, family Arecaceae), uncertainty remains in resolution/support among major clades and for the placement of the ...palms among the commelinid monocots. Palms and related commelinids represent a classic case of substitution rate heterogeneity that has not been investigated in the genomic era.
To address questions of relationships, support and rate variation among palms and commelinid relatives, 39 plastomes representing the palms and related family Dasypogonaceae were generated via genome skimming and integrated within a monocot-wide matrix for phylogenetic and molecular evolutionary analyses.
Support was strong for ‘deep’ relationships among the commelinid orders, among the five palm subfamilies, and among tribes of the subfamily Coryphoideae. Additionally, there was extreme heterogeneity in the plastid substitution rates across the commelinid orders indicated by model based analyses, with c. 22 rate shifts, and significant departure from a global clock.
To date, this study represents the most comprehensively sampled matrix of plastomes assembled for monocot angiosperms, providing genome-scale support for phylogenetic relationships of monocot angiosperms, and lays the phylogenetic groundwork for comparative analyses of the drivers and correlates of such drastic differences in substitution rates across a diverse and significant clade.
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We have recently disclosed (dtbpy)2RuCl2 as an effective precatalyst for chemoselective C–H hydroxylation of C(sp3)–H bonds and have noted a marked disparity in reaction performance between ...4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy)- and 2,2′-bipyridine (bpy)-derived complexes. A desire to understand the origin of this difference and to further advance this catalytic method has motivated the comprehensive mechanistic investigation described herein. Details of this reaction have been unveiled through evaluation of ligand structure–activity relationships, electrochemical and kinetic studies, and pressurized sample infusion high-resolution mass spectrometry (PSI-MS). Salient findings from this investigation include the identification of more than one active oxidant and three disparate mechanisms for catalyst decomposition/arrest. Catalyst efficiency, as measured by turnover number, has a strong inverse correlation with the rate and extent of ligand dissociation, which is dependent on the identity of bipyridyl 4,4′-substituent groups. Dissociated bipyridyl ligand is oxidized to mono- and bis-N-oxide species under the reaction conditions, the former of which is found to act as a potent catalyst poison, yielding a catalytically inactive tris-ligated Ru(dtbpy)2(dtbpy N-oxide)2+ complex. Insights gained through this work highlight the power of PSI-MS for studies of complex reaction processes and are guiding ongoing efforts to develop high-performance, next-generation catalyst systems for C–H hydroxylation.
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Indole and indazole synthetic cannabinoids (SCs) featuring l-valinate or l-tert-leucinate pendant group have recently emerged as prevalent recreational drugs, and their use has been associated with ...serious adverse health effects. Due to the limited pharmacological data available for these compounds, 5F-AMBICA, 5F-AMB, 5F-ADB, AMB-FUBINACA, MDMB-FUBINACA, MDMB-CHMICA, and their analogues were synthesized and assessed for cannabimimetic activity in vitro and in vivo. All SCs acted as potent, highly efficacious agonists at CB1 (EC50 = 0.45–36 nM) and CB2 (EC50 = 4.6–128 nM) receptors in a fluorometric assay of membrane potential, with a general preference for CB1 activation. The cannabimimetic properties of two prevalent compounds with confirmed toxicity in humans, 5F-AMB and MDMB-FUBINACA, were demonstrated in vivo using biotelemetry in rats. Bradycardia and hypothermia were induced by 5F-AMB and MDMB-FUBINACA doses of 0.1–1 mg/kg (and 3 mg/kg for 5F-AMB), with MDMB-FUBINACA showing the most dramatic hypothermic response recorded in our laboratory for any SC (>3 °C at 0.3 mg/kg). Reversal of hypothermia by pretreatment with a CB1, but not CB2, antagonist was demonstrated for 5F-AMB and MDMB-FUBINACA, consistent with CB1-mediated effects in vivo. The in vitro and in vivo data indicate that these SCs act as highly efficacious CB receptor agonists with greater potency than Δ9-THC and earlier generations of SCs.
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The development of an electrochemically driven, ruthenium-catalyzed C–H hydroxylation reaction of amine-derived substrates bearing tertiary C–H bonds is described. The reaction is performed under ...constant current electrolysis in a divided cell to afford alcohol products in yields comparable to those of our previously reported process, which requires the use of stoichiometric H5IO6 for catalytic turnover. With aqueous acid as solvent, the cathodic electrode reaction simply involves the reduction of protons to evolve hydrogen gas. The optimized protocol offers a convenient, efficient, and atom-economical method for sp3-C–H bond oxidation.
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Mechanochemistry continues to reveal new possibilities in chemistry including the opportunity for "greening" reactions. Nevertheless, a clear understanding of the energetic transformations within ...mechanochemical systems remains elusive. We employed a uniquely modified ball mill and strategically chosen Diels-Alder reactions to evaluate the role of several ball-milling variables. This revealed three different energetic regions that we believe are defining characteristics of most, if not all, mechanochemical reactors. Relative to the locations of a given ball mill's regions, activation energy determines whether a reaction is energetically easy (Region I), challenging (Region II), or unreasonable (Region III) in a given timeframe. It is in Region II, that great sensitivity to mechanochemical conditions such as vial material and oscillation frequency emerge. Our unique modifications granted control of reaction vessel temperature, which in turn allowed control of the locations of Regions I, II, and III for our mill. Taken together, these results suggest envisioning vibratory mills (and likely other mechanochemical methodologies) as molecular-collision facilitating devices that act upon molecules occupying a thermally-derived energy distribution. This unifies ball-milling energetics with solution-reaction energetics
a common tie to the Arrhenius equation, but gives mechanochemistry the unique opportunity to influence either half of the equation. In light of this, we discuss a strategy for translating solvent-based reaction conditions to ball milling conditions. Lastly, we posit that the extra control
frequency factor grants mechanochemistry the potential for greater selectivity than conventional solution reactions.
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Dirhodium-catalyzed C–H amination is hypothesized to proceed via Rh2-nitrene intermediates in either the Rh2(II,II) or Rh2(II,III) redox state. Herein, we report joint theoretical and experimental ...studies of the ground electronic state (GES), redox potentials, and C–H amination of Rh2 II,III(O2CCH3)4(L) n + (1_L) (L = none, Cl–, and H2O), Rh2(esp)2+ (2), and Rh2(espn)2Cl (3) (esp = α,α,α′,α′-tetramethyl-1,3-benzenedipropanoate and espn = α,α,α′,α′-tetramethyl-1,3-benzenedipropanamidate). CASSCF calculations on 1_L yield a wave function with two closely weighted configurations, (δ*)2(π1*)2(π2*)1 and (δ*)2(π1*)1(π2*)2, consistent with reported EPR g values Chem. Phys. Lett. 1986, 130, 20−23 . In contrast, EPR spectra of 2 show g values consistent with the DFT-computed (π*)4(δ*)1 GES. EPR spectra and Cl K-edge XAS for 3 are consistent with a (π*)4(δ*)1 GES, as supported by DFT. Nitrene intermediates 2N_L and 3N_L are also examined by DFT (the nitrene is an NSO3R species). DFT calculations suggest a doublet GES for 2N_L and a quartet GES for 3N_L. CASSCF calculations describe the GES of 2N as Rh2(II,II) with a coordinated nitrene radical cation, (π*)4(δ*)2(πnitrene,1)1(πnitrene,2)0. Conversely, the GES of 3N is Rh2(II,III) with a coordinated triplet nitrene, (π*)4(δ*)1(πnitrene,1)1(πnitrene,2)1. Quartet transition states (4TSs) are found to react via a stepwise radical mechanism, whereas 2TSs are found to react via a concerted mechanism that is lower in energy compared to 4TSs for both 2N_L and 3N_L. The experimental (determined by intramolecular competition) and 2TS-calculated kinetic isotopic effect (KIE) shows a KIE ∼ 3 for both 2N and 3N, which is consistent with a concerted mechanism.
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Summary
Ferns appear in the fossil record some 200 Myr before angiosperms. However, as angiosperm‐dominated forest canopies emerged in the Cretaceous period there was an explosive diversification of ...modern (leptosporangiate) ferns, which thrived in low, blue‐enhanced light beneath angiosperm canopies. A mechanistic explanation for this transformative event in the diversification of ferns has remained elusive.
We used physiological assays, transcriptome analysis and evolutionary bioinformatics to investigate a potential connection between the evolution of enhanced stomatal sensitivity to blue light in modern ferns and the rise of angiosperm‐dominated forests in the geological record.
We demonstrate that members of the largest subclade of leptosporangiate ferns, Polypodiales, have significantly faster stomatal response to blue light than more ancient fern lineages and a representative angiosperm. We link this higher sensitivity to levels of differentially expressed genes in blue‐light signaling, particularly in the cryptochrome (CRY) signaling pathway. Moreover, CRYs of the Polypodiales examined show gene duplication events between 212.9–196.9 and 164.4–151.8 Ma, when angiosperms were emerging, which are lacking in other major clades of extant land plants.
These findings suggest that evolution of stomatal blue‐light sensitivity helped modern ferns exploit the shady habitat beneath angiosperm forest canopies, fueling their Cretaceous hyperdiversification.
See also the Commentary on this article by Chater, 230: 886–888.
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Sequencing of target-enriched libraries is an efficient and cost-effective method for obtaining DNA sequence data from hundreds of nuclear loci for phylogeny reconstruction. Much of the cost of ...developing targeted sequencing approaches is associated with the generation of preliminary data needed for the identification of orthologous loci for probe design. In plants, identifying orthologous loci has proven difficult due to a large number of whole-genome duplication events, especially in the angiosperms (flowering plants). We used multiple sequence alignments from over 600 angiosperms for 353 putatively single-copy protein-coding genes identified by the One Thousand Plant Transcriptomes Initiative to design a set of targeted sequencing probes for phylogenetic studies of any angiosperm group. To maximize the phylogenetic potential of the probes, while minimizing the cost of production, we introduce a k-medoids clustering approach to identify the minimum number of sequences necessary to represent each coding sequence in the final probe set. Using this method, 5–15 representative sequences were selected per orthologous locus, representing the sequence diversity of angiosperms more efficiently than if probes were designed using available sequenced genomes alone. To test our approximately 80,000 probes, we hybridized libraries from 42 species spanning all higher-order groups of angiosperms, with a focus on taxa not present in the sequence alignments used to design the probes. Out of a possible 353 coding sequences, we recovered an average of 283 per species and at least 100 in all species. Differences among taxa in sequence recovery could not be explained by relatedness to the representative taxa selected for probe design, suggesting that there is no phylogenetic bias in the probe set. Our probe set, which targeted 260 kbp of coding sequence, achieved a median recovery of 137 kbp per taxon in coding regions, a maximum recovery of 250 kbp, and an additional median of 212 kbp per taxon in flanking non-coding regions across all species. These results suggest that the Angiosperms353 probe set described here is effective for any group of flowering plants and would be useful for phylogenetic studies from the species level to higher-order groups, including the entire angiosperm clade itself.
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