Dissecting the Structure of Thiopeptides: Assessment of Thiazoline and Tail Moieties of Baringolin and Antibacterial Activity Optimization

Diversity-oriented routes to thiopeptide antibiotics: total synthesis and biological evaluation of micrococcin P2

We report the first total synthesis of micrococcin P2 (MP2, 1) by a diversity-oriented route that incorporates a number of refinements relative to earlier syntheses. Biological data regarding the activity of 1 against a range of human pathogens are also provided. Furthermore, we disclose a chemical property of MP2 that greatly facilitates medicinal chemistry work in the micrococcin area and describe a method to obtain MP2 by fermentation in B. subtilis.

Dassonmycins A and B, Polycyclic Thioalkaloids from a Marine Sponge-Derived Nocardiopsis dassonvillei SCSIO 40065

Two polycyclic thioalkaloides dassonmycins A (1) and B (2) were isolated from Nocardiopsis dassonvillei SCSIO 40065 associated with marine sponge Petrosia sp. Structures of 1 and 2 were elucidated by comprehensive spectroscopic analysis and confirmed by single-crystal X-ray diffraction experiments, to have a 6/6/6/6-fused tetracyclic ring featuring a naphthoquinone[2,3-e]piperazine[1,2-c]thiomorpholine scaffold. Compound 2 formed a caged core through an additional ether bridge. Both compounds exhibited moderate antibacterial and cytotoxic activities.

Introduction to Thiopeptides: Biological Activity, Biosynthesis, and Strategies for Functional Reprogramming

Thiopeptides (also known as thiazolyl peptides) are structurally complex natural products with rich biological activities. Known for over 70 years for potent killing of Gram-positive bacteria, thiopeptides are experiencing a resurgence of interest in the last decade, primarily brought about by the genomic revolution of the 21st century. Every area of thiopeptide research-from elucidating their biological function and biosynthesis to expanding their structural diversity through genome mining-has made great strides in recent years. These advances lay the foundation for and inspire novel strategies for thiopeptide engineering. Accordingly, a number of diverse approaches are being actively pursued in the hope of developing the next generation of natural-product-inspired therapeutics. Here, we review the contemporary understanding of thiopeptide biological activities, biosynthetic pathways, and approaches to structural and functional reprogramming, with a special focus on the latter.

Naturally Occurring Oxazole-Containing Peptides

Oxazole-containing peptides are mostly of marine origin and they form an intriguing family with a broad range of biological activities. Here we classify these peptides on the basis of their chemical structure and discuss a number of representatives of each class that reflect the extraordinary potential of this family as a source of new drugs.

Heteroaryl Rings in Peptide Macrocycles

This Review is devoted to the chemistry of macrocyclic peptides having heterocyclic fragments in their structure. These motifs are present in many natural products and synthetic macrocycles designed against a particular biochemical target. Thiazole and oxazole are particularly common constituents of naturally occurring macrocyclic peptide molecules. This frequency of occurrence is because the thiazole and oxazole rings originate from cysteine, serine, and threonine residues. Whereas other heteroaryl groups are found less frequently, they offer many insightful lessons that range from conformational control to receptor/ligand interactions. Many options to develop new and improved technologies to prepare natural products have appeared in recent years, and the synthetic community has been pursuing synthetic macrocycles that have no precedent in nature. This Review attempts to summarize progress in this area.

Structural Simplification of Natural Products

Natural products (NPs) are important sources of clinical drugs due to their structural diversity and biological prevalidation. However, the structural complexity of NPs leads to synthetic difficulties, unfavorable pharmacokinetic profiles, and poor drug-likeness. Structural simplification by truncating unnecessary substructures is a powerful strategy for overcoming these limitations and improving the efficiency and success rate of NP-based drug development. Herein, we will provide a comprehensive review of the structural simplification of NPs with a focus on design strategies, case studies, and new technologies. In particular, a number of successful examples leading to marketed drugs or drug candidates will be discussed in detail to illustrate how structural simplification is applied in lead optimization of NPs.

Frontier Between Cyclic Peptides and Macrocycles

This review describes a selection of macrocyclic natural products and structurally modified analogs containing peptidic and non-peptidic elements as structural features that potentially modulate cellular permeability. Examples range from exclusively peptidic structures like cyclosporin A or phepropeptins to compounds with mostly non-peptidic character, such as telomestatin or largazole. Furthermore, semisynthetic approaches and synthesis platforms to generate general and focused libraries of compounds at the interface of cyclic peptides and non-peptidic macrocycles are discussed.

Geninthiocins C and D from Streptomyces as 35-membered macrocyclic thiopeptides with modified tail moiety

Geninthiocin is a thiopeptide with 35-membered macrocyclic core moiety. It has potent anti-Gram-positive (G⁺) bacteria activity. Herein, we reported two new congeners (2-3) of geninthiocin (geninthiocin A, 1) from Streptomyces sp. CPCC 200267, and designated them as geninthiocins C and D, whose structures were determined by NMR. Geninthiocins A, C and D had the same 35-membered macrocyclic core moiety, but possessed a -Dha-Dha-NH₂, -Dha-Ala-NH₂, and -NH₂ tail, respectively. Besides, the Ala residue in geninthiocin C was determined as L- configuration by C₃ Marfey's method. In vitro assays indicated that geninthiocins C-D showed no antibacterial activity, in contrast to the potent anti-G⁺ bacteria activity displayed by geninthiocin A. Therefore, the -Dha-Dha-NH₂ tail of geninthiocin A played an important role in its potent activity against G⁺ bacteria.

Thiazolium-derivative functionalized silver nanocomposites for suppressing bacterial resistance and eradicating biofilms

Commercial antibiotic therapies are becoming less efficient due to the emergence of bacterial resistance and the formation of bacterial biofilms.

Single Continuous Near-Infrared Laser-Triggered Photodynamic and Photothermal Ablation of Antibiotic-Resistant Bacteria Using Effective Targeted Copper Sulfide Nanoclusters

The emergence of antibiotic-resistant bacterial strains has made conventional antibiotic therapies less efficient. The development of a novel nanoantibiotic approach for efficiently ablating such bacterial infections is becoming crucial. Herein, a collection of poly(5-(2-ethyl acrylate)-4-methylthiazole-g-butyl)/copper sulfide nanoclusters (PATA-C4@CuS) was synthesized for efficient capture and effective ablation of levofloxacin-resistant Gram-negative and Gram-positive bacteria upon tissue-penetrable near-infrared (NIR) laser irradiation. In this work, we took advantage of the excellent photothermal and photodynamic properties of copper sulfide nanoparticles (CuSNPs) upon NIR laser irradiation and thiazole derivative as a membrane-targeting cationic ligand toward bacteria. The conjugated nanoclusters could anchor the bacteria to trigger the bacterial aggregation quickly and efficiently kill them. These conjugated nanoclusters could significantly inhibit levofloxacin-resistant Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Bacillus amyloliquefaciens at 5.5 μg/mL under NIR laser irradiation (980 nm, 1.5 W cm^-2, 5 min), which suggested that the heat and reactive oxygen species (ROS) generated from the irradiated CuSNPs attached to bacteria were effective in eliminating and preventing the regrowth of the bacteria. Importantly, the conjugated nanoclusters could promote healing in bacteria-infected rat wounds without nonspecific damage to normal tissue. These findings highlight the promise of the highly versatile multifunctional nanoantibiotics in bacterial infection.

YcaO-Dependent Posttranslational Amide Activation: Biosynthesis, Structure, and Function

With advances in sequencing technology, uncharacterized proteins and domains of unknown function (DUFs) are rapidly accumulating in sequence databases and offer an opportunity to discover new protein chemistry and reaction mechanisms. The focus of this review, the formerly enigmatic YcaO superfamily (DUF181), has been found to catalyze a unique phosphorylation of a ribosomal peptide backbone amide upon attack by different nucleophiles. Established nucleophiles are the side chains of Cys, Ser, and Thr which gives rise to azoline/azole biosynthesis in ribosomally synthesized and posttranslationally modified peptide (RiPP) natural products. However, much remains unknown about the potential for YcaO proteins to collaborate with other nucleophiles. Recent work suggests potential in forming thioamides, macroamidines, and possibly additional post-translational modifications. This review covers all knowledge through mid-2016 regarding the biosynthetic gene clusters (BGCs), natural products, functions, mechanisms, and applications of YcaO proteins and outlines likely future research directions for this protein superfamily.