3,28-Di-O-(dimethylsuccinyl)-betulin isomers as anti-HIV agents

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^⊕ BN and 3,28-bisTPP^⊕ 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^⊕-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.

Enhancing effect of cystamine in its amides with betulinic acid as antimicrobial and antitumor agent in vitro

Amides of betulinic acid with cystamine were synthesized to investigate their antimicrobial and antitumor activity, and their influence on the cell cycle and cell apoptosis. The former target amide (6) displayed cytotoxicity in CEM cell line after 72 h of treatment (IC₅₀ = 3.0 ± 0.7 μM; TI = 20), and induced apoptosis by caspase-3/7 activation in CEM cells. The latter target amide (9) displayed antimicrobial activity against Streptococcus mutans (MIC 3.125 μM; MBC 3.125 μM) and Bacillus cereus (MIC 25 μM; MBC 25 μM). The achieved results demonstrate enhancing of their biological activity over that of the parent compounds. However, two intermediate compounds (2 and 7) displayed either considerable cytotoxicity (2; 7.5 ± 0.8 μM; TI = 10, against G361) or antimicrobial activity (7; both against Actinomyces odontolycus and Clostridium perfrigens with MIC 12.5 µM and MBC 12.5 µM). The experimental data were compared with the in silico calculated physico-chemical and ADME parameters of the target compounds, including successful intermediates.

Tissue-specific study across the stem reveals the chemistry and transcriptome dynamics of birch bark

Tree bark is a highly specialized array of tissues that plays important roles in plant protection and development. Bark tissues develop from two lateral meristems; the phellogen (cork cambium) produces the outermost stem-environment barrier called the periderm, while the vascular cambium contributes with phloem tissues. Although bark is diverse in terms of tissues, functions and species, it remains understudied at higher resolution. We dissected the stem of silver birch (Betula pendula) into eight major tissue types, and characterized these by a combined transcriptomics and metabolomics approach. We further analyzed the varying bark types within the Betulaceae family. The two meristems had a distinct contribution to the stem transcriptomic landscape. Furthermore, inter- and intraspecies analyses illustrated the unique molecular profile of the phellem. We identified multiple tissue-specific metabolic pathways, such as the mevalonate/betulin biosynthesis pathway, that displayed differential evolution within the Betulaceae. A detailed analysis of suberin and betulin biosynthesis pathways identified a set of underlying regulators and highlighted the important role of local, small-scale gene duplication events in the evolution of metabolic pathways. This work reveals the transcriptome and metabolic diversity among bark tissues and provides insights to its development and evolution, as well as its biotechnological applications.

Synthesis, modification, and cytotoxic evaluation of 2,3-secotriterpenic β-ketoesters

A set of β-ketoesters was synthesized from 2,3-seco-18αH-oleanane and 2,3-secolupane bromomethyl ketones. Additionally, hydroxy derivatives with the A-seco- or five-membered A ring were obtained as a result of the reduction or of alkaline hydrolysis of acetic acid β-ketoesters 4, 9. Cytotoxic screening revealed the compound 4 with marked activity (IC₅₀ 3.07-3.61 µM) against the HCT 116, MS, RD TE32 cancer cells. The studies of the cytotoxic mechanism enabled elucidating the fact that treatment of the HCT 116 cells with compound 4 for 18 h leads to induction of apoptosis in a dose-dependent manner. This observation was confirmed by registration of chromatin condensation, by the fluorescence increased during Annexin V-FITC staining, and by appearance of a sub-G0 peak in the cell cycle analysis with DAPI. Compound 4 also inhibited migration of cancer cells in the wound healing assay.

Picolyl amides of betulinic acid as antitumor agents causing tumor cell apoptosis

A series of picolyl amides of betulinic acid (3a-3c and 6a-6c) was prepared and subjected to the cytotoxicity screening tests. Structure-activity relationships studies resulted in finding differences in biological activity in dependence on o-, m- and p-substitution of the pyridine ring in the target amides, when cytotoxicity data of 3a-3c and 6a-6c were obtained and compared. The amides 3b and 3a displayed cytotoxicity (given in the IC₅₀ values) in G-361 (0.5 ± 0.1 μM and 2.4 ± 0.0 μM, respectively), MCF7 (1.4 ± 0.1 μM and 2.2 ± 0.2 μM, respectively), HeLa (2.4 ± 0.4 μM and 2.3 ± 0.5 μM, respectively) and CEM (6.5 ± 1.5 μM and 6.9 ± 0.4 μM, respectively) tumor cell lines, and showed weak effect in the normal human fibroblasts (BJ). Selectivity against all tested cancer cells was determined and compared to normal cells with therapeutic index (TI) between 7 and 100 for compounds 3a and 3b. The therapeutic index (TI = 100) was calculated for human malignant melanoma cell line (G-361) versus normal human fibroblasts (BJ). The cytotoxicity of other target amides (3c and 6a-6c) revealed lower effects than 3a and 3b in the tested cancer cell lines.

Synthesis and Cytotoxic Evaluation of Betulin–Triazole–AZT Hybrids

Betulin was converted to the corresponding alkyne-functionalized esters and amides and subsequently deployed as substrates for a ‘click’ chemistry-mediated coupling with 3'-azido-3'-deoxythydimine (AZT) to furnish a novel betulin–triazole–AZT hybrid compounds. Eleven new hybrids were thus successfully prepared and evaluated as cytotoxic agents, revealing an interesting anticancer activity in KB and HepG2 cancer cell lines.

Spectral and microscopic study of self-assembly of novel cationic spermine amides of betulinic acid

Supramolecular characteristics of two spermine amides of betulinic acid (1 and 2) were studied by measuring and evaluating their UV-VIS-NIR spectra in aqueous acetonitrile and DOSY-NMR spectra in tetradeuteromethanol, accompanied by atomic force microscopy (AFM) images, scanning electron microscopy (SEM) micrographs, and transmission electron microscopy (TEM) micrographs. Fibrous supramolecular self-assembly of 1 and 2 was observed by AFM images, as well as by the SEM and TEM micrographs. Bathochromic shifts of the absorbance maximum at 870nm to 1015-970nm in the UV-VIS-NIR spectra were observed with increasing water content in the acetonitrile/water systems, indicating formation of fibrous J-type aggregates. Variable temperature DOSY-NMR spectral measurement showed non-linear dependence that also suggests self-assembly behavior of the studied systems. Chiral supramolecular structures were formed by self-assembling due to the chirality of the monomeric molecules. Application of aqueous media during self-assembly procedures is an important factor in the development of targeted drug delivery systems.

Polyamine derivatives of betulinic acid and β-sitosterol: A comparative investigation

β-Sitosterol and betulinic acid were used in designing their conjugates with selected polyamines bearing either an amide bond, or an ester and an amide bond simultaneously in the target molecule. The synthesized compounds were subjected to basic cytotoxic and antimicrobial tests. The synthetic protocol is described separately for each of the three series of the target amides, because each series of compounds required a different synthetic approach. The cytotoxicity was tested on cells derived from human T-lymphoblastic leukemia, breast adenocarcinoma and cervical cancer, and compared with the tests on normal human fibroblasts. Most of the target compounds (5a-5c, 11a-11c and 16a-16c) showed medium to high cytotoxicity (0.7-7.8 μM), however, in some cases the compounds showed high cytotoxicity even toward normal human fibroblasts (11a-11c). Two compounds of this series (11c and 16c) also displayed antimicrobial activity with high and selective microbe specificity. The compound 11c was potent against Escherichia coli (minimal inhibition concentration (MIC) 6.25 μg mL(-1), i.e. 9.75 nM mL(-1)) and Staphylococcus aureus (MIC 12.5 μg mL(-1), i.e. 19.5 nM mL(-1)), and showed medium activity against Pseudomonas aeruginosa. The compound 16c was highly active against Enterococcus faecalis and S. aureus (both, MIC 3.125 μg mL(-1), i.e. 4.22 nM mL(-1)), both Gram-positive bacteria, however showed only weak activity against E. coli and no activity against P. aeruginosa, both Gram-negative bacteria, which indicates possible microbe specificity of 16c. Comparing β-sitosterol-based series (5a-5c) and betulinic acid series (11a-11c and 16a-16c) of the target compounds, the latter one gave more promising structures. The compounds 11c and 16c showed effects which may be described as multifarious activity (pleiotropic effects).

Conjugates of betulin derivatives with AZT as potent anti-HIV agents

Fourteen novel conjugates of 3,28-di-O-acylbetulins with AZT were prepared as anti-HIV agents, based on our previously reported potent anti-HIV triterpene leads, including 3-O-acyl and 3,28-di-O-acylbetulins. Nine of the conjugates (49-53, 55, 56, 59, and 60) exhibited potent anti-HIV activity at the submicromolar level, with EC(50) values ranging from 0.040 to 0.098muM in HIV-1(NL4-3) infected MT-4 cells. These compounds were equipotent or more potent than 3-O-(3',3'-dimethylsuccinyl)betulinic acid (2), which is currently in Phase IIb anti-AIDS clinical trial.

Enhancing the divergent activities of betulinic acid via neoglycosylation

Using neoglycosylation, the impact of differential glycosylation upon the divergent anticancer and anti-HIV properties of the triterpenoid betulinic acid (BA) was examined. Each member from a library of 37 differentially glycosylated BA variants was tested for anticancer and anti-HIV activities. Enhanced analogs for both desired activities were discovered with the corresponding antitumor or antiviral enhancements diverging, on the basis of the appended sugar, into two distinct compound subsets.

Triterpene based compounds with potent anti-maturation activity against HIV-1

Efforts towards developing orally bioavailable HIV-1 maturation inhibitors starting from betulinic acid 1 are described. SAR resulted in improved potency, physicochemical properties, and enhanced oral absorption in rats.

Birch bark research and development

This review will detail progress made in the previous decade on the chemistry and bioactivity of birch bark extractive products. Current and future applications of birch bark natural products in pharmaceuticals, cosmetics, and dietary supplements for the prevention and treatment of cancer, HIV,and other human pathogens are reviewed. Current developments in the technology of birch bark processing are discussed. New approaches for the synthesis of potentially valuable birch bark triterpenoid derivatives are also reviewed.

Pharmacological properties of the ubiquitous natural product betulin

Betulin (lup-20(29)-ene-3beta,28-diol) is an abundant naturally occurring triterpene and it is found predominantly in bushes and trees forming the principal extractive (up to 30% of dry weight) of the bark of birch trees. Presently, there is no significant use for this easily isolable compound, which makes it a potentially important raw material for polymers and a precursor of biologically active compounds. Betulin can be easily converted to betulinic acid, which possesses a wide spectrum of biological and pharmacological activities. Betulinic acid has antimalarial and anti-inflammatory activities. Betulinic acid and its derivatives have especially shown anti-HIV activity and cytotoxicity against a variety of tumor cell lines comparable to some clinically used drugs. A new mechanism of action has been confirmed for some of the most promising anti-HIV derivatives, which makes them potentially useful additives to the current anti-HIV therapy. Betulinic acid is specifically cytotoxic to several tumor cell lines by inducing apoptosis in cells. Moreover, it is non-toxic up to 500 mg/kg body weight in mice. The literature concerning derivatization of betulin for structure-activity relationship (SAR) studies and its pharmacological properties is reviewed.

Biological activity and pharmacological prospects of lupane terpenoids: II. Semisynthetic lupane derivatives

The discussion of lupane triterpenoids as prospective medicinal preparations is continued, and semisynthetic triterpenoids are being discussed. Acyl derivatives that mainly exhibit high anti-HIV, antitumor, and organo-protective activities are described. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2006, vol. 32, no. 3; see also http://www.maik.ru.

3-O-Glutaryl-dihydrobetulin and related monoacyl derivatives as potent anti-HIV agents

3-O-Acyl-betulin and -dihydrobetulin derivatives were prepared and evaluated for anti-HIV activity. 3-O-Glutaryl-dihydrobetulin (17) demonstrated extremely potent anti-HIV activity with an EC(50) value of 2 x 10(-5) microM and a TI value of 1.12 x 10(6). 3-O-(3',3'-Dimethylsuccinyl)- and 3-O-(3',3'-dimethylglutaryl)-dihydrobetulins (15, 16) were also potent anti-HIV compounds with EC(50) values of 0.0017 and 0.0013 microM, respectively, and TI values of 16,160 and 19,530, respectively.

Lupane triterpenes and derivatives with antiviral activity

Betulin and betulinic acid have been modified at the C-3 and C-28 positions and the antiviral activity of derivatives has been evaluated in vitro. It was found that simple modifications of the parent structure of lupane triterpenes produced highly effective agents against influenza A and herpes simplex type 1 viruses.

Anti-AIDS agents 49. Synthesis, anti-HIV, and anti-fusion activities of IC9564 analogues based on betulinic acid

The betulinic acid derivative IC9564 inhibits human immunodeficiency virus (HIV)-1 entry. Among a series of IC9564 derivatives, 5 and 20 were the most promising compounds against HIV infection with EC(50) values of 0.33 and 0.46 microM, respectively. Both compounds inhibited syncytium formation with EC(50) values of 0.40 and 0.33 microM, respectively. The comparable EC(50) values in the two assays suggested that these compounds are fusion inhibitors. The structure-activity relationship data also indicated that a double bond in IC9564 can be eliminated and the statine moiety can be replaced with L-leucine while retaining anti-HIV activity.