Phellodonic acid, a new biologically active hirsutane derivative from Phellodon melaleucus (Thelephoraceae, Basidiomycetes)

Antibacterial Compounds from Mushrooms: A Lead to Fight ESKAPEE Pathogenic Bacteria?

Infectious diseases are among the greatest threats to global health in the 21st century, and one critical concern is due to antibiotic resistance developed by an increasing number of bacterial strains. New resistance mechanisms are emerging with many infections becoming more and more difficult if not impossible to treat. This growing phenomenon not only is associated with increased mortality but also with longer hospital stays and higher medical costs. For these reasons, there is an urgent need to find new antibiotics targeting pathogenic microorganisms such as ESKAPEE bacteria. Most of currently approved antibiotics are derived from microorganisms, but higher fungi could constitute an alternative and remarkable reservoir of anti-infectious compounds. For instance, pleuromutilins constitute the first class of antibiotics derived from mushrooms. However, macromycetes still represent a largely unexplored source. Publications reporting the antibacterial potential of mushroom extracts are emerging, but few purified compounds have been evaluated for their bioactivity on pathogenic bacterial strains. Therefore, the aim of this review is to compile up-to-date data about natural products isolated from fruiting body fungi, which significantly inhibit the growth of ESKAPEE pathogenic bacteria. When available, data regarding modes of action and cytotoxicity, mandatory when considering a possible drug development, have been discussed in order to highlight the most promising compounds.

Cytotoxic triquinane-type sesquiterpenoids from the endophytic fungus Cerrena sp. A593

The culture broth of Cerrena sp. A593, which was isolated from Pogostemon cablin, showed potent cytotoxicity against several human tumor cell lines. The following chemical study resulted in the isolation of two new triquinane-type sesquiterpenoids, named cerrenins D (1) and E (2), along with two known compounds plerocybellone A (3) and chloriolin B (4). Their structures were fully assigned with the aid of extensive spectroscopic analysis (¹H and ¹³C NMR, HSQC, HMBC, ¹H-¹H COSY, HRESIMS, and IR) and data from the literature. Moreover, cytotoxic activity in vitro of compounds 1-4 were evaluated against SF-268, MCF-7, NCI-H460, and HepG-2 tumor cell lines. The new compound 1 exhibited weak growth inhibitory activity against all the four tumor cell lines with IC₅₀ values of 41.01, 14.43, 29.67, 44.32 μM.

Additional New Cytotoxic Triquinane-Type Sesquiterpenoids Chondrosterins K-M from the Marine Fungus Chondrostereum sp

By the method of ¹H NMR prescreening and tracing the diagnostic proton signals of the methyl groups, three additional new triquinane-type sesquiterpenoids—chondrosterins K–M (1–3) and the known sesquiterpenoid anhydroarthrosporone (4)—were isolated from the marine fungus Chondrostereum sp. Their structures were elucidated on the basis of MS, 1D, and 2D NMR data. Chondrosterin K is a rare hirsutane sesquiterpenoid, in which a methyl group was migrated from C-2 to C-6 and has a double bond between C-2 and C-3. Compounds 1–3 showed significant cytotoxicities against various cancer cell lines in vitro.

Vialinin A, a Novel 2,2-Diphenyl-1-picrylhydrazyl (DPPH) Radical Scavenger from an Edible Mushroom in China

While screening for bioactive compounds from edible mushrooms, a new potent antioxidant, vialinin A (1), together with a known compound, ganbajunin B (2), and a mixture of ganbajunins D (3) and E (4), were isolated from the dry fruiting bodies of Thelephora vialis. The structure of 1, 5',6'-bis(phenylacetoxy)-1,1':4',1''-terphenyl-2',3',4,4''-tetraol, was elucidated by spectroscopic and chemical methods. This compound had strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical-scavenging activity with an EC(50) value of 14.0 microM, nearly equal to that of butylated hydroxytoluene (BHT; EC(50) = 10.0 microM). A radical scavenging experiment using 1 and DPPH radicals indicated that 1 donated two hydrogen atoms to two molecules of the DPPH radical under hydrophobic conditions.

Induced marine fungus Chondrostereum sp. as a means of producing new sesquiterpenoids chondrosterins I and J by using glycerol as the carbon source

Chondrostereum sp., a marine fungus isolated from a soft coral Sarcophyton tortuosum, can yield hirsutane framework sesquiterpenoids. However, the metabolites profiles vary dramatically with the composition change of the culture media. This fungus was cultured in a liquid medium containing glycerol as the carbon source, and two new metabolites, chondrosterins I and J (1 and 2), were obtained. Their structures were elucidated primarily based on MS, NMR and X-ray single-crystal diffraction data. By comparison with the known hirsutane sesquiterpenoids, chondrosterins I and J have unique structural features, including a methyl was migrated from C-2 to C-6, and the methyl at C-3 was carboxylated. Compound 2 exhibited potent cytotoxic activities against the cancer cell lines CNE-1 and CNE-2 with the IC₅₀ values of 1.32 and 0.56 μM.

The Chemoenzymatic Total Synthesis of Phellodonic Acid, a Biologically Active and Highly Functionalized Hirsutane Derivative Isolated from the Tasmanian Fungus Phellodon melaleucus

A total synthesis of the title natural product, 1, has been achieved using the cis-1,2-dihydrocatechol 7 as starting material. Compound 7 is readily obtained in large quantity and in an enantiomerically pure form through the whole-cell biotransformation of toluene using the genetically engineered microorganism E. coli JM109 (pDTG601) that overexpresses the enzyme toluene dioxygenase (TDO). Three key chemical steps were employed in the synthesis, the first of which was the microwave-promoted Diels–Alder cycloaddition reaction between diene 8 and cyclopent-1-en-2-one to give adduct 9. The second key step was the photochemically promoted oxa-di-π-methane rearrangement of the bicyclo[2.2.2]octenone derivative 15 of 9 to give the epimers 16 and 17, and the third key step was the reductive cleavage of the last pair of compounds so as to afford the linear triquinane 19. Elaboration of compound 19 to target 1 followed established procedures. Single-crystal X-ray analyses were carried out on compounds 11 and 19.

Thelephantins A, B and C: three benzoyl p-terphenyl derivatives from the inedible mushroom Thelephora aurantiotincta

Three benzoyl p-terphenyl derivatives named thelephantins A, B and C were isolated from the ethyl acetate extract of fruit bodies of the Thelephoraceous Basidiomycete Thelephora aurantiotincta. Their structures were elucidated by analysis of high-resolution 2D NMR, MS, IR and UV spectra.