New triterpenoids from the roots of Rhododendron molle as positive modulators of GABAA receptors

Analgesic Grayanane-Derived Diterpenoids from the Flowers of Rhododendron molle

Ten new grayanane-derived diterpenoids, rhodomollein LVII-LXVI (1-10), along with the known compound rhodomollein XLIII (11), were isolated from the flowers of Rhododendron molle. Their structures were elucidated by detailed spectroscopic analysis, X-ray diffraction crystallography, and ECD calculations. Rhodomollein LVII-LIX (1-3) are the first-discovered 3-O-(E)-p-coumaroylquinic acid, nicotinic acid, and 2-furoic acid derivatives of grayanane diterpenoids, respectively. In an acetic acid-induced writhing test, compounds 1 and 3 demonstrated significant antinociceptive effects with writhing inhibition rates of 77.2% and 71.5%, respectively, at a dose of 0.2 mg/kg. Compound 1 was found to be twice as potent as morphine, exhibiting significantly lower toxicity (LD50 = 130.90 mg/kg, i.p.) compared to rhodojaponin VI (LD50 = 1.79 mg/kg, i.p.).

Three new antinociceptive diterpenoids from the fruits of Rhododendron molle

Investigation of the fruits of Rhododendron molle G. Don led to the isolation of three new grayanane-type diterpenoids, rhodomolleins LIV-LVI (1-3). The structures and absolute configurations of new compounds were fully elucidated by spectroscopic analysis and single-crystal X-ray diffraction, including HRESIMS, 1 D and 2 D NMR data. Compounds 1-3 were evaluated for analgesic activities utilizing an acetic acid-induced writhing test in mice. Compound 1 showed a significant antinociceptive effect with writhe inhibition rates of 72.9% and 100% at doses of 6 mg/kg and 20 mg/kg in mice, respectively. The binding mode of 1 to N-ethylmaleimide-sensitive factor (NSF, PDB: 6IP2) was explored by molecular docking, indicating the presence of hydrogen bond interactions which account for its analgesic activity.

Structurally diverse analgesic diterpenoids from the flowers of Rhododendron molle

Thirteen diterpenoids (1-13), classified into four structurally diverse carbon skeletons, including 1,5-seco-kalmane (1 and 6), grayanane (2-11), kalmane (12), and rhodomollane (13), were isolated from the flowers extract of Rhododendron molle. Among them, rhodomollinols A - E (1-5) were five new diterpenoids and their structures were elucidated by extensive spectroscopic methods including HRESIMS, UV, IR, 1D and 2D NMR, as well as quantum ECD calculations. Rhodomollinol A (1) is the first representative of a 6-deoxy-1,5-seco-kalmane diterpenoid. The abnormal NMR phenomenon of the presence of only 9 carbon resonances instead of 20 carbons in the 13C NMR spectrum of 1 was observed and elucidated by the quantum NMR calculations. All diterpenoids 1-13 showed significant analgesic activities in an acetic acid-induced writhing model. It's the first time to report the analgesic activity of a rhodomollane-type diterpenoid. At a dose of 1.0 mg/kg, diterpenoids 1-3, 6, 8, 9, and 12 reduced the writhe numbers with inhibition rates over 50%, and 9 exhibited stronger analgesic activity with a writhe inhibition rate of 89.7% than that of the positive control morphine. Importantly, even at the lowest dose of 0.04 mg/kg, rhodomollinols A (1) and B (2), rhodomollein X (7), and 2-O-methylrhodojaponin VI (9) still showed more potent analgesic effects than morphine with the writhe inhibition rates of 51.8%, 48.0%, 61.7%, and 60.0%, respectively. A preliminary structure-activity relationship might provide some clues to design potential analgesics on the basis of structurally diverse Ericaceae diterpenoids.

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.

The complete chloroplast genome of Rhododendron molle and its phylogenetic position within Ericaceae

Rhododendron mole (Blume) G. Don is an attractive ornamental and valuable medicinal plant which widely distributed in the southern regions of China. In order to promote the studies on the genetic diversity of this species, we assembled the complete chloroplast (cp) genome of R. molle by using the genome skimming approach. The results showed that the cp genome of R. molle exhibited a quadripartite cycle with 197,877 bp, comprising of two inverted repeats (IRs) of 43,831 bp separated by a large single copy (LSC) region of 110,189 bp and a quite small single copy (SSC) region of 26 bp. It encodes 146 genes, including 92 protein-coding, 46 tRNA, and eight rRNA genes. The overall GC content of the cp genome was 36.0%. The phylogenetic analysis indicated that R. molle is closely related to R. delavayi. Thus, the cp genome sequence of R. molle provides a rich source of genetic information for studies on Rhododendron taxonomy, phylogeny, and evolution, as well as lays the foundation for further development and utilization of R. molle.