Triphenylphosphonium Analogues of Betulin and Betulinic Acid with Biological Activity: A Comprehensive Review

Chemopreventive and Chemotherapeutic Potential of Betulin and Betulinic Acid: Mechanistic Insights From In Vitro, In Vivo and Clinical Studies

Betulin is a bioactive compound found in large quantities in birch bark and has a triterpene pentacyclic structure. Through the oxidation of betulin, betulinic acid is obtained, which is found in large quantities in nature. Betulin and betulinic acid have multiple pharmacological properties such as antiviral, anti-inflammatory, and anticancer properties. This comprehensive review aims to deepen the knowledge of the chemopreventive and chemotherapeutic effects of betulin and betulinic acid by presenting in vitro, in vivo, and clinical studies evaluating the anticancer mechanisms of betulin, betulinic acid, and their derivatives. The databases searched using specific MESh terms to conduct this review were PubMed/MEDLINE, Web of Science, TRIP database, Wiley, and Scopus. The anticancer properties of betulin and betulinic acid have been reported in a variety of experimental pharmacological studies using different types of cancer cell lines. It has been indicated that induction of apoptosis is the primary anticancer activity of these compounds by selectively affecting cancer cells. As shown by various research, the apoptotic cell death by these compounds is mainly related to factors such as type of cancer and cancer cell line, tumor size, source of betulin/betulinic acid, dose, treatment time, and the type of the drug delivery system employed. Numerous preclinical pharmacological studies and clinical trials on the chemopreventive and antitumour effects of betulin, betulinic acid, and their derivatives have been published. Future translational pharmacological studies establishing the exact anticancer dose effective in humans are needed.

Exploring Phytochemical Profile and Biological Activities of Callistemon viminalis (Sol. ex Gaertn.) G.Don ex Loudon) By In vitro and In silico Approaches

Callistemon viminalis (Sol. ex Gaertn.) G.Don ex Loudon) (family: Myrtaceae) is used for its medicinal properties in treating various metabolic disorders. We investigated the chemical characterization and biological screening of the n-hexane extract of C. viminalis. The total phenolic content was (37.45±7.40 mg GA.E/g D.E±S.D) and the total flavonoid content was (18.43±6.34 mg R.E/g D.E±S.D). GC-MS screening of the n-hexane extract tentatively identified 70 bioactive phytochemicals. The maximum antioxidant potential (289.99±9.01 mg T.E/g D.E±S.D) was observed via the FRAP assay. Enzyme inhibition assays revealed that n-hexane extract of C. viminalis showed enzyme inhibition against the enzymes including α-glucosidase (6.9±0.13 mmol of ACA.E/g D.E±S.D); α-amylase (7.2±0.56 mmol of ACA.E/g D.E±S.D), urease (4.95±0.9 mg of TU.E/g D.E±S.D), acetylcholinesterase (2.9±0.08 mg GALA.E/g D.E±S.D), lipoxygenase (4.93±1.05 mg of Indo.E/g D.E±S.D) and tyrosinase (4.33±0.62 mg of KA.E/g D.E±S.D). The extract showed maximum antibacterial activity against Staphylococcus aureus (71.30±4.44 %) followed by Bacillus subtilis (68.55±2.70 %), Pseudomonas aeruginosa (57.86±6.02 %), and Salmonella typhi (53.90±5.05 %). Docking studies revealed good docking interactions between ligands and the studied enzymes, whereas ADME analysis revealed the pharmacokinetic profiles of the phytoconstituents. C. viminalis possesses promising therapeutic potential and can be further explored for drug development and drug design.

Boswellic Acid and Betulinic Acid Pre-treatments Can Prevent the Nephrotoxicity Caused by Cyclophosphamide Induction

Cyclophosphamide (CYP) is a chemotherapeutic drug used to treat various cancers. However, its clinical use is limited due to severe organ damage, particularly to the kidneys. While several phytochemicals have been identified as potential therapeutic targets for CYP nephrotoxicity, the nephroprotective effects of boswellic acid (BOSW) and betulinic acid (BET) have not yet been investigated. Our study used 42 rats divided into six equal groups. The study included six groups: control, CYP (200 mg/kg), CYP+BOSW20 (20 mg/kg), CYP+BOSW40 (40 mg/kg), CYP+BET20 (20 mg/kg), and CYP+BET40 (40 mg/kg). The pre-treatments with BOSW and BET lasted for 14 days, while the application of cyclophosphamide was performed intraperitoneally only on the 4th day of the study. After the experimental protocol, the animals were sacrificed, and their kidney tissues were isolated. Renal function parameters, histological examination, oxidative stress, and inflammation parameters were assessed both biochemically and at the molecular level in kidney tissue. The results showed that oxidative stress and inflammatory response were increased in the kidney tissue of rats treated with CYP, leading to impaired renal histology and function parameters (p < 0.05). Oral administration of both doses of BET and especially high doses of BOSW improved biochemical, oxidative, and inflammatory parameters significantly (p < 0.05). Histological studies also showed the restoration of normal kidney tissue architecture. BOSW and BET have promising biological activity against CYP-induced nephrotoxicity by attenuating inflammation and oxidative stress and enhancing antioxidant status.

Drug Delivery Systems of Betulin and Its Derivatives: An Overview

Natural origin products are regarded as promising for the development of new therapeutic therapies with improved effectiveness, biocompatibility, reduced side effects, and low cost of production. Betulin (BE) is very promising due to its wide range of pharmacological activities, including its anticancer, antioxidant, and antimicrobial properties. However, despite advancements in the use of triterpenes for clinical purposes, there are still some obstacles that hinder their full potential, such as their hydrophobicity, low solubility, and poor bioavailability. To address these concerns, new BE derivatives have been synthesized. Moreover, drug delivery systems have emerged as a promising solution to overcome the barriers faced in the clinical application of natural products. The aim of this manuscript is to summarize the recent achievements in the field of delivery systems of BE and its derivatives. This review also presents the BE derivatives mostly considered for medical applications. The electronic databases of scientific publications were searched for the most interesting achievements in the last ten years. Thus far, it is mostly nanoparticles (NPs) that have been considered for the delivery of betulin and its derivatives, including organic NPs (e.g., micelles, conjugates, liposomes, cyclodextrins, protein NPs), inorganic NPs (carbon nanotubes, gold NPs, silver), and complex/hybrid and miscellaneous nanoparticulate systems. However, there are also examples of microparticles, gel-based systems, suspensions, emulsions, and scaffolds, which seem promising for the delivery of BE and its derivatives.

Betulinic Acid Potentiates Mast Cell Degranulation by Compromising Cell Membrane Integrity and Without Involving Fcεri Receptors

Mast cells play important role in acquired and natural immunity making these favorable therapeutic targets in various inflammatory diseases. Here we observed that, pentacyclic tri terpenoid betulinic acid (BA) treatment resulted in a significantly high number (9%) of cells positive for Hoechst and negative for annexin-V indicating that BA could interfere with plasma membrane integrity. The degranulation of both activated and non-activated mast cells was enhanced upon treatment with BA. The pre-treatment of BA had remarkable effect on calcium response in activated mast cells which showed increased calcium influx relative compared to untreated cells. The results also showed potentially less migration of BA treated mast cells signifying the possible effect of BA on cell membrane. BA treatment resulted in a significant increase in mRNA levels of IL-13 while as mRNA levels of other target cytokines, IL-6 and TNF-α seem to be not affected. Moreover, there was global Increase in phosphorylation of signaling proteins and no significant change in phosphorylation of FcεRI receptors indicating that the effect of BA was independent of signaling cascade or FcεRI receptor mediated mast cell aggregation. Overall, these results portray BA potentiates mast cell effector functions by compromising the membrane integrity and independent of FcεRI involvement.

Self-constructed water-in-oil Pickering emulsions as a tool for increasing bioaccessibility of betulin

Self-constructed water-in-oil emulsions can be stabilized by a natural pentacyclic triterpenoid, betulin. A higher betulin concentration (3%) results in smaller emulsion droplet sizes. Microscopy, confocal laser scanning microscopy and rheology indicate that the stabilizing mechanism is attributed to betulin crystals on the emulsion interface and within the continuous phase, thereby enabling excellent freeze/thaw and thermal stability. The betulin Pickering emulsion (1%) significantly increased betulin bioaccessibility (22.4%) compared to betulin alone (0.2%) and betulin-oil physical mixture (7.9%). A higher level of betulin at 3% leads to smaller emulsion particle size, potentially resulting in a greater surface area. This, in return, promotes a higher release of free fatty acids (FFA), contributing to the release and solubilization of betulin from emulsions. Additionally, it leads to the formation of micelles, further increasing betulin bioaccessibility (29.3%). This study demonstrates Pickering emulsions solely stabilized by phytochemical betulin provides an innovative way to improve its bioaccessibility.

Neuroprotective properties of Betulin, Betulinic acid, and Ursolic acid as triterpenoids derivatives: a comprehensive review of mechanistic studies

Cognitive deficits are the main outcome of neurological disorders whose occurrence has risen over the past three decades. Although there are some pharmacologic approaches approved for managing neurological disorders, it remains largely ineffective. Hence, exploring novel nature-based nutraceuticals is a pressing need to alleviate the results of neurodegenerative diseases, such as Alzheimer's disease (AD) and other neurodegenerative disorders. Some triterpenoids and their derivates can be considered potential therapeutics against neurological disorders due to their neuroprotective and cognitive-improving effects. Betulin (B), betulinic acid (BA), and ursolic acid (UA) are pentacyclic triterpenoid compounds with a variety of biological activities, including antioxidative, neuroprotective and anti-inflammatory properties. This review focuses on the therapeutic efficacy and probable molecular mechanisms of triterpenoids in damage prevention to neurons and restoring cognition in neurodegenerative diseases. Considering few studies on this concept, the precise mechanisms that mediate the effect of these compounds in neurodegenerative disorders have remained unknown. The findings can provide sufficient information about the advantages of these compounds against neurodegenerative diseases.

Synthesis of Hydrazide Derivative of Betulinic Acid, Its Organometallic Complexes, Characterization and Bioassay

Betulinic acid and its derivatives comprehend an immense prospective toward the development of cytotoxic, antiviral, antimicrobial and antioxidant agents. Cisplatin (cytotoxic drug) divert the attentions to develop organometallic compounds with pronounced biological activities. The current study was aimed for the first time to synthesize, characterize and evaluate biologically a series of metal (Fe, Cu, Zn, Sn and Sb) complexes of betulinic acid hydrazide. First step involved the formation of hydrazide derivative of betulinic acid (ligand) by modification at C-28 carboxylic acid moiety of betulinic acid with hydrazine followed by the synthesis of its metal complexes using salts of different metals (Fe, Cu, Zn, Sn and Sb). Physical state, melting point, Fourier-transform infrared (FT-IR) and 1 H nuclear magnetic resonance (1 H-NMR) spectral techniques were used to characterized the ligand and its metal complexes. Agar well diffusion method and agar tube dilution assay were performed to evaluate its antibacterial and antifungal activities respectively. DPPH assay was carried out to develop antioxidant properties by the reported methods.

Synthesis and in vitro evaluation of antibacterial and antibiofilm activities of novel triphenylphosphonium-functionalized substituted pyrimidines

The increase in the prevalence of antibiotic-resistant pathogens leads to a decrease in the number of antimicrobial agents for the treatment of infections and prompts researchers to search for new effective antimicrobial drugs. This study reports the synthesis of novel triphenylphosphonium-functionalized substituted pyrimidines and in vitro evaluation of their antibacterial and antibiofilm activity. Most of the synthesized derivatives showed high antibacterial activity (MIC = 0.39-1.56 μg/mL) against the methicillin-resistant strain of S. aureus 222. Compounds 2a and 11 exhibited a high level of antibiofilm activity against S. aureus 222 and E. coli 311. The triphenylphosphonium-containing pyrimidines 11 and 2a reduced S. aureus 222 biofilm formation by 99.1% and 95.8%, respectively. In addition, compound 2a was the most active against E. coli 311 biofilm formation (the biomass decreased by 98.4%).

Synthesis of methotrexate-betulonic acid hybrids and evaluation of their effect on artificial and Caco-2 cell membranes

An efficient protocol for the synthesis of novel methotrexate-betulonic acid hybrids with a (tert-butoxycarbonylamino)-3,6-dioxa-8-octanamine (Boc-DOOA) linkage has been developed. Reaction of N-(2-(2-(2-aminoethoxy)ethoxy)ethyl)-betulonamide with methotrexate resulted in a mixture of isomeric conjugates which were separated by column chromatography. Their structures and composition have been fully established by 1H NMR, 13C spectra, FAB mass spectrometry and elemental analysis. The identity of conjugates was confirmed by LC-MS data. Membranotropic properties of the new hybrids were assessed on the basis of their interactions with artificial lipid membranes by differential scanning calorimetry (DSC) method. The ability of the conjugates to penetrate Caco-2 cells is inferior to methotrexate. Probably, this is due to the increasing lipophilicity, the affinity of these hybrid molecules for the lipid bilayer increases, which is confirmed by experiments with artificial membranes.

Enhanced Cytotoxicity and Antimelanoma Activity of Novel Semisynthetic Derivatives of Betulinic Acid with Indole Conjugation

The prevalence and severity of skin cancer, specifically malignant melanoma, among Caucasians remains a significant concern. Natural compounds from plants have long been explored as potential anticancer agents. Betulinic acid (BI) has shown promise in its therapeutic properties, including its anticancer effects. However, its limited bioavailability has hindered its medicinal applications. To address this issue, two recently synthesized semisynthetic derivatives, N-(2,3-indolo-betulinoyl)diglycylglycine (BA1) and N-(2,3-indolo-betulinoyl)glycylglycine (BA2), were compared with previously reported compounds N-(2,3-indolo-betulinoyl)glycine (BA3), 2,3-indolo-betulinic acid (BA4), and BI. These compounds were evaluated for their effects on murine melanoma cells (B164A5) using various in vitro assays. The introduction of an indole framework at the C2 position of BI resulted in an increased cytotoxicity. Furthermore, the cytotoxicity of compound BA4 was enhanced by conjugating its carboxylic group with an amino acid residue. BA2 and BA3, with glycine and glycylglycine residues at C28, exhibited approximately 2.20-fold higher inhibitory activity compared to BA4. The safety assessment of the compounds on human keratinocytes (HaCaT) has revealed that concentrations up to 10 µM slightly reduced cell viability, while concentrations of 75 µM resulted in lower cell viability rates. LDH leakage assays confirmed cell membrane damage in B164A5 cells when exposed to the tested compounds. BA2 and BA3 exhibited the highest LDH release, indicating their strong cytotoxicity. The NR assay revealed dose-dependent lysosome disruption for BI and 2,3-indolo-betulinic acid derivatives, with BA1, BA2, and BA3 showing the most cytotoxic effects. Scratch assays demonstrated concentration-dependent inhibition of cell migration, with BA2 and BA3 being the most effective. Hoechst 3342 staining revealed that BA2 induced apoptosis, while BA3 induced necrosis at lower concentrations, confirming their anti-melanoma properties. In conclusion, the semisynthetic derivatives of BI, particularly BA2 and BA3, show promise as potential candidates for further research in developing effective anti-cancer therapies.

Betulinic acid in the treatment of breast cancer: Application and mechanism progress

Betulinic acid (BA) is a pentacyclic triterpene compound, which can be obtained by separation, chemical synthesis and biotransformation. BA has excellent biological activities, especially its role in the treatment of breast cancer deserves attention. Its mechanisms mainly include inducing mitochondrial oxidative stress, regulating specific protein (Sp) transcription factors, inhibiting breast cancer metastasis, inhibiting glucose metabolism and NF-κB pathway. In addition, BA can also increase the sensitivity of breast cancer cells to other chemotherapy drugs such as paclitaxel and reduce its toxic side effects. This article reviews the application and possible mechanism of BA in the treatment of breast cancer.

A Novel Betulinic Acid Analogue: Synthesis, Solubility, Antitumor Activity and Pharmacokinetic Study in Rats

Betulinic acid (BA) and betulin (BE) are naturally pentacyclic triterpenes with documented biological activities, especially antitumor and anti-inflammatory activity. However, their bioavailability in vivo is not satisfactory in terms of medical applications. Thus, to improve the solubility and bioavailability so as to improve the efficacy, 28-O-succinyl betulin (SBE), a succinyl derivative of BE, was synthesized and its solubility, in vitro and in vivo anti-tumor activities, the apoptosis pathway as well as the pharmacokinetic properties were investigated. The results showed that SBE exhibited significantly higher solubility in most of the tested solvents, and showed a maximum solubility of 7.19 ± 0.66 g/L in n-butanol. In vitro and in vivo anti-tumor activity assays indicated both BA and SBE exhibited good anti-tumor activities, and SBE demonstrated better potential compared to BA. An increase in the ratio of Bad/Bcl-xL and activation of caspase 9 was found in SBE treated Hela cells, suggesting that the intrinsic mitochondrial pathway is involved in SBE induced apoptosis. Compared with BA, SBE showed much-improved absorption and bioavailability in pharmacokinetic studies.

Comparison of Bioactive Secondary Metabolites and Cytotoxicity of Extracts from Inonotus obliquus Isolates from Different Host Species

Inonotus obliquus, a wood-decaying mushroom, has been used as a health-promoting supplement and nutraceutical for centuries. It is a source of bioactive compounds accumulated in both the conks (pseudosclerotia/sclerotia) and the biomass obtained in vitro. This study aimed to qualitatively and quantitatively analyze the bioelements and selected metabolites produced in mycelial cultures obtained from different host species. The mycochemical potential of mycelial cultures isolated from pseudosclerotia grown in Betula pendula, Alnus glutinosa, and Carpinus betulus was compared. Parent cultures were obtained in two types of medium (malt extract agar substrates without and with birch wood). Experimental cultures were developed in 2 L bioreactors for 10 days. The content of bioelements was determined using FAAS and FAES methods. Organic compounds were estimated using the RP-HPLC-DAD method. The cytotoxicity of the extracts was evaluated in human keratinocytes HaCaT, human skin fibroblasts BJ, human liver cancer HepG2, human melanoma A375, and mouse melanoma B16-F10. The extracts showed the presence of bioelements: sodium, potassium, magnesium, calcium, zinc, manganese, iron, and copper; phenolic acids: p-hydroxybenzoic, caffeic, p-coumaric, and protocatechuic; sterols: lanosterol, ergosterol, ergosterol peroxide; triterpene compounds: betulin, betulinic acid, inotodiol; indole compounds: L-tryptophan, tryptamine, 5-methyltryptamine, melatonin. The content of bioactive substances in the biomass was dependent on both the origin of the host species of the fungus isolate and the type of culture medium. Based on the results of this study, mycelial cultures can be proposed as a potential source of bioactive compounds and are promising naturally derived cytotoxic agents.

Synthesis and Cytotoxicity Evaluation of Betulin Cycloolefin Derivatives by Ruthenium-Catalyzed Ring-Closing Metathesis

The combination of ring-closing metathesis with betulin enables the design and synthesis of novel biomolecules representing a library of triterpenoid derivatives for potential pharmacological research. In this work, cyclic olefin betulin derivatives were attempted to be prepared by the combination of ring-closing metathesis with betulin. Dicyclohexyl carbodiimide coupling reaction allowed the transformation of betulin into two types of linear olefin derivatives that have different methylene spacer lengths between the olefin and ester groups. Subsequently, betulin-based cycloolefins were synthesized by ring-closing metathesis using Grubbs first-generation catalyst. The influence of different parameters including solvents, temperature, catalysts, and catalyst loading on ring-closing metathesis was investigated. Cytotoxicity results indicated that these betulin-based olefin derivatives, derived from renewable bioresources, have potential applications in the biomedical field.

A Small Sugar Molecule with Huge Potential in Targeted Cancer Therapy

The number of cancer-related diseases is still growing. Despite the availability of a large number of anticancer drugs, the ideal drug is still being sought that would be effective, selective, and overcome the effect of multidrug resistance. Therefore, researchers are still looking for ways to improve the properties of already-used chemotherapeutics. One of the possibilities is the development of targeted therapies. The use of prodrugs that release the bioactive substance only under the influence of factors characteristic of the tumor microenvironment makes it possible to deliver the drug precisely to the cancer cells. Obtaining such compounds is possible by coupling a therapeutic agent with a ligand targeting receptors, to which the attached ligand shows affinity and is overexpressed in cancer cells. Another way is to encapsulate the drug in a carrier that is stable in physiological conditions and sensitive to conditions of the tumor microenvironment. Such a carrier can be directed by attaching to it a ligand recognized by receptors typical of tumor cells. Sugars seem to be ideal ligands for obtaining prodrugs targeted at receptors overexpressed in cancer cells. They can also be ligands modifying polymers' drug carriers. Furthermore, polysaccharides can act as selective nanocarriers for numerous chemotherapeutics. The proof of this thesis is the huge number of papers devoted to their use for modification or targeted transport of anticancer compounds. In this work, selected examples of broad-defined sugars application for improving the properties of both already-used drugs and substances exhibiting anticancer activity are presented.

Synthesis of Novel Pentacyclic Triterpenoid Derivatives that Induce Apoptosis in Cancer Cells through a ROS-dependent, Mitochondrial-Mediated Pathway

Betulinic acid (BA) and oleanolic acid (OA) are plant-derived conjugates found in various medicinal plants that have emerged as potential antitumor agents. Herein, a series of novel BA and OA derivatives were synthesized by conjugation with per-O-methylated-β-cyclodextrin (PM-β-CD), and their anticancer properties against a panel of three human cancer cell lines were evaluated. Two OA-PM-β-CD conjugates (48 and 50) were observed to be the most potent conjugates against the three cell lines (MCF-7, BGC-823, and HL-60), with a 15- to 20-fold decrease in the IC₅₀ values (IC₅₀: 6.06-8.47 μM) compared with their parental conjugate (OA). Annexin V-FITC/propidium iodide staining and Western blot analysis revealed that both conjugates induced apoptosis in HL-60 cells. Additionally, in the representative conjugate 48-treated HL-60 cells, a decrease in mitochondrial membrane potential and subsequent release of cytochrome c into the cytosol were observed, indicating the activation of the intrinsic apoptosis pathway. Furthermore, 48 dramatically induced the generation of reactive oxygen species (ROS) in HL-60 cells, and the corresponding effect could be reversed using the ROS scavenger N-acetylcysteine. Collectively, these results suggest that the novel pentacyclic triterpenoid derivatives trigger the intrinsic apoptotic pathways via the ROS-mediated activation of caspase-3 signaling, inducing cell death in human cancer cells.

Inhibition of the NF-κB pathway and ERK-mediated mitochondrial apoptotic pathway takes part in the mitigative effect of betulinic acid on inflammation and oxidative stress in cyclophosphamide-triggered renal damage of mice

Betulinic acid (BA), an occurring pentacyclic triterpenoid, has various biological activities, such as anti-inflammation and antioxidation. Previous studies found that BA attenuated cyclophosphamide (CYP)-induced intestinal mucosal damage by inhibiting intestinal mucosal barrier dysfunctions and cell apoptosis. However, the effects and regulation mechanisms of BA on CYP-induced renal damage has not been reported in literature. Here, we found that BA pretreatment alleviated the elevation of serum urea level and inhibited the increase in serum neutrophil gelatinase-associated lipocalin level induced by CYP. Meanwhile, BA ameliorated renal tubular epithelial cell edema, and vacuolization of renal cortical tubular and renal glomerulus. Moreover, pretreatment with BA inhibited the mRNA expressions of pro-inflammatory cytokines interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α, and increased mRNA expressions of anti-inflammatory cytokines such as IL-10 and transforming growth factor-β by inactivation nuclear factor kappa-B. Simultaneously, BA decreased the accumulation of reactive oxygen species and malondialdehyde, and lowered the levels of superoxide dismutase and glutathione, while increased the activity of glutathione peroxidase in CYP-induced kidney damage mice. Besides, BA reduced the phosphorylation of extracellular signal-regulated kinases (ERK), inhibited the ratio of Bcl-2/Bax and cell apoptosis in CYP-triggered kidney damage. Furthermore, BA and/or PD98059 (an inhibitor of ERK) regulated mitigation of CYP-elicited renal injury and deactivation of the ERK pathway and mitochondrial apoptotic pathway, indicating that the protective effect of BA on CYP-induced renal damage may be associated with the down-regulation of ERK-mediated mitochondrial apoptotic pathway. Thus, BA could be a candidate agent against chemotherapy drug-induced nephrotoxicity by reducing inflammation and oxidative stress through suppression of ERK-mediated mitochondrial apoptotic pathway.

Design, Synthesis and Preliminary Evaluation of the Cytotoxicity and Antibacterial Activity of Novel Triphenylphosphonium Derivatives of Betulin

For several decades, natural products have been widely researched and their native scaffolds are the basis for the design and synthesis of new potential therapeutic agents. Betulin is an interesting biologically attractive natural parent molecule with a high safety profile and can easily undergo a variety of structural modifications. Herein, we describe the synthesis of new molecular hybrids of betulin via covalent linkage with an alkyltriphenylphosphonium moiety. The proposed strategy enables the preparation of semi-synthetic derivatives (28-TPP^&oplus; BN and 3,28-bisTPP^&oplus; BN) from betulin through simple transformations in high yields. The obtained results showed that the presence of a lipophilic cation improved the solubility of the tested analogs compared to betulin, and increased their cytotoxicity. Among the triphenylphosphonium derivatives tested, analogs 7a (IC₅₀ of 5.56 µM) and 7b (IC₅₀ of 5.77 µM) demonstrated the highest cytotoxicity against the colorectal carcinoma cell line (HCT 116). TPP^&oplus;-conjugates with betulin showed antimicrobial properties against Gram-positive reference Staphylococcus aureus ATCC 25923 and Staphylococcus epidermidis ATCC 12228 bacteria, at a 200 µM concentration in water. Hence, the conjugation of betulin's parent backbone with a triphenylphosphonium moiety promotes transport through the hydrophobic barriers of the mitochondrial membrane, making it a promising strategy to improve the bioavailability of natural substances.

The genus Alphitonia Reissek ex Endl. (Rhamnaceae): A review of its customary uses, phytochemistry and biological activities

ETHNOPHARMACOLOGICAL RELEVANCE

Alphitonia Reissek ex Endl. is a relatively small genus of the family Rhamnaceae. Plants of this genus are found predominantly in the tropical regions of Southeast Asia, Australia and the Pacific, with some species being widely distributed and others endemic to a region. Almost half of the species of the Alphitonia genus have been reported for their customary (traditional and contemporary) medicinal uses. This includes for the treatment of skin conditions, headache, stomachache, inflammation, and body pain such as joint pain and childbirth.

AIM OF THE REVIEW

The aim of this review is to provide the first comprehensive account on the customary uses including ethnomedicinal uses, and phytochemistry and biological activities of the Alphitonia genus, and to identify gaps in current knowledge and scope for future research of plants of this genus.

MATERIALS AND METHODS

Information relevant to the genus Alphitonia was collected by searching the scientific databases (SciFinder, Google Scholar, ACS publications, PubMed, Wiley Online Library and International Plant name Index). Species names were validated using the World Flora Online database (www.worldfloraonline.org).

RESULTS

Eight plants from the Alphitonia genus have been reported to be used as customary medicines, i.e. A. excelsa, A. ferruginea, A. franguloides, A. incana, A. neocaledonica, A. petriei, A. philippinensis and A. zizyphoides. A. excelsa, A. petriei, A. philippinensis and A. zizyphoides, have been shown to have biological activities that align with their customary uses, including antimicrobial, antioxidant and anti-inflammatory activities. Only five Alphitonia species reported for their medicinal customary uses have been explored for their phytochemistry, i.e. A. excelsa, A. neocaledonica, A. petriei, A. philippinensis and A. zizyphoides. Compounds identified from these plants include those that are well known for their medicinal importance. A. macrocarpa, A. whitei and A. xerocarpus have also been examined for their phytochemistry and have been found to have the same or similar bioactive compounds to those found in customarily used Alphitonia species. No biological activities or phytochemistry studies have been reported for the known customarily used medicinal plants A. ferruginea, A. franguloides and A. incana.

CONCLUSIONS

This review highlights the customary uses, biological activities and phytochemistry of plants of the Alphitonia Reissek ex Endl. genus and highlights the significance of the knowledge systems of Indigenous peoples. Of the plants that have been researched for their biological activities and phytochemistry, there is good correlation with these properties and their customary medicinal uses. However, over half of the plants of the Alphitonia genus, including those that are already reported in the public domain for their customary medicinal uses, have had none or limited biological activities or phytochemistry studies conducted. While only eight species of the Alphitonia genus have been reported as customary medicines, other Alphitonia species also possess medicinally important compounds, and it is possible that they are customary medicines but their uses have not been shared publicly by the Indigenous knowledge custodians. There is clearly much scope for further investigation of this genus with regards to their ethnomedicinal uses and therapeutic potential.

Minor terpenoids from the stems and twigs of Rhododendron ovatum

Four minor undescribed terpenoids, including a monoterpenoid (1) and three triterpenoids (3, 6 and 7), together with 26 known terpenoids were isolated from the stems and twigs of Rhododendron Ovatum. Their structures were identified by extensive spectroscopic analyses and electronic circular dichroism (ECD) techniques. Compound 10 showed excellent cytotoxicity against human colon cancer cell (HCT-116) with IC₅₀ value of 2.56 μM. Compounds 9 and 19 exhibited partly inhibitory effects on nitric oxide production stimulated by lipopolysaccharide-induced neuroinflammation in microglia cells at 10 μM with inhibition ratios of 39.70% and 28.08%, respectively.

Synthesis of 3-O-Acetyl-11-keto-β-boswellic Acid (AKBA)-Derived Amides and Their Mitochondria-Targeted Antitumor Activities

In this study, we synthesized a series of amide and mitochondria-targeted derivatives with 3-O-acetyl-11-keto-β-boswellic acid (AKBA) as the parent structure and an ethylenediamine moiety as the link chain. Compound 5e, a mitochondrial-targeting potential derivative, showed significantly stronger antitumor activity than that of AKBA, and it could induce vacuolization of A549 cells and stimulate the production of reactive oxygen species (ROS) in a time- and concentration-dependent manner. The antioxidant N-acetylcysteine (NAC) could inhibit the ROS level but could not suppress vacuolization and cell death induced by 5e. Further studies demonstrated that 5e caused abnormal opening of mitochondrial permeability transition pore (MPTP) and a decrease of mitochondrial membrane potential; additionally, it caused cell cycle arrest in G₀/G₁ but did not induce apoptosis. 5e represented a compound with improved antiproliferative effects for cancer therapy working through new mechanisms.

The Role of KLF2 in the Regulation of Atherosclerosis Development and Potential Use of KLF2-Targeted Therapy

Kruppel like factor 2 (KLF2) is a mechanosensitive transcription factor participating in the regulation of vascular endothelial cells metabolism. Activating KLF2 in endothelial cells induces eNOS (endothelial nitric oxide synthase) expression, subsequent NO (nitric oxide) release, and vasodilatory effect. In addition, many KLF2-regulated genes participate in the anti-thrombotic, antioxidant, and anti-inflammatory activities, thereby preventing atherosclerosis development and progression. In this review, we summarise recent evidence suggesting that KLF2 plays a major role in regulating atheroprotective effects in endothelial cells. We also discuss several recently identified repurposed drugs and natural plant-based bioactive compounds with KLF2-mediated atheroprotective activities. Herein, we present a comprehensive overview of the role of KLF2 in atherosclerosis and as a pharmacological target for different drugs and natural compounds and highlight the potential application of these phytochemicals for the treatment of atherosclerosis.

Mitochondria-Targeted Triphenylphosphonium Conjugated C-3 Modified Betulin: Synthesis, Antitumor Properties and Mechanism of Action

A series of mitochondria-targeted triphenylphosphonium conjugated C-3 modified betulin were synthesized and evaluated against tumor cells. As a result, a new derivative 13 i, the conjugate of 3-O-(3'-acetylphenylacetate)-betulin with triphenylphosphonium, was identified as the one with the best anti-tumor effect. Conjugate 13 i significantly inhibited HCT116 cells with IC₅₀ at 0.66 μM. While betulin, C-3 modified betulin, and the triphenylphosphonium moiety showed no inhibition of HCT116 cell proliferation at 20 μM. More importantly, 13 i exhibited a more cytotoxic effect against the tumor cell HCT116 than normal cell NCM460. Mode of action studies demonstrated that 13 i induced the G2/M phase cell cycle arrest and apoptosis in HCT116 cells through the mitochondrial pathway. Structure-activity relationship analysis revealed that integration of triphenylphosphonium moiety into the C-28 of betulin can greatly improve cytotoxicity. Appropriate modification on C-3 of the conjugate would improve the selectivity.

Betulin Targets Lipin1/2-Meidated P2X7 Receptor as a Therapeutic Approach to Attenuate Lipid Accumulation and Metaflammation

The present study focused on the potential mechanism of betulin (BT), a pentacyclic triterpenoid isolated from the bark of white birch (Betula pubescens), against chronic alcohol-induced lipid accumulation and metaflammation. AML-12 and RAW 264.7 cells were administered ethanol (EtOH), lipopolysaccharide (LPS) or BT. Male C57BL/6 mice were fed Lieber-DeCarli liquid diets containing 5% EtOH for 4 weeks, followed by single EtOH gavage on the last day and simultaneous treatment with BT (20 or 50 mg/kg) by oral gavage once per day. In vitro, MTT showed that 0-25 mM EtOH and 0-25 μM BT had no toxic effect on AML-12 cells. BT could regulate sterolregulatory-element-binding protein 1 (SREBP1), lipin1/2, P2X7 receptor (P2X7r) and NOD-like receptor family, pyrin domains-containing protein 3 (NLRP3) expressions again EtOH-stimulation. Oil Red O staining also indicated that BT significantly reduced lipid accumulation in EtOH-stimulated AML-12 cells. Lipin1/2 deficiency indicated that BT might mediate lipin1/2 to regulate SREBP1 and P2X7r expression and further alleviate lipid accumulation and inflammation. In vivo, BT significantly alleviated histopathological changes, reduced serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and triglyceride (TG) levels, and regulated lipin1/2, SREBP1, peroxisome proliferator activated receptor α/γ (PPARα/γ) and PGC-1α expression compared with the EtOH group. BT reduced the secretion of inflammatory factors and blocked the P2X7r-NLRP3 signaling pathway. Collectively, BT attenuated lipid accumulation and metaflammation by regulating the lipin1/2-mediated P2X7r signaling pathway.

Design and Synthesis of Novel Betulin Derivatives Containing Thio-/Semicarbazone Moieties as Apoptotic Inducers through Mitochindria-Related Pathways

Two new series of betulin derivatives with semicarbazone (7a-g) or thiosemicarbazone (8a-g) groups at the C-28 position were synthesized. All compounds were evaluated for their in vitro cytotoxicities in human hepatocellular carcinoma cells (HepG2), human breast carcinoma cells (MCF-7), human lung carcinoma cells (A549), human colorectal cells (HCT-116) and normal human gastric epithelial cells (GES-1). Among these compounds, 8f displayed the most potent cytotoxicity with an IC₅₀ value of 5.86 ± 0.61 μM against MCF-7 cells. Furthermore, the preliminary mechanism studies in MCF-7 cells showed that compound 8f could trigger the intracellular mitochondrial-mediated apoptosis pathway by losing MMP level, which was related with the upregulation of Bax, P53 and cytochrome c expression; the downregulation of Bcl-2 expression; activation of the expression levels of caspase-3, caspase-9, cleaved caspase-3 and cleaved caspase-9; and an increase in the amounts of intracellular reactive oxygen species. These results indicated that compound 8f may be used as a valuable skeleton structure for developing novel antitumor agents.

Recent progress on betulinic acid and its derivatives as antitumor agents: a mini review

Natural products are one of the important sources for the discovery of new drugs. Betulinic acid (BA), a pentacyclic triterpenoid widely distributed in the plant kingdom, exhibits powerful biological effects, including antitumor activity against various types of cancer cells. A considerable number of BA derivatives have been designed and prepared to remove their disadvantages, such as poor water solubility and low bioavailability. This review summarizes the current studies of the structural diversity of antitumor BA derivatives within the last five years, which provides prospects for further research on the structural modification of betulinic acid.

Substituted dienes prepared from betulinic acid - Synthesis, cytotoxicity, mechanism of action, and pharmacological parameters

A set of new substituted dienes were synthesized from betulinic acid by its oxidation to 30-oxobetulinic acid followed by the Wittig reaction. Cytotoxicity of all compounds was tested in vitro in eight cancer cell lines and two noncancer fibroblasts. Almost all dienes were more cytotoxic than betulinic acid. Compounds 4.22, 4.30, 4.33, 4.39 had IC₅₀ below 5 μmol/L; 4.22 and 4.39 were selected for studies of the mechanism of action. Cell cycle analysis revealed an increase in the number of apoptotic cells at 5 × IC₅₀ concentration, where activation of irreversible changes leading to cell death can be expected. Both 4.22 and 4.39 led to the accumulation of cells in the G0/G1 phase with partial inhibition of DNA/RNA synthesis at 1 × IC₅₀ and almost complete inhibition at 5 × IC₅₀. Interestingly, compound 4.39 at 5 × IC₅₀ caused the accumulation of cells in the S phase. Higher concentrations of tested drugs probably inhibit more off-targets than lower concentrations. Mechanisms disrupting cellular metabolism can induce the accumulation of cells in the S phase. Both compounds 4.22 and 4.39 trigger selective apoptosis in cancer cells via intrinsic pathway, which we have demonstrated by changes in the expression of the crucial apoptosis-related protein. Pharmacological parameters of derivative 4.22 were superior to 4.39, therefore 4.22 was the finally selected candidate for the development of anticancer drug.

Synthesis of 2-Aminoethanesulfonamides of Betulinic and Betulonic Acids

New potentially biologically active sulfonamide derivatives of pentacyclic lupane-type triterpenoids, the sulfonamide group of which was bonded to C-17 of the triterpene skeleton through an amidoethane spacer, were synthesized via conjugation of 2-aminoethanesulfonamides to betulinic and betulonic acids in the presence of Mukaiyama reagent (2-bromo-1-methylpyridinium iodide).

Synthesis and Characterization of Methacrylate-Functionalized Betulin Derivatives as Antibacterial Comonomer for Dental Restorative Resins

Secondary caries is the primary cause of composite restoration failures, resulting from marginal leakage and bacterial accumulation in the oral environment. Antibacterial dental composites, especially antibacterial monomers, have emerged as a promising strategy to inhibit secondary caries, which is pivotal to prolonging the lifespan of dental restorations. In this work, monomethacrylate- and dimethacrylate-functionalized betulin derivatives (M₁Bet and M₂Bet) were synthesized via an esterification reaction and served as antibacterial comonomers to develop novel dental resin formulations, in which M₁Bet and M₂Bet were incorporated to partially or completely replace bisphenol A glycerolate dimethacrylate (Bis-GMA). The control resin was a mixture based on Bis-GMA and tri(ethyleneglycol) dimethacrylate (TEGDMA) with a weight ratio of 50:50 (5B5T). The effect of the resin compositions and the chemical structures of M₁Bet and M₂Bet on the rheology behavior, optical property, polymerization kinetics, mechanical performance, cell viability, and antibacterial activity of dental resins were systematically investigated. Among all materials, the 1M₂Bet4B5T resin with 10 wt % substitution of Bis-GMA by M₂Bet exhibited comparable viscosity, higher light transmittance, improved degree of conversion, and mechanical properties compared with 5B5T. After incubation for 24 h, this optimal resin also possessed the best antibacterial activity against Streptococcus mutans, which had a significantly lower bacterial concentration (1.53 × 10⁹ CFU/mL) than 5B5T (9.03 × 10⁹ CFU/mL). Introducing betulin-based comonomers into dental resins is a potential strategy to develop antibacterial dental materials without sacrificing physical-mechanical properties.

Targeting mitochondrial ion channels for cancer therapy

Pharmacological targeting of mitochondrial ion channels is emerging as a promising approach to eliminate cancer cells; as most of these channels are differentially expressed and/or regulated in cancer cells in comparison to healthy ones, this strategy may selectively eliminate the former. Perturbation of ion fluxes across the outer and inner membranes is linked to alterations of redox state, membrane potential and bioenergetic efficiency. This leads to indirect modulation of oxidative phosphorylation, which is/may be fundamental for both cancer and cancer stem cell survival. Furthermore, given the crucial contribution of mitochondria to intrinsic apoptosis, modulation of their ion channels leading to cytochrome c release may be of great advantage in case of resistance to drugs triggering apoptotic events upstream of the mitochondrial phase. In the present review, we give an overview of the known mitochondrial ion channels and of their modulators capable of killing cancer cells. In addition, we discuss state-of-the-art strategies using mitochondriotropic drugs or peptide-based approaches allowing a more efficient and selective targeting of mitochondrial ion channel-linked events.

Multiple Myeloma Inhibitory Activity of Plant Natural Products

A literature search on plant natural products with antimyeloma activity until the end of 2020 resulted in 92 compounds with effects on at least one human myeloma cell line. Compounds were divided in different compound classes and both their structure-activity-relationships as well as eventual correlations with the pathways described for Multiple Myeloma were discussed. Each of the major compound classes in this review (alkaloids, phenolics, terpenes) revealed interesting candidates, such as dioncophyllines, a group of naphtylisoquinoline alkaloids, which showed pronounced and selective induction of apoptosis when substituted in position 7 of the isoquinoline moiety. Interestingly, out of the phenolic compound class, two of the most noteworthy constituents belong to the relatively small subclass of xanthones, rendering this group a good starting point for possible further drug development. The class of terpenoids also provides noteworthy constituents, such as the highly oxygenated diterpenoid oridonin, which exhibited antiproliferative effects equal to those of bortezomib on RPMI8226 cells. Moreover, triterpenoids containing a lactone ring and/or quinone-like substructures, e.g., bruceantin, whitaferin A, withanolide F, celastrol, and pristimerin, displayed remarkable activity, with the latter two compounds acting as inhibitors of both NF-κB and proteasome chymotrypsin-like activity.

A novel selective mitochondrial-targeted curcumin analog with remarkable cytotoxicity in glioma cells

Naturally occurring polyphenol curcumin (4) or demethoxycurcumin (5) and their synthetic derivatives display promising anticancer activities. However, their further development is limited by low bioavailability and poor selectivity. Thus, a mitochondria-targeted compound 14 (DMC-TPP) was prepared in the present study by conjugating a triphenylphosphine moiety to the phenolic hydroxyl group of demethoxycurcumin to enhance its bioavailability and treatment efficacy. The in vitro biological experiments of DMC-TPP showed that it not only displayed higher cytotoxicity as compared with its parent compound 5, but also exhibited superior mitochondria accumulation ability. Glioma cells were more sensitive to DMC-TPP, which inhibited the proliferation of U251 cells with an IC₅₀ of 0.42 μM. The mechanism studies showed that DMC-TPP triggers mitochondria-dependent apoptosis, caused by caspase activation, production of reactive oxygen species (ROS) and decrease of mitochondrial membrane potential (MMP). In addition, DMC-TPP efficiently inhibited cellular thioredoxin reductase, which contributed to its cytotoxicity. Significantly, DMC-TPP delayed tumor progression in a mouse xenograft model of human glioma cancer. Taken together, the potent in vitro and in vivo antitumor activity of DMC-TPP warrant further comprehensive evaluation as a novel anti-glioma agent.

Chemical Strategies towards the Synthesis of Betulinic Acid and Its More Potent Antiprotozoal Analogues

Betulinic acid (BA, 3β-hydroxy-lup-20(29)-en-28-oic acid) is a pentacyclic triterpene acid present predominantly in Betula ssp. (Betulaceae) and is also widely spread in many species belonging to different plant families. BA presents a wide spectrum of remarkable pharmacological properties, such as cytotoxic, anti-HIV, anti-inflammatory, antidiabetic and antimicrobial activities, including antiprotozoal effects. The present review first describes the sources of BA and discusses the chemical strategies to produce this molecule starting from betulin, its natural precursor. Next, the antiprotozoal properties of BA are briefly discussed and the chemical strategies for the synthesis of analogues displaying antiplasmodial, antileishmanial and antitrypanosomal activities are systematically presented. The antiplasmodial activity described for BA was moderate, nevertheless, some C-3 position acylated analogues showed an improvement of this activity and the hybrid models—with artesunic acid—showed the most interesting properties. Some analogues also presented more intense antileishmanial activities compared with BA, and, in addition to these, heterocycles fused to C-2/C-3 positions and amide derivatives were the most promising analogues. Regarding the antitrypanosomal activity, some interesting antitrypanosomal derivatives were prepared by amide formation at the C-28 carboxylic group of the lupane skeleton. Considering that BA can be produced either by isolation of different plant extracts or by chemical transformation of betulin, easily obtained from Betula ssp., it could be said that BA is a molecule of great interest as a starting material for the synthesis of novel antiprotozoal agents.

Glycoconjugation of Betulin Derivatives Using Copper-Catalyzed 1,3-Dipolar Azido-Alkyne Cycloaddition Reaction and a Preliminary Assay of Cytotoxicity of the Obtained Compounds

Pentacyclic lupane-type triterpenoids, such as betulin and its synthetic derivatives, display a broad spectrum of biological activity. However, one of the major drawbacks of these compounds as potential therapeutic agents is their high hydrophobicity and low bioavailability. On the other hand, the presence of easily transformable functional groups in the parent structure makes betulin have a high synthetic potential and the ability to form different derivatives. In this context, research on the synthesis of new betulin derivatives as conjugates of naturally occurring triterpenoid with a monosaccharide via a linker containing a heteroaromatic 1,2,3-triazole ring was presented. It has been shown that copper-catalyzed 1,3-dipolar azide-alkyne cycloaddition reaction (CuAAC) provides an easy and effective way to synthesize new molecular hybrids based on natural products. The chemical structures of the obtained betulin glycoconjugates were confirmed by spectroscopic analysis. Cytotoxicity of the obtained compounds was evaluated on a human breast adenocarcinoma cell line (MCF-7) and colorectal carcinoma cell line (HCT 116). The obtained results show that despite the fact that the obtained betulin glycoconjugates do not show interesting antitumor activity, the idea of adding a sugar unit to the betulin backbone may, after some modifications, turn out to be correct and allow for the targeted transport of betulin glycoconjugates into the tumor cells.

Mitocanic Di- and Triterpenoid Rhodamine B Conjugates

The combination of the “correct” triterpenoid, the “correct” spacer and rhodamine B (RhoB) seems to be decisive for the ability of the conjugate to accumulate in mitochondria. So far, several triterpenoid rhodamine B conjugates have been prepared and screened for their cytotoxic activity. To obtain cytotoxic compounds with EC₅₀ values in a low nano-molar range combined with good tumor/non-tumor selectivity, the Rho B unit has to be attached via an amine spacer to the terpenoid skeleton. To avoid spirolactamization, secondary amines have to be used. First results indicate that a homopiperazinyl spacer is superior to a piperazinyl spacer. Hybrids derived from maslinic acid or tormentic acid are superior to those from oleanolic, ursolic, glycyrrhetinic or euscaphic acid. Thus, a tormentic acid-derived RhoB conjugate 32, holding a homopiperazinyl spacer can be regarded, at present, as the most promising candidate for further biological studies.

The presence of a cationic center is not alone decisive for the cytotoxicity of triterpene carboxylic acid amides

3-O-Acetyl-ursolic acid (2) and 3-O-acetyl oleanolic acid (8) were converted into piperazinylamides holding a distal NH, NMe or a NMe₂ group. These compounds as well as the corresponding N-methyl-N-oxides were accessed. Their cytotoxicity was assessed in SRB assays employing a panel of human tumor cell lines and non-malignant fibroblasts (NIH 3T3). As a result, compounds holding a quaternary distal N-substituent were less cytotoxic that those holding a NH-moiety. Hence, the presence of a distal cationic center seems not to be a sufficient criterion for obtaining triterpenoids of high cytotoxicity and selectivity.

Cytotoxic triterpenoid-safirinium conjugates target the endoplasmic reticulum

Safirinium P and Q fluorescence labels were synthesized and conjugated with spacered triterpenoic acids to access hybrid structures. While the parent safirinium compounds were not cytotoxic at all, many triterpenoid safirinium P and Q conjugates showed moderate cytotoxicity. An exception, however, was safirinium P derived compound 30 holding low EC₅₀ = 5.4 μM (for A375 cells) to EC₅₀ = 7.5 μM (for FaDu cells) as well as EC₅₀ = 6.6 μM for non-malignant fibroblasts NIH 3T3. Fluorescence imaging showed that the safirinium core structures cannot enter the cells (not even after a prolonged incubation time of 24 h), while the conjugates (as exemplified for 30) are accumulating in the endoplasmic reticulum but not in the mitochondria. The development of safirinium-hybrids targeting the endoplasmic reticulum can be regarded as a promising strategy in the development of cytotoxic agents.

Dealkenylative Alkenylation: Formal σ-Bond Metathesis of Olefins

The dealkenylative alkenylation of alkene C(sp3 )-C(sp2 ) bonds has been an unexplored area for C-C bond formation. Herein 64 examples of β-alkylated styrene derivatives, synthesized through the reactions of readily accessible feedstock olefins with β-nitrostyrenes by ozone/FeII -mediated radical substitutions, are reported. These reactions proceed with good efficiencies and high stereoselectivities under mild reaction conditions and tolerate an array of functional groups. Also demonstrated is the applicability of the strategy through several synthetic transformations of the products, as well as the syntheses of the natural product iso-moracin and the drug (E)-metanicotine.

Betulinic acid triggers apoptosis and inhibits migration and invasion of gastric cancer cells by impairing EMT progress

Gastric cancer (GC) is one of the most prevalent types of malignancies. Betulinic acid (BA) is a natural pentacyclic triterpene with a lupine structure. However, to the best of our knowledge, there is no research study on the anti‐tumour and anti‐metastasis effect of BA on GC. In this study, we assessed the anti‐cancer effect of BA on human GC cells in vitro and in vivo. We first investigated the cytotoxicity and anti‐proliferation effect of BA on GC cells of SNU‐16 and NCI‐N87. The results indicated that BA had significant cytotoxic and inhibitory effects on GC cells in a dose‐ and time‐dependent manner. To further study the cytotoxic action of BA on GC cells, we assessed the apoptotic induction effect of BA on SNU‐16 cells and found that BA distinctly induced apoptosis in SNU‐16 cells. In addition, BA inhibited the migratory and invasive abilities of SNU‐16 cells. Western‐blot analysis revealed that BA suppressed the migration and invasion of GC cells by impairing epithelial‐mesenchymal transition progression. Furthermore, in vivo experiments showed that BA could delay tumour growth and inhibit pulmonary metastasis, which is consistent with the results of in vitro studies. Overall, we evaluated the anti‐cancer effect of BA on human GC cells in vivo and in vitro, and the present study provides new evidence on the use of BA as a potential anti‐cancer drug for GC treatment.

Significance of the study

BA significantly suppressed proliferation and triggered apoptosis in GC cells. Additionally, BA remarkably inhibited migration and invasion of GC cells by impairing the epithelial‐mesenchymal transition signalling pathway. It is worth noting that BA drastically retarded tumour growth in the xenograft mouse model of GC. Our results indicated that BA can be considered a candidate drug for GC therapy.

Synthesis, cytotoxicity and anti-inflammatory activity of rhamnose-containing ursolic and betulinic acid saponins

Betulinic acid and ursolic acid are ubiquitous, naturally-occurring triterpenoids exhibiting various pharmacological activities including cytotoxic and anti-inflammatory activities. However, these triterpenoids display unfavorable pharmacokinetic properties as well as low aqueous solubility. It has been shown that the presence of α-l-rhamnose moieties positively modulates the anticancer activity of secondary metabolites. Herein we report the synthesis and in vitro evaluation of cytotoxic and anti-inflammatory activities of a series of rhamnose-containing ursolic and betulinic acid saponins. Relying on Schmidt's normal and inverse procedures, monorhamnosides, (1→4)-linked dirhamnosides as well as branched trirhamnosides and tetrarhamnosides were synthesized in high yields with full control of stereoselectivity. A betulinic acid saponin bearing a 3-O-α-l-rhamnopyranosyl-(1→4)-α-l-rhamnopyranosyl residue was found to be a potent cytotoxic agent against human colorectal adenocarcinoma cells without damaging the healthy cells (selectivity ratio > 20) whereas rhamnose-containing ursolic acid saponins potently inhibited NO overproduction induced by LPS-stimulated macrophages. Our results reveal that rhamnose-containing ursolic and betulinic acid saponins represent promising therapeutic agents.

Rhamnose-containing saponins featuring betulinic and ursolic acid as aglycones were synthesized using both Schmidt's normal and inverse procedures. Some of these synthetic saponins exhibited selective cytotoxic and/or anti-inflammatory activities.