Andrew M. Beekman

First syntheses of the biologically active fungal metabolites pestalotiopsones A, B, C and F

A synthetic approach accessing the pestalotiopsones, fungal chromones possessing a rare skeletal subtype, is reported for the first time. The synthesis of pestalotiopsone A (1) has been achieved in 7 linear steps (28%), from commercially available 3,5-dimethoxybenzoic acid and subsequently the first syntheses of pestalotiopsone B (2), C (3) and F (4) were performed utilising this chemistry. The key steps include a newly described homologation of a substituted benzoic acid to afford phenylacetate derivatives utilising Birch reductive alkylation conditions, a microwave mediated chromanone formation proceeding through an oxa-Michael cyclisation, and an IBX induced dehydrogenation to the desired chromone skeleton. The synthetic natural products were completely characterised for the first time, confirming their structures and their biological activities evaluated against a panel of bacterial pathogens.

Fungal metabolites as pharmaceuticals

Natural products, their derivatives or compounds based on natural product leads constitute ~50 % of clinically used pharmaceuticals. This review highlights pharmaceuticals currently used in Australia and New Zealand that have their origins in fungal metabolites, discussing the natural products chemistry and medicinal chemistry leading to their application as pharmaceuticals.

Syntheses of the fungal metabolites boletopsins 7, 11, and 12 from the Papua New Guinea medicinal mushroom Boletopsis sp.

Boletopsins 7 (1), 11 (2), and 12 (3) are p-terphenyl dibenzofuran compounds, isolated from the Papua New Guinean medicinal mushroom Boletopsis sp. The first syntheses of these fungal metabolites are reported, allowing for an investigation of their antibiotic activity. The key steps include sequential Suzuki-Miyaura couplings to rapidly form the p-terphenyl backbone and an Ullmann ether synthesis on a formate ester to create the dibenzofuran moiety. Biological evaluation of the synthetic compounds and intermediates against a panel of bacterial nosocomial pathogens was performed.

Stereochemical assignment of the fungal metabolites Pestalotiopsones D and E through enantiopure synthesis

The pestalotiopsones are fungal metabolites isolated from an endophytic fungus Pestalotiopsis sp. found in the mangrove Rhizophora mucronata, used in traditional Chinese medicine to treat symptoms of dysentery. The absolute configurations of pestalotiopsones D (4) and E (5) were elucidated through total synthesis of both the R and S enantiomers, allowing for the assignment of the stereochemistry of the natural compounds as the (+)-S enantiomers. The key steps include homologation of a substituted benzoic acid to the appropriate phenylacetate derivative using Birch reductive alkylation, an oxa-Michael cyclization induced by microwave irradiation to form the chromanone substructure, and an IBX-mediated dehydrogenation yielding the chromone skeleton. Assessment of the synthetic compounds against clinical pathogens was performed.

Identification of Small‐Molecule Inhibitors of the Antiapoptotic Protein Myeloid Cell Leukaemia‐1 (Mcl‐1)

Protein–protein interactions (PPIs) control many cellular processes in cancer and tumour growth. Of significant interest is the role PPIs play in regulating apoptosis. The overexpression of the antiapoptosis regulating Bcl‐2 family of proteins is commonly observed in several cancers, leading to resistance towards both radiation and chemotherapies. From this family, myeloid cell leukemia‐1 (Mcl‐1) has proven the most difficult to target, and one of the leading causes of treatment resistance. Exploiting the selective PPI between the apoptosis‐regulating protein Noxa and Mcl‐1, utilising a fluorescence polarization assay, we have identified four small molecules with the ability to modulate Mcl‐1. The identified compounds were computationally modelled and docked against the Mcl‐1 binding interface to obtain structural information about their binding sites allowing for future analogue design. When examined for their activity towards pancreatic cell lines that overexpress Mcl‐1 (MiaPaCa‐2 and BxPC‐3), the identified compounds demonstrated growth inhibition, suggesting effective Mcl‐1 modulation.

Discovery and Synthesis of Boletopsins 13 and 14, Brominated Fungal Metabolites of Terrestrial Origin

Here we report the discovery and synthesis of complex polybrominated p-terphenyl ethers isolated from a mushroom (Boletopsis sp.) used as a traditional medicine by the Kiovi people in the highlands of Papua New Guinea. Boletopsins 13 and 14 represent the first report of polybrominated fungal metabolites to be produced by a terrestrial fungus. The synthetic method employs 2,4,4,6-tetrabromo-2,5-cyclohexadienone to achieve selective polybromination of the extended aromatic system in a selective and sequential manner.

Syntheses of Cytosporones A, C, J, K, and N, Metabolites from Medicinal Fungi

The syntheses of the fungal metabolites cytosporones A, (±)-C, and N are reported. And the syntheses of cytosporones J and K are described for the first time. The preparation of racemic cytosporone J and racemic cytosporone K, natural products containing the rare 3-isochromanone substructure, was achieved in 8 linear steps with an overall yield of 45 % and 7 linear steps in 46 % yield, respectively, resulting in the complete characterization of these compounds for the first time. The key steps included a recently described homologation of benzoic acid to the analogous phenyl acetate using Birch reductive alkylation conditions, acylation of the appropriate phenyl acetate derivative, and a selective reduction and spontaneous biomimetic lactonization to yield the 3-isochromanone skeleton. The synthesized natural products were evaluated for their biological activity against several clinical strains of human pathogens with all compounds displaying weak antimicrobial activity.

Rac1 plays a role in CXCL12 but not CCL3-induced chemotaxis and Rac1 GEF inhibitor NSC23766 has off target effects on CXCR4

Cell migration towards a chemotactic stimulus relies on the re-arrangement of the cytoskeleton, which is triggered by activation of small G proteins RhoA, Rac1 and Cdc42, and leads to formation of lamellopodia and actin polymerisation amongst other effects. Here we show that Rac1 is important for CXCR4 induced chemotaxis but not for CCR1/CCR5 induced chemotaxis. For CXCL12-induced migration via CXCR4, breast cancer MCF-7 cells are reliant on Rac1, similarly to THP-1 monocytes and Jurkat T-cells. For CCL3-induced migration via CCR1 and/or CCR5, Rac1 signalling does not regulate cell migration in either suspension or adherent cells. We have confirmed the involvement of Rac1 with the use of a specific Rac1 blocking peptide. We also used a Rac1 inhibitor EHT 1864 and a Rac1-GEF inhibitor NSC23766 to probe the importance of Rac1 in chemotaxis. Both inhibitors did not block CCL3-induced chemotaxis, but they were able to block CXCL12-induced chemotaxis. This confirms that Rac1 activation is not essential for CCL3-induced migration, however NSC23766 might have secondary effects on CXCR4. This small molecule exhibits agonistic features in internalisation and cAMP assays, whereas it acts as an antagonist for CXCR4 in migration and calcium release assays. Our findings strongly suggest that Rac1 activation is not necessary for CCL3 signalling, and reveal that NSC23766 could be a novel CXCR4 receptor ligand.

Peptide-Directed Binding for the Discovery of Modulators of α-Helix-Mediated Protein–Protein Interactions: Proof-of-Concept Studies with the Apoptosis Regulator Mcl-1

Abstract Targeting PPIs with small molecules can be challenging owing to large, hydrophobic binding surfaces. Herein, we describe a strategy that exploits selective α‐helical PPIs, transferring these characteristics to small molecules. The proof of concept is demonstrated with the apoptosis regulator Mcl‐1, commonly exploited by cancers to avoid cell death. Peptide‐directed binding uses few synthetic transformations, requires the production of a small number of compounds, and generates a high percentage of hits. In this example, about 50 % of the small molecules prepared showed an IC50 value of less than 100 μm, and approximately 25 % had IC50 values below 1 μm to Mcl‐1. Compounds show selectivity for Mcl‐1 over other anti‐apoptotic proteins, possess cytotoxicity to cancer cell lines, and induce hallmarks of apoptosis. This approach represents a novel and economic process for the rapid discovery of new α‐helical PPI modulators.