Bioactive cembrane-type diterpenoids from the gum-resin of Boswellia carterii

Characteristic cembrane-type diterpenoids with nitric oxide inhibitory activity from the gum resin of Boswellia carterii Birdw

Five new characteristic cembrane-type diterpenoids (olibacartiols A-E, 1-5) were acquired from the gum resin of Boswellia carterii. The structures of these diterpenoids were characterized by detailed spectroscopic analysis, and compounds 1-3 were unambiguously confirmed by single-crystal X-ray diffraction experiments. The anti-inflammatory activities of the isolated compounds were evaluated using LPS-induced BV2 cell model and compounds 2-5 showed moderate NO inhibitory effects with IC50 values of 8.84 ± 1.02, 9.82 ± 1.95, 9.75 ± 2.24, and 7.39 ± 1.24 μM, respectively.

Medicinal plant resin natural products: structural diversity and biological activities

Covering: up to the mid of 2023Plants secrete defense resins rich in small-molecule natural products under abiotic and biotic stresses. This comprehensive review encompasses the literature published up to mid-2023 on medicinal plant resin natural products from six main contributor genera, featuring 275 citations that refer to 1115 structurally diverse compounds. The scope of this review extends to include essential information such as the racemic nature of metabolites found in different species of plant resins, source of resins, and revised structures. Additionally, we carefully analyze the reported biological activities of resins, organizing them based on the their structures. The findings offer important insights into the relationship between their structure and activity. Furthermore, this detailed examination can be valuable for researchers and scientists in the field of medicinal plant resin natural products and will promote continued exploration and progress in this area.

Boswellianols A-I, Structurally Diverse Diterpenoids from the Oleo-Gum Resin of Boswellia carterii and Their TGF-β Inhibition Activity

Olibanum, a golden oleo-gum resin from species in the Boswellia genus (Burseraceae family), is a famous traditional herbal medicine widely used around the world. Previous phytochemical studies mainly focused on the non-polar fractions of olibanum. In this study, nine novel diterpenoids, boswellianols A-I (1-9), and three known compounds were isolated from the polar methanolic fraction of the oleo-gum resin of Boswellia carterii. Their structures were determined through comprehensive spectroscopic analysis as well as experimental and calculated electronic circular dichroism (ECD) data comparison. Compound 1 is a novel diterpenoid possessing an undescribed prenylmaaliane-type skeleton with a 6/6/3 tricyclic system. Compounds 2-4 were unusual prenylaromadendrane-type diterpenoids, and compounds 5-9 were new highly oxidized cembrane-type diterpenoids. Compounds 1 and 5 showed significant transforming growth factor β (TGF-β) inhibitory activity via inhibiting the TGF-β-induced phosphorylation of Smad3 and the expression of fibronectin and N-cadherin (the biomarker of the epithelial-mesenchymal transition) in a dose-dependent manner in LX-2 human hepatic stellate cells, indicating that compounds 1 and 5 should be potential anti-fibrosis agents. These findings give a new insight into the chemical constituents of the polar fraction of olibanum and their inhibitory activities on the TGF-β/Smad signaling pathway.

Cembrane diterpenoids: Chemistry and pharmacological activities

Cembrane diterpenoids (cembranoids), characterized by a 14-membered carbon ring and wide variety of functional groups, found in marine and terrestrial organisms. Many studies have shown that cembrane diterpenoids have cytotoxic and anti-inflammatory activities and are widely used in the development of new drugs. This review covered publications from 2011 to 2022 and classified the cembrane-type diterpenoids into isopropyl (ene) type, γ-lactone or unsaturated five-membered ring, δ-lactone or unsaturated six-membered ring, ε-lactone or unsaturated seven-membered ring, and other cembrane diterpenes. In addition, the biological activity and structure-activity relationship were summarized. This will provide guidance for new cembrane-type diterpenes as lead compounds to explore their potential application for treating cancer and inflammatory diseases.

In Vitro and In Silico Evaluations of Boswellia carterii Resin Dermocosmetic Activities

Boswellia carterii is a plant species belonging to the Burseraceae family. It grows up in trees or shrubs, and it is known for producing an aromatic resin commonly named frankincense or olibanum. This resin has been used in traditional medicine to treat various conditions such as inflammations, gastrointestinal disorders and traumatic injuries. Virtual screening and molecular docking are two in silico approaches used to predict potential interactions between ligands and the active site of a protein. These approaches are mainly used in natural product chemistry and pharmacology as a screening tool to select plant extracts or fractions for in vitro testing, as well as for the prediction of mechanisms of action. The aim of this research is the in silico and in vitro evaluations of the potential collagenase and elastase inhibitory activities of Boswellia carterii resin organic extracts (viz., methanol, n-hexane and ethyl acetate). The obtained results revealed that methanol and n-hexane exhibited the best collagenase inhibitory activity with values superior to 85%, whereas the methanol and ethyl acetate showed the highest elastase inhibition activity with inhibition values ranging between 40 and 60%. The molecular docking prediction confirmed the experimental results; moreover, the visualization of the ligand–protein interactions showed that the main compounds of the organic extracts may have mechanisms of action similar to the positive controls. Those findings are very promising and open new perspectives for the exploitation of Boswellia carterii resin as active agents for the development of anti-aging cosmeceuticals.

Frankincense diterpenes as a bio-source for drug discovery

INTRODUCTION

Frankincense (Boswellia sp.) gum resins have been employed as an incense in cultural and religious ceremonies for many years. Frankincense resin has over the years been employed to treat depression, inflammation, and cancer in traditional medicines.

AREAS COVERED

This inclusive review focuses on the significance of frankincense diterpenoids, and in particular, incensole derivatives for establishment future treatments of depression, neurological disorders, and cancer. The authors survey the available literature and furnish an overview of future perspectives of these intriguing molecules.

EXPERT OPINION

Numerous diterpenoids including cembrane, prenylaromadendrane, and the verticillane-type have been isolated from various Boswellia resins. Cembrane-type diterpenoids occupy a crucial position in pharmaceutical chemistry and related industries because of their intriguing biological and encouraging pharmacological potentials. Several cembranes have been reported to possess anti-Alzheimer, anti-inflammatory, hepatoprotective, and antimalarial effects along with a good possibility to treat anxiety and depression. Although some slight drawbacks of these compounds have been noted, including the selectivity of these diterpenoids, there is a great need to address these in future research endeavors. Moreover, it is vitally important for medicinal chemists to prepare libraries of incensole-heterocyclic analogs as well as hybrid compounds between incensole or its acetate and anti-depressant or anti-inflammatory drugs.

Review of the Chemical Composition, Pharmacological Effects, Pharmacokinetics, and Quality Control of Boswellia carterii

OBJECTIVE

This review aimed to systematically summarize studies that investigated the bioactivities of compounds and extracts from Boswellia.

METHODS

A literature review on the pharmacological properties and phytochemicals of B. carterii was performed. The information was retrieved from secondary databases such as PubMed, Chemical Abstracts Services (SciFinder), Google Scholar, and ScienceDirect.

RESULTS

The various Boswellia extracts and compounds demonstrated pharmacological properties, such as anti-inflammatory, antitumour, and antioxidant activities. B. carterii exhibited a positive effect on the treatment and prevention of many ageing diseases, such as diabetes, cancer, cardiovascular disease, and neurodegenerative diseases.

CONCLUSION

Here, we highlight the pharmacological properties and phytochemicals of B. carterii and propose further evidence-based research on plant-derived remedies and compounds.

Populusene A, an Anti-inflammatory Diterpenoid with a Bicyclo[8,4,1]pentadecane Scaffold from Populus euphratica Resins

Populusene A (1), an unprecedented carbon skeleton featuring a bicyclo[8.4.1]pentadecane nucleus and a bridgehead double bond (anti-Bredt system), and populusin A (2), a cembrane-type diterpenoid possessing an uncommon dioxatricyclo[6.6.1.1^2,5]hexadecane scaffold, were isolated from the exudates of Populus euphratica. Their structures were elucidated by spectroscopic, computational, and crystallographic methods. A plausible biosynthetic route for 1 and 2 was proposed. Compounds 1 and 2 were found to significantly inhibit the production of TNF-α and IL-6 and the expression of iNOS, COX-2, and p-NF-κB at 125 nM in RAW264.7 cells.

Cembranoids from Boswellia species

Frankincense of Boswellia species has long been used in traditional medicines, mainly for its interesting anti-inflammatory and anti-depressant properties of its di- and triterpenes. Boswellic acids (triterpenes) and cembranoids (diterpenes) are the major constituents of frankincense from all reported species which are responsible for the overall biological activity of frankincense. Boswellic acids have been thoroughly investigated for decades but cembranoids have attracted considerable attention only recently, and a good number of publications have highlighted the important role of these 14-membered rings in contributing to the superior anti-inflammatory activity of the sacred resin. Partial and total syntheses of some cembranoids from frankincense have been reported. Their therapeutic potential is not limited to the well proven anti-inflammatory activity but also to their recently reported anti-depressant properties. There is a considerable number of publications in the field of cembranoids of Boswellia species where we feel a review in this topic will be of interest to the readership of Phytochemistry. In this article we have discussed the chemistry (isolation and chemical structures as well as synthetic studies), biogenesis and bioactivity of the reported cembranoids of Boswellia species. The structural discrepancies due to wrongly assigned structures of some cembranoids have been highlighted and corrected. We have covered the related literature up to the end of 2020.

Inhibition of SARS-CoV-2 reproduction using Boswellia carterii: A theoretical study

This study investigated the possibility of inhibition of the SARS-CoV-2 virus using the compounds alpha-Boswellic acid (ABA) and beta-Boswellic acid (BBA) which are active components in the well-known natural product Boswellia carterii (BC). The SARS-CoV-2 virus reproduces in the body by linking its spike with the cell receptor. At the same time, a pH range (4.5-6) of the cell's lysosomes is considered as a perfect environment to release RNA in the cell cytoplasm. In view of these, docking studies were employed to study the interaction between the spikes of the virus and ABA or BBA using Molecular Graphic Laboratory (MGL) tools and AutoDock Vina application. The binding of the ABA and BBA with the spike of the virus could inhibit its reproduction or provide sufficient time for the immune system to recognize the virus and hence, produce suitable antibodies. In addition, the pKa of ABA, BBA and hydroxychloroquine (HCQ) were calculated using HF/6-311G (d,p) method and then they were compared with the experimental pKa of HCQ. The Lethal Concentrations (LC50) of ABA and BBA were also calculated. In addition, molecular electrostatic potential is reported which indicates the active sites of ABA and BBA.

Prenylaromadendrane-type diterpenoids from the gum resin of Boswellia sacra flueck and their cytotoxic effects

Two new prenylaromadendrane-type diterpenoids, and three known analogues, were isolated from the ethanol extract of the gum resin of B. sacra Flueck. The structures of the new compounds were elucidated using 1 D and 2 D NMR spectroscopic analyses, mass spectrometric data, circular dichroism spectra, and comparison with the other compounds in the literature. One diterpenoid represents the first example of an acetoxyl-substituted prenylaromadendranoid in frankincense. All compounds exhibited notable cytotoxicity against human malignant glioma (U87-MG) cell line, with inhibitory rates exceeding that of the positive control 5-fluorouracil. However, nitric oxide inhibition induced by lipopolysaccarides was not observed in primary mouse peritoneal macrophages.

Sacraoxides A-G, Bioactive Cembranoids from Gum Resin of Boswellia sacra

Seven undescribed cembranoids, sacraoxides A–G (1, 3–8) were isolated from the gum resin of Boswellia sacra. Their structures were elucidated by extensive physicochemical and spectroscopic analysis, as well as ECD calculation, modified Mosher’s method and X-ray diffraction crystallography. Compounds 6 and 7 exhibited inhibitory activities on nitric oxide (NO) production induced by lipopolysaccharide in RAW264.7 cells with IC₅₀ values of 24.9 ± 1.7 and 36.4 ± 2.9 μM.

Ten undescribed cembrane-type diterpenoids from the gum resin of Boswellia sacra and their biological activities

Ten undescribed cembrane-type diterpenes boscartins AL-AU, as well as five known analogues were isolated from Boswellia sacra Flueck. The relative configurations of these boscartins were established by extensive spectroscopic analysis of NMR spectra, IR and MS. The absolute configurations of boscartin AL, boscartin AN and isoincensole oxide were unequivocally assigned by single crystal X-ray diffraction. Meanwhile, the absolute configurations of boscartin AM, boscartin AP and boscartin AQ were determined by an empirical in situ formed Rh-complex ECD method. Biological evaluations showed that four compounds exhibited obvious hepatoprotective activities against paracetamol-induced HepG2 cell damage at 10 μM. Regarding neuroprotective activity, some isolates displayed moderate to evident protective effects against glutamate-induced toxicity in primary cultured fetal rat cortical neurons or oxygen-glucose deprivation toxicity in SK-N-SH Cells at 10 μM.

Bioactive cembrane diterpenoids from the gum resin of Boswellia carterii

Eight new cembrane-type diterpenoids, boscartins AP-AW (1-8) were obtained from the gum resin of Boswellia carterii. Among which, six ones (2-7) were isomers, with one hydroxy group and two double bonds migrating along the carbocycle. The structures were elucidated by spectroscopic examination. All isolates were evaluated for anti-inflammatory activity and hepatoprotective activity by cell models of LPS-induced RAW 264.7 mouse peritoneal macrophages and APAP-induced HepG2 cells, respectively. As for anti-inflammatory activity assay, compound 1 exhibited potent activity against NO production (IC₅₀ of 13.1 μM), with the other ones exhibiting weak anti-inflammatory activity (IC₅₀ > 50 μM). As for hepatoprotective activity assay, compound 1 exhibited more significant activity (inhibition rate of 30.7%) than that of the positive control (bicyclol, inhibition rate of 27.2%), and compounds 4, and 6 showed nearly the same activities as the control (inhibition rates of 26.7% and 25.9%, respectively), with the other ones exhibiting weak hepatoprotective activity.

Cembrane-type diterpenoids from the gum resin of Boswellia carterii and their biological activities

Cembrane-type diterpenoids from the gum resin of Boswellia carterii.