Anti-infammatory scalemic chromanoids and chromenoids from Rhododendron dauricum

Chromene meroterpenoids from Rhododendron dauricum L. and their anti-inflammatory effects

Rhododendron dauricum L. is a perennial herb belonging to the genus Rhododendron, commonly utilized in formulations for treating coughs and bronchitis, as well as in herbal teas for enhancing immunity and preventing tracheitis. In this study, fifteen previously undescribed chromene meroterpenoids (1a/1b-4a/4b, 5-8, 9b, 10a, 11b), along with twenty-one known compounds were isolated from the dried twigs and leaves of Rhododendron dauricum L. Of these, (-)-rhodonoid E (9b), (+)-confluentin (10a), and (-)-rubiginosin D (11b) were separated for the first time by chiral HPLC separation. The elucidation of their structures, including absolute configurations, was achieved through a combination of techniques such as NMR, HRESIMS, modified Mosher's method and quantum-chemical calculation of electronic circular dichroism (ECD) spectra. Seven pairs of enantiomers, compounds 1a/1b-4a/4b and 9a/9b-11a/11b, were initially obtained in a racemic manner and were further separated by chiral HPLC preparation. The biological assessment of these compounds against NO production was conducted in the LPS-induced RAW264.7 macrophage cells model. Compounds 9a, 9b, and 11a displayed inhibitory rates exceeding 80%, with IC50 values ranging from 8.69 ± 0.94 to 13.01 ± 1.11 μM. A preliminary examination of the structure-activity relationship (SAR) for these isolates indicated that chromene meroterpenoids with α, β-unsaturated ketone carbonyl and Δ12(13) double bond functionalities exhibited enhanced anti-inflammatory properties.

Discovery, biosynthesis, organic synthesis, and bioactivities of meroterpenoids from Rhododendron species

Meroterpenoids discovered in Rhododendrons species possess unique chemical structures and biological activities and are expected to become new drug targets for Alzheimer's disease, metabolic disorders, and chronic kidney disease, and these compounds have attracted increasing attention in recent years. In this study, Rhododendron meroterpenoids and their structures, classifications, racemate distribution, biosynthetic pathways, chemical synthesis, and bioactivities are reviewed prior to 2023.

Two new terpenoids from the branches and leaves of Rhododendron dauricum L. with neuroprotective activity

Two new terpenoids were isolated from the branches and leaves of Rhododendron dauricum L., named as rhodayritions A (1) and B (2), together with five known compounds which were identified litseachromolaevane A (3), 11-αH-dihydrodehydrocostus lactone (4), (+)-9β-hydroxyeudesma-4,11(13)-dien-12-al (5), macrostachyoside B (6) and aglaiabbreviatin E (7), respectively. The structures of isolated compounds were determined by UV, HR-ESI-MS, NMR analysis and X-Ray. Their neuroprotective activity was studied on serum deprivation-induced PC12 cells by the MTT method, compounds 1, 6, and 7 exhibited significant neuroprotective activity at 20 μΜ.

Integrated metabolomics and transcriptomics reveal molecular mechanisms of corolla coloration in Rhododendron dauricum L

Rhododendron dauricum L. is a semi-evergreen shrub of high ornamental and medicinal values in Northeast China. To study the molecular mechanisms of corolla coloration in R. dauricum, integrated metabolomics and transcriptomics were performed in R. dauricum featuring purple flowers and R. dauricum var. album featuring white flowers. Comparative metabolomics revealed 25 differential metabolites in the corolla of the two distinct colors, enriched in flavonoids that are closely related to pigmentation in the flower. Differential analysis of the transcriptomics data revealed enrichment of structural genes for flavonoid biosynthesis (99 up- and 58 down-regulated, respectively, in purple corollas compared to white ones). Significantly, CHS and CHI, key genes in the early stage of anthocyanin synthesis, as well as F3H, F3'H, F3'5'H, DFR, ANS, and UFGT that promote the accumulation of pigments in the late stage of anthocyanin synthesis, were up-regulated in R. dauricum (purple color). In R. dauricum var. album, FLS were key genes determining the accumulation of flavonols. In addition, transcriptome-metabolome correlation analysis identified 16 R2R3 MYB transcription factors (out of 83 MYBs) that are important for corolla coloration. Five negative and four positive MYBs were further identified by integrated transcriptional and metabolic network analysis, revealing a key role of MYBA and MYB12 in regulating anthocyanins and flavonols, respectively. Moreover, we validated the function of RdMYBA by creating stable transgenic plants and found that RdMYBA promotes anthocyanin biosynthesis. In summary, we systematically characterized the transcriptome and metabolome of two R. dauricum cultivars with different flower colors and identified MYBs as key factors in modulating corolla coloration.

An updated review of the genus Rhododendron since 2010: Traditional uses, phytochemistry, and pharmacology

Rhododendron, the largest genus of Ericaceae, consists of approximately 1000 species that are widely distributed in Europe, Asia, and North America but mainly exist in Asia. Rhododendron plants have not only good ornamental and economic value but also significant medicinal potential. In China, many Rhododendron plants are used as traditional Chinese medicine or ethnic medicine for the treatment of respiratory diseases, pain, bleeding and inflammation. Rhododendron is known for its abundant metabolites, especially diterpenoids. In the past 13 years, a total of 610 chemical constituents were reported from Rhododendron plants, including 222 diterpenoids, 122 triterpenoids, 103 meroterpenoids, 71 flavonoids and 92 other constituents (lignans, phenylpropanoids, phenolic acids, monoterpenoids, sesquiterpenoids, coumarins, steroids, fatty acids). Moreover, the bioactivities of various extracts and isolates, both in vitro and in vivo, were also investigated. Our review summarized the research progress of Rhododendron regarding traditional uses, phytochemistry and pharmacology in the past 13 years (2010 to December 2022), which will provide new insight for prompting further research on Rhododendron application and drug development.

A new anti-neuroinflammation labdane diterpenoid from Salvia tricuspis

One new labdane diterpenoid, tricuspion A (1), as well as five known triterpenoids (2-6) were isolated from Salvia tricuspis Franch (family Labiatae). The structure of tricuspion A was identified by extensive spectroscopic analysis and by comparison with previously reported data. Compounds 1-6 were evaluated for their inhibitory effects on the NO production in LPS-stimulated BV-2 microglia cells, and 1 exhibited potent inhibitory activity with IC50 value of 14.92 ± 0.51 μM. Compound 1 might exert anti-neuroinflammatory activity through inhibiting the excessive production of NO and down-regulating the protein expression of iNOS and COX-2. As such, labdane diterpenoid (tricuspion A) could provide promising anti-neuroinflammatory lead compound for further structural modification.