Chemical tools for unpicking plant specialised metabolic pathways.

Elucidating the biochemical pathways of specialised metabolites in plants is key to enable or improve their sustainable biotechnological production. Chemical tools can greatly facilitate the discovery of biosynthetic genes and enzymes. Here, we summarise transdisciplinary approaches where methods from chemistry and chemical biology helped to overcome key challenges of pathway elucidation.

Development of the Synthesis of Desepoxy-Tedanolide C.

We are presenting the development of our route for the total synthesis of desepoxy-tedanolide C. Through the obtained analytical data, the proposed structure of tedanolide C is questioned and a different configuration for this natural product is proposed. Key steps of the synthesis are a Kiyooka aldol reaction that builds up the tertiary alcohol flanked by three oxygenated carbon atoms and two aldol reactions used for fragment couplings.

Stereoselective Construction of β-chiral Homoallyl Functionalities by Substrate- and Reagent-Controlled Iterative 1,2-Metallate Rearrangements.

Homoallylic alcohols possessing chiral β-centers are considered highly valuable in the synthesis of polyketide-based natural products. Therefore, there is a significant demand for new methods that allow for their stereoselective access. In pursuit of this objective, we have successfully combined our substrate-controlled protocol of Hoppe-Matteson-Aggarwal chemistry with iterative 1,2-metallate rearrangements.

Stereoselective Synthesis of Allylic Alcohols via Substrate Control on Asymmetric Lithiation.

Allylic alcohols are a privileged motif in natural product synthesis and new methods that access them in a stereoselective fashion are highly sought after. Toward this goal, we found that chiral acetonide-protected polyketide fragments performing the Hoppe-Matteson-Aggarwal rearrangement in the absence of sparteine with high yields and diastereoselectivities rendering this protocol a highly valuable alternative to the Nozaki-Hiyama-Takai-Kishi reaction. Various stereodyads and -triads were investigated to determine their substrate induction.

1,2-Metallate Rearrangement as a Toolbox for the Synthesis of Allylic Alcohols.

The development of new methods and protocols for the synthesis of biologically active substances remains one of the most important pillars in organic chemistry, and one of these privileged structural motifs are allylic alcohols. The method of choice to date for the synthesis of these is the Nozaki-Hiyama-Takai-Kishi reaction. We describe here a valuable alternative to the synthesis of allylic alcohols via 1,2-metallate rearrangement.

Sparteine-Free, Highly Stereoselective Construction of Complex Allylic Alcohols Using 1,2-Metallate Rearrangements.

Stereotriads bearing allylic alcohols are privileged structures in natural products, and new methods accessing these in a stereoselective fashion are highly sought after. Toward this goal, we found that the use of chiral polyketide fragments allows for performing the Hoppe-Matteson-Aggarwal rearrangement in the absence of sparteine with high yields and diastereoselectivities, rendering this protocol a highly valuable alternative to the Nozaki-Hiyama-Takai-Kishi reaction. The switch of directing groups in most cases resulted in the reversed stereochemical outcome, which could be explained by conformational analysis on density functional theory level and a Felkin-like model.

The influence of sample mass (scaling effect) on the synthesis and structure of non-graphitizing carbon (biochar) during the analytical pyrolysis of biomass.

The porous non-graphitizing carbon (NGC) known as biochar is derived from the pyrolytic conversion of organic precursors and is widely investigated due to its multifunctional applications. At present, biochar is predominantly synthesized in custom lab-scale reactors (LSRs) to determine the properties of carbon, while a thermogravimetric reactor (TG) is utilized for pyrolysis characterization. This results in inconsistencies in the correlation between the structure of biochar carbon and the pyrolysis process.

Cooperative Functionalities in Porous Nanoparticles for Seeking Extracellular DNA and Targeting Pathogenic Biofilms via Photodynamic Therapy.

Many pathogenic bacteria are getting more and more resistant against antibiotic treatment and even become up to 1.000× times more resilient in the form of a mature biofilm. Thus, one is currently prospecting for alternative methods for treating microbial infections, and photodynamic therapy is a highly promising approach by creating so-called reactive oxygen species (ROS) produced by a photosensitizer (PS) upon irradiation with light.

Silmitasertib (CX-4945), a Clinically Used CK2-Kinase Inhibitor with Additional Effects on GSK3β and DYRK1A Kinases: A Structural Perspective.

A clinical casein kinase 2 inhibitor, CX-4945 (silmitasertib), shows significant affinity toward the DYRK1A and GSK3β kinases, involved in down syndrome phenotypes, Alzheimer's disease, circadian clock regulation, and diabetes. This off-target activity offers an opportunity for studying the effect of the DYRK1A/GSK3β kinase system in disease biology and possible line extension. Motivated by the dual inhibition of these kinases, we solved and analyzed the crystal structures of DYRK1A and GSK3β with CX-4945.

Isotope-Guided Metabolomics Reveals Divergent Incorporation of Valine into Different Flavor Precursor Classes in Chives.

Plants of the genus Allium such as chives, onions or garlic produce S-alk(en)yl cysteine sulfoxides as flavor precursors. Two major representatives are S-propenyl cysteine sulfoxide (isoalliin) and S-propyl cysteine sulfoxide (propiin), which only differ by a double bond in the C side chain. The propenyl group of isoalliin is derived from the amino acid valine, but the source of the propyl group of propiin remains unclear.

Specific Signal Enhancement on an RNA-Protein Interface by Dynamic Nuclear Polarization.

Invited for the cover of this issue are the groups of Alexander Marchanka at the Leibniz University of Hannover and Björn Corzilius at the University of Rostock. The image depicts the local generation of nuclear spin hyperpolarization, which selectively "illuminates" the interaction surface of a ribonuclear protein complex for solid-state NMR spectroscopy. Read the full text of the article at 10.

Multiformin-Type Azaphilones Prevent SARS-CoV-2 Binding to ACE2 Receptor.

Protein microarray screenings identified fungal natural products from the azaphilone family as potent inhibitors of SARS-CoV-2 spike protein binding to host ACE2 receptors. Cohaerin F, as the most potent substance from the cohaerin group, led to more than 50% less binding of ACE2 and SARS-CoV-2 spike protein. A survey for structurally related azaphilones yielded the structure elucidation of six new multiformins E-J (-) and the revision of the stereochemistry of the multiformins.

Structural insights into the activity regulation of full-length non-structural protein 1 from SARS-CoV-2.

Non-structural protein 1 (Nsp1) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a major virulence factor and thus an attractive drug target. The last 33 amino acids of Nsp1 have been shown to bind within the mRNA entry tunnel of the 40S ribosomal subunit, shutting off host gene expression. Here, we report the solution-state structure of full-length Nsp1, which features an α/β fold formed by a six-stranded, capped β-barrel-like globular domain (N-terminal domain [NTD]), flanked by short N-terminal and long C-terminal flexible tails.

Specific Signal Enhancement on an RNA-Protein Interface by Dynamic Nuclear Polarization.

Sensitivity and specificity are both crucial for the efficient solid-state NMR structure determination of large biomolecules. We present an approach that features both advantages by site-specific enhancement of NMR spectroscopic signals from the protein-RNA binding site within a ribonucleoprotein (RNP) by dynamic nuclear polarization (DNP). This approach uses modern biochemical techniques for sparse isotope labeling and exploits the molecular dynamics of C-labeled methyl groups exclusively present in the protein.

Nucleic acid-protein interfaces studied by MAS solid-state NMR spectroscopy.

Solid-state NMR (ssNMR) has become a well-established technique to study large and insoluble protein assemblies. However, its application to nucleic acid-protein complexes has remained scarce, mainly due to the challenges presented by overlapping nucleic acid signals. In the past decade, several efforts have led to the first structure determination of an RNA molecule by ssNMR.

Total Synthesis of (-)-Antroalbocin A Enabled by a Strain Release-Controlled Photochemical 1,3-Acyl Shift.

The first bioinspired, enantioselective, and protecting group free total synthesis of the antibacterial sesquiterpenoid (-)-antroalbocin A () has been achieved in 12 steps (5.4% overall yield) from dimedone. An organocatalytic Robinson annulation gave rapid access to the tricyclic enone () as starting material for the photochemical domino process of deconjugation and sigmatropic 1,3-acyl shift.

A genomic journey in the secondary metabolite diversity of fungal plant and insect pathogens: from functional to population genomics.

Fungal pathogens produce a broad array of secondary metabolites (SMs), which allow the fungus to thrive in its natural habitat and gain competitive advantage. Analysis of the genetically encoded blueprints for SM assembly highlighted that only a small portion of the SMs these fungi are capable of producing are known, and even fewer have been investigated for their natural function. Using molecular tools, a lot of progress has been made recently in identifying the blueprint products and linking them to their ecological purpose such as the peptide virulence factor fusaoctaxin A released by Fusarium graminearum during infection of wheat or the F.

A20 and ABIN-1 cooperate in balancing CBM complex-triggered NF-κB signaling in activated T cells.

T cell activation initiates protective adaptive immunity, but counterbalancing mechanisms are critical to prevent overshooting responses and to maintain immune homeostasis. The CARD11-BCL10-MALT1 (CBM) complex bridges T cell receptor engagement to NF-κB signaling and MALT1 protease activation. Here, we show that ABIN-1 is modulating the suppressive function of A20 in T cells.

Acriflavine, a clinically approved drug, inhibits SARS-CoV-2 and other betacoronaviruses.

The COVID-19 pandemic caused by SARS-CoV-2 has been socially and economically devastating. Despite an unprecedented research effort and available vaccines, effective therapeutics are still missing to limit severe disease and mortality. Using high-throughput screening, we identify acriflavine (ACF) as a potent papain-like protease (PL) inhibitor.

TRAF6 prevents fatal inflammation by homeostatic suppression of MALT1 protease.

Balanced control of T cell signaling is critical for adaptive immunity and protection from autoimmunity. By combining genetically engineered mouse models, biochemical analyses and pharmacological interventions, we describe an unexpected dual role of the tumor necrosis factor receptor–associated factor 6 (TRAF6) E3 ligase as both a positive and negative regulator of mucosa-associated lymphoid tissue 1 (MALT1) paracaspase. Although MALT1-TRAF6 recruitment is indispensable for nuclear factor κB signaling in activated T cells, TRAF6 counteracts basal MALT1 protease activity in resting T cells.

Strategies for RNA Resonance Assignment by C/N- and H-Detected Solid-State NMR Spectroscopy.

Magic angle spinning (MAS) solid-state NMR (ssNMR) is an established tool that can be applied to non-soluble or non-crystalline biomolecules of any size or complexity. The ssNMR method advances rapidly due to technical improvements and the development of advanced isotope labeling schemes. While ssNMR has shown significant progress in structural studies of proteins, the number of RNA studies remains limited due to ssNMR methodology that is still underdeveloped.

Oxazaborolidinone-Mediated Asymmetric Bisvinylogous Mukaiyama Aldol Reaction.

A bisvinylogous Mukaiyama aldol reaction using oxazaborolidinones as a source of chirality was developed. This methodology allows the fast assembly of conjugated dienols by expanding the vinylogy principle by two additional carbons, and can be conducted using a readily available Lewis acid at reasonable reaction times. A broad range of aromatic and aliphatic aldehydes can be used providing access to complex building blocks for polyketide synthesis.

Secondary metabolite biosynthetic diversity in the fungal family and .

To date little is known about the genetic background that drives the production and diversification of secondary metabolites in the . With the recent availability of high-quality genome sequences for 13 representative species and one relative () we attempted to survey the diversity of biosynthetic pathways in these organisms to investigate their true potential as secondary metabolite producers. Manual search strategies based on the accumulated knowledge on biosynthesis in fungi enabled us to identify 783 biosynthetic pathways across 14 studied species, the majority of which were arranged in biosynthetic gene clusters (BGC).

Eukaryotic Box C/D methylation machinery has two non-symmetric protein assembly sites.

Box C/D ribonucleoprotein complexes are RNA-guided methyltransferases that methylate the ribose 2'-OH of RNA. The central 'guide RNA' has box C and D motifs at its ends, which are crucial for activity. Archaeal guide RNAs have a second box C'/D' motif pair that is also essential for function.