Acetylenic acids from the aerial parts of Nanodea muscosa

Construction of Conjugated 1,3-Enynes via Pd-Catalyzed Cascade Alkynylation of Aryl Phenol-Tethered Alkynes with Alkynyl Bromides

An efficient Pd-catalyzed cascade alkynylation of aryl phenol-tethered alkynes with alkynyl bromides is described. This protocol could provide various conjugated 1,3-enynes possessing a polysubstituted spirocyclohexadienone, as well as an all-carbon tetrasubstituted alkene moiety. The products could also undergo ring-expansion and cyclization transformations under different conditions to convert to diverse fused cyclic scaffolds.

Transition metal-catalyzed C-H/C-C activation and coupling with 1,3-diyne

This review provides a broad overview of the recent developments in the field of transition metal-catalyzed C-H/C-C bond activation and coupling with 1,3-diyne for assembling alkynylated heterocycles, bis-heterocycles, and 1,3-enynes. Transition metal-catalyzed inert bond (C-H/C-C) activation has been the focus of attention among synthetic chemists in recent times. Enormous developments have taken place in C-H/C-C bond activation chemistry in the last two decades. In recent years the use of 2π-unsaturated units as coupling partners for the synthesis of heterocycles through C-H/C-C bond activation and annulation sequence has received immense attention. Among the unsaturated units employed for assembling heterocycles, the use of 1,3-diynes has garnered significant attention due to its ability to render bis-heterocycles in a straightforward manner. The C-H bond activation and coupling with 1,3-diyne has been very much explored in recent years. However, the development of strategies for the use of 1,3-diynes in the analogous C-C bond activation chemistry is less explored. Earlier methods employed to assemble bis-heterocycle used heterocycles that were preformed and pre-functionalized via transition metal-catalyzed coupling reactions. The expensive pre-functionalized halo-heterocycles and sensitive and expensive heterocyclic metal reagents limit its broad application. However, the transition metal-catalyzed C-H activation obviates the need for expensive heterocyclic metal reagents and pre-functionalized halo-heterocycles. The C-H bond activation strategy makes use of C-H bonds as functional groups for effecting the transformation. This renders the overall synthetic sequence both step and cost economic. Hence, this strategy of C-H activation and subsequent reaction with 1,3-diyne could be used for the larger-scale synthesis of chemicals in the pharmaceutical industry. Despite these advances, there is still the possibility of exploration of earth-abundant and cost-effective first-row transition metals (Ni, Cu, Mn. Fe, etc.) for the synthesis of bis-heterocycles. Moreover, the Cp*-ligand-free, simple metal-salt-mediated synthesis of bis-heterocycles is also less explored. Thus, more exploration of reaction conditions for the Cp*-free synthesis of bis-heterocycles is called for. We hope this review will inspire scientists to investigate these unexplored domains.

Palladium-catalyzed selective C-C bond cleavage and stereoselective alkenylation between cyclopropanol and 1,3-diyne: one-step synthesis of diverse conjugated enynes

The stereoselective synthesis of 1,3-enynes from 1,3-diynes is demonstrated by palladium-catalyzed selective C–C bond cleavage of cyclopropanol. Exclusive formation of mono-alkenylated adducts was achieved by eliminating the possibility of di-functionalization with high stereoselectivity. Indeed, this protocol worked very well with electronically and sterically diverse substrates. Several studies, including deuterium labeling experiments and intermolecular competitive experiments, were carried out to understand the mechanistic details. The atomic-level mechanism followed in the catalytic process was also validated using DFT calculations, and the rate-controlling states in the catalytic cycle were identified. Furthermore, preliminary mechanistic investigations with radical scavengers revealed the non-involvement of the radical pathway in this transformation.

Palladium-catalyzed tandem activation and functionalization of readily accessible cyclopropanols have been demonstrated to access valuable conjugated enynes from 1,3-diynes with high stereo-selectivity.

Tetrasubstituted 1,3-Enynes by Gold-Catalyzed Direct C(sp2)-H Alkynylation of Acceptor-Substituted Enamines

A gold-catalyzed synthesis of tetrasubstituted 1,3-enynes from hypervalent iodine(III) reagents and activated alkenes is reported. This reaction involves an in situ formed alkynyl Au(III) species and a subsequent direct C(sp²)-H functionalization of alkenes, offering 26 enynes in 62-92% yield with excellent functional group tolerance.

Electro-alkynylation: Intramolecular Rearrangement of Trialkynylorganoborates for Chemoselective C(sp2)-C(sp) Bond Formation

An alternative and complementary transformation for the synthesis of aryl- and heteroaryl-substituted alkynes is presented that relies on a chemoselective electrocoupling process. Tetraorganoborate substrates were logically designed and simply accessed by transmetalations using readily or commercially available organotrifluoroborate salts.

A Review on the Progress and Prospects of Dengue Drug Discovery Targeting NS5 RNA- Dependent RNA Polymerase

Dengue virus (DENV) infection threatens the health and wellbeing of almost 100 million people in the world. Vectored by mosquitoes, DENV may cause a severe disease in human hosts called Dengue hemorrhagic fever (DHF)/Dengue shock syndrome (DSS), which is not preventable by any known drug. In the absence of a universally-accepted vaccine, a drug capable of inhibiting DENV multiplication is an urgent and unmet clinical need. Here we summarize inhibitory strategies by targeting either host biochemical pathways or virus-encoded proteins. A variety of approaches have been generated to design Directly-acting anti-virals or DAAs targeting different DENV proteins, with diverse success. Among them, DAAs targeting genome replicating viral enzymes have proven effective against many viruses including, Human Immuno-deficiency Virus and Hepatitis C Virus. DAAs may be derived either from existing compound libraries of novel molecules and plant secondary metabolites or devised through Computer-aided Drug design (CADD) methods. Here, we focus on compounds with reported DAA-activity against the DENV RNA-dependent RNA polymerase (RdRp), which replicate the viral RNA genome. The structure-activity relationship (SAR) and toxicity of the natural compounds, including secondary plant metabolites, have been discussed in detail. We have also tabulated novel compounds with known anti-RdRp activity. We concluded with a list of DAAs for which a co-crystal structure with RdRp is reported. Promising hit compounds are often discarded due to poor selectivity or unsuitable pharmacokinetics. We hope this review will provide a useful reference for further studies on the development of an anti-DENV drug.

Radical trans-Hydroboration of Substituted 1,3-Diynes with an N-Heterocyclic Carbene Borane

Monohydroboration of substituted 1,3-diynes with an N-heterocyclic carbene borane (NHC-borane) occurs under radical conditions using an azo initiator, such as ACCN and AIBN, and a thiol as a polarity-reversal catalyst. The reaction is highly regio- and stereoselective and provides stable NHC-(E)-alkynylalkenylboranes.

Biosynthesis of alkyne-containing natural products

Alkyne-containing natural products are important molecules that are widely distributed in microbes and plants. Inspired by the advantages of acetylenic products used in the fields of medicinal chemistry, organic synthesis and material science, great efforts have focused on discovering the biosynthetic enzymes and pathways for alkyne formation. Here, we summarize the biosyntheses of alkyne-containing natural products and introduce de novo biosynthetic strategies for alkyne-tagged compound production.

Copper-Catalyzed One-Pot Synthesis of 1,3-Enynes from 2-Chloro-N-(quinolin-8-yl)acetamides and Terminal Alkynes

A method for the chemo-, regio-, and stereoselective one-pot synthesis of 1,3-enynes is described. The reaction of 2-chloro-N-(quinolin-8-yl)acetamides with terminal alkynes proceeds smoothly in the presence of a copper catalyst at room temperature to produce (E)-1,3-enynes in satisfactory to excellent yields. The mechanism study reveals that the cross-dimerization of internal alkynes generated in situ with terminal alkynes proceeds via allene intermediates. The directing group 8-aminoquinoline plays a key role in the current selective synthesis of (E)-1,3-enynes.

Tailored Palladium Catalysts for Selective Synthesis of Conjugated Enynes by Monocarbonylation of 1,3-Diynes

For the first time, the monoalkoxycarbonylation of easily available 1,3-diynes to give synthetically useful conjugated enynes has been realized. Key to success was the design and utilization of the new ligand 2,2'-bis(tert-butyl(pyridin-2-yl)phosphanyl)-1,1'-binaphthalene (Neolephos), which permits the palladium-catalyzed selective carbonylation under mild conditions, providing a general preparation of functionalized 1,3-enynes in good-to-high yields with excellent chemoselectivities. Synthetic applications that showcase the possibilities of this novel methodology include an efficient one-pot synthesis of 4-aryl-4H-pyrans as well as the rapid construction of various heterocyclic, bicyclic, and polycyclic compounds.

Copper-catalyzed 1,1-alkynylalkylation of alkynes: access toward conjugated enynes

A copper-catalyzed 1,1-alkynylalkylation of alkynes with α-haloacetamides for the construction of conjugated enynes has been developed.

Anti-oral common pathogenic bacterial active acetylenic acids from Thesium chinense Turcz

Discovery of agents for oral infectious diseases is always encouraged in natural products chemistry. A bioassay-guided isolation led to the isolation of two new acetylenic acids (1, 2) along with seven known ones (3-9) from the ethanol extract of Thesium chinense Turcz, a commonly used oral anti-bacterial and anti-inflammatory herb. Their structures were elucidated on the basis of spectroscopic and chemical evidence. Exocarpic acid (3) demonstrated the most promising activity against three tested oral pathogenic bacterial strains, Porphyromonas gingivalis, Fusobacterium nucleatum, and Streptococcus mutans, with minimum inhibitory concentration values of 0.86, 3.43, and 13.70 μg/mL, respectively. Compounds 1, 2, 4, 5 and 7 also showed potential activities against periodontal bacteria (P. gingivalis, F. nucleatum).

An aqueous medium-controlled stereospecific oxidative iodination of alkynes: efficient access to (E)-diiodoalkene derivatives

A new and versatile approach for the stereospecific iodination of alkynes has been developed in aqueous media. Scale-up reactions (up to 5 g) established the proficiency of this protocol and highlight the feasibility of large scale reactions.

Two new unsaturated fatty acids from the whole plant of Pothos chinensis

Two new unsaturated fatty acids, (Z)-octadec-13-en-11-ynoic acid (1) and (Z)-octadec-16-en-12,14-diynoic acid (2), along with six known compounds were isolated from the whole plant of Pothos chinensis. The structures of these compounds were elucidated by detailed spectroscopic analysis, including 1D and 2D NMR data. Compound 2 showed moderate antibacterial activity against Staphylococcus aureus.

N-Substitution dependent stereoselectivity switch in palladium catalyzed hydroalkynylation of ynamides: a regio and stereoselective synthesis of ynenamides

A palladium catalysed regioselective hydroalkynylation of ynamides for ynenamides is achieved with an N-substitution dependent stereoselectivity switch.

One-pot synthesis of 1,3-enynes with a CF3 group on the terminal sp2 carbon by an oxidative Sonogashira cross-coupling reaction

One-pot synthesis of 1,3-enynes with a CF₃ group on the terminal sp² carbon was achieved by an oxidative Sonogashira cross-coupling reaction with (E)-trimethyl(3,3,3-trifluoroprop-1-enyl)silane.

Catalytic asymmetric synthesis of 1,3-enyne scaffolds: design and synthesis of conjugated nitro dienynes as novel Michael acceptors and development of a new synthetic methodology

A catalytic enantioselective synthesis of 1,3-enynes for the development of nitro dienynes as novel Michael acceptors has been developed.

A co-operative Ni–Cu system for Csp–Csp and Csp–Csp2 cross-coupling providing a direct access to unsymmetrical 1,3-diynes and en-ynes

An efficient cross coupling of alkynes with alkynyl and alkenyl halides catalysed by a Ni–Cu system without any ligand leading to the synthesis of a series of functionalised 1,3-di-ynes and en-ynes has been achieved.

Chemical constituents of Anacolosa pervilleana and their antiviral activities

In an effort to identify novel inhibitors of Chikungunya (CHIKV) and Dengue (DENV) virus replication, a systematic study with 820 ethyl acetate extracts of Madagascan plants was performed in a virus-cell-based assay for CHIKV and a DENV NS5 RNA-dependant RNA polymerase (RdRp) assay. The extract obtained from the leaves of Anacolosa pervilleana was selected for its significant activity in both assays. One new (E)-tridec-2-en-4-ynedioic acid named anacolosine (1), together with three known acetylenic acids, the octadeca-9,11,13-triynoic acid (2), (13E)-octadec-13-en-9,11-diynoic acid (3), (13E)-octadec-13-en-11-ynoic acid (4), two terpenoids, lupenone (5) and β-amyrone (6), and one cyanogenic glycoside, (S)-sambunigrin (7) were isolated. Their structures were elucidated by comprehensive analyses of NMR spectroscopy and mass spectrometry data. The inhibitory potency of these compounds was evaluated on CHIKV, DENV RdRp and West-Nile polymerase virus (WNV RdRp). Both terpenoids showed a moderate activity against CHIKV (EC(50) 77 and 86 μM, respectively) and the acetylenic acids produced IC(50) values around 3 μM in the DENV RdRp assay.

SAR studies of gymnasterkoreayne derivatives with cancer chemopreventive activities

We synthesized diyne triols based on gymnasterkoreayne and evaluated their cancer chemopreventive activities in terms of the chemopreventive index (CI) to reveal the structure-activity relationship, and discovered more active compounds than natural diynes.

A convergent approach to (R)-Tiagabine by a regio- and stereocontrolled hydroiodination of alkynes

The occurrence of unsaturated systems in natural products combined with the mildness and the wide range of applicability of CeCl(3) promoted methodologies suggest several potential future synthetic applications within the field of total synthesis of biologically active molecules. On this concept, the use of CeCl(3).7H(2)O-NaI system as an efficient heterogeneous promoter has been highlighted in the iodofunctionalization of carbon-carbon triple bonds. The study has shown that this method would be particularly interesting for the stereoselective formation of trisubstituted (Z)- or (E)-iodoalkenes by simply changing the nature of the solvent. The methodology has been successfully applied to the synthesis of (R)-1-[4,4-bis-(3-methyl-2-thienyl)-3-butenyl]-3-piperidinecarboxylic acid , named (R)-Tiagabine, which is a potent and selective gamma-aminobutyric acid (GABA) uptake inhibitor with proven anticonvulsant efficacy in humans.