Betulin Derivatives Research Articles

One-pot Synthesis of Betulin Triterpenoid Quaternized Pyridine Derivatives and their Antimicrobial Activity

Background: A wide range of biological activity, relatively low toxicity and multiple pharmacological effects of triterpenoids are major advantages of these compounds in the prevention and treatment of various diseases. They include the lupane- type triterpenoids that proved to be a promising platform for the synthesis of analogs with a wide range of biological activities, including anti-inflammatory, antitumor, antiparasitic and antiviral properties. The main disadvantage complicating the use of all known derivatives of lupane acids in medical practice is low bioavailability associated with poor solubility in biologic fluids, limiting their effective interaction with the biological targets. Objective: The objective of this study is the synthesis of new amphiphilic betulin derivatives on the base of pyridinium salts with antifungal and antibacterial activity. Methods: In this study we have developed an effective one-pot method for the preparation of new quaternized pyridine derivatives 4-6 of the betulinic series based on the reaction of the initial triterpenes 1-3 with the Tempo+Br3 - reagent in the pyridine. The synthesized and initial compounds were tested for their antimicrobial and antifungal activity. Results: The data presented in this document indicate that all synthesized compounds 4-6 exhibited high activity against both gram-positive Staphylococcus aureus bacteria and gram-negative Pseudomonas aeruginosa strains, as well as Candida albicans and Cryptococcus neoformans fungi with the >90% coverage of the inhibition zone. The best result in a series of compounds 4-6 was found for the derivative 6 at the minimum inhibitory concentration of 1 µg/ml against S. aureus bacteria, C. albicans and C. neoformans fungi at the concentration of 8 µg/ml. Conclusion: Thus, we have demonstrated the first example of the pyridine quaternization using the betulin triterpenoids as the lipophilic substrates and Tempo+Br3 - cation. The obtained quaternized pyridine analogs of betulin triterpenes showed high antibacterial and antifungal activity in comparison with the initial compounds.

BETULIN DERIVATIVES. BIOLOGICAL ACTIVITY AND SOLUBILITY IMPROVEMENT

In the review the biological properties (antitumor, antiviral, hypolipidemic, anti-inflammatory, etc.) and bioavailability of betulin and betulinic acid derivatives were discussed. These compounds are isolated from various natural sources, including birch bark (Betula, Betulaceae). The structure-activity correlation was considered for well-known betulinic acid derivatives. The perspectivity of this compounds as active pharmaceutical ingredients was demonstrated by in vitro, in vivo, and ex vivo experiments. The type of antitumor actions, generally, depends on substituents at the C-3 and C-28 carbon atoms of the lupane skeleton. It is very important that the carboxyl group of betulinic acid in the C-28 position was present. In this case, the cytotoxicity of C-3 modified derivatives is extremely high for all tested cell lines. The use of these compounds in the medical practice is complicated because they have low bioavailability and poor water solubility (from 1 to 100 µg*l-1). The main chemical syntheses for solubility improvement of betulin derivatives by grafting of hydrophilic groups were discussed. Moreover, the colloid-chemical approaches for the bioavailability improving of triterpenoids include: 1) including of these compounds in liposomes, vesicles and other nanoparticles; 2) obtaining of micelles with high-molecular compounds; 3) colloid-chemical dissolution due to physico-mechanical action; 4) inclusion complexes formation; 5) using of polymers for triterpenoids grafting. Chemical modification of betulin and betulinic acid by polar groups, such as phosphate/phosphonate, sulfate, amino acids, etc. has been shown for bioavailability improving.

Strong complexation of water-soluble betulin derivatives with (2-hydroxypropyl)-γ-cyclodextrin studied by affinity capillary electrophoresis.

The complexation between (2-hydroxypropyl)-γ-cyclodextrin (HP-γ-CD) and water-soluble betulin derivatives, betulin 3,28-disulfate (DSB) and betulin 3-acetate-28-sulfate (ASB), belonging to the class of pentacyclic lupane triterpenoids, was studied using mobility shift ACE (ms ACE). It was found that the complexation is a high-affinity interaction. In this case, a very low amount of HP-γ-CD should be added to the BGE, and triangular peaks are observed as a result of ligand deficiency in the sample zone. Le Saux etal. showed in 2005 that using the parameter a1 of the Haarhoff-Van der Linde (HVL) function instead of the migration time measured at the peak apex eliminates the effect of ligand deficiency on effective electrophoretic mobility. Therefore, the electrophoretic mobilities of asymmetrical peaks of DSB and ASB were calculated in this way. The obtained experimental data correspond to 1:1 complexes. The calculated values of binding constants logarithms at 25°C are 6.70±0.05 and 7.03±0.10 for the HP-γ-CD complexes of DSB and ASB, respectively.

Design, synthesis, and biological evaluation of ligustrazine - betulin amino-acid/dipeptide derivatives as anti-tumor agents

The ligustrazine - betulin derivative (TB), TB amino acids derivatives (TB-01 — TB-09) and TB dipeptide derivatives (TB-10 — TB-18) were designed and synthesized. And their in vitro cytotoxic activities were evaluated against four cancer cell lines (Hela, HepG2, BGC-823 and HT-29) and normal cells MDCK by standard methylthiazol tetrazolium (MTT) assay. Most of them demonstrated better antitumor activity than the relevant material betulin. Among them, compound TB-01 showed the best anti-tumor effect on the cancer cells and the lowest toxicity on the normal cells. For example, the cytotoxicity of TB-01 against the cancer cells (mean IC50 = 4.86 ± 1.16 μM) was 3-fold higher than that against the normal cells MDCK (IC50 = 16.11 ± 2.29 μM). Moreover, TB-01 showed better cytotoxic than positive drug cisplatin (DDP) on tumor cells. Besides, the Zebrafish toxicity evaluation test showed that TB-01 demonstrated high biosafety. Subsequently, fluorescent staining, apoptosis detection and cell cycle analysis indicated that TB-01 induced early apoptosis in HepG2 cells and blocked the cell cycle in the G1 phase. In addition, the structure-activity relationships of these derivatives were briefly discussed.

Synthesis and Antitumor Activity of C-3(R) Hydroxy Modified Betulinic Acid Derivatives

Four novel betulinic acid (BA) derivatives modified at the C-3 position were prepared by the Mitsunobu reaction and subsequently evaluated for antitumor activity against four common cancer cell lines in vitro. The results from the MTT assay revealed that the four tested compounds showed remarkable cytotoxic activity against four cancer cell lines, much better than BA. Western blotting results indicated that the four compounds, especially compound 2c, caused a significant up-regulation expression of the caspase-12 in CT26 cell. Our results showed that configuration inversions of chiral C-3 of BA could also produce BA derivatives with potent antitumor activity.

Betulinic acid derivatives can protect human Müller cells from glutamate-induced oxidative stress

Müller cells are the predominant retinal glial cells. One of the key roles of Müller cells is in the uptake of the neurotransmitter glutamate and in its conversion to glutamine. Müller cell dysfunction due to oxidative stress elicited by high glutamate concentrations can lead to toxicity, which promote the pathogenesis of retinal diseases like diabetic retinopathy and glaucoma. This study investigated the anti-oxidant activity and mechanisms of betulinic acid (BA) and its derivatives in human Müller cells. Human MIO-M1 Müller cells were pre-treated in the presence or absence of BA, BE as well as their derivatives (named H3–H20) followed by incubation with glutamate. Cell viability was evaluated with the MTT and calcein-AM assays. Reactive oxygen species (ROS) production in MIO-M1 cells was measured using CM-H2DCFDA and flow cytometry. The activation of cellular apoptosis and necrosis was analyzed with annexin V/PI staining and flow cytometry. The modulation of signaling pathways involved in glutamate-mediated cytotoxicity and ROS production was evaluated by immunoblotting. The BA derivatives H3, H5 and H7 exhibited minimal cytotoxicity and significant anti-oxidant activity. These compounds significantly suppressed ROS production and attenuated cellular necrosis elicited by glutamate-induced oxidative stress. The protective effects of H3, H5 and H7 in MIO-M1 cells were associated with the attenuation of Akt, Erk, and JNK signaling. The BA analogues H3, H5 and H7 are protective against glutamate-induced oxidative stress in human Müller cells, and elicit their actions by modulation of the Erk, Akt and JNK signaling pathways. These agents are potential candidate molecules for the prevention or treatment of human retinal diseases.

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

Naturally occurring pentacyclic lupane triterpenoids such as betulin (1) or betulinic acid (2) and their synthetic derivatives display a broad spectrum of biological activities and, therefore, have been the subject of great interest. However, the use of these compounds as potential therapeutic agents is limited by their low bioavailability, high hydrophobicity, and insufficient intracellular accumulation. In this context, research on modifications of the parent structures that will improve their pharmacokinetic properties is particularly important. In the past few years, methods of synthesis as well as cytotoxic and antiparasitic properties of a series of lupane triterpenoids modified by introducing one or two triphenylphosphonium moieties at the C-2, C-3, C-28, or C-30 positions by carbon-carbon or ester bonds have been described. The presence of triphenylphosphonium groups affects not only physical properties but also the mechanism of action of a potential drug. This review summarizes published findings on synthetic methods and biological properties of the triphenylphosphonium derivatives of betulin and betulinic acid.

Synthesis and Antitumor Evaluation in Vitro of NO-Donating Ursolic Acid-Benzylidene Derivatives.

Antitumor activity of triterpenoid and its derivatives has attracted great attention recently. Our previous efforts led to the discovery of a series of NO-donor betulin derivatives with potent antitumor activity. Herein, we prepared eight compounds derived from ursolic acid (UA). All the compounds were evaluated for their in vitro cytotoxicity against four human cancer cell lines (HepG-2, MCF-7, HT-29 and A549). Among the compounds tested, compound 4a was found to be most active against HT-29 (IC50 =4.28 μm). Further biological assays demonstrated that compound 4a could induce cell cycle arrest at G1 phase and apoptosis in a dose-dependent manner. In addition, compound 4a was found to upregulate pro-apoptotic Bax, p53 and downregulate anti-apoptotic Bcl-2. All these results suggested that compound 4a is a potential candidate drug for the therapy of colon cancer.

Imidazolium-Sulfobetaine Based on Betulin with Proliferative Activity for HEK293 and T-Lymphocyte Cells

A betulin derivative with an (imidazolium)butane-1-sulfonate fragment was synthesized and promoted proliferation in vitro of HEK293 and human T-lymphocyte cells, suggesting that this compound had immunostimulant properties.

Thermodynamic parameters for the complexation of water-insoluble betulin derivatives with (2-hydroxypropyl)-γ-cyclodextrin determined by phase-solubility technique combined with capillary zone electrophoresis.

The complexation of betulinic and betulonic acids (BIA and BOA) (pentacyclic lupane triterpenoids) with (2-hydroxypropyl)-γ-cyclodextrin (HP-γ-CD) was studied at different temperatures using the method combining phase-solubility technique and CZE. In contrast to mobility shift ACE utilizing the electrophoretic mobility, in this approach, the peak areas are used. The apparent binding (stability, formation) constants are obtained by the Higuchi and Connors method from the linear segment of compound solubility diagrams in CD solutions. It was found that the apparent binding constants of the HP-γ-CD complexes of BIA and BOA decrease with increasing temperature. The binding constants of BOA complexes are slightly higher than those of BIA complexes; this can be explained by difference in the hydration degrees of carbonyl and hydroxyl groups. On the basis of the binding constants obtained and their temperature dependences (van't Hoff plot), the enthalpy as well as entropy changes and Gibbs free energies were calculated. It was found that the complexation was characterized by negative changes of enthalpy and entropy, that is, it was controlled by enthalpy changes. The results obtained can be used for the optimization of microcapsulation processes of BOA and BIA with the HP-γ-CD application in order to increase solubility and bioavailability of these compounds.

New phosphate derivatives of betulin as anticancer agents: Synthesis, crystal structure, and molecular docking study

Betulin derivatives exhibit an antiproliferative activity and have been tested for many cancer cell lines. This paper describes a new series of 3-phosphate derivatives of betulin bearing different substituents at C28 position. The synthesized compounds were tested in vitro for their antiproliferative effect against human leukemia (MV-4-11 and CCRF/CEM), lung carcinoma (A549), prostate cancer (DU 145), melanoma (Hs 294T) cell lines, and murine leukemia P388. To explore the possible mechanism of anticancer activity for the most in vitro active compounds (4, 5, 7 and 8) and betulin, molecular docking was performed to the binding sites of potential anticancer targets, described for the various triterpene derivatives, including topoisomerase I and II, epidermal growth factor receptor (EGFR) and vascular endothelial growth factor (VEGFR), transcription factor NF-κB, anti-apoptotic protein Bcl-2 and peroxisome proliferator-activated receptor (PPARγ). According to the results of the docking, the best fit to the binding pocket of PPARγ was shown by compound 4.

Thermodynamic parameters for the complexation of water-soluble betulin derivatives with (2-hydroxypropyl)-β-cyclodextrin determined by affinity capillary electrophoresis

The interaction between (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) and water-soluble betulin derivatives, betulin 3,28-disulfate (DSB) and betulin 3-acetate-28-sulfate (ASB), belonging to the class of pentacyclic lupane triterpenoids, was studied using affinity capillary electrophoresis. It was found that 1:1 and 1:2 complexes were formed. The stability constants of the complexes in the temperature range of 293.15–318.15 K were determined. The values obtained are sufficiently large; log K (1:1) and log K (1:2) are 4.25–5.02 and 6.08–7.59, respectively. This phenomenon can be explained by the presence of broad hydrophobic regions in the molecules of the compound studied. The stability constants decrease with increasing temperature. The stability constants for ASB complexes are slightly higher as compared to the constants for DSB complexes. The thermodynamic parameters for the complexation were calculated from the van't Hoff plots. The complexation was found to be controlled by the enthalpy change. The obtained values of stability constants at 298 K were compared with values for the β-CD complexes of the compounds under study and for the HP-β-CD and β-CD complexes of water-insoluble betulin derivatives. It was found that water-soluble betulin derivatives form more stable complexes with CDs as compared to water-insoluble derivatives (betulonic and betulinic acids), and the HP-β-CD complexes are more stable than the β-CD complexes.

Biological Activity and In Silico Study of 3-Modified Derivatives of Betulin and Betulinic Aldehyde.

A series of 3-substituted derivatives of betulin and betulinic aldehyde were synthesized as promising anticancer agents. The newly triterpenes were tested against five human cancer cell lines like biphenotypic B myelomonocytic leukaemia (MV-4-11), adenocarcinoma (A549), prostate (Du-145), melanoma (Hs294T), breast adenocarcinoma (MCF-7) and normal human mammary gland (MCF-10A). The compound 9 showed towards Du-145, MCF-7 and Hs294T cells significant antiproliferative activity with IC50 ranging from 7.3 to 10.6 μM. The evaluation of ADME properties of all compounds also includes their pharmacokinetic profile. The calculated TPSA values for synthetized derivatives are in the range between 43.38 Å2 and 55.77 Å2 suggesting high oral bioavailability. The molecular docking calculations showed that triterpene 9 fits the active site of the serine/threonine protein kinase Akt.

Application of TLC for Evaluation of the Lipophilicity of Newly Synthetized Esters: Betulin Derivatives.

The problem of designing a new drug is nowadays very important for researches representing many branches of science. This work considers the usefulness of the analytical method such as thin-layer chromatography for the lipophilicity of newly synthesized compounds, betulin derivatives, which could be potential drugs with anticancer activity. The two mobile phases were used for the purpose of experimental determination of lipophilicity for mono- and diesters investigated. The first mobile phase consists of acetate and Tris buffer, whilst the second consists of 1,4-dioxane and acetate buffer. The value of the retardation factor was recalculation into the RM value, and then RM0 values were obtained by extrapolating acetone or 1,4-dioxane concentration to zero. The chromatographic data of lipophilicity were correlated with theoretically obtained values of ALOGPS, AClogP, miLogP, ALOGP, MLOGP, XLOGP2, and XLOGP3. The particular correlation equations were obtained. The cluster analysis was also used to find similarity between the esters investigated on the basis of the experimental or theoretical value of lipophilicity obtained. The good correlation between experimentally and theoretically calculated lipophilicity gives the possibility of prediction of this value on the basis of the correlation equation. On the basis of similarity analysis was stated strong connections between the structure and the value of lipophilicity, for both experimental and theoretical values.

Preparation of Betulone Via Betulin Oxidation Over Ru Nanoparticles Deposited on Graphitic Carbon Nitride

Derivatives of betulin obtained by oxidation have broad pharmacological applications, demonstrating anti-inflammatory, antioxidant, hepatoprotective, and anticancer activity. Ru supported catalysts based on graphitic carbon nitride or N-doped carbon were prepared via a mild reduction of the initial Ru precursor with hydrazine. These catalysts along with Ru supported on carbon nanofibers and a mesoporous carbon support Sibunit were studied in catalytic oxidation of betulin. Ru/carbon nitride demonstrated catalytic activity in betulin oxidation higher than Ru/N-doped carbon (conversion of betulin up to ca. 70% and 30%, respectively). Selectivity to different oxidation products was dependent on the properties of the carbon supports.Graphical

Novel polymeric derivatives of betulin with anticancer activity.

In order to provide novel polymeric biomaterials for chemotherapeutic purposes, in this paper we described the synthesis and the characterization of the physicochemical properties of a betulin-based polyanhydride exhibiting anti-cancer effects. The polyanhydride was obtained by a melt polycondensation of a disuccinate betulin (3,28-di-O-succinyl betulin), and was thoroughly characterized through 1H NMR and 13C NMR spectroscopies, correlation spectroscopy, heteronuclear single quantum correlation, size exclusion chromatography, differential scanning calorimetry and FT-IR spectroscopy. It was confirmed, that the obtained polyanhydride undergoes hydrolytic degradation, releasing disuccinate betulin as a degradation product. Polyanhydride of a disuccinate betulin was tested for cytostatic activity against a wide range of cancer cell lines (HeLa, MCF-7, A-549, U-87MG, KB and HepG2), proving its efficiency in inhibiting the growth of selected cancer cells. To realize the concept of an easily administrated drug release system, polyanhydride was fabricated in a form of micro- (1–30 μm) and nanospheres (∼400 nm) by using an emulsion solvent evaporation method. The micro- and nanospheres were characterized by SEM.

A New Betulin Derivative Stimulates the Synthesis of Collagen in Human Fibroblasts Stronger than its Precursor.

The exploration of substances that stimulate collagen synthesis and retard the aging process of the skin is an active field of current research. The natural environment and plants used in traditional medicine have been a source of such substances. The aim of this study was to compare the stimulatory effect of betulin (BE), betulinic acid (BA) and the new derivative - betulin ester with diaminobutyl acid (BE-Dab-NH2) on collagen synthesis in human normal fibroblasts. Primary fibroblast cultures were obtained from the gums of a healthy patient. The effect of the above-mentioned compounds was assessed by Sircol collagen assay, immunocytochemistry, and proliferation test. Fibroblasts cultured in the presence of BE-Dab-NH2 produced 6.85 times more collagen than control cells, 7.85 times more than those cultured in the presence of BA and 6.31 times more than those cultured in the presence of BE. An intense immunocytochemical reaction for collagen type I and III was found in fibroblasts cultured in the presence of BE-Dab-NH2 Conclusion: BE-Dab-NH2 stimulates significantly more collagen synthesis in normal human fibroblasts than its precursor.

Novel betulin derivatives inhibit IFN-γ and modulates COX-2 expression

Betulin (BE) is a pentacyclic triterpenes, obtained from natural sources and with several biological activities described, such as anti-tumoral and anti-inflammatory activities. The BE esterification at hydroxyl group (C-3 and C-28) resulted in five new ester derivatives with different numbers of carbons or halogens (chlorine and fluorine). Among these BE derivatives, two (2a e 2c) were able to significantly decrease IFN-g (*p = 0.0391; **p = 0.0156) and 2c modulated the expression of COX-2 better than Dexamethasone (DEXA). Regarding to cytotoxic assay, the best results were obtained for BE without modifications, with emphasis on tumoral cell lines Raji and MCF-7. The derivatives 2a and 2c showed immunomodulation activity (for the cytokines IFN-g). The presence of chorine in BE seems to be important for the ability of modulate COX-2 expression, since the ester chloride derivative 2c at 100 μM is more powerful inhibitor of COX-2 than DEXA.

Bioresorbable filomicelles for targeted delivery of betulin derivative – In vitro study

Filomicelles (worm-like micelles) possess high drug loading capacity and long circulation time in the bloodstream. A novel approach can be filomicelles with folic acid (FA) as a targeting moiety. Folate-drug delivery systems can target FA receptors (FAR) that are overexpressed in several human carcinomas, which can potentially maximize therapeutic efficacy while minimizing side effects. The aim of this study was to develop filomicelles from combination of poly(L-lactide)-Jeffamine-folic acid and poly(L-lactide)-poly(ethylene glycol) for delivery of betulin derivative. Phosphate derivative of betulin reveals high cytotoxicity against cancer cells, however its application is restricted due to poor solubility in water. Incorporation into hydrophobic core of micelles can effectively solubilize the drug. Three kinds of micelles were obtained with high drug loading capacity. Based on TEM analysis, the copolymers formed exclusively filomicelles or mixture of filomicelles and spherical micelles. All kinds of micelles provided release of betulin derivative for over 9 days and apart the very initial phase displayed similar release profile. The influence of PLA block on initial burst effect was revealed. The in vitro cytotoxicity of betulin derivative loaded micelles against FAR-positive HeLa cells was confirmed, which proves their usefulness for targeted delivery of cytostatic drug.

Novel betulin derivative is responsible for the anticancer folk use of Ziziphus spina-christi from the hot environmental habitat of UAE

Ethnopharmacological relevanceSeveral natural products derived from plant sources are developed to remarkable medicines based on their traditional uses. Ziziphus, a worldwide known plant, is proven for potential cytotoxic activity. However, the plant growing at the unique hot environmental climate of UAE was never investigated. Different phytochemicals may be produced from the same plant genotype at different climates leading to variable pharmacological activities. Aim of the studyThe study was conducted in order to investigate phytochemicals in the UAE native Z. spina-christi plant and its anticancer activity. Materials and methodsZ. spina-christi plant were collected, dried and dissected into leaves, stems and thorns. The plant organs were subjected to comparative fractionation-based anticancer assay followed by spectroscopic analysis of a uniquely isolated compound. ResultsThe results indicate that a novel betulin derivative (13-dehydrobetulin) isolated from plant stem exhibited substantial anticancer activity specifically against liver cancer and with wide therapeutic range. ConclusionsGrowth of cytotoxic traditionally-known plant remedy at harsh environmental habitat advances its anticancer activity due to production of novel phytochemical with optimum activity and minimal toxicity. Furthermore, such approach may be a future to develop novel lead compounds with optimum activity.