Modifications, biological origin and antibacterial activity of naphthalenoid ansamycins

A review of recent advancement in covalent organic framework (COFs) synthesis and characterization with a focus on their applications in antibacterial activity

The primary objective of this review is to present a comprehensive examination of the synthesis, characterization, and antibacterial applications of covalent organic frameworks (COFs). COFs represent a distinct category of porous materials characterized by a blend of advantageous features, including customizable pore dimensions, substantial surface area, and adaptable chemical properties. These attributes position COFs as promising contenders for various applications, notably in the realm of antibacterial activity. COFs exhibit considerable potential in the domain of antibacterial applications, owing to their amenability to functionalization with antibacterial agents. The scientific community is actively exploring COFs that have been imbued with metal ions, such as copper or silver, given their observed robust antibacterial properties. These investigations strongly suggest that COFs could be harnessed effectively as potent antibacterial agents across a diverse array of applications. Finally, COFs hold immense promise as a novel class of materials for antibacterial applications, shedding light on the synthesis, characterization, and functionalization of COFs tailored for specific purposes. The potential of COFs as effective antibacterial agents beckons further exploration and underscores their potential to revolutionize antibacterial strategies in various domains.

The antimicrobial potential of adarotene derivatives against Staphylococcus aureus strains

Multidrug-resistant (MDR) pathogens are severely impacting our ability to successfully treat common infections. Here we report the synthesis of a panel of adarotene-related retinoids showing potent antimicrobial activity on Staphylococcus aureus strains (including multidrug-resistant ones). Fluorescence and molecular dynamic studies confirmed that the adarotene analogues were able to induce conformational changes and disfunctions to the cell membrane, perturbing the permeability of the phospholipid bilayer. Since the major obstacle for developing retinoids is their potential cytotoxicity, a selected candidate was further investigated to evaluate its activity on a panel of human cell lines. The compound was found to be well tolerated, with IC50 5-15-fold higher than the MIC on S. aureus strains. Furthermore, the adarotene analogue had a good pharmacokinetic profile, reaching a plasma concentration of about 6 μM after 0.5 h after administration (150 mg/kg), at least twice the MIC observed against various bacterial strains. Moreover, it was demonstrated that the compound potentiated the growth-inhibitory effect of the poorly bioavailable rifaximin, when used in combination. Overall, the collected data pave the way for the development of synthetic retinoids as potential therapeutics for hard-to-treat infectious diseases caused by antibiotic-resistant Gram-positive pathogens.

Microbial diversity in camel milk from Xinjiang, China as revealed by metataxonomic analysis

The quality of raw camel milk is affected by its bacterial composition and diversity. However, few studies have investigated the bacterial composition and diversity of raw camel milk. In this study, we obtained 20 samples of camel milk during spring and summer in Urumqi and Hami, Xinjiang, China. Single-molecule real-time sequencing technology was used to analyze the bacterial community composition. The results revealed that there were significant seasonal differences in the bacterial composition and diversity of camel milk. Overall, Epilithonimonas was the most abundant bacterial genus in our samples. Through the annotated genes inferred by PICRUSt2 were mapped against KEGG database. Non-parametric analysis of the bacterial community prediction function revealed a strong bacterial interdependence with metabolic pathways (81.83%). There were clear regional and seasonal differences in level 3 metabolic pathways such as fat, vitamins, and amino acids in camel milk. In addition, we identified lactic acid bacteria in camel milk with antibacterial and anti-tumor activities. Our findings revealed that camel milk from Xinjiang had serious risk of contamination by psychrophilic and pathogenic bacteria. Our research established a crucial theoretical foundation for ensuring the quality and safety of camel milk, thereby contributing significantly to the robust growth of China's camel milk industry.

Double Bond Geometric Isomers of Pentaketide Ansamycins from Streptomyces sp. S008

Six new pentaketide ansamycins, namely, shengliangmycins A-F (1-6, respectively), were obtained from the fermentation products of Streptomyces sp. S008OEslmR2 that was derived by constitutive expression of LAL regulator gene slmR2. The structures of 1-6 were determined through comprehensive spectroscopic analysis and single-crystal X-ray diffraction. Compound 1 has a cis-C6═C7 bond, which is different from that of compounds 2-5. Compounds 3-6 feature a morpholinone structural moiety, whereas 5 is characterized by a pyrazoline ring, which is rare in natural products.

Cascade Transformation of the Ansamycin Benzoquinone Core into Benzoxazole Influencing Anticancer Activity and Selectivity

The metal-free cascade transformation of geldanamycin benzoquinone core is proposed at relatively mild conditions. This approach yields new benzoxazole ansamycin antibiotics and enables their functionalization in an atom-economic manner, irrespective of the type of amine used. The analysis of the heterocyclization course reveals the dependence of its rate on the nature of the para-substituent within the benzylamine moiety (EDG/EWG) and the strength of the base. The reduction of the ansamycin core enables an increase in anticancer potency and selectivity.

Nagimycins A and B, Antibacterial Ansamycin-Related Macrolactams from Streptomyces sp. NA07423

Chemical investigation of Streptomyces sp. NA07423 led to the discovery of two unreported macrolactams, nagimycins A (1) and B (2). Their structures were elucidated by NMR, HRESIMS, X-ray crystallography, and comparison of experimental and theoretical ECD spectra. The nagimycins have a unique butenolide moiety rarely found in ansamycin antibiotics. Genome analysis revealed the putative biosynthetic gene cluster for nagimycins, and a likely biosynthetic pathway was proposed. Notably, compounds 1 and 2 exhibited potent antibacterial activity against two pathogenic Xanthomonas bacteria.

Trienomycin A-simplified analogs: Synthesis and anti-neuroinflammatory activity

A series of novel trienomycin A (TA)-mimetic compounds (5a-p) have been designed, synthesized, and evaluated for their in vitro anti-neuroinflammatory and neuroprotective activities. Among them, compounds 5h, 5n, and 5o exhibits relatively strong NO inhibitory activity in LPS-activated BV-2 cells with the EC₅₀ values of 12.4, 17.3, and 8.9 μM, respectively. Moreover, 5h showed evidently neuroprotective effect against H₂O₂-induced PC-12 cells without cytotoxicity at 20 μM. Overall, these compounds can provide a better understanding of the structure-activity relationship of TA and furnish research ideas for anti-neuroinflammatory and neuroprotective agents.