Total synthesis of thelephantin O, vialinin A/terrestrin A, and terrestrins B-D

A concise synthesis of marine natural product (-)-15-oxopuupehenol from (+)-sclarelide

A step-economical synthesis of (-)-15-oxopuupehenol from cheap and readily available (+)-sclarelide is achieved with 20.3% overall yield in 9 steps. The key features of this synthetic mythology include a palladium catalyzed tandem carbine migratory insertion reaction to construct the key skeleton, a DDQ-mediated isomerization/oxidation of allyl alcohol to afford α, β-unsaturated ketone, and a NaOH-induced intramolecular Michael addition followed by acetonide deprotection to give (-)-15-oxopuupehenol.

Total Synthesis of Marine Natural Products (+)-Strongylin A and Corallidictyal D by Regio- and Stereoselective Cyclization of Alkenyl Benzenes

An expeditious access to marine natural products (+)-strongylin A and corallidictyal D is described. A TFA/Et₃SiH-induced reductive isomerization of enols I to alkenyl benzenes II followed by a selectivity-controlled cyclization in the presence of HCl and BF₃·Et₂O affords benzofuran III and benzopyran IV, respectively. The applicability of this HCl-induced cyclization is showcased by a regio- and stereoselective synthesis of corallidictyal D, while BF₃·Et₂O-promoted cyclization posterior to rearrangement of an alkenyl benzene provides a regioselectively different benzopyran, (+)-strongylin A.

Binding of Vialinin A and p-Terphenyl Derivatives to Ubiquitin-Specific Protease 4 (USP4): A Molecular Docking Study

The para-terphenyl derivative vialinin A (Vi-A), isolated from Thelephora fungi, has been characterized as a potent inhibitor of the ubiquitin-specific protease 4 (USP4). Blockade of USP4 contributes to the anti-inflammatory and anticancer properties of the natural product. We have investigated the interaction of Vi-A with USP4 by molecular modeling, to locate the binding site (around residue V98 within the domain in USP segment) and to identify the binding process and interaction contacts. From this model, a series of 32 p-terphenyl compounds were tested as potential USP4 binders, mainly in the vialinin, terrestrin and telephantin series. We identified 11 compounds presenting a satisfactory USP4 binding capacity, including two fungal products, vialinin B and aurantiotinin A, with a more favorable empirical energy of USP4 interaction (ΔE) than the reference product Vi-A. The rare p-terphenyl aurantiotinin A, isolated from the basidiomycete T. aurantiotincta, emerged as a remarkable USP4 binder. Structure-binding relationships have been identified and discussed, to guide the future design of USP4 inhibitors based on the p-terphenyl skeleton. The docking study should help the identification of other protease inhibitors from fungus.

Anti-inflammatory and anticancer p-terphenyl derivatives from fungi of the genus Thelephora

Fungi from the genus Thelephora have been exploited to identify bioactive compounds. The main natural products characterized are para-terphenyl derivatives, chiefly represented by the lead anti-inflammatory compound vialinin A isolated from species T. vialis and T. terrestris. Different series of p-terphenyls have been identified, including vialinins, ganbajunins, terrestrins, telephantins and other products. Their mechanism of action is not always clearly identified, and different potential molecule targets have been proposed. The lead vialinin A functions as a protease inhibitor, efficiently targeting ubiquitin-specific peptidases USP4/5 and sentrin-specific protease SENP1 which are prominent anti-inflammatory and anticancer targets. Protease inhibition is coupled with a powerful inhibition of the cellular production of tumor necrosis factor TNFα. Other mechanisms contributing to the anti-inflammatory or anti-proliferative action of these p-terphenyl compounds have been invoked, including the formation of cytotoxic copper complexes for derivatives bearing a catechol central unit such vialinin A, terrestrin B and telephantin O. These p-terphenyl compounds could be further exploited to design novel anticancer agents, as evidenced with the parent compound terphenyllin (essentially found in Aspergillus species) which has revealed marked antitumor and anti-metastatic effects in xenograft models of gastric and pancreatic cancer. This review shed light on the structural and functional diversity of p-terphenyls compounds isolated from Thelephora species, their molecular targets and pharmacological properties.

Synthesis and Evaluation of Bifunctional [2.2.2]-Cryptands for Nuclear Medicine Applications

For the first time, synthesis of bifunctional [2.2.2]-cryptands (CRYPT) and demonstration of radiolabeling with lead(II) (Pb²⁺) isotopes are disclosed herein. The synthesis is convenient and high-yielding and gives access to three distinct bifunctional handles (azide (-N₃), isothiocyanate (-NCS), and tetrazine (-Tz)) that can enable the construction of radioimmunoconjugates for targeted and pretargeted therapy. Proof-of-principle CRYPT radiolabeling was successful with lead-203 ([²⁰³Pb]Pb²⁺) and demonstrated complexation efficiency superior to that of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and efficiency comparable to that of the current industry standard TCMC (1,4,7,10-tetraaza-1,4,7,10-tetra-(2-carbamoylmethyl)-cyclododecane). In vitro human serum stability assays demonstrated excellent [²⁰³Pb]Pb-CRYPT stability over 72 h (91.7 ± 0.56%; n = 3). [²⁰³Pb]Pb-CRYPT-radioimmunoconjugates were synthesized from the corresponding CRYPT-immunoconjugate or by conjugating [²⁰³Pb]Pb-Tz-CRYPT to transcyclooctene modified trastuzumab (TCO-trastuzumab) via the inverse electron-demand Diels-Alder (IEEDA) reaction. This investigation reveals the potential for CRYPT ligands to become new industry standards for therapeutic and diagnostic radiometals in radiopharmaceutical elaboration.

Esterification of Carboxylic Acids with Aryl Halides via the Merger of Paired Electrolysis and Nickel Catalysis

Electrochemistry has been successfully applied in metal catalysis to avoid the usage of chemical redox agents. This strategy proved to be a powerful approach to construct carbon-carbon (C-C) and carbon-heteroatom (C-X) bonds. However, most of the developed methods are based on either anodic oxidation or cathodic reduction, in which a sacrificial reaction occurs at the counter electrode. Paired electrolysis merging with metal catalysis is underdeveloped, wherein both anodic and cathodic processes are taking place simultaneously. Herein, we demonstrated that by using esterification of carboxylic acids with aryl halides via paired electrolysis using nickel as the catalyst the respective aryl esters were obtained in good to excellent yields at room temperature in an undivided electrochemical cell.

Benzenetriol-Derived Compounds against Citrus Canker

In order to replace the huge amounts of copper salts used in citrus orchards, alternatives have been sought in the form of organic compounds of natural origin with activity against the causative agent of citrus canker, the phytopathogen Xanthomonas citri subsp. Citri. We synthesized a series of 4-alkoxy-1,2-benzene diols (alkyl-BDOs) using 1,2,4-benzenetriol (BTO) as a starting material through a three-step synthesis route and evaluated their suitability as antibacterial compounds. Our results show that alkyl ethers derived from 1,2,4-benzenetriol have bactericidal activity against X. citri, disrupting the bacterial cell membrane within 15 min. Alkyl-BDOs were also shown to remain active against the bacteria while in solution, and presented low toxicity to (human) MRC-5 cells. Therefore, we have demonstrated that 1,2,4-benzenetriol—a molecule that can be obtained from agricultural residues—is an adequate precursor for the synthesis of new compounds with activity against X. citri.

Direct C2-arylation of N-acyl pyrroles with aryl halides under palladium catalysis

C2-arylation of N-acyl pyrroles with aryl halides is developed for the first time using Pd(PPh3)4 as a catalyst in combination with Ag2CO3 under air, which allowed the application of a good compatibility catalytic system. This protocol provides a straightforward method for the preparation of valuable arylated pyrroles in moderate to good yields under the standard conditions with good substrate tolerance. Interestingly, while N-benzoyl pyrroles reacted well, the use of substrates with a thiophene or furan ring indicated that the thiophene and furan rings are more reactive than pyrrole for the present catalytic system.

Synthesis of Functionalized Biaryls and Poly(hetero)aryl Containing Medium-Sized Lactones with Cyclic Diaryliodonium Salts

A novel one-pot procedure is described for the transition-metal catalyzed sequential difunctionalization of diaryliodonium reagents. Reaction of commercially available anthranilic acid derivatives with readily available cyclic diaryliodonium salts followed by a Sonogashira coupling afforded various alkyne substituted biaryls in good to excellent yields. The functionalized biaryls were then utilized for the rapid and efficient one-pot synthesis of novel poly(hetero)aryl containing 10-membered lactones which are potential G-quadruplex binders and telomerase inhibitors.

p-terphenyl derivatives from the mushroom Thelephora aurantiotincta suppress the proliferation of human hepatocellular carcinoma cells via iron chelation

A novel 2',3'-dihydroxy-p-terphenyl derivative, thelephantin O (TO), which has cancer-selective cytotoxicity, was isolated. This study investigated the underlying basis of the cytotoxicity of 2',3'-dihydroxy-p-terphenyl compounds in view of their ability to chelate metal ions. FeCl(2) significantly reduced TO-induced cytotoxicity, whereas several other salts of transition metals and alkaline-earth metals did not. A structure-activity relationship study using newly synthesized p-terphenyl derivatives revealed that o-dihydroxy substitution of the central benzene ring was necessary for both the cytotoxicity and Fe(2+) chelation of the compounds. Real-time PCR array and cell cycle analysis revealed that the TO-induced cytotoxicity was attributed to cell cycle arrest at the G1 phase via well-known cell cycle-mediated genes. The TO-induced changes in the cell cycle and gene expression were completely reversed by the addition of FeCl(2). Thus, it was concluded that Fe(2+) chelation occurs upstream in the pivotal pathway of 2',3'-dihydroxy-p-terphenyl-induced inhibition of cancer cell proliferation.