Total synthesis of himastatin

Identification of four novel Streptomyces isolated from machair grassland soil using a culture-based bioprospecting strategy: Streptomyces caledonius sp. nov., Streptomyces machairae sp. nov., Streptomyces pratisoli sp. nov. and Streptomyces achmelvichensis sp. nov

A culture-dependent bioprospecting strategy, based on the use of several selective isolation media, revealed the presence of relatively high numbers of streptomycete-like colonies from machair grassland soil, in which carbonate minerals dominate. Representatives were shown to be bioactive in primary and secondary antimicrobial screens conducted through standard plug assays. The comparison of the whole-genome sequences showed that four of the isolates were novel species in the genus Streptomyces, for which the names Streptomyces caledonius sp. nov. (=DSM 118365; =NCIMB 15554), Streptomyces machairae sp. nov. (=DSM 118363; =NCIMB 15553), Streptomyces pratisoli sp. nov. (=DSM 118364; =NCIMB 15555) and Streptomyces achmelvichensis sp. nov. (=NCIMB 15556; =DSM 118366) are proposed. Genomes of the novel strains were found to be rich in biosynthetic gene clusters predicted to encode for diverse, specialized metabolites, notably antibiotics. They also contained stress-related genes that provided an insight into how streptomycetes cope with the prevailing conditions in machair grassland soils. It can be concluded that selective isolation and dereplication of streptomycetes from the unique machair habitat provides a practical way of isolating novel Streptomyces strains for ecological and biotechnological studies.

Selective Synthesis of Cyclopeptides with a 2-Oxindole or 3a-Hydroxy-hexahydropyrrolo-[2,3-b]indole Structure by Cytochrome P450 Enzymes

The structural groups of 2-oxindole and tricyclic 3a-hydroxy-hexahydropyrrolo-[2,3-b]indole (HO-HPI) are important pharmacophores. Chemical synthesis of complex alkaloids containing a 2-oxindole or HO-HPI moiety, especially the latter one, has been a long-standing challenge. Herein, we characterized the P450 enzyme AfnD, and its homologue proteins, HmtT, ClpD, KtzM, and LtzR, as cyclopeptide 2-oxindole and HO-HPI monooxygenases (cpOPMOs) that could introduce a 2-oxindole or HO-HPI moiety into the tryptophan-containing cyclopeptides in a pH-dependent manner. A universal catalytic mechanism was proposed for the five cpOPMOs, in which two conserved residues, Asp and Ser (Thr for LtzR), were proposed to divergently open the epoxide intermediates, thereby forming a 2-oxindole or HO-HPI moiety. Based on this, we constructed ten Asp or Ser/Thr mutants of cpOPMOs, which could synthesize cyclopeptides with an HO-HPI or 2-oxindole structure, selectively, under appropriate reaction conditions. All of the ten cpOPMO mutants exhibited high substrate promiscuities and usually performed well with cyclopeptides that are structurally similar to their native substrates. Overall, our work discovers a group of intriguing P450 enzymes, the cpOPMOs, and provides a powerful enzymatic toolkit for the selective synthesis of HO-HPI- or 2-oxindole-containing cyclopeptides.

Natural Cyclic Peptides: Synthetic Strategies and Biomedical Applications

Natural cyclic peptides, a diverse class of bioactive compounds, have been isolated from various natural sources and are renowned for their extensive structural variability and broad spectrum of medicinal properties. Over 40 cyclic peptides or their derivatives are currently approved as medicines, underscoring their significant therapeutic potential. These compounds are employed in diverse roles, including antibiotics, antifungals, antiparasitics, immune modulators, and anti-inflammatory agents. Their unique ability to combine high specificity with desirable pharmacokinetic properties makes them valuable tools in addressing unmet medical needs, such as combating drug-resistant pathogens and targeting challenging biological pathways. Due to the typically low concentrations of cyclic peptides in nature, effective synthetic strategies are indispensable for their acquisition, characterization, and biological evaluation. Cyclization, a critical step in their synthesis, enhances metabolic stability, bioavailability, and receptor binding affinity. Advances in synthetic methodologies-such as solid-phase peptide synthesis (SPPS), chemoenzymatic approaches, and orthogonal protection strategies-have transformed cyclic peptide production, enabling greater structural complexity and precision. This review compiles recent progress in the total synthesis and biological evaluation of natural cyclic peptides from 2017 onward, categorized by cyclization strategies: head-to-tail; head-to-side-chain; tail-to-side-chain; and side-chain-to-side-chain strategies. Each account includes retrosynthetic analyses, synthetic advancements, and biological data to illustrate their therapeutic relevance and innovative methodologies. Looking ahead, the future of cyclic peptides in drug discovery is bright. Emerging trends, including integrating computational tools for rational design, novel cyclization techniques to improve pharmacokinetic profiles, and interdisciplinary collaboration among chemists, biologists, and computational scientists, promise to expand the scope of cyclic peptide-based therapeutics. These advancements can potentially address complex diseases and advance the broader field of biological drug development.

Regioselective Electrochemical Construction of Csp2-Csp2 Linkage at C5-C5' Position of 2-Oxindoles via an Intermolecular Anodic Dehydrogenative Coupling

Applying electricity as a reagent in synthetic organic chemistry has attracted particular attention from synthetic chemists worldwide as an environmentally benign and cost-effective technique. Herein, we report the construction of the Csp2-Csp2 linkage at the C5-C5' position of 2-oxindole utilizing electricity as the traceless oxidant in an anodic dehydrogenative homo-coupling process. A variety of 3,3-disubstituted-2-oxindoles were subjected to dimerization, achieving yields of up to 70 % through controlled potential electrolysis at an applied potential of 1.5 V versus Ag/Ag+ nonaqueous reference electrode. This electro-synthetic approach facilitates the specific assembly of C5-C5' (para-para coupled) dimer of 3,3-disubstituted-2-oxindole without the necessity of any external oxidants or additives and DFT (Density Functional Theory) calculations provided confirmation of this pronounced regioselectivity. Furthermore, validation through control experiments and voltammetric analyses substantiated the manifestation of radical-radical coupling (or biradical pathway) for the dimerization process.

Genomic Characterization and Establishment of a Genetic Manipulation System for Trichoderma sp. (Harzianum Clade) LZ117

Trichoderma species have been reported as masters in producing cellulolytic enzymes for the biodegradation of lignocellulolytic biomass and biocontrol agents against plant pathogens and pests. In our previous study, a novel Trichoderma strain LZ117, which shows potent capability in cellulase production, was isolated. Herein, we conducted multilocus phylogenetic analyses based on DNA barcodes and performed time-scaled phylogenomic analyses using the whole genome sequences of the strain, annotated by integrating transcriptome data. Our results suggest that this strain represents a new species closely related to T. atrobrunneum (Harzianum clade). Genes encoding carbohydrate-active enzymes (CAZymes), transporters, and secondary metabolites were annotated and predicted secretome in Trichoderma sp. LZ117 was also presented. Furthermore, genetic manipulation of this strain was successfully achieved using PEG-mediated protoplast transformation. A putative transporter gene encoding maltose permease (Mal1) was overexpressed, which proved that this transporter does not affect cellulase production. Moreover, overexpressing the native Cre1 homolog in LZ117 demonstrated a more pronounced impact of glucose-caused carbon catabolite repression (CCR), suggesting the importance of Cre1-mediated CCR in cellulase production of Trichoderma sp. LZ117. The results of this study will benefit further exploration of the strain LZ117 and related species for their applications in bioproduction.

Hemiprotonic ph-ph+ with two targets inhibits metastatic breast cancer and concurrent candidiasis

Concurrent infection in breast cancer patients is the direct cause of the high mortality rate of the disease. However, there is no available method to increase the survival rate until now. To address the problem, we propose one drug with two target strategy to treat the refractory disease. A small chemical, ph-ph+, was attempted to be used in the study to explore the feasibility of the approach in anticancer and antifungus at the same time. The results showed that ph-ph+ could prevent the proliferation and metastasis of breast cancer cells, and kill C. albicans simultaneously. The molecular mechanism was associated with the activation of an evolutionarily conserved protease CLpP in the cancer and C. albicans cells. Also, the signaling pathway mediated by PLAGL2 that highly expressed in cancer cells participated in preventing cell metastasis and inducing apoptosis of ph-ph+. The one drug with dual targets inhibited the growth and metastasis of the cancer cells, and meanwhile eliminated C. albicans in tissues in the experimental animals. The results suggested that ph-ph+ with dual targets of CLpP and PLAGL2 would be a feasible approach to prolong the survival rate in patients with metastatic breast cancer and pathogenic infection.

Highly chemoselective oxidative dimerization of indolosesquiterpene alkaloids: a biomimetic approach to dixiamycin

Dimeric indolosesquiterpene alkaloids, typically N-N- and C-N-linked xiamycin dimers, feature a pentacyclic framework with four contiguous stereogenic centers at the periphery of a trans-decalin scaffold to which a carbazole unit is attached. In comparison with actual biosynthetic dixiamycin derivatives, we designed C-C-linked xiamycin dimers, aiming to use them as a powerful tool to create unique scaffolds as drug candidates. In this work, we disclose the first synthetic route to access a C-C dimeric indolosesquiterpene skeleton, featuring a hypervalent iodine (PIFA)-catalyzed oxidative dimerization reaction in a single-step operation with overwhelming control over the chemoselectivity and regioselectivity. This strategy has been successfully applied to the synthesis of a C-C dimer of xiamycin A (3) and xiamycin A methyl ester (15) that demonstrates a new synthetic pathway for dimeric indolosesquiterpene alkaloids.

Total Synthesis of Incarnatapeptins A and B

The first total synthesis of incarnatapeptins A and B, two novel marine natural products, was accomplished from readily available (S)-1-benzyloxycarbonylhexahydropyridazine-3-carboxylic acid. This route, whose longest linear sequence was 12 steps, provided the incarnatapeptins A and B in yields of 26.5 % and 19.7 %, respectively, and enabled the structure and stereochemistry of both natural products to be unambiguously confirmed. Highlights of our synthesis include the photoredox-mediated decarboxylative 1,4-addition reaction and a novel and practical N-acylation paradigm promoted by silver carbonate. The unusual facile atropisomerism of some linear peptidic intermediates was also observed by TLC analysis in the course of this work.

Electrochemical bromocyclization enables 3,5-diversification of heterocyclic indolines

Electrophilic bromocyclization reactions are widely used as key steps in the synthesis of diverse functionalized tetrahydrofuroindolines and hexahydropyrroloindolines. However, the direct dibromination variants of these reactions for the synthesis of 3,5-dibromoindolines remain undeveloped. Here, we report a protonic-acid-promoted electrooxidative protocol for the dearomative C3,C5-dibromocyclizations of tryptophol and tryptamine derivatives. This electrosynthetic approach, which enables direct selective construction of heterocyclic 3a,5a-dibromoindolines with inexpensive, non-hazardous NaBr as both the electrolyte and Br source, provides a convenient, practical method for the late-stage 3,5-diversification of heterocyclic indolines.

Concise Total Synthesis and Biological Evaluation of Pargamicin A and its Diastereomer, Piperazic Acid-containing Cyclopeptides

We have accomplished the total synthesis, structure determination, and biological evaluation of pargamicin A and one of its diastereomers. Two key tripeptide segments were synthesized using a linear peptide elongation process that includes the direct coupling of a poorly nucleophilic piperazic acid derivative. The resulting tripeptides were coupled using triphosgene/collidine at ambient temperature leading to a precursor for the final cyclization step. T3P-promoted macrolactamization under high-dilution conditions, followed by the removal of the benzyl protecting group was used to furnish two putative structures of pargamicin A. Comparison of the 1 H and 13 C NMR spectra and the antibacterial activity of the natural and synthetic products successfully revealed that the absolute configuration of the N-hydroxy-Ile residue of pargamicin A is 2S,3S. A biological evaluation of synthetically obtained pargamicin A and its diastereomer suggested that the stereostructure of the cyclic peptide scaffold of the natural product plays a crucial role in determining the strength of its antibacterial activity.

A one-step gram-scale protocol for stereoselective domino dimerization to asperazine A analogs

Here, we present an efficient protocol for stereoselective 4N-based domino dimerization in one single step, establishing a 22-membered library of asperazine A analogs. We describe steps for performing a gram-scale 2N-monomer to access the unsymmetrical 4N-dimer. We detail the synthesis of the desired dimer 3a as a yellow solid in 78% yield. This process demonstrates the 2-(iodomethyl)cyclopropane-1,1-dicarboxylate to be an iodine cation source. The protocol is limited to unprotected aniline of 2N-monomer. For complete details on the use and execution of this protocol, please refer to Bai et al. (2022).1.

Epipolythiodioxopiperazine-Based Natural Products: Building Blocks, Biosynthesis and Biological Activities

Epipolythiodioxopiperazines (ETPs) are fungal secondary metabolites that share a 2,5-diketopiperazine scaffold built from two amino acids and bridged by a sulfide moiety. Modifications of the core and the amino acid side chains, for example by methylations, acetylations, hydroxylations, prenylations, halogenations, cyclizations, and truncations create the structural diversity of ETPs and contribute to their biological activity. However, the key feature responsible for the bioactivities of ETPs is their sulfide moiety. Over the last years, combinations of genome mining, reverse genetics, metabolomics, biochemistry, and structural biology deciphered principles of ETP production. Sulfurization via glutathione and uncovering of the thiols followed by either oxidation or methylation crystallized as fundamental steps that impact expression of the biosynthesis cluster, toxicity and secretion of the metabolite as well as self-tolerance of the producer. This article showcases structure and activity of prototype ETPs such as gliotoxin and discusses the current knowledge on the biosynthesis routes of these exceptional natural products.

MGCEP 1.0: A Genetic-Engineered Marine-Derived Chassis Cell for a Scaled Heterologous Expression Platform of Microbial Bioactive Metabolites

Marine microorganisms produce a variety of bioactive secondary metabolites, which represent a significant source of novel antibiotics. Heterologous expression is a valuable tool for discovering marine microbial secondary metabolites; however, marine-derived chassis cell is very scarce. Here, we build an efficient plug-and-play marine-derived gene clusters expression platform 1.0 (MGCEP 1.0) by the systematic engineering of the deep-sea-derived Streptomyces atratus SCSIO ZH16. For a proof of concept, four families of microbial bioactive metabolite biosynthetic gene clusters (BGCs), including alkaloids, aminonucleosides, nonribosomal peptides, and polyketides, were efficiently expressed in this platform. Moreover, 19 compounds, including two new angucycline antibiotics, were produced in MGCEP 1.0. Dynamic patterns of global biosynthetic gene expression in MGCEP 1.0 with or without a heterologous gene cluster were revealed at the transcriptome level. The platform MGCEP 1.0 provides new possibilities for expressing microbial secondary metabolites, especially of marine origin.

Application of Plant-Derived Nanoparticles (PDNP) in Food-Producing Animals as a Bio-Control Agent against Antimicrobial-Resistant Pathogens

Antibiotics are regularly used in animal husbandry to treat diseases. This practice is beneficial to animals' health and helps ensure food security. However, the misuse of antibiotics, especially in food-producing animals, has resulted in the advent of antimicrobial resistance (AMR) and its dissemination among foodborne pathogens. The occurrence of AMR in bacteria pathogens that cause infections in animals and those associated with food spoilage is now considered a global health concern affecting humans, animals and the environment. The search for alternative antimicrobial agents has kindled the interest of many researchers. Among the alternatives, using plant-derived nanoparticles (PDNPs) for treating microbial dysfunctions in food-producing animals has gained significant attention. In traditional medicine, plant extracts are considered as safe, efficient and natural antibacterial agents for various animal diseases. Given the complexity of the AMR and concerns about issues at the interface of human health, animal health and the environment, it is important to emphasize the role of a One Health approach in addressing this problem. This review examines the potential of PDNPs as bio-control agents in food-producing animals, intending to provide consumers with microbiologically safe food while ensuring food safety and security, better health for animals and humans and a safe environment.

Biosynthesis of pyrroloindoline-containing natural products

Covering: up to 2022Pyrroloindoline is a privileged tricyclic indoline motif widely present in many biologically active and medicinally valuable natural products. Thus, understanding the biosynthesis of this molecule is critical for developing convenient synthetic routes, which is highly challenging for its chemical synthesis due to the presence of rich chiral centers in this molecule, especially the fully substituted chiral carbon center at the C3-position of its rigid tricyclic structure. In recent years, progress has been made in elucidating the biosynthetic pathways and enzymatic mechanisms of pyrroloindoline-containing natural products (PiNPs). This article reviews the main advances in the past few decades based on the different substitutions on the C3 position of PiNPs, especially the various key enzymatic mechanisms involved in the biosynthesis of different types of PiNPs.