Prediction and Determination of the Stereochemistry of the 1,3,5-Trimethyl-Substituted Alkyl Chain in Verucopeptin, a Microbial Metabolite

Steroids and Epicoccarines from Penicillium aurantiancobrunneum

Lichens are symbiotic organisms comprised of mycobionts and photobiont partners. They are known to produce bioactive secondary metabolites and most of these are biosynthesized by mycobionts. Investigations of cultures of isolated lichen-associated fungi have shown promise for the discovery of cytotoxic compounds. Thus, the lichen-associated fungus Penicillium aurantiacobrunneum was studied for its potential to produce novel compounds and the new sterols (20S*)-hydroxy-24(28)-dehydrocampesterol (1), 7α-methoxy-8β-hydroxypaxisterol (2), 14-nor-epicoccarine A (3) and 14-nor-epicoccarine B (4), as well as the known compound PF1140 (5), were isolated. The structures of these compounds were elucidated using methods including nuclear magnetic resonance (NMR) spectroscopy and high-resolution electrospray ionization mass spectrometry (HRESIMS). Following cytotoxicity assays, compound 1 demonstrated activity against the pancreatic adenocarcinoma epithelial HPAC cell line at 17.76 ± 5.35 μM. Since the structures of compounds 3 and 4 were very similar to tetramic acid derivatives that were reported to be biosynthesized from a polyketide synthase- non-ribosomal peptide synthetase (PKS-NRPS) hybrid pathway, a plausible biosynthetic route for production in P. aurantiacobrunneum is proposed herein.

Convergent synthesis of tetrahydropyranyl side chain of verucopeptin, an antitumor antibiotic active against multidrug-resistant cancers

A concise synthesis of the tetrahydropyranyl side chain of verucopeptin, an antitumor antibiotic cyclodepsipeptide efficacious against MDR cancers in vivo, is achieved using 12 steps in the longest linear sequence and 21 total steps, in which Julia-Kocienski olefination for the segments coupling, asymmetric hydroxylation as well as stereoselective synthesis of stable tetrahydropyran ring from a D-isoascorbic acid derivative are key steps. This convergent synthetic strategy enables the structural modification and mechanism study of verucopeptin for its clinical applications.

Absolute configuration of polypropionate derivatives: Decempyrones A-J and their MptpA inhibition and anti-inflammatory activities

Under guidance of ¹H NMR, ten new polypropionate derivatives, decempyrones A-J (1-10) along with two known analogues (11 and 12), were isolated from the marine-derived fungusFusarium decemcellulare SYSU-MS6716. The planar structures were elucidated on the basis of extensive spectroscopic analyses (1D and 2D NMR, and HR-ESIMS). The absolute configuration of the chiral centers in the side chain is a major obstacle for the structure identification of natural polypropionate derivatives. Herein, the J-based configurational analysis (JBCA), chemical degradation, geminal proton rule, and the modified Mosher's method were adopted to fix their absolute configurations in the side chain. Compounds 3 and 10 exhibited potent anti-inflammatory activity by inhibiting the production of NO in RAW264.7 cells activated by lipopolysaccharide with IC₅₀values 22.4 ± 1.8 and 21.7 ± 1.1 μM. In addition, compounds 3 and 10 displayed MptpA inhibitory activity with an IC₅₀ value of 19.2 ± 0.9 and 33.1 ± 2.9 µM. Structure-activity relationships of the polypropionate derivatives were discussed.

Applying a Chemogeographic Strategy for Natural Product Discovery from the Marine Cyanobacterium Moorena bouillonii

The tropical marine cyanobacterium Moorena bouillonii occupies a large geographic range across the Indian and Western Tropical Pacific Oceans and is a prolific producer of structurally unique and biologically active natural products. An ensemble of computational approaches, including the creation of the ORCA (Objective Relational Comparative Analysis) pipeline for flexible MS¹ feature detection and multivariate analyses, were used to analyze various M. bouillonii samples. The observed chemogeographic patterns suggested the production of regionally specific natural products by M. bouillonii. Analyzing the drivers of these chemogeographic patterns allowed for the identification, targeted isolation, and structure elucidation of a regionally specific natural product, doscadenamide A (1). Analyses of MS² fragmentation patterns further revealed this natural product to be part of an extensive family of herein annotated, proposed natural structural analogs (doscadenamides B–J, 2–10); the ensemble of structures reflect a combinatorial biosynthesis using nonribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) components. Compound 1 displayed synergistic in vitro cancer cell cytotoxicity when administered with lipopolysaccharide (LPS). These discoveries illustrate the utility in leveraging chemogeographic patterns for prioritizing natural product discovery efforts.

Biosynthesis and Chemical Diversification of Verucopeptin Leads to Structural and Functional Versatility

A synthesis program for structurally complex macrocycles is very challenging. Herein, we propose a biosynthesis pathway of the pyranylated cyclodepsipeptide verucopeptin to make enough supply and to diversify verucopeptin by genetic manipulation and one-step semisynthesis. The synthesis relies on the intrinsic reactivity of the interchangeable hemiketal pyrane and opened keto along with adjacent alkene. Biological evaluation of verucopeptin-oriented analogs delivers a potent AMP-activated protein kinase (AMPK) agonist, antibacterial agent, and selective NFκB modulator.

Structure elucidation of bacterial nonribosomal lipopeptides

We provide a summary of the tools, which allow elucidate the structures of nonribosomal lipopetides.

Total synthesis of verucopeptin, an inhibitor of hypoxia-inducible factor 1 (HIF-1)

Verucopeptin is an inhibitor of hypoxia-inducible factor 1 (HIF-1), which is a promising target for cancer chemotherapy. Here, we report the first total synthesis of verucopeptin via condensation of the depsipeptide core and the polyketide side chain unit including three branched methyl groups after the synthesis of each segment.

Natural products-prompted chemical biology: phenotypic screening and a new platform for target identification

Covering: 1993 to 2016The exploitation of small molecules from natural sources, such as microbial metabolites, has contributed to the discovery of not only new drugs but also new research tools for chemical biology. My research team has discovered several novel bioactive small molecules using in vivo cell-based phenotypic screening, and has investigated their modes of action using chemical genetics and chemical genomics. This highlight focuses on our recent discoveries and chemical genetics approaches for bioactive microbial metabolites that target cancer cells, the cancer microenvironment and cell membrane signalling. In addition, the development of two new platforms, 5-sulfonyl tetrazole-based and thiourea-modified amphiphilic lipid-based probe technologies, to identify the cellular targets of these molecules is also discussed.

Biakamides A-D, Unique Polyketides from a Marine Sponge, Act as Selective Growth Inhibitors of Tumor Cells Adapted to Nutrient Starvation

Biakamides A-D, novel unusually unique polyketides, were isolated from an Indonesian marine sponge (Petrosaspongia sp.) with a constructed bioassay using PANC-1 human pancreatic cancer cells. Through detailed analyses of the one- and two-dimensional NMR spectra of biakamides, planar chemical structures possessing a terminal thiazole, two N-methyl amides, a chloromethylene, and a substituted butyryl moiety were obtained. After elucidation of the configuration of the secondary alcohol moiety in biakamides A and B, the absolute stereostructures of the two secondary methyl groups in biakamides A-D were determined by the asymmetric total syntheses of all possible stereoisomers from the optically pure monoprotected 2,4-dimethyl-1,5-diol. Biakamides A-D showed selective antiproliferative activities against PANC-1 cells cultured under glucose-deficient conditions in a concentration-dependent manner. The primary mode of action of biakamides was found to be inhibition of complex I in the mitochondrial electron transport chain.

Structure Elucidation of Verucopeptin, a HIF-1 Inhibitory Polyketide-Hexapeptide Hybrid Metabolite from an Actinomycete

The transcriptional factor, hypoxia inducible factor-1 (HIF-1), is a promising target for cancer chemotherapy. From an actinomycete, verucopeptin (1) was identified as a HIF-1 signaling inhibitor. By a combination of chemical degradation and spectroscopic analyses, the absolute stereochemistry of metabolite 1 was determined to be 10R, 15S, 16S, 23S, 27S, 28R, 31S, 33S, 35R. Moreover, metabolite 1 was revealed to attenuate the HIF-1α and mTORC1 pathway, indicating that verucopeptin (1) would be a potent lead compound for anticancer chemotherapy.

Stereospecific cross-coupling reactions of aryl-substituted tetrahydrofurans, tetrahydropyrans, and lactones

The stereospecific ring-opening of O-heterocycles to provide acyclic alcohols and carboxylic acids with controlled formation of a new C-C bond is reported. These reactions provide new methods for synthesis of acyclic polyketide analogs with complex stereochemical arrays. Stereoselective synthesis of the cyclic template is utilized to control relative configuration; subsequent stereospecific nickel-catalyzed ring-opening affords the acyclic product. Aryl-substituted tetrahydrofurans and tetrahydropyrans undergo nickel-catalyzed Kumada-type coupling with a range of Grignard reagents to furnish acyclic alcohols with high diastereoselectivity. Enantioenriched lactones undergo Negishi-type cross-coupling with dimethylzinc to afford enantioenriched carboxylic acids. Application in a two-step enantioselective synthesis of an anti-dyslipidemia agent is demonstrated.