Anti-neuroinflammatory diterpenoids from the endangered conifer Podocarpus imbricatus

A comprehensive review on the medicinal usage of Podocarpus species: Phytochemistry and pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Plants of the Podocarpus species belong to the Podocarpaceae family and are largely distributed in the southern hemisphere. Beside the commercially and ecologically valuable, plants of the Podocarpus species are also used in traditional medicines in some countries for treating asthma, fever, venereal diseases, eye diseases, etc. AIM OF THE STUDY: In recent decades, the identities and pharmacological activities of phytochemicals extracted from Podocarpus plants have been widely studied. However, there have been no comprehensive and systematic reviews. This article aims to systematically review the latest research on the putative mechanisms underlying pharmacological actions of phytochemicals from the Podocarpus species, as well as to lay a foundation for promoting the development of plant resources from this genus, further drug research, and product development.

MATERIALS AND METHODS

A comprehensive search of PubMed, Google Scholar, Web of Science, Elsevier and CNKI databases was conducted using the keywords "Podocarpus", "traditional usage", "phytochemistry", "pharmacology", "nagilactone", etc. Related papers published among July 1964 to February 2023 were collected to summarize the research progress. All plant names were determined through the "The Plant List" (http://www.theplantlist.org/).

RESULTS

To date, 262 chemical constituents have been isolated and identified from 26 Podocarpus plants; among these, norditerpene bilactone is the main pharmacologically active component. Norditerpene bilactones are reported to have anti-cancer, anti-inflammatory, antioxidant, antibacterial, anti-tyrosinase, neuroprotective, anti-plasmodial, anti-mutagenic, and anti-atherosclerotic properties as well as other pharmacological activities, which support its traditional uses.

CONCLUSION

Extensive studies on phytochemistry and pharmacology of Podocarpus species lead to discovery of a series of hopeful leading compounds with unique chemical structure, especially the nor- and bis-norditerpenoid dilactones with four isoprene units. These compounds have been proved to possess various pharmacological activities. This review will provide a reference for further research and promote the idea of combining modern research with traditional medicinal applications of Podocarpus plants.

Natural Terpenoids as Neuroinflammatory Inhibitors in LPS-stimulated BV-2 Microglia

Neuroinflammation is a typical feature of many neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Microglia, the resident immune cells of the brain, readily become activated in response to an infection or an injury. Uncontrolled and overactivated microglia can release pro-inflammatory and cytotoxic factors and are the major culprits in neuroinflammation. Hence, research on novel neuroinflammatory inhibitors is of paramount importance for the treatment of neurodegenerative diseases. Bacterial lipopolysaccharide, widely used in the studies of brain inflammation, initiates several major cellular activities that critically contribute to the pathogenesis of neuroinflammation. This review will highlight the progress on terpenoids, an important and structurally diverse group of natural compounds, as neuroinflammatory inhibitors in lipopolysaccharidestimulated BV-2 microglial cells over the last 20 years.

Amentotaxins C-V, Structurally Diverse Diterpenoids from the Leaves and Twigs of the Vulnerable Conifer Amentotaxus argotaenia and Their Cytotoxic Effects

A phytochemical investigation of the MeOH extract of the leaves and twigs of Amentotaxus argotaenia, a relict vulnerable coniferous species endemic to China, led to the isolation and characterization of 35 diterpenoids/norditerpenoids. Twenty of these are new, including 11 ent-kaurane-type (amentotaxins C-M, 1-11, respectively), three icetexane-type [= 9(10→20)abeo-abietane-type (amentotaxins N-P, 12-14, respectively)], four ent-labdane-type (amentotaxins Q-T, 15-18, respectively), and two isopimarane-type [amentotaxins U (19) and V (20)] compounds. Their structures were elucidated on the basis of spectroscopic data, single-crystal X-ray diffraction, the modified Mosher's method, and electronic circular dichroism data analyses. Compounds 1-9 are rare 18-nor-ent-kaurane-type diterpenoids featuring a 4β,19-epoxy ring. All the isolates were evaluated for their cytotoxic effects against a small panel of cultured human cancer cell lines (HeLa, A-549, MDA-MB-231, SKOV3, Huh-7, and HCT-116), and some of them exhibited cytotoxicities with IC₅₀ values ranging from 1.5 to 10.0 μM.

Diterpenoids from the Root Bark of Pinus massoniana and Evaluation of Their Phosphodiesterase Type 4D Inhibitory Activity

Thirty-two diterpenoids were obtained from the root bark of Pinus massoniana, and, among them, five compounds (pinmassins A-E) were identified as undescribed analogues. Spectroscopic methods, X-ray single-crystal diffraction analysis, and ECD calculations were applied to establish the structure of the new isolates. Pinmassin D (4) and abieta-8,11,13,15-tetraen-18-oic acid (23) showed moderate phosphodiesterase type 4D (PDE4D) inhibitory effects with IC₅₀ values of 2.8 ± 0.18 and 3.3 ± 0.50 μM, respectively, and their binding modes were investigated by a molecular docking study.

Phytochemical and biological studies on rare and endangered plants endemic to China. Part XV. Structurally diverse diterpenoids and sesquiterpenoids from the vulnerable conifer Pseudotsuga sinensis

An extensive phytochemical investigation on the chemical constituents from the needles and twigs of the vulnerable conifer Pseudotsuga sinensis yielded 19 diterpenoids and 21 sesquiterpenoids with various carbocyclic skeletons. Among them, 13 (named pseudosinins A-M, resp.) were undescribed compounds. Their structures with absolute configurations were characterized by a combination of spectroscopic methods, calculated and experimental electronic circular dichroism (ECD) data, quantum chemical calculations of the chemical shifts, and single crystal X-ray diffraction analyses. In particular, an array of labdane-derived norditerpenoids with C₁₉-, C₁₈-, and C₁₆-skeletons, and related drimane-type sesquitepenoids with C₁₅- and C₁₃-skeletons were found in the title plant. The possible biogenetic relationships of these degraded terpenoids were briefly discussed. Among the isolates, pseudosinin D, cis-communic acid, and 4β,15-dihydroxy-19-norabieta-8,11,13-trien-7-one showed moderate inhibitory activities against the enzyme ATP-citrate lyase (ACL), a potential drug target for the treatment of hyperlipidemia and hypercholesterolemia.

Structurally Diverse Sesquiterpenoids from the Endangered Ornamental Plant Michelia shiluensis

A preliminary phytochemical investigation on the MeOH extract of the leaves and twigs of the endangered ornamental plant Michelia shiluensis led to the isolation of 16 sesquiterpenoids. The isolated compounds comprised germacrane- (1-4, 13, 14), guaiane- (5-9, 15), amorphane- (10), and eudesmane-type (11, 12, 16) sesquiterpenoids. The new structures (1-12) were elucidated by spectroscopic and computational methods, and their absolute configurations (except for 9) were assigned by single-crystal X-ray diffraction crystallographic data and/or electronic circular dichroism spectra. Shiluolides (A-D, 1-4) are unprecedented C₁₆ or C₁₇ homogermacranolides, and their putative biosynthetic pathways are briefly discussed. Shiluone D (8) is a rare 1,10- seco-guaiane sesquiterpenoid featuring a new ether-containing spirocyclic ring, whereas shiluone E (9) represents the first example of a 1,5-4,5-di- seco-guaiane with a rare 5,11 -lactone moiety. Shiluone F (10) is the first amorphane-type sesquiterpenoid possessing an oxetane ring bridging C-1 and C-7. Bioassay evaluations indicated that lipiferolide (13) showed noteworthy cytotoxicities toward human cancer cell lines MCF-7 and A-549, with IC₅₀ values of 1.5 and 7.3 μM, respectively. Shiluone D (8) exerted inhibition against protein tyrosine phosphatase 1B (IC₅₀: 46.3 μM).

LC-MS guided isolation of sinodamines A and B: Chimonanthine-type alkaloids from the endangered ornamental plant Sinocalycanthus chinensis

Two previously undescribed chimonanthine-type [sinodamines A and B] and five related known dimeric tryptamine-derived alkaloids were isolated and characterized from the leaves of the endangered ornamental plant Sinocalycanthus chinensis under the guidance of LC-MS detection and dereplication analyses, along with conventional isolation procedures. Their structures were established on the basis of spectroscopic methods and chemical transformations. Sinodamine A can be regarded as the naturally occurring N-oxide derivative of its pseudo-mesomer sinodamine B. An acid-catalyzed Meisenheimer rearrangement from sinodamine A to its oxazine-form with a final equilibrium of 1:2 was observed by monitoring their NMR spectra. (-)-Folicanthine showed significant cytotoxicity against human lung carcinoma A549 and colorectal carcinoma HT29 cells, with IC₅₀ values of 7.76 and 6.16 μM, respectively.

A new 12,17-cyclo-labdane diterpenoid from the twigs of Dacrycarpus imbricatus

A new 12,17-cyclo-labdane diterpenoid, podoimbricatin C (1), along with 15 known compounds was isolated from the twigs of Dacrycarpus imbricatus. Their structures were elucidated by means of extensive spectroscopic analysis. Compound 1 is the second example of the unusual 12,17-cyclo-labdane diterpenoids. It showed no inhibitory effects against five human tumour lines (HL-60, SMMC-7721, A-549, MCF-7 and SW-480).