WLIP, WLIPβ, and WLIPγ Produced from Pseudomonas canadensis Q3-1 via Precursor-Directed Biosynthesis and Their Roles on Biocontrol of Phytophthora Blight in Peppers

White line-inducing principle (WLIP, 1), together with two new cyclic lipopeptides (CLPs) WLIPβ (2) and WLIPγ (3), were characterized from the supernatant of Pseudomonas canadensis Q3-1 via precursor-directed biosynthesis (PDB) in the current study. They were purified from the supernatant of P. canadensis Q3-1 by solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC), and their structures were mainly determined via bioinformatic analyses, spectrometric and spectroscopic techniques, as well as single crystal X-ray diffraction (XRD). These WLIPs share (R)-3-hydroxydecanoic acid (HDA), but they differ from each other in the composition of peptidic sequences. In addition, these CLPs showed biocontrol activities against Phytophthora blight (caused by Phytophthora capsici) in peppers. Collectively, this study has shown that PDB could be used for generating new CLPs in Pseudomonas spp. Moreover, we have confirmed that WLIP, WLIPβ, and WLIPγ could be used as lead agrochemicals to control Phytophthora blight in peppers.

Myxadazoles, Myxobacterium-Derived Isoxazole-Benzimidazole Hybrids with Cardiovascular Activities

There is a continuous need for novel microbial natural products to fill the drying-up drug development pipeline. Herein, we report myxadazoles from Myxococcus sp. SDU36, a family of novel chimeric small molecules that consist of N-ribityl 5,6-dimethylbenzimidazole and a linear fatty acid chain endowed with an isoxazole ring. The experiments of genome sequencing, gene insertion mutation, isotope labelling, and precursor feeding demonstrated that the fatty acid chain was encoded by a non-canonical PKS/NRPS gene cluster, whereas the origin of N-ribityl 5,6-dimethylbenzimidazole was related to the vitamin B₁₂ metabolism. The convergence of these two distinct biosynthetic pathways through a C-N coupling led to the unique chemical framework of myxadazoles, which is an unprecedented hybridization mode in the paradigm of natural products. Myxadazoles exhibited potent vasculogenesis promotion effect and moderate antithrombotic activity, underscoring their potential usage for the treatment of cardiovascular diseases.

An E. coli-Based Biosynthetic Platform Expands the Structural Diversity of Natural Benzoxazoles

Benzoxazoles are frequently found in synthetic pharmaceuticals and medicinally active natural products. To facilitate benzoxazole-based drug development, an eco-friendly and rapid platform for benzoxazole production is required. In this study, we have completed the biosynthesis of benzoxazoles in E. coli by coexpressing the minimal set of enzymes required for their biosynthesis. Moreover, by coupling this E. coli-based platform with precursor-directed biosynthesis, we have shown that the benzoxazole biosynthetic system is highly promiscuous in incorporating fluorine, chlorine, nitrile, picolinic, and alkyne functionalities into the scaffold. Our E. coli-based system thus paves the way for straightforward generation of novel benzoxazole analogues through future protein engineering and combinatorial biosynthesis.

CMB-F214

Chemical analysis of an M1 agar plate cultivation of a marine fish-gut-derived fungus, Chrysosporium sp. CMB-F214, revealed the known chrysosporazines A-D (11-14) in addition to a suite of very minor aza analogues 1-6. A microbioreactor (MATRIX) cultivation profiling analysis failed to deliver cultivation conditions that significantly improved the yields of 1-6; however, it did reveal that M2 agar cultivation produced the new natural product 15. A precursor-directed biosynthesis strategy adopting supplementation of a CMB-F214 M1 solid agar culture with sodium nicotinate enhanced production of otherwise inaccessible azachrysposorazines A1 (1), A2 (2), B1 (3), C1 (4), C2 (5) and D1 (6), in addition to four new chrysosporazines; chrysosporazines N-P (7-9) and spirochrysosporazine A (10). Structures inclusive of absolute configurations were assigned to 1-15 based on detailed spectroscopic and chemical analyses, and biosynthetic considerations. Non-cytotoxic to human carcinoma cells, azachrysosporazies 1-5 were capable of reversing doxorubicin resistance in P-glycoprotein (P-gp)-overexpressing human colon carcinoma cells (SW620 Ad300), with optimum activity exhibited by the C-2' substituted analogues 3-5.

Expanding the Myxochelin Natural Product Family by Nicotinic Acid Containing Congeners

Myxobacteria represent a viable source of chemically diverse and biologically active secondary metabolites. The myxochelins are a well-studied family of catecholate-type siderophores produced by various myxobacterial strains. Here, we report the discovery, isolation, and structure elucidation of three new myxochelins N1-N3 from the terrestrial myxobacterium Corallococcus sp. MCy9049, featuring an unusual nicotinic acid moiety. Precursor-directed biosynthesis (PDB) experiments and total synthesis were performed in order to confirm structures, improve access to pure compounds for bioactivity testing, and to devise a biosynthesis proposal. The combined evaluation of metabolome and genome data covering myxobacteria supports the notion that the new myxochelin congeners reported here are in fact frequent side products of the known myxochelin A biosynthetic pathway in myxobacteria.

Precursor-Directed Biosynthesis of Aminofulvenes: New Chalanilines from Endophytic Fungus Chalara sp

The plant endophyte Chalara sp. is able to biotransform the epigenetic modifier vorinostat to form unique, aniline-containing polyketides named chalanilines. Here, we sought to expand the chemical diversity of chalaniline A-type molecules by changing the aniline moiety in the precursor vorinostat. In total, twenty-three different vorinostat analogs were prepared via two-step synthesis, and nineteen were incorporated by the fungus into polyketides. The highest yielding substrates were selected for large-scale precursor-directed biosynthesis and five novel compounds, including two fluorinated chalanilines, were isolated, purified, and structurally characterized. Structure elucidation relied on 1D and 2D NMR techniques and was supported by low- and high-resolution mass spectrometry. All compounds were tested for their bioactivity but were not active in antimicrobial or cell viability assays. Aminofulvene-containing natural products are rare, and this high-yielding, precursor-directed process allows for the diversification of this class of compounds.

Exploiting Spermidine N-Hydroxycinnamoyltransferase Diversity and Substrate Promiscuity to Produce Various Trihydroxycinnamoyl Spermidines and Analogues in Engineered Yeast

Trihydroxycinnamoyl spermidines (THCSpd) are plant specialized metabolites with promising pharmacological activities as antifungals, antibacterial, antiviral, and antidepressant drugs. However, their characterization and potential pharmaceutical exploitation are greatly impaired by the sourcing of these compounds, restricted to the pollen of core Eudicot plant species. In this work, we developed a precursor-directed biosynthesis of THCSpd in yeast using a dual enzymatic system based on 4-coumarate-CoA ligases (4CL) and spermidine N-hydroxycinnamoyltransferases (SHT). The system relies on the yeast endogenous spermidine pool and only requires hydroxycinnamic acids as exogenous precursors. By exploring 4CL isoforms and SHT diversity among plants, we have driven the production of 8 natural THCSpd, using single or mixed hydroxycinnamic acid precursors. Substrate promiscuities of 4CL and SHT were genuinely exploited to produce 8 new-to-nature THCSpd from exotic hydroxycinnamic and dihydrohydroxycinnamic acids, together with 3 new-to-nature THCSpd containing halogenated hydroxycinnamoyl moieties. In this work, we established a versatile and modular biotechnological production platform allowing the tailor-made THCSpd synthesis, constituting pioneer metabolic engineering for access to these valuable natural products.

Identification and heterologous reconstitution of a 5-alk(en)ylresorcinol synthase from endophytic fungus Shiraia sp. Slf14

A new type III polyketide synthase gene (Ssars) was discovered from the genome of Shiraia sp. Slf14, an endophytic fungal strain from Huperzia serrata. The intron-free gene was cloned from the cDNA and ligated to two expression vectors pET28a and YEpADH2p-URA3 for expression in Escherichia coli BL21(DE3) and Saccharomyces cerevisiae BJ5464, respectively. SsARS was efficiently expressed in E. coli BL21(DE3), leading to the synthesis of a series of polyketide products. Six major products were isolated from the engineered E. coli and characterized as 1,3-dihydroxyphenyl-5-undecane, 1,3-dihydroxyphenyl-5-cis-6'-tridecene,1,3-dihydroxyphenyl-5-tridecane, 1,3-dihydroxyphenyl-5-cis-8'-pentadecene, 1,3-dihydroxyphenyl-5-pentadecane, and 1,3-dihydroxyphenyl-5-cis-10'-heptadecene, respectively, based on the spectral data and biosynthetic origin. Expression of SsARS in the yeast also led to the synthesis of the same polyketide products, indicating that this enzyme can be reconstituted in both heterologous hosts. Supplementation of soybean oil into the culture of E. coli BL21(DE3)/SsARS increased the production titers of 1-6 and led to the synthesis of an additional product, which was identified as 5-(8'Z,11'Z-heptadecadienyl) resorcinol. This work thus allowed the identification of SsARS as a 5-alk(en)ylresorcinol synthase with flexible substrate specificity toward endogenous and exogenous fatty acids. Desired resorcinol derivatives may be synthesized by supplying corresponding fatty acids into the culture medium.

coli

A novel biosynthetic pathway was designed and verified reversely leading to the production of 5-hydroxytryptophan (5-HTP) from glucose. This pathway takes advantage of the relaxed substrate selectivities of relevant enzymes without employing the unstable tryptophan 5-hydroxylase. First, high-titer of 5-HTP was produced from 5-hydroxyanthranilate (5-HI) by the catalysis of E. coli TrpDCBA. Then, a novel salicylate 5-hydroxylase was used to convert the non-natural substrate anthranilate to 5-HI. After that, the production of 5-HI from glucose was achieved and optimized with modular optimization. In the end, we combined the full pathway and adopted a two-stage strategy to realize the de novo production of 5-HTP. This work demonstrated the application of enzyme promiscuity in non-natural pathway design.

Generating a generation of proteasome inhibitors: from microbial fermentation to total synthesis of salinosporamide a (marizomib) and other salinosporamides

The salinosporamides are potent proteasome inhibitors among which the parent marine-derived natural product salinosporamide A (marizomib; NPI-0052; 1) is currently in clinical trials for the treatment of various cancers. Methods to generate this class of compounds include fermentation and natural products chemistry, precursor-directed biosynthesis, mutasynthesis, semi-synthesis, and total synthesis. The end products range from biochemical tools for probing mechanism of action to clinical trials materials; in turn, the considerable efforts to produce the target molecules have expanded the technologies used to generate them. Here, the full complement of methods is reviewed, reflecting remarkable contributions from scientists of various disciplines over a period of 7 years since the first publication of the structure of 1.