Three-Component cine,ipso-Disubstitution of Nitrocoumarins.

The development of a three-component cine,ipso-disubstitution of nitrocoumarins is reported. The reaction leverages the electrophilicity of nitrocoumarins, the nucleophilicity of nitronates, and the leaving group ability of nitrite (NO2-) to yield complex polyfunctionalized biaryls that often display stable axial chirality.

Altered methionine metabolism impacts phenylpropanoid production and plant development in Arabidopsis thaliana.

Phenylpropanoids are specialized metabolites derived from phenylalanine. Glucosinolates are defense compounds derived mainly from methionine and tryptophan in Arabidopsis. It was previously shown that the phenylpropanoid pathway and glucosinolate production are metabolically linked. The accumulation of indole-3-acetaldoxime (IAOx), the precursor of tryptophan-derived glucosinolates, represses phenylpropanoid biosynthesis through accelerated degradation of phenylalanine-ammonia lyase (PAL). As PAL functions at the entry point of the phenylpropanoid pathway which produces indispensable specialized metabolites such as lignin, aldoxime-mediated phenylpropanoid repression is detrimental to plant survival. Although methionine-derived glucosinolates in Arabidopsis are abundant, any impact of aliphatic aldoximes (AAOx) derived from aliphatic amino acids such as methionine on phenylpropanoid production remains unclear. Here, we investigate the impact of AAOx accumulation on phenylpropanoid production using Arabidopsis aldoxime mutants, ref2 and ref5 . REF2 and REF5 metabolize aldoximes to respective nitrile oxides redundantly, but with different substrate specificities. ref2 and ref5 mutants have decreased phenylpropanoid contents due to the accumulation of aldoximes. As REF2 and REF5 have high substrate specificity toward AAOx and IAOx respectively, it was assumed that ref2 accumulates AAOx, not IAOx. Our study indicates that ref2 accumulates both AAOx and IAOx. Removing IAOx partially restored phenylpropanoid production in ref2 , but not to the wild-type level. However, when AAOx biosynthesis was silenced, phenylpropanoid production and PAL activity in ref2 were completely restored, suggesting an inhibitory effect of AAOx on phenylpropanoid production. Further feeding studies revealed that the abnormal growth phenotype commonly observed in Arabidopsis mutants lacking AAOx production is a consequence of methionine accumulation. Significance Statement: Aliphatic aldoximes are precursors of various specialized metabolites including defense compounds. This study reveals that aliphatic aldoximes repress phenylpropanoid production and that altered methionine metabolism affects plant growth and development. As phenylpropanoids include vital metabolites such as lignin, a major sink of fixed carbon, this metabolic link may contribute to available resource allocation during defense.

Axially Chiral Cannabinoids: Design, Synthesis, and Cannabinoid Receptor Affinity.

The resorcinol-terpene phytocannabinoid template is a privileged scaffold for the development of diverse therapeutics targeting the endocannabinoid system. Axially chiral cannabinols (axCBNs) are unnatural cannabinols (CBNs) that bear an additional C10 substituent, which twists the cannabinol biaryl framework out of planarity creating an axis of chirality. This unique structural modification is hypothesized to enhance both the physical and biological properties of cannabinoid ligands, thus ushering in the next generation of endocannabinoid system chemical probes and cannabinoid-inspired leads for drug development. In this full report, we describe the philosophy guiding the design of axCBNs as well as several synthetic strategies for their construction. We also introduce a second class of axially chiral cannabinoids inspired by cannabidiol (CBD), termed axially chiral cannabidiols (axCBDs). Finally, we provide an analysis of axially chiral cannabinoid (axCannabinoid) atropisomerism, which spans two classes (class 1 and 3 atropisomers), and provide first evidence that axCannabinoids retain─and in some cases, strengthen─affinity and functional activity at cannabinoid receptors. Together, these findings present a promising new direction for the design of novel cannabinoid ligands for drug discovery and exploration of the complex endocannabinoid system.

Altered methionine metabolism impacts phenylpropanoid production and plant development in Arabidopsis thaliana.

Phenylpropanoids are specialized metabolites derived from phenylalanine. Glucosinolates are defense compounds derived mainly from methionine and tryptophan in Arabidopsis. It was previously shown that the phenylpropanoid pathway and glucosinolate production are metabolically linked. The accumulation of indole-3-acetaldoxime (IAOx), the precursor of tryptophan-derived glucosinolates, represses phenylpropanoid biosynthesis through accelerated degradation of phenylalanine ammonia lyase (PAL). As PAL functions at the entry point of the phenylpropanoid pathway, which produces indispensable specialized metabolites such as lignin, aldoxime-mediated phenylpropanoid repression is detrimental to plant survival. Although methionine-derived glucosinolates in Arabidopsis are abundant, any impact of aliphatic aldoximes (AAOx) derived from aliphatic amino acids such as methionine on phenylpropanoid production remains unclear. Here, we investigate the impact of AAOx accumulation on phenylpropanoid production using Arabidopsis aldoxime mutants, ref2 and ref5. REF2 and REF5 metabolize aldoximes to respective nitrile oxides redundantly, but with different substrate specificities. ref2 and ref5 mutants have decreased phenylpropanoid contents due to the accumulation of aldoximes. As REF2 and REF5 have high substrate specificity toward AAOx and IAOx, respectively, it was assumed that ref2 accumulates AAOx, not IAOx. Our study indicates that ref2 accumulates both AAOx and IAOx. Removing IAOx partially restored phenylpropanoid content in ref2, but not to the wild-type level. However, when AAOx biosynthesis was silenced, phenylpropanoid production and PAL activity in ref2 were completely restored, suggesting an inhibitory effect of AAOx on phenylpropanoid production. Further feeding studies revealed that the abnormal growth phenotype commonly observed in Arabidopsis mutants lacking AAOx production is a consequence of methionine accumulation.

Vicinal stereocenters via asymmetric allylic alkylation and Cope rearrangement: a straightforward route to functionally and stereochemically rich heterocycles.

An asymmetric allylic alkylation/Cope rearrangement (AAA/[3,3]) capable of stereoselectively constructing vicinal stereocenters has been developed. Strategically integrated 4-methylation on the 3,3-dicyano-1,5-diene controls stereoselectivity and drives Cope rearrangement equilibrium in the forward direction. The AAA/[3,3] sequence rapidly converts abundant achiral and racemic starting materials into valuable (hetero)cycloalkane building blocks bearing significant functional and stereochemical complexity, highlighting the value of (hetero)cyclohexylidenemalononitriles as launching points for complex heterocycle synthesis. On this line, the resulting alkylidenemalononitrile moiety can be readily converted into amides via Hayashi-Lear amidation to ultimately yield amido-piperidines, tropanes, and related scaffolds with 3-5 stereocenters and drug-like functionality.

Metabolic link between auxin production and specialized metabolites in Sorghum bicolor.

Aldoximes are amino acid derivatives that serve as intermediates for numerous specialized metabolites including cyanogenic glycosides, glucosinolates, and auxins. Aldoxime formation is mainly catalyzed by cytochrome P450 monooxygenases of the 79 family (CYP79s) that can have broad or narrow substrate specificity. Except for SbCYP79A1, aldoxime biosynthetic enzymes in the cereal sorghum (Sorghum bicolor) have not been characterized. This study identified nine CYP79-encoding genes in the genome of sorghum. A phylogenetic analysis of CYP79 showed that SbCYP79A61 formed a subclade with maize ZmCYP79A61, previously characterized to be involved in aldoxime biosynthesis. Functional characterization of this sorghum enzyme using transient expression in Nicotiana benthamiana and stable overexpression in Arabidopsis thaliana revealed that SbCYP79A61 catalyzes the production of phenylacetaldoxime (PAOx) from phenylalanine but, unlike the maize enzyme, displays no detectable activity against tryptophan. Additionally, targeted metabolite analysis after stable isotope feeding assays revealed that PAOx can serve as a precursor of phenylacetic acid (PAA) in sorghum and identified benzyl cyanide as an intermediate of PAOx-derived PAA biosynthesis in both sorghum and maize. Taken together, our results demonstrate that SbCYP79A61 produces PAOx in sorghum and may serve in the biosynthesis of other nitrogen-containing phenylalanine-derived metabolites involved in mediating biotic and abiotic stresses.

Adiabatic Passage through Level Anticrossings in Systems of Chemically Inequivalent Protons Incorporating Parahydrogen: Theory, Experiment, and Prospective Applications.

Level anticrossings (LACs) are ubiquitous in quantum systems and have been exploited for spin-order transfer in hyperpolarized nuclear magnetic resonance spectroscopy. This paper examines the manifestations of adiabatic passage through a specific type of LAC found in homonuclear systems of chemically inequivalent coupled protons incorporating parahydrogen (pH2). Adiabatic passage through such a LAC is shown to elicit translation of the pH2 spin order. As an example, with prospective applications in biomedicine, proton spin polarizations of at least 19.8 ± 2.6% on the methylene protons and 68.7 ± 0.5% on the vinylic protons of selectively deuterated allyl pyruvate ester are demonstrated experimentally. After ultrasonic spray injection of a precursor solution containing propargyl pyruvate and a dissolved Rh catalyst into a chamber pressurized with 99% para-enriched H2, the products are collected and transported to a high magnetic field for NMR detection. The LAC-mediated hyperpolarization of the methylene protons is significant because of the stronger spin coupling to the pyruvate carbonyl 13C, setting up an ideal initial condition for subsequent coherence transfer by selective INEPT. Furthermore, the selective deuteration of the propargyl side arm increases the efficiency and polarization level. LAC-mediated translation of parahydrogen spin order completes the first step toward a new and highly efficient route for the 13C NMR signal enhancement of pyruvate via side-arm hydrogenation with parahydrogen.

Diastereoselective Indole-Dearomative Cope Rearrangements by Compounding Minor Driving Forces.

Reported herein is the discovery of a diastereoselective indole-dearomative Cope rearrangement. A suite of minor driving forces promote dearomatization: (i) steric congestion in the starting material, (ii) alkylidene malononitrile and stilbene conjugation events in the product, and (iii) an unexpected intramolecular π-π* stack on the product side of the equilibrium. The key substrates are rapidly assembled from simple starting materials, resulting in many successful examples. The products are structurally complex and bear vicinal stereocenters generated by the dearomative Cope rearrangement. They also contain a variety of functional groups for interconversion to complex architectures.

Construction of vicinal 4°/3°-carbons via reductive Cope rearrangement.

Herein reported is a strategy for constructing vicinal 4°/3° carbons via reductive Cope rearrangement. Substrates have been designed which exhibit Cope rearrangement kinetic barriers of ∼23 kcal mol-1 with isoenergetic favorability (ΔG ∼ 0). These fluxional/shape-shifting molecules can be driven forward by chemoselective reduction to useful polyfunctionalized building blocks.

1,2,4-Trifunctionalized Cyclohexane Synthesis via a Diastereoselective Reductive Cope Rearrangement and Functional Group Interconversion Strategy.

Polyfunctionalized cyclohexanes are privileged scaffolds in drug discovery. Reported herein is a method for synthesizing 1,2,4-trifunctionalized cyclohexanes via diastereoselective reductive Cope rearrangement. The scaffolds obtained can be derivatized by orthogonal functional group interconversion to cyclohexanes bearing a 1-amide, 2-branched arylallyl, and variable 4-functional group.

Aldoximes are precursors of auxins in Arabidopsis and maize.

Two natural auxins, phenylacetic acid (PAA) and indole-3-acetic acid (IAA), play crucial roles in plant growth and development. One route of IAA biosynthesis uses the glucosinolate intermediate indole-3-acetaldoxime (IAOx) as a precursor, which is thought to occur only in glucosinolate-producing plants in Brassicales. A recent study showed that overproducing phenylacetaldoxime (PAOx) in Arabidopsis increases PAA production. However, it remains unknown whether this increased PAA resulted from hydrolysis of PAOx-derived benzyl glucosinolate or, like IAOx-derived IAA, is directly converted from PAOx. If glucosinolate hydrolysis is not required, aldoxime-derived auxin biosynthesis may occur beyond Brassicales. To better understand aldoxime-derived auxin biosynthesis, we conducted an isotope-labelled aldoxime feeding assay using an Arabidopsis glucosinolate-deficient mutant sur1 and maize, and transcriptomics analysis. Our study demonstrated that the conversion of PAOx to PAA does not require glucosinolates in Arabidopsis. Furthermore, maize produces PAA and IAA from PAOx and IAOx, respectively, indicating that aldoxime-derived auxin biosynthesis also occurs in maize. Considering that aldoxime production occurs widely in the plant kingdom, aldoxime-derived auxin biosynthesis is likely to be more widespread than originally believed. A genome-wide transcriptomics study using PAOx-overproduction plants identified complex metabolic networks among IAA, PAA, phenylpropanoid and tryptophan metabolism.

Aromatic Cope rearrangements.

Reviewed herein is the aromatic Cope rearrangement, a Cope rearrangement where one (or both) of the alkenes of the 1,5-diene are part of a greater aromatic system. While the Cope rearrangement of 1,5-dienes has seen wide utility, variation, and application in chemical synthesis, the aromatic Cope rearrangement, comparatively, has not. This review summarizes the ∼40 papers dating back to 1956 on this topic and is divided into the following sections: (1) introduction, including kinetic and thermodynamic challenges of the aromatic Cope rearrangement, and (2) key substrate features, of which there are four general types: (i) α-allyl-α-aryl malonates (and related substrates), (ii) 1-aryl-2-vinylcyclopropanes, and (iii) anion-accelerated aromatic oxy-Cope substrates, and (iv) the concept of synchronized aromaticity. Ultimately, we hope this review will draw attention to a potentially valuable transformation for arene functionalization that warrants further studies and development.

[3,3] Ring Rearrangement of Oxo- or Aza-Bridged Bicyclo[3.2.1]octene-Based 1,5-Dienes.

We report that oxo- or aza-bridged alkylidenemalononitrile-cycloheptenes undergo a [3,3] ring rearrangement to yield cyclopenta-fused dihydro-furans or pyrroles. Described herein are the origins of the serendipitous discovery, scope studies, and representative functional group interconversion chemistry.

Overcoming Kinetic and Thermodynamic Challenges of Classic Cope Rearrangements.

Systematic evaluation of 1,5-dienes bearing 3,3-electron-withdrawing groups and 4-methylation results in the discovery of a Cope rearrangement for Meldrum's acid-containing substrates that have unexpectedly favorable kinetic and thermodynamic profiles. The protocol is quite general due to a concise and convergent synthesis from abundant starting materials. Furthermore, products with an embedded Meldrum's acid moiety are prepared, which, in turn, can yield complex amides under neutral conditions. We have now expanded the scope of the reductive Cope rearrangement, which, via chemoselective reduction, can promote thermodynamically unfavorable [3,3] sigmatropic rearrangements of 3,3-dicyano-1,5-dienes to form reduced Cope rearrangement products. The Cope rearrangement is found to be stereospecific and can yield enantioenriched building blocks when chiral, nonracemic 1,3-disubstituted allylic electrophiles are utilized. We expand further the use of Cope rearrangements for the synthesis of highly valuable building blocks for complex- and drug-like molecular synthesis.

Function-Oriented and Modular (+/-)-cis-Pseudoguaianolide Synthesis: Discovery of New Nrf2 Activators and NF-κB Inhibitors.

Described herein is a function-oriented synthesis route and biological evaluation of pseudoguaianolide analogues. The 10-step synthetic route developed retains the topological complexity of the natural product, installs functional handles for late-stage diversification, and forges the key bioactive Michael acceptors early in the synthesis. The analogues were found to be low-micromolar Nrf2 activators and micromolar NF-κB inhibitors and dependent on the local environment of the Michael acceptor moieties.

Modern approaches to the development of synthetic cannabinoid receptor probes.

The endocannabinoid system, which spans the central and peripheral nervous systems and regulates many biologic processes, is an important target for probe discovery and medications development. Whereas the earliest endocannabinoid receptor probes were derivatives of the non-selective phytocannabinoids isolated from Cannabis species, modern drug discovery techniques have expanded the definitions of what constitutes a CB1R or CB2R cannabinoid receptor ligand. This review highlights recent advances in synthetic cannabinoid receptor chemistry and pharmacology. We provide examples of new CB1R- and CB2R-selective probes, and discuss rational approaches to the design of peripherally-restricted agents. We also describe structural classes of positive- and negative allosteric modulators (PAMs and NAMs) of CB1R and CB2R. Finally, we introduce new opportunities for cannabinoid receptor probe development that have emerged in recent years, including biased agonists that may lead to medications lacking adverse effects.

Selective ring-rearrangement or ring-closing metathesis of bicyclo[3.2.1]octenes.

Explored was the competitive ring-closing metathesis vs. ring-rearrangement metathesis of bicyclo[3.2.1]octenes prepared by a simple and convergent synthesis from bicyclic alkylidenemalono-nitriles and allylic electrophiles. It was uncovered that ring-closing metathesis occurs exclusively on the tetraene-variant, yielding unique, stereochemically and functionally rich polycyclic bridged frameworks, whereas the reduced version (a triene) undergoes ring-rearrangement metathesis to 5-6-5 fused ring systems resembling the isoryanodane core.

Axially Chiral Cannabinols: A New Platform for Cannabinoid-Inspired Drug Discovery.

Phytocannabinoids (and synthetic analogs thereof) are gaining significant attention as promising leads in modern medicine. Considering this, new directions for the design of phytocannabinoid-inspired molecules is of immediate interest. In this regard, we have hypothesized that axially-chiral-cannabinols (ax-CBNs), unnatural and unknown isomers of cannabinol (CBN) may be valuable scaffolds for cannabinoid-inspired drug discovery. There are two main factors directing our interest to these scaffolds: (a) ax-CBNs would have ground-state three-dimensionality; ligand-receptor interactions can be more significant with complimentary 3D-topology, and (b) ax-CBNs at their core structure are biaryl molecules, generally attractive platforms for pharmaceutical development due to their ease of functionalization and stability. Herein we report a synthesis of ax-CBNs, examine physical properties experimentally and computationally, and perform a comparative analysis of ax-CBN and THC in mice behavioral studies.

Diastereoselective Synthesis of 2,3,4-Trisubstituted Tetrahydrofurans via Thermally Reactive 1,5-Diene-tert-butyl Carbonates.

We report that 3,3-dicyano-1,5-dienes bearing tert-butyl carbonates can be thermally converted to 2,3,4-trisubstituted tetrahydrofurans. The transformation relies on two thermally reactive functional groups, a 1,5-diene and a tert-butyl carbonate, that react cooperatively to yield the furan scaffolds by thermal Cope rearrangement, Boc deprotection, and oxy-Michael addition. Described herein is background related to the discovery, optimization, and scope of the key transformation and representative functional group interconversion chemistry for the tetrahydrofuran scaffolds.