Xanthchrysones A-C: Rearranged Phenylpropanoyl-Phloroglucinol Dimers with Unusual Skeletons from Xanthostemon chrysanthus

High-resolution neuraminidase inhibition profiling of Arnebia euchroma (Royle) I.M. Johnst. based on HR-MS and target isolation: An example study of anti-infectious constituents in traditional Chinese medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese Medicines (TCMs) are an important source to discover new anti-infectious drugs. Neuraminidases (NAs) not only play a key role on human health, but also are promising targets for anti-infectious drugs. Arnebia euchroma which is a widely used traditional Chinese medicine with the effect of cooling blood and detoxifying showed potential inhibitory activities on both bacterial NA and virus NA, suggesting that the material basis of A. euchroma deserves in-depth study.

AIM OF THE STUDY

To investigate the anti-infectious constituents of A. euchroma based on NA inhibition.

MATERIAL AND METHODS

A HPLC-DAD system incorporated an auto-sampler was used for micro-fractionation. A nanoliter liquid handler and a high sensitive multimode plate reader system were used for high throughput NA inhibition screening. Thus a high-resolution NA inhibition profiling platform was constructed. The structures of potential active components in A. euchroma obtained by the high-resolution bioassay profiling were identified by DAD and MS in parallel. Then, a target and rapid isolation of NAIs from A. euchroma was achieved under the guidance of the spectrum-effect relationship obtained above. Finally, the isolated compounds were elucidated by extensive spectroscopic methods and their bioactivities were validated by in vitro assay and molecular docking.

RESULTS

16 potential active ingredients in A. euchroma were isolated and identified, including a new mero-monoterpenoid. The in vitro bioassay results revealed that 12 out of the 16 isolated compounds showed potent inhibitory activities on bacterial NA (IC50s = 1-6 μM) and five of them exhibited potent anti-microbial activities on methicillin-resistant Staphylococccus aureus (MRSA) with MICs in the range of 0.5-4 μg/mL. Furthermore, some isolated compounds showed equal or even better inhibitory activities on oseltamivir resistant viral NA than oseltamivir sensitive NA. The mechanism study in silicon revealed that these natural compounds possessed absolutely different binding modes on the bacterial and viral NAs.

CONCLUSIONS

Our study gave a clear spectrum-effect relationship of A. euchroma, providing a scientific evidence for future study of the multi-components synergistic effect of TCMs.

Five New Phenylpropanoyl Phloroglucinol Derivatives from Leptospermum scoparium

Leptosperols C-G (1-5), five new phenylpropanoyl phloroglucinol derivatives were isolated from the leaves of Leptospermum scoparium. Compounds 1-3 are phenylpropanoyl phloroglucinol-sesquiterpene adducts with new carbon skeletons. Their structures with absolute configurations were elucidated by detailed spectroscopic analyses, single-crystal X-ray diffraction, and electronic circular dichroism (ECD) calculation. Compounds 2 and 3 exhibited moderate anti-inflammatory activity in zebrafish acute inflammatory models.

(+)- and (-)-Xanthostones A-D: Four Pairs of Enantiomeric Cinnamoyl-β-Triketone Derivatives from Xanthostemon chrysanthus

Four pairs of cinnamoyl-β-triketone derivative enantiomers, (+)- and (-)-xanthostones A-D ((+)- and (-)-1-4), were isolated from Xanthostemon chrysanthus. Compounds 1 and 2 feature a new rearranged cinnamoyl-phloroglucinol scaffold fused with a cinnamyl-β-triketone framework. Compounds 1, 3, and 4 are the first examples of natural products with a peculiar phenethyl-pyranone acid unit. Their structures with absolute configurations were determined by spectroscopic data, X-ray diffraction analysis and electronic circular dichroism (ECD) calculation. Interestingly, these novel compounds showed a tautomeric behavior in solution, which was revealed by NMR spectroscopy and density functional theory calculation. A plausible biosynthetic pathway toward xanthostones A-D was proposed. Additionally, the anti-inflammatory and antibacterial activities of xanthostones A-D were evaluated.

Natural Enantiomers: Occurrence, Biogenesis and Biological Properties

The knowledge that natural products (NPs) are potent and selective modulators of important biomacromolecules (e.g., DNA and proteins) has inspired some of the world’s most successful pharmaceuticals and agrochemicals. Notwithstanding these successes and despite a growing number of reports on naturally occurring pairs of enantiomers, this area of NP science still remains largely unexplored, consistent with the adage “If you don’t seek, you don’t find”. Statistically, a rapidly growing number of enantiomeric NPs have been reported in the last several years. The current review provides a comprehensive overview of recent records on natural enantiomers, with the aim of advancing awareness and providing a better understanding of the chemical diversity and biogenetic context, as well as the biological properties and therapeutic (drug discovery) potential, of enantiomeric NPs.

Eugenunilones A–H: rearranged sesquiterpenoids from Eugenia uniflora

Six rearranged sesquiterpenoids (1–6) with four types of new polycyclic caged skeletons were isolated from Eugenia uniflora.

Phloroglucinol-derived lipids from the leaves of Syzygium cumini and their neuroprotective activities

Based on the typical HPLC-UV-MS profiles and characteristic ¹H NMR signals, twelve new phloroglucinol-derived lipids (1-12), featuring a long linear aliphatic side chain, together with three known ones (13-15) were isolated from the ethanol extract of the leaves of Syzygium cumini. Their structures were elucidated on the basis of extensive NMR spectroscopic analyses and mass spectrometric data. Compounds 1-5 characterize an enolizable β,β'-tricarbonyl motif with a cyclohexa-3,5-dien-1-one core that is hitherto undescribed in phloroglucinol-derived lipids. Compounds 4 and 10-12 are novel phloroglucinol-derived lipids containing an uncommon methylene interrupted trans double bond in their polyunsaturated aliphatic side chains. A polyketide biogenetic pathway for those phloroglucinol-derived lipids was also proposed. In addition, the isolates were evaluated for their neuroprotective activities against oxygen-glucose deprivation and re‑oxygenation (OGD/R)-induced Neuro-2a cell injury. Notably, compounds 1, 5, and 10-12 significantly improved viability of Neuro-2a cells after OGD/R damage.

Dimeric Acylphloroglucinol Derivatives with New Skeletons from Leptospermum scoparium

Leptosparones A-F (1-6), six new dimeric acylphloroglucinol derivatives with unprecedented skeletons, were isolated from Leptospermum scoparium. Compounds 1-3 and 5-6 are phenylpropanoyl-phloroglucinol dimers, while 4 is a phenylpropanoylphloroglucinol-isovalerylphloroglucinol hybrid. Structurally, these compounds represent the first examples of dimeric phloroglucinols with unprecedented C(7')-C(8) linkage between the phloroglucinol core and the acyl side chain. Their structures were elucidated by comprehensive analyses of spectroscopic data, single crystal X-ray diffraction and chemical calculations. In addition, all compounds showed inhibitory effects against α-glucosidase with IC₅₀ values ranging from 39.5 to 186.8 μM.

Gelserancines A–E, monoterpenoid indole alkaloids with unusual skeletons from Gelsemium elegans

Five monoterpenoid indole alkaloids (MIAs) with unusual skeletons, gelserancines A–E (1–5), were isolated from the roots of Gelsemium elegans.

Antibacterial Triketone-Phloroglucinol-Triketone Adducts from Myrtus communis

Myrtucyclitones A-C ((+)- and (-)-1-3), three pairs of new triketone-phloroglucinol-triketone hybrids were isolated from the plant Myrtus communis. Their structures with absolute configurations were established by NMR analysis and chemical calculations. Myrtucyclitones B and C exhibited remarkable antibacterial effect.

Chiral Isolation and Absolute Configuration of (+)- and (-)-Xanchryones F and G from Xanthostemon chrysanthus

(+)- and (-)-Xanchryones F and G ((+)- and (-)-1 and 2) were isolated from the plant Xanthostemon chrysanthus by chiral separation. Compounds 1 and 2 featured a new carbon skeleton with cinnamoyltriketone-flavone adducts. Their structures with absolute configurations were elucidated by detailed spectroscopic analyses and chemical calculations. The antibacterial and anti-inflammatory activities of (+)- and (-)-1 and 2 were evaluated.