Cytotoxic Naphthoquinone Analogues, Including Heterodimers, and Their Structure Elucidation Using LR-HSQMBC NMR Experiments

Unlocking the potential of 1,4-naphthoquinones: A comprehensive review of their anticancer properties

Cancer encompasses a group of pathologies with common characteristics, high incidence, and prevalence in all countries. Although there are treatments available for this disease, they are not always effective or safe, often failing to achieve the desired results. This is why it is necessary to continue the search for new therapies. One of the strategies for obtaining new antitumor drugs is the use of 1,4-naphthoquinone as a scaffold in synthetic or natural products with antitumor activity. This review focuses on compiling studies related to the antitumor activity of 1,4-naphthoquinone and its natural and synthetic derivatives over the last 10 years. The work describes the main natural naphthoquinones with antitumor activity and classifies the synthetic naphthoquinones based on the structural modifications made to the scaffold. Additionally, the formation of metal complexes using naphthoquinones as a ligand is considered. After a thorough review, 197 synthetic compounds with potent biological activity against cancer have been classified according to their chemical structures and their mechanisms of action have been described.

Antimicrobial and Cytotoxic Naphthoquinones from Microbial Origin: An Updated Review

Naphthoquinones (NQs) are small molecules bearing two carbonyl groups. They have been the subject of much research due to their significant biological activities such as antiproliferative, antimicrobial, anti-inflammatory, antioxidant, and antimalarial effects. NQs are produced mainly by bacteria, fungi and higher plants. Among them, microorganisms are a treasure of NQs with diverse skeletons and pharmacological properties. The purpose of the present study is to provide a comprehensive update on the structural diversity and biological activities of 91 microbial naphthoquinones isolated from 2015 to 2022, with a special focus on antimicrobial and cytotoxic activities. During this period, potent cytotoxic NQs such as naphthablin B (46) and hygrocin C (30) against HeLa (IC50=0.23 μg/ml) and MDA-MB-431 (IC50=0.5 μg/ml) cell lines was reported, respectively. In addition, rubromycin CA1 (39), exhibited strong antibacterial activity against Staphylococcus aureus (MIC of 0.2 μg/ml). As importance bioactive compounds, NQs may open new horizon for treatment of cancer and drug resistant bacteria. As such, it is hoped that this review article may stimulates further research into the isolation of further NQs from microbial, and other sources as well as the screening of such compounds for biological activity and beneficial uses.

Correlative metabologenomics of 110 fungi reveals metabolite-gene cluster pairs

Natural products research increasingly applies -omics technologies to guide molecular discovery. While the combined analysis of genomic and metabolomic datasets has proved valuable for identifying natural products and their biosynthetic gene clusters (BGCs) in bacteria, this integrated approach lacks application to fungi. Because fungi are hyper-diverse and underexplored for new chemistry and bioactivities, we created a linked genomics-metabolomics dataset for 110 Ascomycetes, and optimized both gene cluster family (GCF) networking parameters and correlation-based scoring for pairing fungal natural products with their BGCs. Using a network of 3,007 GCFs (organized from 7,020 BGCs), we examined 25 known natural products originating from 16 known BGCs and observed statistically significant associations between 21 of these compounds and their validated BGCs. Furthermore, the scalable platform identified the BGC for the pestalamides, demystifying its biogenesis, and revealed more than 200 high-scoring natural product-GCF linkages to direct future discovery.

Complete Structure Assignment of Azathioprine as a Proton-Deficient Nucleic Acid Analogue Using 1H-13C Long-Range Heteronuclear Single Quantum Multiple Bond Correlation

In this Note, the successful structural assignment of a proton-deficient nucleic acid analogue using the ¹H-¹³C long-range heteronuclear single quantum multiple bond correlation (LR-HSQMBC) technique is described. LR-HSQMBC is a 2D NMR technique for the sensitive detection of weak C-H spin couplings. The immunosuppressant drug, azathioprine, served as the target compound. The LR-HSQMBC measurements revealed the existence of covalent bonds between the purine and imidazole rings based on observations of ⁵J_CH and ⁶J_CH with good sensitivity.

Genomic and Phenotypic Trait Variation of the Opportunistic Human Pathogen Aspergillus flavus and Its Close Relatives

Fungal diseases affect millions of humans annually, yet fungal pathogens remain understudied. The mold Aspergillus flavus can cause both aspergillosis and fungal keratitis infections, but closely related species are not considered clinically relevant. To study the evolution of A. flavus pathogenicity, we examined genomic and phenotypic traits of two strains of A. flavus and three closely related species, Aspergillus arachidicola (two strains), Aspergillus parasiticus (two strains), and Aspergillus nomiae (one strain). We identified >3,000 orthologous proteins unique to A. flavus, including seven biosynthetic gene clusters present in A. flavus strains and absent in the three nonpathogens. We characterized secondary metabolite production for all seven strains under two clinically relevant conditions, temperature and salt concentration. Temperature impacted metabolite production in all species, whereas salinity did not affect production of any species. Strains of the same species produced different metabolites. Growth under stress conditions revealed additional heterogeneity within species. Using the invertebrate fungal disease model Galleria mellonella, we found virulence of strains of the same species varied widely; A. flavus strains were not more virulent than strains of the nonpathogens. In a murine model of fungal keratitis, we observed significantly lower disease severity and corneal thickness for A. arachidicola compared to other species at 48 h postinfection, but not at 72 h. Our work identifies variations in key phenotypic, chemical, and genomic attributes between A. flavus and its nonpathogenic relatives and reveals extensive strain heterogeneity in virulence that does not correspond to the currently established clinical relevance of these species. IMPORTANCE Aspergillus flavus is a filamentous fungus that causes opportunistic human infections, such as aspergillosis and fungal keratitis, but its close relatives are considered nonpathogenic. To begin understanding how this difference in pathogenicity evolved, we characterized variation in infection-relevant genomic, chemical, and phenotypic traits between strains of A. flavus and its relatives. We found extensive variation (or strain heterogeneity) within the pathogenic A. flavus as well as within its close relatives, suggesting that strain-level differences may play a major role in the ability of these fungi to cause disease. Surprisingly, we also found that the virulence of strains from species not considered to be pathogens was similar to that of A. flavus in both invertebrate and murine models of disease. These results contrast with previous studies on Aspergillus fumigatus, another major pathogen in the genus, for which significant differences in infection-relevant chemical and phenotypic traits are observed between closely related pathogenic and nonpathogenic species.

Application of Feature-Based Molecular Networking for Comparative Metabolomics and Targeted Isolation of Stereoisomers from Algicolous Fungi

Seaweed endophytic (algicolous) fungi are talented producers of bioactive natural products. We have previously isolated two strains of the endophytic fungus, Pyrenochaetopsis sp. FVE-001 and FVE-087, from the thalli of the brown alga Fucus vesiculosus. Initial chemical studies yielded four new decalinoylspirotetramic acid derivatives with antimelanoma activity, namely pyrenosetins A-C (1-3) from Pyrenochaetopsis sp. strain FVE-001, and pyrenosetin D (4) from strain FVE-087. In this study, we applied a comparative metabolomics study employing HRMS/MS based feature-based molecular networking (FB MN) on both Pyrenochaetopsis strains. A higher chemical capacity in production of decalin derivatives was observed in Pyrenochaetopsis sp. FVE-087. Notably, several decalins showed different retention times despite the same MS data and MS/MS fragmentation pattern with the previously isolated pyrenosetins, indicating they may be their stereoisomers. FB MN-based targeted isolation studies coupled with antimelanoma activity testing on the strain FVE-087 afforded two new stereoisomers, pyrenosetins E (5) and F (6). Extensive NMR spectroscopy including DFT computational studies, HR-ESIMS, and Mosher's ester method were used in the structure elucidation of compounds 5 and 6. The 3'R,5'R stereochemistry determined for compound 6 was identical to that previously reported for pyrenosetin C (3), whose stereochemistry was revised as 3'S,5'R in this study. Pyrenosetin E (5) inhibited the growth of human malignant melanoma cells (A-375) with an IC50 value of 40.9 μM, while 6 was inactive. This study points out significant variations in the chemical repertoire of two closely related fungal strains and the versatility of FB MN in identification and targeted isolation of stereoisomers. It also confirms that the little-known fungal genus Pyrenochaetopsis is a prolific source of complex decalinoylspirotetramic acid derivatives.

Fungal Naphthalenones; Promising Metabolites for Drug Discovery: Structures, Biosynthesis, Sources, and Pharmacological Potential

Fungi are well-known for their abundant supply of metabolites with unrivaled structure and promising bioactivities. Naphthalenones are among these fungal metabolites, that are biosynthesized through the 1,8-dihydroxy-naphthalene polyketide pathway. They revealed a wide spectrum of bioactivities, including phytotoxic, neuro-protective, cytotoxic, antiviral, nematocidal, antimycobacterial, antimalarial, antimicrobial, and anti-inflammatory. The current review emphasizes the reported naphthalenone derivatives produced by various fungal species, including their sources, structures, biosynthesis, and bioactivities in the period from 1972 to 2021. Overall, more than 167 references with 159 metabolites are listed.

Identification of Tricyclic Guanidino Compounds from the Tetrodotoxin-Bearing Newt Taricha granulosa

The biosynthesis of the potent neurotoxin tetrodotoxin (TTX, 1) is still unresolved. We used MS-guided screening and nuclear magnetic resonance analyses including long-range HSQMBC to characterize two novel skeletal tricyclic guanidino compounds, Tgr-288 (2a and 2b) and Tgr-210 (3), from the TTX-bearing newt, Taricha granulosa. The presence of these compounds in toxic newts is congruent with a previously proposed pathway for TTX biosynthesis in terrestrial organisms that includes a monoterpene precursor and the production of structurally diversified guanidino compounds.