Synthesis of A-seco derivatives of betulinic acid with cytotoxic activity

An asiatic acid derived trisulfamate acts as a nanomolar inhibitor of human carbonic anhydrase VA

This investigation delves into the inhibitory capabilities of a specific set of triterpenoic acids on diverse isoforms of human carbonic anhydrase (hCA). Oleanolic acid (1), maslinic acid (2), betulinic acid (3), platanic acid (4), and asiatic acid (5) were chosen as representative triterpenoids for evaluation. The synthesis involved acetylation of parent triterpenoic acids 1-5, followed by sequential reactions with oxalyl chloride and benzylamine, de-acetylation of the amides, and subsequent treatment with sodium hydride and sulfamoyl chloride, leading to the formation of final compounds 21-25. Inhibition assays against hCAs I, II, VA, and IX demonstrated noteworthy outcomes. A derivative of betulinic acid, compound 23, exhibited a Ki value of 88.1 nM for hCA VA, and a derivative of asiatic acid, compound 25, displayed an even lower Ki value of 36.2 nM for the same isoform. Notably, the latter compound displayed enhanced inhibitory activity against hCA VA when compared to the benchmark compound acetazolamide (AAZ), which had a Ki value of 63.0 nM. Thus, this compound surpasses the inhibitory potency and isoform selectivity of the standard compound acetazolamide (AAZ). In conclusion, the research offers insights into the inhibitory potential of selected triterpenoic acids across diverse hCA isoforms, emphasizing the pivotal role of structural attributes in determining isoform-specific inhibitory activity. The identification of compound 25 as a robust and selective hCA VA inhibitor prompts further exploration of its therapeutic applications.

Preparation of Simple Bicyclic Carboxylate-Rich Alicyclic Molecules for the Investigation of Dissolved Organic Matter

Dissolved organic matter (DOM) is a vast and complex chemical mixture that plays a key role in the mediation of the global carbon cycle. Fundamental understanding of the source and fate of oceanic organic matter is obscured due to poor definition of the key molecular contributors to DOM, which limits accurate sample analysis and prediction of the Earth's carbon cycle. Previous work has attempted to define the components of the DOM through a variety of chromatographic and spectral techniques. However, modern preparative and analytical methods have not isolated or unambiguously identified molecules from DOM. Therefore, previously proposed structures are based solely on the mixture's aggregate properties and do not accurately describe any true individual molecular component. In addition to this, there is a lack of appropriate analogues of the individual chemical classes within DOM, limiting the scope of experiments that probe the physical, chemical, and biological contributions from each class. To address these problems, we synthesized a series of analogues of carboxylate-rich alicyclic molecules (CRAM), a molecular class hypothesized to exist as a major contributor to DOM. Key analytical features of the synthetic CRAMs were consistent with marine DOM, supporting their suitability as chemical substitutes for CRAM. This new approach provides access to a molecular toolkit that will enable previously inaccessible experiments to test many unproven hypotheses surrounding the ever-enigmatic DOM.

Bifunctionalized Betulinic Acid Conjugates with C-3-Monodesmoside and C-28-Triphenylphosphonium Moieties with Increased Cancer Cell Targetability

A convenient synthesis is presented for a new class of bioactive bifunctionalized conjugates of lupane-type triterpenoids with triphenylphosphonium (TPP) and glycopyranosyl targeting moieties. The main synthesis steps include glycosylation of haloalkyl esters of the triterpene acid at the C-3 position by the imidate derivatives of glycopyranose followed by the product modification at the C-28 position with triphenylphosphine. The conjugates of betulinic acid (BetA) with TPP and d-glucose, l-rhamnose, or d-mannose moieties were thus synthesized as potential next-generation BetA-derived anticancer compounds. LC-MS/MS analysis in glucose-free physiological solution indicated that the glycosides showed better accumulation in PC-3 prostate cancer cells than both BetA and TPP-BetA conjugate, while the transporting effect of monosaccharide residues increased as follows: d-mannose < l-rhamnose ≈ d-glucose. At saturated concentrations, the glycosides caused a disturbing effect on mitochondria with a more drastic drop in transmembrane potential but weaker overproduction of mitochondrial reactive oxygen species (ROS) compared to TPP-BetA conjugate. Cytotoxicity of the glycosides in culture medium was comparable with or higher than that of the nonglycosylated conjugate, depending on the cancer cell line, whereas the compounds were less active toward primary fibroblasts. Glycosylation tended to increase pro-apoptotic and decrease pro-autophagic activities of the BetA derivatives. Cytotoxicity of the synthesized glycosides was considered in comparison with the summarized data on the natural and modified BetA glycosides. The results obtained are important for the development of bifunctionalized conjugates of triterpenoids with an increased cancer cell targetability.

Lupane Triterpene Derivatives Improve Antiproliferative Effect on Leukemia Cells through Apoptosis Induction

Leukemia is one of the most frequent types of cancer. No effective treatment currently exists, driving a search for new compounds. Simple structural modifications were made to novel triterpenes isolated from Phoradendron wattii. Of the three resulting derivatives, 3α-methoxy-24-hydroxylup-20(29)-en-28-oic acid (T1m) caused a decrease in the median inhibitory concentration (IC₅₀) on the K562 cell line. Its mode of action was apparently apoptosis, ROS generation, and loss of mitochondrial membrane potential (MMP). Molecular docking analysis showed T1m to produce lower binding energies than its precursor for the Bcl-2 and EGFR proteins. Small, simple, and viable modifications to triterpenes can improve their activity against leukemia cell lines. T1m is a potentially promising element for future research. Clarifying the targets in its mode of action will improve its applicability.

Effect of modification of betulinic acid at the C3-carbon atom of homolupane triterpenoids on the antiproliferative activity in vitro

In search of new cytotoxic derivatives based on the lupane scaffold, methyl betulonate and methyl 20,29-dihydrobetulonate were conjugated with Reformatsky reagents to provide homolupanes extended at the C3-carbon atom. Further transformations of the functional groups afforded a series of derivatives with 2-hydroxyethyl and allyl alcohol moieties. Their varying antiproliferative activity in vitro was then investigated in four cancer cell lines and in normal human BJ fibroblasts. In cervical carcinoma HeLa cells, derivatives 5, 6 and 17 were the most promising with lower micromolar IC50s and no toxicity to fibroblasts, thus showing a high therapeutic index. In addition, induction of apoptosis was found in HeLa cells after 24 h treatment with compounds 5, 6, 13 and 29. This newly synthesized series is more interesting than the published lupane and homolupane triterpenes and saponins, due to their nontoxicity towards healthy human cells and stronger cytotoxicity to various cancer cell lines. This approach increases their potential as anticancer agents.

Synthesis and cytotoxicity of betulin and betulinic acid derived 30-oxo-amides

Betulin and betulinic acid derived 30-oxo-amides were prepared by hydroboration, subsequent oxidation and amidation; these novel compounds were screened for their cytotoxic activity by SRB assays. All of the compounds showed significant cytotoxic activity for different human tumor cell lines. Small changes in the structure, however, resulted in significant changes in the cytotoxicity of the compounds. Of special interest were compounds 11 and 12, each holding an extra ethylenediamine moiety. These C-30 amides which showed low EC₅₀ values, and both of them acted mainly by apoptosis.

Rhodamine 101 Conjugates of Triterpenoic Amides Are of Comparable Cytotoxicity as Their Rhodamine B Analogs

Pentacyclic triterpenoic acids (betulinic, oleanolic, ursolic, and platanic acid) were selected and subjected to acetylation followed by the formation of amides derived from either piperazine or homopiperazine. These amides were coupled with either rhodamine B or rhodamine 101. All of these compounds were screened for their cytotoxic activity in SRB assays. As a result, the cytotoxicity of the parent acids was low but increased slightly upon their acetylation while a significant increase in cytotoxicity was observed for piperazinyl and homopiperazinyl amides. A tremendous improvement in cytotoxicity was observed; however, for the rhodamine B and rhodamine 101 conjugates, and compound 27, an ursolic acid derived homopiperazinyl amide holding a rhodamine 101 residue showed an EC50 = 0.05 µM for A2780 ovarian cancer cells while being less cytotoxic for non-malignant fibroblasts. To date, the rhodamine 101 derivatives presented here are the first examples of triterpene derivatives holding a rhodamine residue different from rhodamine B.

DU8+ Computations Reveal a Common Challenge in the Structure Assignment of Natural Products Containing a Carboxylic Anhydride Moiety

DU8+ computations of NMR spectra revealed a relatively common error in the structure assignment of carboxylic anhydride-containing natural products. Computationally driven revisions of ten of these structures are reported in this Note. The majority of the misassigned structures featured a hydroxy group that is proximal to the proposed anhydride moiety and capable of lactone formation.

Total Synthesis of Kadcoccinic Acid A Trimethyl Ester

The first total synthesis of the trimethyl ester of kadcoccinic acid A is described. The central structural element of our synthesis is a cyclopentenone motif that allows the assembly of the natural product skeleton. A gold(I)-catalyzed cyclization of an enynyl acetate led to efficient construction of the cyclopentenone scaffold. In this step, optimization studies revealed that the stereochemistry of the enynyl acetate dictates regioisomeric cyclopentenone formation. The synthesis further highlights an efficient copper-mediated conjugate addition, merged with a gold(I)-catalyzed Conia-ene reaction to connect the two fragments, thereby forging the D-ring of the natural product. The synthetic strategy reported herein can provide a general platform to access the skeleton of other members of this family of natural products.

Betulonic Acid Derivatives Interfering with Human Coronavirus 229E Replication via the nsp15 Endoribonuclease

To develop antiviral therapeutics against human coronavirus (HCoV) infections, suitable coronavirus drug targets and corresponding lead molecules must be urgently identified. Here, we describe the discovery of a class of HCoV inhibitors acting on nsp15, a hexameric protein component of the viral replication-transcription complexes, endowed with immune evasion-associated endoribonuclease activity. Structure-activity relationship exploration of these 1,2,3-triazolo-fused betulonic acid derivatives yielded lead molecule 5h as a strong inhibitor (antiviral EC50: 0.6 μM) of HCoV-229E replication. An nsp15 endoribonuclease active site mutant virus was markedly less sensitive to 5h, and selected resistance to the compound mapped to mutations in the N-terminal part of HCoV-229E nsp15, at an interface between two nsp15 monomers. The biological findings were substantiated by the nsp15 binding mode for 5h, predicted by docking. Hence, besides delivering a distinct class of inhibitors, our study revealed a druggable pocket in the nsp15 hexamer with relevance for anti-coronavirus drug development.

Biocatalysis in the Chemistry of Lupane Triterpenoids

Pentacyclic triterpenes are important representatives of natural products that exhibit a wide variety of biological activities. These activities suggest that these compounds may represent potential medicines for the treatment of cancer and viral, bacterial, or protozoal infections. Naturally occurring triterpenes usually have several drawbacks, such as limited activity and insufficient solubility and bioavailability; therefore, they need to be modified to obtain compounds suitable for drug development. Modifications can be achieved either by methods of standard organic synthesis or with the use of biocatalysts, such as enzymes or enzyme systems within living organisms. In most cases, these modifications result in the preparation of esters, amides, saponins, or sugar conjugates. Notably, while standard organic synthesis has been heavily used and developed, the use of the latter methodology has been rather limited, but it appears that biocatalysis has recently sparked considerably wider interest within the scientific community. Among triterpenes, derivatives of lupane play important roles. This review therefore summarizes the natural occurrence and sources of lupane triterpenoids, their biosynthesis, and semisynthetic methods that may be used for the production of betulinic acid from abundant and inexpensive betulin. Most importantly, this article compares chemical transformations of lupane triterpenoids with analogous reactions performed by biocatalysts and highlights a large space for the future development of biocatalysis in this field. The results of this study may serve as a summary of the current state of research and demonstrate the potential of the method in future applications.

Triterpenoid compound betulin attenuates allergic airway inflammation by modulating antioxidants, inflammatory cytokines and tissue transglutaminase in ovalbumin-induced asthma mice model

OBJECTIVES

This study hypothesized that to analyse the anti-inflammatory effect of triterpenoid compound betulin in ovalbumin (OVA)-induced asthmatic mice.

METHODS

In this study, betulin was intraperitoneally administered in OVA-challenged and sensitized mice. The effect of betulin on inflammatory cells, lung function, reactive oxygen species (ROS) production, antioxidants status, oxidative stress markers, serum IgE level and inflammatory cytokines status in BALF was examined by enzyme-linked immunosorbent assay. The expression of tTG, TGF-β1, MMP-9 and TIMP-1 in lung tissue was scrutinized by RT-qPCR analysis, and the expression of TREM-1, p-IκB-α and NF-κBp65 proteins in lung tissue was examined by western blot analysis.

KEY FINDINGS

We found that the betulin treatment has effectively attenuated the proliferation of inflammatory cells, reduced the ROS generation, elevated the antioxidant enzymes and attenuated the level of oxidative markers in asthma induced mice. Moreover, reduced the level of serum IgE and pro-inflammatory cytokines, and increased the anti-inflammatory cytokine IFN-γ. Betulin treatment down-regulated the expression of MMP-9, tTG and TGF-β1 genes; moreover, betulin treatment effectively down-regulated the TREM-1, p-IκB-α and NF-κBp65 proteins level in lung.

CONCLUSION

Betulin exhibited effective anti-asthmatic activity by attenuating the accumulation of inflammatory cells, expression of tTG, TGF-β1 and MMP-9 genes in lung tissue.

Identification of Bioactive Natural Product from the Stems and Stem Barks of Cornus walteri: Benzyl Salicylate Shows Potential Anti-Inflammatory Activity in Lipopolysaccharide-Stimulated RAW 264.7 Macrophages

Cornus walteri (Cornaceae), known as Walter's dogwood, has been used to treat dermatologic inflammation and diarrheal disease in traditional oriental medicine. As part of an ongoing research project to discover natural products with biological activities, the anti-inflammatory potential of compounds from C. walteri in lipopolysaccharide (LPS)-stimulated mouse RAW 264.7 macrophages were explored. Phytochemical analysis of the methanol extract of the stem and stem bark of C. walteri led to the isolation of 15 chemical constituents. These compounds were evaluated for their inhibitory effects on the production of the proinflammatory mediator nitric oxide (NO) in LPS-stimulated macrophages, as measured by NO assays. The molecular mechanisms underlying the anti-inflammatory activity were investigated using western blotting. Our results demonstrated that among 15 chemical constituents, lupeol and benzyl salicylate inhibited NO production in LPS-activated RAW 264.7 macrophages. Benzyl salicylate was more efficient than NG-monomethyl-L-arginine mono-acetate salt (L-NMMA) in terms of its inhibitory effect. In addition, the mechanism of action of benzyl salicylate consisted of the inhibition of phosphorylation of IκB kinase alpha (IKKα), IκB kinase beta (IKKβ), inhibitor of kappa B alpha (IκBα), and nuclear factor kappa B (NF-κB) in LPS-stimulated macrophages. Furthermore, benzyl salicylate inhibited the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Taken together, these results suggest that benzyl salicylate present in the stem and stem bark of C. walteri has potential anti-inflammatory activity, supporting the potential application of this compound in the treatment of inflammatory diseases.

Natural pentacyclic triterpenoid acids potentially useful as biocompatible nanocarriers

The importance of natural raw materials has grown recently because of their ready availability, renewable nature, biocompatibility and controllable degradability. One such group of plant-derived substances includes the triterpenoid acids, terpenic compounds consisting of six isoprene units, a carboxyl group and other functional groups producing various isomers. Most can be easily extracted from different parts of the plant and modified successfully. By themselves or as aglycones (genins) of triterpene saponins, they have potentially useful pharmaceutical activity. This review focuses on the supramolecular properties of triterpenoid acids with regard to their subsequent use as biocompatible nanocarriers. The review also considers the current list of pentacyclic triterpene acids for which molecular self-assembly has been confirmed without the need for structural modification.

Synthesis, Anticancer, and Antibacterial Activity of Betulinic and Betulonic Acid C-28-Triphenylphosphonium Conjugates with Variable Alkyl Linker Length

BACKGROUND

Conjugation of triterpenoids such as betulinic acid 1 with the Triphenylphosphonium (TPP) group is a powerful approach to generating medicinal compounds. Their development proposes structure optimization in respect of availability and activity towards target cells and organelles. Selection of 1 or its precursor betulonic acid 2 and the optimal linker is of particular importance for drug candidate identification among the TPP-triterpenoid conjugates.

OBJECTIVE

In this study, new C-28-TPP conjugated derivatives of 1 and 2 with the alkyl/alkoxyalkyl linkers of variable length were synthesized and compared regarding their anticancer, antibacterial, and mitochondriatargeted effects.

METHODS

The TPP conjugates of 1 and 2 [6a-f, 7a-f] were synthesized by the reaction of halogenalkyl esters [3a-f, 4a-f, 5] with triphenylphosphine in acetonitrile upon heating. Cytotoxicity (MTT assay), antibacterial activity (microdilution assay), and mitochondrial effects (flow cytofluorometry) were studied.

RESULTS

Conjugation with the TPP group greatly increased the cytotoxicity of the triterpenoids up to 30 times. The conjugates were up to 10-17 times more active against MCF-7 (IC50 = 0.17μM, 72h, 6c) and PC-3 (IC50 = 0.14μM, 72h, 6a) cancer cells than for human skin fibroblasts. The enhanced antibacterial (bactericidal) activity of the TPP-triterpenoid conjugates with MIC for Gram-positive bacteria as low as 2μM (6a, 7a) was for the first time revealed. The conjugates were found to effectively inhibit fluorescence of 2′,7′-dichlorofluorescin probe in the cytosol upon oxidation, decrease transmembrane potential, and increase superoxide radical level in mitochondria.

CONCLUSION

Relationships between the effects and structure of the TPP-triterpenoid conjugates were evaluated and discussed. Based on the results, 6a can be selected for further preclinical investigation as a potential anticancer compound.

Betulinic acid derived amides are highly cytotoxic, apoptotic and selective

Betulinic and platanic acid derived amides were prepared and screened for their cytotoxic activity. All of the compounds were shown to be cytotoxic for a panel of human tumor cell lines, and especially apoptotic betulinic acid derived compounds 6, 8 and 19 showed low EC₅₀ values. Of special interest was a 4-isoquinolinyl amide of 3-O-acetyl-betulinic acid (compound 19), being the most cytotoxic compound of this series and holding EC₅₀ values as low as EC₅₀ = 1.48 μM (A375 melanoma cells) while being significantly less cytotoxic for non-malignant fibroblasts NIH 3T3 with a selectivity index of >91.2. This finding parallels previous results obtained for SAA21, a augustic acid derived compound thus making the 4-isoquinolinyl moiety to a privileged scaffold.

Benzyl salicylate from the stems and stem barks of Cornus walteri as a nephroprotective agent against cisplatin-induced apoptotic cell death in LLC-PK1 cells

Benzyl salicylate from Cornus walteri can be a nephroprotective agent against cisplatin-induced oxidative stress and apoptosis.

Synthesis of N-Heterocyclic Analogues of 28-O-Methyl Betulinate, and Their Antibacterial and Antifungal Properties

The paper presents the results on the one-pot pyridine quaternization using betulinic 28-O-methyl ester (1) and Tempo+Br3− cation followed by reduction of the resulting salt (2) to 1,2,5,6-tetrahydropyridine derivative (3). The structures of new compounds are confirmed by means of 1D and 2D-NMR spectroscopy, as well as MALDI TOF/TOF spectrometry. The derivatives 2 and 3 are active against S. aureus at the minimum inhibitory concentration (MIC) of 4 μg/mL and 16 μg/mL, correspondingly.

2-Deoxyglycoside Conjugates of Lupane Triterpenoids with High Cytotoxic Activity-Synthesis, Activity, and Pharmacokinetic Profile

A set of 41 glycosidic conjugates of pentacyclic triterpenes was synthesized in order to improve the solubility of highly cytotoxic parent compounds. Their in vitro cytotoxic activity was evaluated in 25 cancer cell lines and 2 noncancer fibroblasts. Fifteen compounds had high cytotoxicity on the T-lymphoblastic leukemia cell line CCRF-CEM and 6 of them were active in multiple cell lines of various histogenic origin and not toxic in fibroblasts. Compound 11a had IC₅₀ of 0.64 μM in CCRF-CEM cells, 0.60 μM in K-562 cells, and 0.37 μM in PC-3 cells; compound 12a had IC₅₀ of 0.64 μM in CCRF-CEM cells and 0.71 μM in SW620 cells; compound 17b had IC₅₀ of 0.86 μM in HCT116 cells and 0.92 μM in PC-3 cells. Compounds 11b and 12b were slightly less active than the previously mentioned derivatives; however, their solubility was significantly better, and therefore they were selected for the in vivo evaluation of the pharmacokinetic profile in mice. In both compounds, the maximum concentration in plasma was achieved very rapidly-the highest level in plasma was found 1 h after administration (22.2, respectively, 6.4 μM). For compound 12b, the resorption was followed with fast elimination, and 12 h after administration, the compound was not detected in plasma. In contrast, compound 11b was eliminated more slowly; it was still present in plasma after 12 h, but its concentration dropped below the detection limit after 24 h. The elimination half-time determined for compound 11b was 2.4 h and for compound 12b just about 1.4 h. These values are reasonable for further drug development.

Lupane-type conjugates with aminoacids, 1,3,4- oxadiazole and 1,2,5-oxadiazole-2-oxide derivatives: Synthesis, anti-inflammatory activity and in silico evaluation of target affinity

With the purpose to improve anti-inflammatory activity, the impact of introduction of 1,2,5- and 1,3,4-oxadiazole fragments to betulonic acid core as well as hybrids tethered with short ω-amino acids has been studied. The anti-inflammatory activity of synthesized compounds was tested in vivo using models of inflammation induced by concanavalin A and histamine. The majority of new compounds demonstrated higher anti-inflammatory activity compared with starting betulonic acid. To confirm the molecular targets of new derivatives in NRf2 and NFκB pathways the docking at Kelch and BTB active sites of Keap1 as well as IKK was done. The novelty of the present work is the development of new class of low toxic anti-inflammatory substances consisting of amino acid-linked betulonic acid - oxadiazole conjugates. These compounds can be considered as prospective chemopreventive agents.

Betulinic Acid Suppresses Ovarian Cancer Cell Proliferation through Induction of Apoptosis

Ovarian cancer is one of the leading causes of cancer deaths worldwide in women, and the most malignant cancer among the different gynecological cancers. In this study, we explored potentially anticancer compounds from Cornus walteri (Cornaceae), the MeOH extract of which has been reported to show considerable cytotoxicity against several cancer cell lines. Phytochemical investigations of the MeOH extract of the stem and stem bark of C. walteri by extensive application of chromatographic techniques resulted in the isolation of 14 compounds (1–14). The isolated compounds were evaluated for inhibitory effects on the viability of A2780 human ovarian carcinoma cells and the underlying molecular mechanisms were investigated. An 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was employed to assess the anticancer effects of compounds 1–14 on A2780 cells, which showed that compound 11 (betulinic acid) reduced the viability of these cells in a concentration-dependent manner and had an half maximal (50%) inhibitory concentration (IC₅₀) of 44.47 μM at 24 h. Nuclear staining and image-based cytometric assay were carried out to detect the induction of apoptosis by betulinic acid. Betulinic acid significantly increased the condensation of nuclei and the percentage of apoptotic cells in a concentration-dependent manner in A2780 cells. Western blot analysis was performed to investigate the underlying mechanism of apoptosis. The results indicated that the expression levels of cleaved caspase-8, -3, -9, and Bax were increased in A2780 cells treated with betulinic acid, whereas those of Bcl-2 were decreased. Thus, we provide the experimental evidence that betulinic acid can induce apoptosis in A2780 cells through both mitochondria-dependent and -independent pathways and suggest the potential use of betulinic acid in the development of novel chemotherapeutics for ovarian cancer therapy.

Betulin and its derivatives as novel compounds with different pharmacological effects

Betulin (B) and Betulinic acid (BA) are natural pentacyclic lupane-structure triterpenoids which possess a wide range of pharmacological activities. Recent evidence indicates that B and BA have several properties useful for the treatment of metabolic disorders, infectious diseases, cardiovascular disorders, and neurological disorders. In the current review, we discuss B and BA structures and derivatives and then comprehensively explain their pharmacological effects in relation to various diseases. We also explain antiviral, antibacterial and anti-cancer effects of B and BA. Finally, we discuss the delivery methods, in which these compounds most effectively target different systems.

Synthesis, characterization and cytotoxic activity evaluation of ginsengdiol oxidation and nitrogen hybrid derivatives

Panaxadiol (PD), a diol-type ginseng saponin, with a dammarane skeleton plays a potential role in the apoptosis of tumor cells. In this study, 28 oxidation and nitrogen hybrid derivatives of PD were synthesized, of which 20 were novel compounds. All the obtained compounds were screened for their cytotoxic activity in six cell lines. As compared with the positive control, some compounds showed better anti-proliferative activities while having much weaker effect on the growth of normal cells. Among them, ring-A fused pyrazoline of PD (1j) displayed impressive cytotoxic activity with IC₅₀ 9.62 ± 1.34, 11.65 ± 1.71, and 13.45 ± 1.60 μM against A549, HeLa and 8901 cell lines, respectively. Additionally, compound 2f exhibited the most potent activity with an IC₅₀ value of 8.93 ± 1.11 μM against cell line A549. Therefore, our results indicated that 1j and 2f can be promising lead candidates for further studies.

Triterpenes from the fruit of Camptotheca acuminata suppress human hepatocellular carcinoma cell proliferation through apoptosis induction

The fruit of Camptotheca acuminata, a kind of mainly medicinal plant, possesses good antitumor properties. In order to explore the bioactive compounds for the treatment of hepatocellular carcinoma, the study focused on the isolation of cytotoxic compounds from the fruit of Camptotheca acuminata, which led to the discovery of fourteen compounds, including one new triterpene, 3β,20-dihydroxy-30α-methyl,17(29)-β-epoxy-28-norlupane (1), together with thirteen known compounds (2-14). The structures of isolated compounds were demonstrated by spectroscopic methods including 1D and 2D NMR spectroscopy. Moreover, all triterpenes were evaluated for antiproliferative activities against two human hepatocellular carcinoma cell lines, HepG2 and Hep3B. Compound 3 showed the strongest cytotoxic activity against the HepG2 with IC₅₀ value at 29.6 μM. Further study demonstrated that compound 3 exhibited cytotoxic activity through the induction of apoptosis.

Applications of Lawesson's reagent in the synthesis of naturally occurring steroids and terpenoids

Steroids and terpenoids are among the most biologically significant classes of natural products possessing a variety of biological activities. The replacement of one or more oxygen atoms in a steroid or terpenoid molecule by a heteroatom affects the chemical properties of that particular steroid or terpenoid, and that replacement often results in alterations of its biological properties, which is sometimes valuable. One possible modification is the thionation that could have some influence on such activity. Among the various thionating reagents, Lawesson's reagent was found to be most suitable and showed versatile properties, including chemoselectivity and functional group tolerance. In this review, we present the role of Lawesson's reagent in the synthesis of thioanalogues of natural steroids and terpenoids.

Synthesis and antiproliferative properties of new hydrophilic esters of triterpenic acids

To improve the properties of cytotoxic triterpenoid acids 1-5, a large set of hydrophilic esters was synthesized. We choose betulinic acid (1), dihydrobetulinic acid (2), 21-oxoacid 3 along with highly active des-E lupane acids 4 and 5 as a model set of compounds for esterification of which the properties needed to be improved. As ester moieties were used - methoxyethanol and 2-(2-methoxyethoxy)ethanol and glycolic unit (type a-d), pyrrolidinoethanol, piperidinoethanol and morpholinoethanol (type f-h), and monosaccharide groups (type i-l). As a result, 56 triterpenic esters (49 new compounds) were obtained and their cytotoxicity on four cancer cell lines and normal human fibroblasts was tested. All new compounds were fully soluble at all tested concentrations, which used to be a problem of the parent compounds 1 and 2. 16 compounds had IC₅₀ < 10 μM on at least one cancer cell line, 12 compounds had cytotoxicity of <10 μM against at least three of four tested cancer cell lines. The highest activity was found for compound 3c (1.8 μM on MCF7, 2.8 μM on HeLa, and 1.6 μM on G-361 cells) which also had no toxicity on non-cancerous BJ fibroblasts at the highest tested concentration (50 μM). High selective cytotoxicity was also found in compounds 1k, 2k, 3c, and 3i that are ideal candidates for drug development. Therefore, more studies to identify the mechanism of action were performed in case of 1k, 3c, and 3g such as effects on cell cycle and apoptosis. It was found that compounds 3c and 3g can induce apoptosis via caspase-3 activation and modulation of protein Bcl-2 in G-361 cells. In conclusion, compounds 1k, 3c, and 3g show high and selective cytotoxicity, therefore they are significantly better candidates for anti-cancer drug development than the parent acids 1-5.

neo-Clerodane Diterpenoids and Other Constituents of Salvia filipes

A series of neo-clerodane-type diterpenoids were isolated from the aerial parts of Salvia filipes, including the new compounds 4-epi-polystachyne A (1), salvifilines A (3), C (7), and D (8), and salvifiline B, which was isolated as the 15-O-methyl derivatives 4/5. In addition, the five known diterpenoids (2, 9-12), together with ursolic, oleanolic, and betulinic acids, and the flavone eupatorin were also isolated. The structures were determined by analysis of their spectroscopic data, mainly 1D and 2D NMR. The structure of salvifiline D was confirmed by X-ray analysis. The cytotoxic activities of the diterpenoids were evaluated, but all were inactive against a panel of six human cancer cell lines.

Betulin Derivatives Effectively Suppress Inflammation in Vitro and in Vivo

Betulin is a pharmacologically active triterpenoid found in the bark of the birch tree (Betula sp. L.). Betulin and betulinic acid are structurally related to anti-inflammatory steroids, but little is known about their potential anti-inflammatory properties. In the present study, the inflammatory gene expression and the anti-inflammatory properties of betulin, betulinic acid, and 16 semisynthetic betulin derivatives were investigated. Betulin derivatives 3, 4, and 5 selectively inhibited the expression of the inducible nitric oxide synthase (iNOS) in a post-transcriptional manner. They also inhibited nitric oxide (NO) production but had no effect on the other inflammatory factors studied. More interestingly, a new anti-inflammatory betulin derivative 9 with a wide-spectrum anti-inflammatory activity was discovered. Compound 9 was found to suppress the expression of cytokines interleukin-6 (IL-6) and monocyte chemotactic protein-1 (MCP-1), as well as that of prostaglandin synthase-2 (COX-2) in addition to iNOS. The in vivo anti-inflammatory effect of compound 9 was indicated via significant suppression of the carrageenan-induced paw inflammation in mice. The results show, for the first time, that the pyrazole-fused betulin derivative (9) and related compounds have anti-inflammatory properties that could be utilized in drug development.

Betulinic acid derived hydroxamates and betulin derived carbamates are interesting scaffolds for the synthesis of novel cytotoxic compounds

The betulinic acid-derived hydroxamates 5-18, the amides 19-24, and betulin-derived bis-carbamates 25-28 as well as the carbamates 31-40 and 44-48 were prepared and evaluated for their antiproliferative activity in a photometric sulforhodamine B (SRB) assay against several human cancer cell lines and nonmalignant mouse fibroblasts (NIH 3T3). While for 3-O-acetyl hydroxamic acid 5 EC50 values as low as EC50 = 1.3 μM were found, N,O-bis-alkyl substituted hydroxamates showed lowered cytotoxicity (EC50 = 16-20 μM). In general, hydroxamic acid derivatives showed only reduced selectivity for tumor cells, except for allyl substituted compound 13 (EC50 = 5.9 μM for A2780 human ovarian carcinoma cells and EC50 > 30 μM for nonmalignant mouse fibroblasts). The cytotoxicity of betulinic acid derived amides 19-24 and of betulin derived bis-carbamates 25-28 was low, except for N-ethyl substituted 25. Hexyl substituted 39 showed EC50 = 5.6 μM (518A2 cells) while for mouse fibroblasts EC50 > 30 was determined.

Synthesis of piscidinol A derivatives and their ability to inhibit HIV-1 protease

Four types of piscidinol A derivatives were synthesized and evaluated their ability to inhibit HIV-1 protease to understand their structure-activity relationships. Of these tirucallane-type triterpene derivatives, an A-seco derivative (1b) moderately inhibited human immunodeficiency virus (HIV) protease (IC50 38.2 μM). The 2,2-dimethyl succinic acid (DMS) acylated tirucallane derivatives (4b, 6a, and 7b, 50 < IC50 < 100 μM) were more inhibitory against HIV-1 PR than the others (PA, 2a, 4a, 4c-4d, 5a, 6b-6d, and 7a, IC50 > 100 μM). These findings indicated that the 2,3-seco-2,3-dioic acid (1b) and DMS-acylated tirucallane-type derivatives preferably inhibited HIV viral protease.

Betulinic Acid and its Derivatives as Potential Antitumor Agents

Betulinic acid (BA) is a lupane-type pentacyclic triterpene, distributed ubiquitously throughout the plant kingdom. BA and its derivatives demonstrate multiple bioactivities, particularly an antitumor effect. This review critically describes the recent research on isolation, synthesis, and derivatization of BA and its natural analogs betulin and 23-hydroxybetulinic acid. The subsequent part of the review focuses on the current knowledge of antitumor properties, combination treatments, and pharmacological mechanisms of these compounds. A 3D-QSAR analysis of 62 BA derivatives against human ovarian cancer A2780 is also included to provide information concerning the structure-cytotoxicity relationships of these compounds.

Synthesis and antitumor activity of novel 3-oxo-23-hydroxybetulinic acid derivatives

A series of novel derivatives of 3-oxo-23-hydroxybetulinic acid was designed, synthesized, and evaluated for their antiproliferative activity against a panel of cancer cell lines (HL-60, BEL-7402, SF-763, HeLa, B16 and A375). The results indicated that majority of the derivatives exhibited more significant antitumor activity than the parent compound. In particular compound 10e showed the most potent activity with IC50 values of 5.85, 6.23 and 7.22 μM against B16, SF-763 and BEL-7402 cells, respectively. Furthermore, 10e inhibited tumor growth by 51.8% and 62.7% (w/w) in H22 and B16 xenograft mouse models, comparable to cyclophosphamide and 5-fluorouracil, respectively.

Antineoplastic agents. 595. Structural modifications of betulin and the X-ray crystal structure of an unusual betulin amine dimer

The lupane-type triterpene betulin (1) has been subjected to a series of structural modifications for the purpose of evaluating resultant cancer cell growth inhibitory activity. The reaction sequence 7→11→12 was especially noteworthy in providing a betulin-derived amine dimer. Other unexpected synthetic results included the 11 and 13/14→17 conversions, which yielded an imidazo derivative. X-ray crystal structures of dimer 12 and intermediate 25 are reported. All of the betulin modifications were examined for anticancer activity against the P388 murine and human cell lines. Significant cancer cell growth inhibition was found for 4, 8, 9, 15/16, 19, 20, 24, and 26, which further defines the utility of the betulin scaffold.