Asymmetric Synthesis of Gonytolide A: Strategic Use of an Aryl Halide Blocking Group for Oxidative Coupling

Gold(I)-Catalyzed Synthesis of 2,2'-Biindoles via One-Pot Double Cycloisomerization Strategy

The first systematic, concise and target-directed gold(I)-catalyzed synthesis of a family of 2,2'-biindoles containing different substitution patterns is described. The developed protocol involves the synthesis of 1,3-diyne-anilines followed by a one-pot gold(I)-catalyzed double cycloisomerization, giving rise to an efficient, broad and general protocol to get different 2,2'-biindoles under mild reaction conditions. Due to the methodological restriction of present methods for accessing this class of compounds, herein we present our synthetic proposal which allowed the preparation of several examples of 2,2'-biindoles. Their functionalization-guided us to the discovery that the chemical stability, is substitution structure-dependent.

Recent advances in oxidative phenol coupling for the total synthesis of natural products

Covering: 2008 to 2023This review will describe oxidative phenol coupling as applied in the total synthesis of natural products. This review covers catalytic and electrochemical methods with a brief comparison to stoichiometric and enzymatic systems assessing their practicality, atom economy, and other measures. Natural products forged by C-C and C-O oxidative phenol couplings as well as from alkenyl phenol couplings will be addressed. Additionally, exploration into catalytic oxidative coupling of phenols and other related species (carbazoles, indoles, aryl ethers, etc.) will be surveyed. Future directions of this particular area of research will also be assessed.

Catalytic Asymmetric Vinylogous Conjugate Addition of Butenolide to 2-Ester-Substituted Chromones: Access to Chiral Chromanone Lactones via Trapping of a Copper(I) Enolate by Trimethyl Borate

A copper-catalyzed asymmetric vinylogous conjugate addition of butenolide to 2-ester-substituted chromones is described, and it delivers syn- or anti-chromanone lactones with high stereoselectivities. The enantioselectivity-determining step varied with the use of B(OMe)3 as an additive, resulting in enhanced stereoselectivities, as revealed by density functional theory calculations, which also provided theoretical insight into the origin of the ligand-dependent diastereodivergence.

Modular Approach for the Synthesis and Bioactivity Profiling of 8,8'-Biflavones

In this work, we report the scalable and modular synthesis of a library of 55 monomeric and dimeric flavonoids including 14 8,8'-biflavones. The sterically demanding tetra-ortho-substituted axis of an acetophenone dimer key intermediate was constructed in a regioselective manner using Fe-mediated oxidative coupling. This step was systematically optimized and performed on up to multigram scale. The biological activities of this compound library were evaluated, including cytotoxicity against healthy and malignant human cell lines, antimicrobial activity against the apicomplexan parasite Toxoplasma gondii, and antioxidant capacity. A marked increase in activity for the 8,8'-dimeric structures compared to that of their monomeric counterparts was observed. Several biflavones were identified with high selectivity indices (low cytotoxicity and high antiprotozoal activity), showing that this class of natural products may serve as lead structures for further investigations.

Asymmetric synthesis of chromanone lactones via vinylogous conjugate addition of butenolide to 2-ester chromones

Chiral chromanone lactones are a class of natural products with important biological activity. We report a direct diastereo- and enantioselective vinylogous conjugate addition of butenolide to 2-ester substituted chromones. The transformation proceeded well in the presence of as low as 1 mol% of a chiral N,N'-dioxide/ScIII complex, 3 Å MS and a catalytic amount of hexafluoroisopropanol (HFIP). The scope of Michael acceptors includes a variety of substituted chromones at different positions, and the desired chromanone lactones upon reduction are afforded in good yield and diastereoselectivity, and excellent enantioselectivity (up to 99% ee). The strategy could be used in the concise synthesis of blennolide C and gonytolide A, C and G.

Furanone-functionalized benzothiazole derivatives: synthesis, in vitro cytotoxicity, ADME, and molecular docking studies

In the present study, a novel series of new furanone-based benzothiazole derivatives (4a-j) were synthesized from 4-(benzo[d]thiazol-2-yl)-4-oxobutanoic acid (3) as potential anticancer agents. In vitro cytotoxicity against three human cancer cell lines (A549, MCF7, and DUI45) revealed substantial activity. Di-substituted compound, 4i emerged as a promising anticancer compound which showed IC50 values of 7.2 ± 0.5, 6.6 ± 1.4, and 7.3 ± 0.1 µM against A549, MCF7, and DUI45 cell lines, respectively. Four compounds 4c, 4e, 4f, and 4i evaluated for their acute toxicity were found to be non-toxic on the two vital organs (liver and heart). Further, these compounds were found to be more efficient and less hepatotoxic in comparison to standard drug doxorubicin. Molecular docking studies carried out with VEGFR-2 revealed compounds 4a and 4i as potential VEGFR-2 kinase inhibitors. In silico ADME evaluation was carried out to estimate and predict drug-likeness. Compound 4i demonstrated the best ADME parameters. Based on the results of docking analyses, ADME, and in vitro cytotoxicity, compound 4i is identified as the lead compound for further development of anticancer agents.

Cobalt-Catalyzed Vinylic C-H Addition to Formaldehyde: Synthesis of Butenolides from Acrylic Acids and HCHO

A carboxyl-assisted C-H functionalization of acrylic acids with formaldehyde to give butenolides is described. It is the first time that the addition of an inert vinylic C-H bond to formaldehyde has been achieved via cobalt-catalyzed C-H activation. The unique reactivity of the cobalt species was observed when compared with related Rh or Ir catalysts. γ-Hydroxymethylated butenolides were produced by the treatment of Na₂CO₃ after the catalytic reaction in one pot.

Recent advances of chromone-based reactants in the catalytic asymmetric domino annulation reaction

Chiral polycyclic chromanones are important heterocyclic frameworks that constitute the core structures of many natural products and bioactive molecules.

Spororrminone A and 2-epi-spororrminone A, two new chromones from an endolichenic fungus Sporormiella irregularis

Two new chromones, spororrminone A (1, (S)-5-hydroxy-2-methyl-4-oxo-2-((S)-5-oxotetrahydrofuran-2-yl)chroman-7-carboxylic acid) and 2-epi-spororrminone A (2, (R)-5-hydroxy-2-methyl-4-oxo-2-((S)-5-oxotetrahydrofuran-2-yl)chroman-7-carboxylic acid), were isolated from an EtOAc extract of an endolichenic fungal strain Sporormiella irregularis (No. 71-11-4-1). The structures of these compounds were identified by spectroscopic analyses. The absolute configuration of 1 was established by single-crystal X-ray diffraction. Spororrminone A (1) and 2-epi-spororrminone A (2) represent the first examples of 2-(5-oxotetrahydrofuran-2-yl) chromones with 7-carboxylic group.

New Developments of the Principle of Vinylogy as Applied to π-Extended Enolate-Type Donor Systems

The principle of vinylogy states that the electronic effects of a functional group in a molecule are possibly transmitted to a distal position through interposed conjugated multiple bonds. As an emblematic case, the nucleophilic character of a π-extended enolate-type chain system may be relayed from the legitimate α-site to the vinylogous γ, ε, ..., ω remote carbon sites along the chain, provided that suitable HOMO-raising strategies are adopted to transform the unsaturated pronucleophilic precursors into the reactive polyenolate species. On the other hand, when "unnatural" carbonyl ipso-sites are activated as nucleophiles (umpolung), vinylogation extends the nucleophilic character to "unnatural" β, δ, ... remote sites. Merging the principle of vinylogy with activation modalities and concepts such as iminium ion/enamine organocatalysis, NHC-organocatalysis, cooperative organo/metal catalysis, bifunctional organocatalysis, dicyanoalkylidene activation, and organocascade reactions represents an impressive step forward for all vinylogous transformations. This review article celebrates this evolutionary progress, by collecting, comparing, and critically describing the achievements made over the nine year period 2010-2018, in the generation of vinylogous enolate-type donor substrates and their use in chemical synthesis.

Regioselective β-Arylation of α-Angelica Lactone through Isomerization/Addition under Mild Conditions

The conversion of biomass-based platform molecules into various high-value chemicals greatly promotes the utilization of renewable biomass resources. Herein, an example of Rh-catalyzed β-arylation of levulinic-acid-derived α-angelica lactone was reported, providing the γ-lactone-structure products with high regioselectivity. Both arylboronic and alkenylboronic acids could be applied in this transformation. This reaction tolerated a variety of synthetically important functional groups. Moreover, the obtained γ-lactone products could be readily converted to high-value products such as 1,4-diols and γ-methoxy-carboxylates.

Synthetic Applications of Oxidative Aromatic Coupling-From Biphenols to Nanographenes

Oxidative aromatic coupling occupies a fundamental place in the modern chemistry of aromatic compounds. It is a method of choice for the assembly of large and bewildering architectures. Considerable effort was also devoted to applications of the Scholl reaction for the synthesis of chiral biphenols and natural products. The ability to form biaryl linkages without any prefunctionalization provides an efficient pathway to many complex structures. Although the chemistry of this process is only now becoming fully understood, this reaction continues to both fascinate and challenge researchers. This is especially true for heterocoupling, that is, oxidative aromatic coupling with the chemoselective formation of a C-C bond between two different arenes. Analysis of the progress achieved in this field since 2013 reveals that many groups have contributed by pushing the boundary of structural possibilities, expanding into surface-assisted (cyclo)dehydrogenation, and developing new reagents.

Synthesis and Anticancer Activity of Structure Simplified Naturally-Inspired Dimeric Chromenone Derivatives

Select dimeric chromenones exhibit low micromolar cyctotoxicity toward lymphoma and leukemia cell lines, L5178Y and HL60, respectively. The bioactive dimeric chromenones were identified from a focused library of structurally-simplified derivatives of naturally-occurring dimeric chromenones and tetrahydroxanthones that was prepared as part of this study. The simple dimeric chromenone scaffolds contain no stereogenic centers, are easily synthesized, and may be utilized as lead compounds in cancer research and drug discovery.

Synthesis of amino acid derivatives of 5-alkoxy-3,4-dihalo-2(5H)-furanones and their preliminary bioactivity investigation as linkers

A series of amino acid derivatives are successfully synthesized via a metal-free C-N coupling reaction of 5-alkoxy-3,4-dihalo-2(5H)-furanones and amino acids. Their structures are well characterized with ¹H NMR, ¹³C NMR, ESI-MS and elemental analysis. As potential linkers of the 2(5H)-furanone unit with other drug moieties containing a hydroxyl or amino group, the effect of amino acids is investigated by comparison with other 2(5H)-furanone compounds by constructing C-O/C-S bonds. The preliminary results of the biological activity assay by the MTT method on a series of cancer cell lines in vitro reveal that the introduction of amino acids basically has no toxic effect. This can lead to these 2(5H)-furanone derivatives being further well-linked with other bioactive moieties with amino or hydroxy groups as expected. Thus, the biological activity assay gives a direction for the design of bioactive 2(5H)-furanones based on these amino acid linkers.

Chiral Dinuclear Vanadium Complex-Mediated Oxidative Coupling of Resorcinols

A method for the highly regio- and enantioselective oxidative coupling of resorcinols has been established by using dibrominated dinuclear vanadium(V) catalyst 1c under air. When resorcinols bearing an aryl substituent were applied as substrates to the coupling, axially chiral biresorcinols were obtained as single regioisomers in high yield with up to 98% ee.

Enantioselective Total Synthesis of Chromanone Lactone Homo- and Heterodimers

A one pot borylation/Suzuki-Miyaura reaction of the 4-bromochromanone lactones 21 and 23, respectively, followed by cleavage of the methyl ether moieties gave the homodimeric chromanone lactones 10 and 11. Reaction of a 1:1 mixture of 21 and 23 under otherwise identical conditions gave a 1:1:2-mixture of the two homodimers 10 and 11 and the heterodimer 12. This is the first example of the preparation of a heterodimeric chromanone lactone. For the enantioselective synthesis of the starting material, phenol 17 was transformed into the chromane 18 using a Wacker-type cyclisation with 99 % ee and 80 % yield.