Evolution of a Strategy for the Total Synthesis of (+)-Cornexistin

Discovery of Novel Pyrazole Acyl Thiourea Skeleton Analogue as Potential Herbicide Candidates

To discover novel transketolase (TKL, EC 2.2.1.1) inhibitors with potential herbicidal applications, a series of pyrazole acyl thiourea derivatives were designed based on a previously obtained pyrazolamide acyl lead compound, employing a scaffold hopping strategy. The compounds were synthesized, their structures were characterized, and they were evaluated for herbicidal activities. The results indicate that 7a exhibited exceptional herbicidal activity against Digitaria sanguinalis and Amaranthus retroflexus at a dosage of 90 g ai/ha, using the foliar spray method in a greenhouse. This performance is comparable to that of commercial products, such as nicosulfuron and mesotrione. Moreover, 7a showed moderate growth inhibitory activity against the young root and stem of A. retroflexus at 200 mg/L in the small cup method, similar to that of nicosulfuron and mesotrione. Subsequent mode-of-action verification experiments revealed that 7a and 7e inhibited Setaria viridis TKL (SvTKL) enzyme activity, with IC50 values of 0.740 and 0.474 mg/L, respectively. Furthermore, they exhibited inhibitory effects on the Brassica napus acetohydroxyacid synthase enzyme activity. Molecular docking predicted potential interactions between these (7a and 7e) and SvTKL. A greenhouse experiment demonstrated that 7a exhibited favorable crop safety at 150 g ai/ha. Therefore, 7a is a promising herbicidal candidate that is worthy of further development.

Pathogenicity of monokaryotic and dikaryotic mycelia of Ganoderma boninense revealed via LC-MS-based metabolomics

This study compared the pathogenicity of monokaryotic (monokaryon) and dikaryotic (dikaryon) mycelia of the oil palm pathogen Ganoderma boninense via metabolomics approach. Ethyl acetate crude extracts of monokaryon and dikaryon were analysed by liquid chromatography quadrupole/time-of-flight-mass spectrometry (LC-Q/TOF-MS) coupled with multivariate data analysis using MetaboAnalyst. The mummichog algorithm was also used to identify the functional activities of monokaryon and dikaryon without a priori identification of all their secondary metabolites. Results revealed that monokaryon produced lesser fungal metabolites than dikaryon, suggesting that monokaryon had a lower possibility of inducing plant infection. These findings were further supported by the identified functional activities. Monokaryon exhibits tyrosine, phenylalanine, and tryptophan metabolism, which are important for fungal growth and development and to produce toxin precursors. In contrast, dikaryon exhibits the metabolism of cysteine and methionine, arginine and proline, and phenylalanine, which are important for fungal growth, development, virulence, and pathogenicity. As such, monokaryon is rendered non-pathogenic as it produces growth metabolites and toxin precursors, whereas dikaryon is pathogenic as it produces metabolites that are involved in fungal growth and pathogenicity. The LC-MS-based metabolomics approach contributes significantly to our understanding of the pathogenesis of Ganoderma boninense, which is essential for disease management in oil palm plantations.

Total Synthesis of Isoxeniolide A

Isoxeniolide A is a highly strained xenicane diterpenoid of marine origin. This natural product is representative for a subfamily of xenicanes incorporating an allylic hydroxy group in the nine-membered ring; members of this xenicane subfamily so far have not been targeted by total synthesis. Herein, we describe the first asymmetric total synthesis of isoxeniolide A. Key to forming the challenging E-configured cyclononene ring was a diastereoselective intramolecular Nozaki-Hiyama-Kishi reaction. Other important transformations include an enzymatic desymmetrization for absolute stereocontrol, a diastereoselective cuprate addition and the use of a bifunctional vinyl silane building block. Our strategy also permits access to the enantiomer of the natural product and holds potential to access a multitude of xenicane natural products and analogs for structure-activity relationship studies.

Synthesis of Waixenicin A: Exploring Strategies for Nine-Membered Ring Formation

We present a comprehensive account on our efforts behind the recently published synthesis of waixenicin A. Our approach for constructing the dihydropyran ring relied on an Achmatowicz rearrangement. For the assembly of the nine-membered ring, four distinct strategies were investigated. Our initial attempts using radical-based addition/fragmentation reactions targeting the C7-C11 bond proved unsuitable for accessing the 6/9-bicycle. By employing anionic fragmentation conditions at the furfuryl alcohol stage, we successfully reached a 5/9-bicycle. However, subsequent ring-expansion was unsuccessful. Alternative approaches, such as Nozaki-Hiyama-Kishi or Heck reactions to connect the C6-C7 bond, also encountered difficulties, with no nine-membered ring formation observed. Our first breakthrough came from our attempts to install the C5-C6 bond via an intramolecular alkylation. Surprisingly, subsequent functional group modifications proved unexpectedly challenging, necessitating a redesign of our synthetic route. Drawing from all our investigations, we concluded that construction of the C9-C10 bond would enable efficient nine-membered ring alkylation and would facilitate the installation of the desired substitution pattern along the southern periphery. Exploration of this strategy yielded further surprises but ultimately led to the successful synthesis of waixenicin A and 9-deacetoxy-14,15-deepoxyxeniculin. For the latter compound, a bioinspired one-step rearrangement to xeniafauranol A was achieved.

Investigations into Simplified Analogues of the Herbicidal Natural Product (+)-Cornexistin

We report the design, synthesis and biological evaluation of simplified analogues of the herbicidal natural product (+)-cornexistin. Guided by an X-Ray co-crystal structure of cornexistin bound to transketolase from Zea mays, we attempted to identify the key interactions that are necessary for cornexistin to maintain its herbicidal profile. This resulted in the preparation of three novel analogues investigating the importance of substituents that are located on the nine-membered ring of cornexistin. One analogue maintained a good level of biological activity and could provide researchers insights in how to further optimize the structure of cornexistin for commercialization in the future.

Total Syntheses of (+)-Waixenicin A, (+)-9-Deacetoxy-14,15-deepoxyxeniculin, and (-)-Xeniafaraunol A

The first asymmetric total synthesis of the Xenia diterpenoid waixenicin A, a potent and highly selective TRPM7 inhibitor, is reported. The characteristic trans-fused oxabicyclo[7.4.0]tridecane ring system was constructed via a diastereoselective conjugate addition/trapping sequence, followed by an intramolecular alkylation to forge the 9-membered ring. While a β-keto sulfone motif enabled efficient ring-closure, the subsequent radical desulfonylation suffered from (E)/(Z)-isomerization of the C7/C8-alkene. Conducting the sequence with a trimethylsilylethyl ester allowed for a fluoride-mediated decarboxylation that proceeded without detectable isomerization. The acid-labile enol acetal of the delicate dihydropyran core was introduced at an early stage and temporarily deactivated by a triflate function. The latter was critical for the introduction of the side chain. Diverting from a common late-stage intermediate provided access to waixenicin A and 9-deacetoxy-14,15-deepoxyxeniculin. A high-yielding base-mediated dihydropyran-cyclohexene rearrangement of 9-deacetoxy-14,15-deepoxyxeniculin led to xeniafaraunol A in one step.

Maleidride biosynthesis - construction of dimeric anhydrides - more than just heads or tails

Covering: up to early 2022Maleidrides are a family of polyketide-based dimeric natural products isolated from fungi. Many maleidrides possess significant bioactivities, making them attractive pharmaceutical or agrochemical lead compounds. Their unusual biosynthetic pathways have fascinated scientists for decades, with recent advances in our bioinformatic and enzymatic understanding providing further insights into their construction. However, many intriguing questions remain, including exactly how the enzymatic dimerisation, which creates the diverse core structure of the maleidrides, is controlled. This review will explore the literature from the initial isolation of maleidride compounds in the 1930s, through the first full structural elucidation in the 1960s, to the most recent in vivo, in vitro, and in silico analyses.

Evolution of a Strategy for the Total Synthesis of (+)-Cornexistin

Herein is given a full account of the evolution of the first total synthesis of (+)-cornexistin. Initial efforts were based on masking the reactive maleic anhydride moiety as a 3,4-substituted furan and on forming the nine-membered carbocycle in an intramolecular Conia-ene or Nozaki-Hiyama-Kishi (NHK) reaction. Those strategies suffered from low yields and were jeopardized by a late-stage installation of the Z-alkene, as well as the stereocenters along the eastern periphery. These issues were addressed by employing a chiral-pool strategy that involved construction of the crucial stereocenters at C2, C3 and C8 at an early stage with installation of the maleic anhydride as late as possible. The successful approach featured an intermolecular NHK coupling to install the Z-alkene, a syn-Evans-aldol reaction to forge the stereocenters along the eastern periphery, an intramolecular allylic alkylation to close the nine-membered carbocycle, and a challenging stepwise hydrolysis of a β-keto nitrile to furnish the maleic anhydride.