Gold-Catalyzed Double Spirocyclization of 3-Ene-1,7-diyne Esters to Dispiroheterocycles

A synthetic method to prepare dispiroheterocycles containing two all-carbon quaternary centers efficiently that relies on the gold(I)-catalyzed double spirocyclization of 3-ene-1,7-diyne esters is described. The suggested mechanism delineates a rare example of a dispirocyclization featuring two 1,n-acyloxy shifts comprising a 1,3-acyloxy migration and an interrupted 1,5-acyl migration that was achieved with the assistance of residual water in the reaction media.

Enantioselective and Regiodivergent Gold and Chiral Brønsted Acid Catalyzed Cycloisomerization/Diels-Alder Reaction of 1,10-Dien-4-yn-3-yl Acetates: Synthesis of Norbornene-Embedded Tricarbocycles

A synthetic method for the enantioselective and regiodivergent synthesis of hexahydro-2H-2,4a-methanonaphthalen-4-yl and octahydro-2,4-methanoazulen-1-yl esters that relies on the gold(I)- and chiral Brønsted acid-catalyzed cycloisomerization/Diels-Alder (CDA) reaction of (E)-1,10-dien-4-yn-3-yl acetates is described.

Gold-Catalyzed Cascade Cycloisomerization of 3-Allyloxy-1,6-diynes to Cyclopropyl- and Cyclobutyl-Fused Benzofurans and Chromen-3a(1H)-ols

A synthetic method for the efficient preparation of partially hydrogenated benzo[f]cyclobuta[cd]cyclopenta[h]benzofurans and cyclopropa[c]chromen-3a(1H)-ols that relies on the gold(I)-catalyzed cascade cycloisomerization of 3-allyloxy-1,6-diynes is described.

Recent Advances in the Gold-Catalyzed Reactions of Propargyl Esters

ConspectusLate-transition-metal-based complexes represent an indispensable catalytic tool in chemical synthesis due to their ability to increase molecular complexity rapidly and efficiently from readily accessible substrates in a single operation. Added to this is the exquisite control of product chemo-, diastereo-, enantio-, and site-selectivities achieved by catalytic systems of the transition-metal salts that have been developed to mediate a wide range of functional group transformations. Within this venerable synthetic toolbox, complexes and salts of Au(I) and Au(III) have emerged in recent years as an invaluable addition as a result of their potent σ- and π-Lewis acidities and ability to stabilize cationic reaction intermediates. The insights provided by mechanistic studies examining the various electronic, steric, and stereoelectronic factors at play in the organogold species that are expected to be formed in the catalytic chemistry of the transition-metal complex have also been pivotal in understanding and exploring their potential synthetic utility. Illustrative of this, for example, is the contribution made by the gold-catalyzed cycloisomerization chemistry of propargyl esters in synthetic strategies to a variety of bioactive natural products and compounds of current pharmaceutical and materials interest. This Account summarizes our efforts over the past decade toward realizing new single-step strategies for carbocyclic and heterocyclic synthesis that relied on the gold-catalyzed reactions of propargyl esters. It outlines synthetic methods developed by the group that exploited the unique reactivities of the gold-carbene species typically generated from the [2,3]-sigmatropic rearrangement of the compound class containing a terminal or electron-deficient alkyne moiety on exposure to the transition-metal salt. This Account also describes the realization of synthetic methods initiated by the gold-catalyzed 1,3-acyloxy migration of propargyl esters with an electronically unbiased disubstituted C≡C bond that delivers the corresponding allenyl ester that is primed for further reactivity on activation by the group 11 metal complex. The studies formed a part of an ongoing overarching program within our group that was focused on determining reactivities in gold catalysis that would enable their application as readily recognizable disconnections in retrosynthetic analysis. They were additionally a part of efforts aimed at evaluating the opportunities offered by the relativistic effects possessed by a Au(I) and Au(III) complex, the most pronounced among the d-block elements and thus the catalyst of choice in alkyne activation chemistry, to generate new chemical space. For instance, we demonstrated in several studies the cycloisomerization of 1,3- and 1,4-enyne esters to be a reliable strategy for the in situ formation of a wide range of 1,4-cyclopentadienyl derivatives. Their further reaction with an appropriately placed functional group or a second starting material was then shown to afford a variety of synthetic targets containing the five-membered ring structure. An example of this was the assembly of a new member of the 1H-isoindole compound family that was found to exhibit potent TNF-α (tumor necrosis factor-α) inhibitor activity.

Gold Catalysed Site-Selective Cross-Coupling of Tertiary -Silylamines with 1-Iodoalkynes Under UVA LED Light

A synthetic method that relies on [Au2(-dppm)2]Cl2 (dppm = bis(diphenylphosphanyl)methane) and UVA LED (LED = light emitting diode) light ( = 365 nm) to mediate the -alkynylation of tertiary -silylamines...

Coassembled Nitric Oxide-Releasing Nanoparticles with Potent Antimicrobial Efficacy against Methicillin-Resistant Staphylococcus aureus (MRSA) Strains

Nitric oxide (NO)-releasing nanoparticles are effective nanomedicines with diverse therapeutic advantages compared with small molecule-based NO donors. Here, we report a new class of furoxan-based NO-releasing nanoparticles using a simple, creative yet facile coassembly approach. This is the first time we demonstrated that the coassembled NO-releasing nanoparticles with poly(ethylene glycol)₁₀₁-block-poly(propylene glycol)₅₆-block-poly(ethylene glycol)₁₀₁ (Pluronic F127) had potent antimicrobial efficacies against methicillin-resistant Staphylococcus aureus (MRSA) strains. Nanoparticles obtained from the coassembly of either 4-(1-(3-methylpentan-5-ol)oxyl)(3-phenylsulfonyl) furoxan (compound 1) or 4-methoxy(3-phenylsulfonyl) furoxan (compound 2) with Pluronic F127 exhibit 4-fold improved antimicrobial activities compared to their self-assembled counterparts without Pluronic F127. 5(6)-Carboxylfluorescein (CF) leakage experiments further reveal that both coassembled NO-releasing nanoparticles show stronger interactions with lipid bilayers than those self-assembled alone. Subsequently, their strong plasma membrane-damaging capabilities are confirmed under both high-resolution optical microscopy and scanning electron microscopy characterizations. This coassembly approach could be readily applied to other small molecule-based antimicrobials, providing new solutions and important insights to further antimicrobial recipe design.

Rhodium(i)-catalysed cycloisomerisation/6π electrocyclisation of 5-(ethynylamino)pent-2-yn-1-yl esters to 2,3-dihydrobenzo[f]indoles

A rare instance in rhodium catalysis of an in situ formed rhodacycle that undergoes a formal 1,8-acyloxy migration-initiated reductive elimination.

PtI4-Catalyzed Oxidative and Hydrogenative Dearomative [3 + 2] Cycloadditions of 1H-Indole N-Tethered o-Alkynylbenzaldehydes

A synthetic method for the chemodivergent assembly of a diverse range of highly functionalized and architecturally challenging cyclohepta[b]indolines that relies on the PtI4-catalyzed oxidative and hydrogenative dearomative [3 + 2]...

Correction: THF-enabled PtBr2-catalyzed desymmetric hydrogenative [3 + 2] cycloaddition of 2-alkynylbenzaldehyde-tethered cyclohexadienones

Correction for ‘THF-enabled PtBr2-catalyzed desymmetric hydrogenative [3 + 2] cycloaddition of 2-alkynylbenzaldehyde-tethered cyclohexadienones’ by Rui Hu et al., Org. Chem. Front., 2022, https://doi.org/10.1039/d2qo00593j.

Ligand-controlled chemoselectivity in gold-catalyzed cascade cyclization of 1,4-diene-tethered 2-alkynylbenzaldehydes

A synthetic method that relies on the gold(i)-catalyzed cascade annulation of skipped 1,4-diene-tethered 2-alkynylbenzaldehydes for the chemo- and stereoselective assembly polycyclic bridged-pyrrolidines and -azepines is described.

THF-Enabled PtBr2-Catalyzed Desymmetric Hydrogenative [3 + 2] Cycloaddition of 2-Alkynylbenzaldehyde-Tethered Cyclohexadienones

A THF-enabled PtBr2-catalyzed desymmetric hydrogenative [3 + 2] cycloaddition of 2-alkynylbenzaldehyde-tethered cyclohexadienones has been developed. The protocol provides a highly functionalized 6-7-6 polycyclic skeleton with four contiguous stereocenters in good...

A robust photoluminescence screening assay identifies uracil-DNA glycosylase inhibitors against prostate cancer

Many cancers have developed resistance to 5-FU, due to removal by the enzyme uracil-DNA glycosylase (UDG), a type of base excision repair enzyme (BER) that can excise uracil and 5-fluorouracil (5-FU) from DNA. However, the development of UDG inhibitor screening methods, especially for the rapid and efficient screening of natural product/natural product-like compounds, is still limited so far. We developed herein a robust time-resolved photoluminescence method for screening UDG inhibitors, which could significantly improve sensitivity over the screening method based on the conventional steady-state spectroscopy, reducing the substantial fluorescence background interference. As a proof-of-concept, two potential UDG inhibitors were identified from a database of natural products and approved drugs. Co-treatment of these two compounds with 5-FU showed synergistic cytotoxicity, providing the basis for treating drug-resistant cancers. Overall, this method provides an avenue for the rapid screening of small molecule regulators of other BER enzyme activities that can avoid false negatives arising from the background fluorescence.

The discovery of UDG inhibitors against prostate cancer by using a robust photoluminescence screening assay that can avoid false negatives arising from the background fluorescence.

Gold Catalysed 1,4-Enyne Acetate Strategy for the Synthesis of 1H-Indenes and Partially Hydrogenated Methanonaphtho[1,2-c]furan-1,3(4H)-diones

A synthetic method to prepare 1H-indenes and partially hydrogenated methanonaphtho[1,2-c]furan-1,3(4H)-diones from gold(i)-catalysed 1,4-enyne acetate cycloisomerisation and oxidation or Diels–Alder reaction with maleic anhydride is described. The proposed mechanism involves Rautenstrauch rearrangement of the 1,4-enyne motif to give an insitu formed 1,3-cyclopentadiene intermediate. This is followed by 6-endo-dig cyclisation of the cyclic adduct and oxidation to give the aromatic carbocycle or Diels–Alder reaction with maleic anhydride to afford the bridged furan product.

Aurone derivatives as Vps34 inhibitors that modulate autophagy

We report in this study the identification of a natural product-like antagonist (1a) of Vps34 as a potent autophagy modulator via structure-based virtual screening. Aurone derivative 1a strongly inhibited Vps34 activity in cell-free and cell-based assays. Significantly, 1a prevents autophagy in human cells induced either by starvation or by an mTOR inhibitor. In silico modeling and kinetic data revealed that 1a could function as an ATP-competitive inhibitor of Vps34. Moreover, it suppressed autophagy in vivo and without inducing heart or liver damage in mice. 1a could be utilized as a new motif for more selective and efficacious antagonists of Vps34 for the potential treatment of autophagy-related human diseases.

Gold-Catalysed Oxidative Cycloisomerisation of 1,6-Diyne Acetates to 1-Naphthyl Ketones

A synthetic method to prepare 1-naphthyl ketones from gold(i)-catalysed oxidative cycloisomerisation of 1,6-diyne acetates is described. The proposed mechanism involves cyclopropenation–cycloreversion of the 1,6-diyne motif initiated by a 1,2-acyloxy migration. This is followed by nucleophilic attack of the ensuing gold carbenoid species by a molecule of water and autoxidation to give the aromatic product.

Chiral Brønsted Acid Catalyzed Enantioselective Dehydrative Nazarov-Type Electrocyclization of Aryl and 2-Thienyl Vinyl Alcohols

An efficient chiral Brønsted acid-catalyzed enantioselective dehydrative Nazarov-type electrocyclization (DNE) of electron-rich aryl- and 2-thienyl-β-amino-2-en-1-ols is described. The 4π conrotatory electrocyclization reaction affords access to a wide variety of the corresponding 1 H-indenes and 4 H-cyclopenta[ b]thiophenes in excellent yields of up to 99% and enantiomeric excess (ee) values of up to 99%. Experimental and computational studies based on a proposed intimate contact ion-pair species that is further assisted by hydrogen bonding between the amino group of the substrate cation and chiral catalyst anion provide insight into the observed product enantioselectivities.

Brønsted Acid-Catalysed Allylic Amination of 1-(2-Aminoaryl)prop-2-en-1-ols to 1,2-Dihydroquinolines

A highly efficient synthetic method to prepare 1,2-dihydroquinolines that relies on trifluoromethanesulfonic acid (TfOH)-catalysed allylic amination of 1-(2-aminoaryl)prop-2-en-1-ols is described. Achieved at a catalyst loading of 0.01 mol-% under mild conditions at room temperature, the reaction was found to be robust, with a wide range of substitution patterns tolerated. The corresponding N-heterocyclic adducts were obtained in good to excellent yields of 45–93 %.

Brønsted Acid-Mediated Cycloaromatization of 1H-Indol-2-yl Propargyl Benzoates to 7H-Benzo[c]carbazoles

A synthetic method for the efficient assembly of benzo[c]carbazole derivatives that relies on silica gel-activated benzoic acid-mediated cycloaromatization of 1H-indol-2-yl propargyl benzoates under atmospheric conditions is described. Robust with a variety of substitution patterns tolerated, the reaction provides a one-step strategy to construct a member of the N-heterocycles family in good to excellent yields. A tentative mechanism is proposed in which the cycloaromatization process is thought to involve a Brønsted acid-mediated formal 1,3-acyloxy migration/6π-electrocyclization pathway.

Brønsted Base-Mediated Aziridination of 2-Alkyl-Substituted-1,3-Dicarbonyl Compounds and 2-Acyl-Substituted-1,4-Dicarbonyl Compounds by Iminoiodanes

The synthesis of α,α-diacylaziridines and α,α,β-triacylaziridines from reaction of 2-alkyl-substituted-1,3-dicarbonyl compounds and 2-acyl-substituted-1,4-dicarbonyl compounds with arylsulfonyliminoiodinanes (ArSO2N=IPh) under Brønsted base-mediated atmospheric conditions is described. The reaction mechanism is thought to involve the formal oxidation of the substrate followed by aziridination of the ensuing α,β-unsaturated intermediate by the hypervalent iodine(iii) reagent.

Gold-Catalyzed Tandem 1,3-Migration/Double Cyclopropanation of 1-Ene-4,n-diyne Esters to Tetracyclodecene and Tetracycloundecene Derivatives

A synthetic method that relies on Au(I)-catalyzed tandem 1,3-acyloxy migration/double cyclopropanation of 1-ene-4,9-diyne and 1-ene-4,10-diyne esters to construct the respective architecturally challenging tetracyclodecene and tetracycloundecene derivatives is described. Achieved under mild reaction conditions, the transformation was shown to be robust with a wide variety of substitution patterns tolerated to give the two members of the carbocyclic family in good to excellent yields and as a single regio- and diastereomer.

Structure-based screening and optimization of cytisine derivatives as inhibitors of the menin-MLL interaction

The natural product-like compound 1 was identified as a direct inhibitor of the menin-MLL interaction by in silico screening. Structure-based optimization furnished analogue 1a, which showed significantly higher potency than both the lead structure 1 and the reference compound MI-2.

Copper-Mediated Cross-Dehydrogenative Coupling of 2-Methylpyridine and 8-Methylquinoline with Methyl Ketones and Benzamides

A synthetic method to prepare (E)-(pyridin-2-yl)enones and (E)-(quinolin-8-yl)enones that relies on the respective copper(I)-catalyzed formal cross-dehydrogenative coupling (CDC) reaction of 2-methylpyridine and 8-methylquinoline with methyl ketones has been discovered. The mechanism was delineated to follow a pathway involving oxidation of the N-heterocycle to its corresponding aldehyde adduct prior to reaction with the methyl ketone. The versatility and substrate dependent divergence in the reactivity of the copper-mediated CDC strategy was exemplified by its application to the synthesis of N-(quinolin-8-ylmethyl)amide and N-(quinolin-8-ylmethyl)aniline adducts on switching the cross-coupling partner to benzamides or an aniline derivative.

Synthesis of 1,4-amino alcohols by Grignard reagent addition to THF and N-tosyliminobenzyliodinane

The synthesis of 1,4-amino alcohols from THF treated with N-tosyliminobenzyliodinane (PhINTs) followed by a Grignard reagent under mild reaction conditions at room temperature is described herein. Various Grignard reagents were shown to be compatible, furnishing the corresponding 4-substituted-N-1,4-tosylamino alcohols in good to excellent yields. A partial or full detosylation of the N-tosyl-1,4-amino alcohol was observed in instances involving a sterically bulky Grignard reagent, leading to the deprotected 1,4-amino alcohol product in moderate to good yields. The synthetic utility of this protocol was demonstrated by the synthesis of a 5-substituted-N-tosyl-1,5-amino alcohol from THP and the conversion of two examples to their corresponding γ-lactam and pyrrolidine adducts.

A label-free G-quadruplex-based mercury detection assay employing the exonuclease III-mediated cleavage of T-Hg2+-T mismatched DNA

We report herein the use of an exonuclease III and G-quadruplex probe to construct a G-quadruplex-based luminescence detection platform for Hg2+. Unlike common DNA-based Hg2+ detection methods, when using the dsDNA probe to monitor the hairpin formation, the intercalation of the dsDNA probe may be influenced by the distortion of dsDNA. This 'mix-and-detect' methodology utilized the G-quadruplex probe as the signal transducer and is simple, rapid, convenient to use and can detect down to 20 nM of Hg2+.

Gold-Catalyzed Cycloisomerization and Diels-Alder Reaction of 1,6-Diyne Esters with Alkenes and Diazenes to Hydronaphthalenes and -cinnolines

A method for the efficient preparation of hydronaphthalene and -cinnoline derivatives by Au(I)-catalyzed cycloisomerzation of 1,6-diyne esters followed by a Diels-Alder reaction with alkenes or diazenes under mild conditions at room temperature with catalyst loadings as low as 1 mol % is described.

Crystal structure of (Z)-1-phenyl-3-styryl-undeca-2-en-4,10-diyn-1-ol

The mol­ecule of the title compound, C₂₅H₂₄O, obtained by acid-catalysed 1,3-migration of an alcohol group, is T-shaped. The planes of the two phenyl rings are inclined to one another by 81.9 (2)°. In the crystal, mol­ecules are linked by O—H⋯O hydrogen bonds, forming chains along [001].