Two Unusual Methylidenecyclopropane Glucosides from Metaxya rostrata C.Presl

Insights into Chemical Diversity and Potential Health-Promoting Effects of Ferns

The scientific community is focusing on how to enhance human health and immunity through functional foods, and dietary supplements are proven to have a positive as well as a protective effect against infectious and chronic diseases. Ferns act as a taxonomical linkage between higher and lower plants and are endowed with a wide chemical diversity not subjected to sufficient scrutinization before. Even though a wealth of traditional medicinal fern uses were recorded in Chinese medicine, robust phytochemical and biological investigations of these plants are lacking. Herein, an extensive search was conducted using the keywords ferns and compounds, ferns and NMR, ferns and toxicity, and the terms ferns and chemistry, lignans, Polypodiaceae, NMR, isolation, bioactive compounds, terpenes, phenolics, phloroglucinols, monoterpenes, alkaloids, phenolics, and fatty acids were utilized with the Boolean operators AND, OR, and NOT. Databases such as PubMed, Web of Science, Science Direct, Scopus, Google Scholar, and Reaxys were utilized to reveal a wealth of information regarding fern chemistry and their health-promoting effects. Terpenes followed by phenolics represented the largest number of isolated active compounds. Regarding the neuroprotective effects, Psilotium, Polypodium, and Dryopteris species possessed as their major phenolics component unique chemical moieties including catechins, procyanidins, and bioflavonoids. In this updated chemical review, the pharmacological and chemical aspects of ferns are compiled manifesting their chemical diversity in the last seven years (2017-2024) together with a special focus on their nutritive and potential health-promoting effects.

Analysis of the Valgamicin Biosynthetic Pathway Reveals a General Mechanism for Cyclopropanol Formation across Diverse Natural Product Scaffolds

Cyclopropanol rings are highly reactive and may function as molecular "warheads" that affect natural product bioactivity. Yet, knowledge on their biosynthesis is limited. Using gene cluster analyses, isotope labeling, and in vitro enzyme assays, we shed first light on the biosynthesis of the cyclopropanol-substituted amino acid cleonine, a residue in the antimicrobial depsipeptide valgamicin C and the cytotoxic glycopeptide cleomycin A2. We decipher the biosynthetic origin of valgamicin C and show that the cleonine cyclopropanol ring is derived from dimethylsulfoniopropionate (DMSP). Furthermore, we demonstrate that part of the biosynthesis is analogous to the formation of malleicyprol polyketides in pathogenic bacteria. By genome mining and metabolic profiling, we identify the potential to produce cyclopropanol rings in other bacterial species. Our results reveal a general mechanism for cyclopropyl alcohol biosynthesis across diverse natural products that may be harnessed for bioengineering and drug discovery.

Tigliane Diterpenoids

The distribution, chemistry, and molecular bioactivity of tiglianes are reviewed from the very beginning of the studies on these diterpenoids, summarizing their clinical and toxicological literature mostly in its more recent and controversial aspects, and critically analyzing various proposals for their biosynthesis.

Computational insights into strain-increase allylborations for alkylidenecyclopropanes

The origins of reactivity of strain-increase allylborations were computationally investigated. The low reactivity of vinylcyclopropyl boronates is due to weak electronic interactions between benzaldehyde and allylboronates. By increasing the acidity...

Cyclopropanol Warhead in Malleicyprol Confers Virulence of Human- and Animal-Pathogenic Burkholderia Species

Burkholderia species such as B. mallei and B. pseudomallei are bacterial pathogens causing fatal infections in humans and animals (glanders and melioidosis), yet knowledge on their virulence factors is limited. While pathogenic effects have been linked to a highly conserved gene locus (bur/mal) in the B. mallei group, the metabolite associated to the encoded polyketide synthase, burkholderic acid (syn. malleilactone), could not explain the observed phenotypes. By metabolic profiling and molecular network analyses of the model organism B. thailandensis, the primary products of the cryptic pathway were identified as unusual cyclopropanol-substituted polyketides. First, sulfomalleicyprols were identified as inactive precursors of burkholderic acid. Furthermore, a highly reactive upstream metabolite, malleicyprol, was discovered and obtained in two stabilized forms. Cell-based assays and a nematode infection model showed that the rare natural product confers cytotoxicity and virulence.

Toblerols: Cyclopropanol-Containing Polyketide Modulators of Antibiosis in Methylobacteria

Trans-AT polyketide synthases (PKSs) are a family of biosynthetically versatile modular type I PKSs that generate bioactive polyketides of impressive structural diversity. In this study, we detected, in the genome of several bacteria a cryptic, architecturally unusual trans-AT PKS gene cluster which eluded automated PKS prediction. Genomic mining of one of these strains, the model methylotroph Methylobacterium extorquens AM1, revealed unique epoxide- and cyclopropanol-containing polyketides named toblerols. Relative and absolute stereochemistry were determined by NMR experiments, chemical derivatization, and the comparison of CD data between the derivatized natural product and a synthesized model compound. Biosynthetic data suggest that the cyclopropanol moiety is generated by carbon-carbon shortening of a more extended precursor. Surprisingly, a knock-out strain impaired in polyketide production showed strong inhibitory activity against other methylobacteria in contrast to the wild-type producer. The activity was inhibited by complementation with toblerols, thus suggesting that these compounds modulate an as-yet unknown methylobacterial antibiotic.