Structural Revision of Thelephantin G by Total Synthesis and the Inhibitory Activity against TNF-α Production

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.

Small-molecule inhibitors targeting small ubiquitin-like modifier pathway for the treatment of cancers and other diseases

SUMOylation is a key post-translational modification that involves the covalent attachment of small ubiquitin-like modifier (SUMO) to the lysine residues of target proteins. The well-balanced SUMOylation is essential for normal cellular behaviors, while disturbance of SUMOylation is associated with various cancers and other diseases. Herein, we summarize the structures and biological functions of proteins involved in the SUMOylation process, their dysregulation in human diseases, and the discovery of small-molecular inhibitors targeting this pathway. In addition, we highlight the emerging trends in this field.

Total Synthesis of Kehokorins A-E, Cytotoxic p-Terphenyls

This paper describes a general method for the synthesis of kehokorins A-E, novel cytotoxic p-terphenyls. 2,4,6-Trihydroxybenzaldehyde served as a common building block for preparation of the central aromatic ring. Construction of their p-terphenyl skeletons was achieved by a stepwise Suzuki-Miyaura coupling, whereas the phenyldibenzofuran moiety was built up by an intramolecular Ullmann reaction. Introduction of an l-rhamnose residue into partly protected kehokorin B was performed by the trichloroacetimidate method.

Vialinin A and thelephantin G, potent inhibitors of tumor necrosis factor-α production, inhibit sentrin/SUMO-specific protease 1 enzymatic activity

Several p-terphenyl compounds have been isolated from the edible Chinese mushroom Thelephora vialis. Vialinin A, a p-terphenyl compound, strongly inhibits tumor necrosis factor-α production and release. Vialinin A inhibits the enzymatic activity of ubiquitin-specific peptidase 5, one of the target molecules in RBL-2H3 cells. Here we examined the inhibitory effect of p-terphenyl compounds, including vialinin A, against sentrin/SUMO-specific protease 1 (SENP1) enzymatic activity. The half maximal inhibitory concentration values of vialinin A and thelephantin G against full-length SENP1 were 1.64±0.23μM and 2.48±0.02μM, respectively. These findings suggest that p-terphenyl compounds are potent SENP1 inhibitors.

Structural revision of kynapcin-12 by total synthesis, and inhibitory activities against prolyl oligopeptidase and cancer cells

Kynapcin-12 is a prolyl oligopeptidase (POP) inhibitor isolated from Polyozellus multiplex, and its structure was assigned as 1 having a p-hydroquinone moiety by spectroscopic analyses and chemical means. This Letter describes the total syntheses of the proposed structure 1 for kynapcin-12 and 2',3'-diacetoxy-1,5',6',4″-tetrahydroxy-p-terphenyl 2 isolated from Boletopsis grisea, revising the structure of kynapcin-12 to the latter. These syntheses involved double Suzuki-Miyaura coupling, CAN oxidation, and LTA oxidation as key steps. The inhibitory activities of synthetic compounds against POP and cancer cells were also evaluated.

Convergent synthesis and structural confirmation of phellodonin and sarcodonin ε

The first synthesis of members of the sarcodonin family, phellodonin and sarcodonin ε, is reported herein. This verifies that the unprecedented and seemingly unstable N,N-dioxide-containing benzodioxazine framework can be constructed in the laboratory and lends further support to the proposed structures. The key step in the synthesis involves a biomimetic hetero-Diels-Alder reaction between a pyrazine N-oxide and an ortho-quinone.

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.

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

The first total synthesis of natural, unsymmetrical 2',3'-diacyloxy-p-terphenyls, thelephantin O (1) and terrestrins C and D (2 and 3, respectively), was achieved via a practical route which was also applicable to the synthesis of the symmetrical diesters vialinin A/terrestrin A (4) and terrestrin B (5). Compounds 1-5 exhibited cytotoxicity against cancer cells (HepG2 and Caco2) with IC(50) values of 13.6-26.7 μmol/L.

Anticancer activities of thelephantin O and vialinin A isolated from Thelephora aurantiotincta

Thelephora aurantiotincta is an edible mushroom belonging to the genus Thelephora; it grows in symbiosis with pine trees. Recently, phytochemical investigations have revealed that the genus Thelephora is an abundant source of p-terphenyl derivatives. However, their bioactivity has not yet been well characterized. In screening for natural materials with anticancer activity, a T. aurantiotincta ethanol extract (TAE) was found to decrease cell viability in human hepatocellular carcinoma cells (HepG2). In this study, a new p-terphenyl derivative, thelephantin O, and a known compound, vialinin A, were isolated as the principal bioactive components of TAE. These compounds decreased cell viability in HepG2 and human colonic carcinoma cells (Caco2), but not in noncancerous human hepatocytes. This is the first report of the isolation from T. aurantiotincta of selective cytotoxic agents against cancer cells.