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.     

New ursolic and betulinic derivatives as potential cytotoxic agents

Fifteen new ursolic and betulinic triterpenoids, bearing various functionalities at C-3 and C-28 were synthesized as potential cytotoxic agents. All compounds were obtained by a hemisynthetic route via ursolic and betulinic acids. Preliminary screening of these compounds on human HT 29 colon cancer cells revealed inhibitory activity for three of them. Beta-D-Glucopyranosyl-3beta-hydroxyurs-12(13)-en-28-oate 1c, 3beta-3-(3-pyridyl)-prop-2-enoyloxyurs-12(13)-en-28-oic acid 1i and the potassium salt of 3beta-cinnamoyloxylup-20(29)-en-28-oic acid 2d demonstrated cytotoxic activity in the micromolar range: 8.0, 45.0 and 8.0 microM, respectively.     

Differentiation-inducing activity of lupane triterpenes on a mouse melanoma cell line

Lupane triterpenes were found to promote melanogenesis, a hallmark of B16 2F2 mouse melanoma cell differentiation. Studies of the structure-activity relationships demonstrated that the keto function at C-3 of the lupane skeleton played important roles in the melanogenic activities of lupane triterpenes on melanoma cells. The carbonyl group at C-17 of lupane triterpenes was essential against their apoptosis-inducing activity against human cancer cells via the inhibition of topoisomerase I. We investigated whether signaling mechanisms were involved in the stimulative effects of lupane triterpenes on the melanogenesis of B16 2F2 cells. In experiments using selective inhibitors against various signal transduction molecules and Western blotting analysis, it was suggested that p38 MAPK was involved in melanoma cell differentiation as a downstream effector of PKA. Lupeol (compound 1), a lupane triterpene, induced dendrite formations, a morphological hallmark of B16 2F2 cell differentiation by rearrangement of the actin cytoskeleton. The activation of cofilin, an actin depolymerizing factor, by compound 1 caused actin fiber disassembly in B16 2F2 cells. Furthermore, compound 1 was shown to inhibit the cell motilities of human melanoma and neuroblastoma in vitro.     

Structural modifications of 2,3-indolobetulinic acid: Design and synthesis of highly potent α-glucosidase inhibitors

A series of nineteen nitrogen-containing lupane triterpenoids was obtained by modification of C2, C3, C20 and C28 positions of betulonic acid and their α-glucosidase inhibiting activity was investigated. Being a leader compound from our previous study, 2,3-indolo-betulinic acid was used as the main template for different modifications at C-(28)-carboxyl group to obtain cyano-, methylcyanoethoxy-, propargyloxy- and carboxamide derivatives. 20-Oxo- and 29-hydroxy-20-oxo-30-nor-analogues of 2,3-indolo-betulinic acid were synthesized by ozonolysis of betulonic acid followed by Fischer indolization reaction. To compare the influence of the fused indole or the seven-membered A-ring on the inhibitory activity, lupane A-azepanones with different substituents at C28 were synthesized. The structure-activity relationships revealed that the enzyme inhibition activity dramatically increased (up to 4730 times) when the carboxylic group of 2,3-indolo-betulinic acid was converted to the corresponding amide. Thus, the IC₅₀ values for glycine amide and L-phenylalanine amides were 0.04 and 0.05 μM, respectively. This study also revealed that 2,3-indolo-platanic acid is 4.5 times more active than the parent triterpenoid with IC₅₀ of 0.4 μM. Molecular modeling suggested that improved potency is due to additional polar interactions formed between C28 side chain and a sub-pocket of the α-glucosidase allosteric site.     

Cytotoxic triterpenoid saponins from the fruits of Aesculus pavia L

Continued chemical investigation on the fruits of North American Aesculus pavia L. resulted in the isolation and identification of 13 polyhydroxyoleanene pentacyclic triterpenoid saponins, named aesculiosides IIe-IIk (1-7), and IIIa-IIIf (8-13), together with 18 known compounds: aesculiosides Ia-Ie (14-18), IIa-IId (19-22), IVa-IVc (23-25), 3-O-[beta-D-galactopyranosyl(1-->2)]-alpha-L-arabinofuranosyl(1-->3)-beta-D-glucuronopyranosyl-21,22-O-diangeloyl-3beta,15 alpha,16 alpha,21 beta,22 alpha,28-hexahydroxyolean-12-ene (26), 3-O-[beta-D-glucopyranosyl(1-->2)]-alpha-L-arabinofuranosyl(1-->3)-beta-D-glucuronopyranosyl-21,22-O-diangeloyl-3beta,16 alpha,21 beta,22 alpha,24 beta,28-hexahydroxyolean-12-ene (27), 3-O-[beta-D-galactopyranosyl(1-->2)]-alpha-L-arabinofuranosyl(1-->3)-beta-D-glucuronopyranosyl-21,22-O-diangeloyl-3beta,16 alpha,21 beta,22 alpha,28-pentahydroxyolean-12-ene (28), R(1)-barrigenol (29), scopolin (30), and 5-methoxyscopolin (31). The structures of these compounds were elucidated by spectroscopic and chemical analyses. Compounds 14-22 and 26-28 were tested in vitro for their activity against 59 cell lines from nine different human cancers including leukemia, non-small cell lung, colon, CNS, melanoma, ovarian, renal, prostate, and breast. It was found that compounds with two-acyl groups at C-21 and C-22 had cytotoxic activity for all cell lines tested with GI(50) 0.175-8.71 microM, while compounds without acyl groups at C-21 and C-22 had weak or no cytotoxic activity. These results suggest that the acyl groups at C-21 and C-22 are essential for their activity.     

Advances in the synthesis and pharmacological activity of lupane-type triterpenoid saponins

Lupeol, betulin and betulinic acid are members of the so-called lupane-type triterpenoids. These natural products found worldwide in quite of lot of vegetables, fruits and plant species exhibit promising pharmacological activities including anti-inflammatory, anti-HIV and antitumor activities. Nevertheless, the poor pharmacokinetic properties of these cholesterol-like triterpenoids hampered further pharmaceutical developments. The synthesis of lupane-type saponins, i.e., sugar-derived lupanes, seems to be a good avenue to improve both their water solubility and pharmacological activity. The aims of this review are twofold: first, to describe the biological activity of naturally occurring lupane-type saponins, and second, report the different methodologies employed for the elaboration of glycosidic linkages at the C-3 and/or C-28 positions on the lupane core. The synthesis of both natural and unnatural lupane-type saponins is discussed with an emphasis on molecules exhibiting relevant biological activities.     

Biotransformation of betulinic and betulonic acids by fungi

Betulinic acid (1), a triterpenoid found in many plant species, has attracted attention due to its important pharmacological properties, such as anti-cancer and anti-HIV activities. The closely related, betulonic acid (2) also has similar properties. In order to obtain derivatives potentially useful for detailed pharmacological studies, both compounds were submitted to incubations with selected microorganisms. In this work, both were individually metabolized by the fungi Arthrobotrys, Chaetophoma and Dematium, isolated from the bark of Platanus orientalis as well as with Colletotrichum, obtained from corn leaves; such fungal transformations are quite rare in the scientific literature. Biotransformations with Arthrobotrys converted betulonic acid (2) into 3-oxo-7beta-hydroxylup-20(29)-en-28-oic acid (3), 3-oxo-7beta,15alpha-dihydroxylup-20(29)-en-28-oic acid (4) and 3-oxo-7beta,30-dihydroxylup-20(29)-en-28-oic acid (5); Colletotrichum converted betulinic acid (1) into 3-oxo-15alpha-hydroxylup-20(29)-en-28-oic (6) acid whereas betulonic acid (2) was converted into the same product and 3-oxo-7beta,15alpha-dihydroxylup-20(29)-en-28-oic acid (4); Chaetophoma converted betulonic acid (2) into 3-oxo-25-hydroxylup-20(29)-en-28-oic acid (7) and both Chaetophoma and Dematium converted betulinic acid (1) into betulonic acid (2). Those fungi, therefore, are useful for mild, selective oxidations of lupane substrates at positions C-3, C-7, C-15, C-25 and C-30.     

Cytotoxic heterocyclic triterpenoids derived from betulin and betulinic acid

The aim of this work was to synthesize a set of heterocyclic derivatives of lupane, lup-20(29)-ene, and 18α-oleanane, and to investigate their cytotoxic activities. Some of those heterocycles were previously known in the oleanane (allobetulin) group; however, to our knowledge the syntheses and biological activities of lupane heterocycles have not been reported before. Starting from betulin (1) and betulinic acid (2), we prepared 3-oxo compounds and 2-bromo-3-oxo compounds 3-10, 2-hydroxymethylene-3-oxo compounds 11-13 and β-oxo esters 14-16. Condensation of these intermediates with hydrazine, phenylhydrazine, hydroxylamine, or thiourea yielded the pyrazole and phenylpyrazole derivatives 17-22, pyrazolones 23-25, isoxazoles 26 and 27, and thiazoles 28-31. Fifteen compounds (14-16, 18-25, and 29-32) have not been reported before. The cytotoxicity was measured using panel of seven cancer cell lines with/without MDR phenotype and non tumor MRC-5 and BJ fibroblasts. The preferential cytotoxicity to cancer cell lines, particularly to hematological tumors was observed, the bromo acids 5, 6 showed highest activity and selectivity against tumor cells.     

Oxidation at C-16 enhances butyrylcholinesterase inhibition in lupane triterpenoids

A set of triterpenoids with different grades of oxidation in the lupane skeleton were prepared and evaluated as cholinesterase inhibitors. Allylic oxidation with selenium oxide and Jones’s oxidation were employed to obtain mono-, di- and tri-oxolupanes, starting from calenduladiol (1) and lupeol (3). All the derivatives showed a selective inhibition of butyrylcholinesterase over acetylcholinesterase (BChE vs. AChE). A kinetic study proved that compounds 2 and 9, the more potent inhibitors of the series, act as competitive inhibitors. Molecular modeling was used to understand their interaction with BChE, the role of carbonyl at C-16 and the selectivity towards this enzyme over AChE. These results indicate that oxidation at C-16 of the lupane skeleton is a key transformation in order to improve the cholinesterase inhibition of these compounds.     

Cytotoxic triterpenoid saponins acylated with monoterpenic acids from fruits of Gleditsia caspica Desf.

Four bisdesmosidic triterpenoid saponins named caspicaosides A-D, were isolated from the fruits of Gleditsia caspica Desf. Their structures were determined by NMR spectroscopy including HOHAHA, ¹H-¹H COSY, ROE, HMQC, HMBC experiments and HRFAB-MS as well as acid hydrolysis. The four 3,28-O-bisdesmosidic triterpenoid saponins comprised echinocystic acid as the aglycone and common oligosaccharide moieties at C3 and C28. The saccharide moiety at C-3 was identified as β-d-xylopyranosyl-(1 → 2)-α-l-arabinopyranosyl-(1 → 6)-β-d-glucopyranosyl while that at C-28 was determined as β-d-xylopyranosyl-(1 → 3)-β-d-xylopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-[α-l-rhamnopyranosyl-(1 → 6)-]β-d-glucopyranosyl. The pentasaccharide moiety linked to C-28 was acylated with monoterpenic acid and or monoterpene-arabinoside moieties at C-2 or C-2 and C-3 of the terminal rhamnose unit. The isolated saponins were assayed for their in vitro cytotoxicities against the three human tumor cell lines HepG2, A549 and HT29 using MTT method. The results showed that caspicaosides B and C bearing two and three monoterpene units, respectively, exhibited significant cytotoxic activities against the used cell lines with IC₅₀ values 1.5-6.5 μM. Caspicaosides A and D with one monoterpene unit exhibited significant cytotoxic activities on HepG2 cell line with IC₅₀ values equal to 4.5 and 5.4 μM, respectively, and IC₅₀ values >10 μM against the other two cell lines. The number of monoterpene units seems to play a main role in determining the activity.     

Cytotoxicity and inhibition of DNA topoisomerase I of polyhydroxylated triterpenoids and triterpenoid glycosides

Cytotoxicity and inhibition on human DNA topoisomerase I (TOP1) and II (TOP2) of 74 plant-originated triterpenoids and triterpenoid glycosides were investigated. The cytotoxic compounds are primarily polyhydroxylated oleananes (GI₅₀ of A549: 1.0–10.19 μM). Sixteen cytotoxic aesculiosides isolated from Aesculus pavia inhibited TOP1 catalytic activity by interacting directly with the free enzyme and preventing the formation of the DNA–TOP1 complex. Interestingly, hydrolysis of six active aesculiosides (1, 4, 6, 8, 10, and 23) lost their TOP1 activities but enhanced their cytotoxicities. None of the test compounds showed any activity against TOP2. Structure–activity relationship (SAR) investigations indicated that cytotoxic oleananes required at least one angeloyl moiety at either C-21 or C-22 but the sugar moiety at C-3 may decrease their cytotoxicities. An angeloyl or tigeloyl group at C-21 is required for oleananes to bind the free TOP1 enzyme although the type and length of acyl moiety at C-22 also affects their activity. However, sugar moiety at C-3 is necessary for their TOP1 activities.     

Preparation,anticholinesterase activity and molecular docking of new lupane derivatives

A set of twenty one lupane derivatives (2–22) was prepared from the natural triterpenoid calenduladiol (1) by transformations on the hydroxyl groups at C-3 and C-16, and also on the isopropenyl moiety. The derivatives were tested for their inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) and some structure–activity relationships were outlined with the aid of enzyme kinetic studies and docking modelization. The most active compound resulted to be 3,16,30-trioxolup-20(29)-ene (22), with an IC₅₀ value of 21.5 μM for butyrylcholinesterase, which revealed a selective inhibitor profile towards this enzyme.     

Lack of anti-TSTA antibodies in mice immunized with a methylcholanthrene-induced fibrosarcoma

Summary The 3-methylcholanthrene (MCA)-induced BALB/c (H-2^d) fibrosarcoma C-1 bears a strong tumor-specific transplantation antigen (TSTA) which, in previous studies, appeared to be distinct from H-2^k alien antigens expressed by this tumor. To see whether a syngeneic anti-C-1 serum obtained by multiple immunizations with C-1 tumor cells contained anti-TSTA-specific antibodies, in vitro cytotoxicity tests were performed. The syngeneic anti-C-1 serum had a high cytotoxic activity on C-1 cells, which allowed an absorption analysis to be carried out. Absorption of the serum with C3Hf, AKR, or B10.BR normal lymphoid cells (all sharing H-2^k antigens) reduced the cytotoxic activity on C-1 cells to 30%–50%. This residual activity could not be absorbed by FMR+ or G+ murine leukemias, by ecotropic endogenous virus obtained from SC-1 cells infected with the C-1 virus, by embryonic cells, or by normal BALB/c or C57BL/6 lymphoid cells. Conversely, the serum activity was abrogated by absorbing with the MCA-induced BALB/c fibrosarcomas C-1, ST2, C-3, GI-17, or CMS-1, and significantly lowered by the MCA-induced C3Hf fibrosarcoma C3H-7. A significant reduction of the anti-C-1 cytotoxicity was also obtained by absorbing with the two BALB/c fibrosarcomas teflon-9 and SCS (both lacking TSTA), by means of fresh newborn BALB/c or C3Hf muscle cells or of in vitro-cultured newborn BALB/c fibroblasts. These results suggest that, in spite of the strong transplantation immunity elicited by C-1 cells, antibodies to the individual TSTA of C-1 were undetectable in the syngeneic anti-C-1 serum obtained from animals highly resistant to the challenge of C-1 cells.     

The synthesis of ursolic acid derivatives with cytotoxic activity and the investigation of their preliminary mechanism of action

Nineteen ursolic acid derivatives (15 novel compounds) modified at the C-3 and the C-28 positions were synthesized. The cytotoxic activity of the derivatives was evaluated against HeLa, BGC-823 and SKOV3 cells by MTT assay. Inducing apoptosis and affecting cell cycle distribution by the derivatives in HeLa cells were assessed by flow cytometry and DNA fragmentation. Compounds 10b and 11b were particularly active to inhibit HeLa cells growth through inducing apoptosis and arresting cell cycle progression. The typical ‘sub-G1 peak’ and DNA ladder formation were checked and cell cycle was arrested at the S phase in a dose-dependent manner.     

The immunotropic activity of lupane and oleanane 2,3-<Emphasis Type="Italic">seco</Emphasis>-triterpenoids

The immunotropic effect of the 2,3-seco derivatives of allobetulon, betulonic acid, and the methyl ester of betulonic acid were studied. It was found that the highest activity is shown by compounds with an oleanane fragment. The presence of a free C28-carboxyl group enhances the activity of lupane 2,3-seco derivatives. A significant contribution to the development of the immune response is introduced by a functional group at the C3 atom in the A ring—the C3-carboxy derivatives intensify the processes of antibody production and alter the number and ratio of leukocyte forms. It is shown that 2,3-seco-1-cyano-19β,28-epoxy-18α-olean-3-oic acid stimulates humoral immunity with a positive influence on hematopoiesis.     

Synthesis and Pharmacological Activity of Betulin Dinicotinate

The assignment of NMR resonances of lupane triterpenoids was refined by the example of 3O,28O-dinicotinoylbetulin, obtained by acylation of betulin. Hepatoprotective, antiulcer, antiinflammatory, reparative, and anti-HIV activities were found for the compound. In addition, it was demonstrated to have immunomodulatory activity, for the first time detected among lupane triterpenoids.     

The design,synthesis and structure-activity relationships associated with C28 amine-based betulinic acid derivatives as inhibitors of HIV-1 maturation

The design and synthesis of a series of C28 amine-based betulinic acid derivatives as HIV-1 maturation inhibitors is described. This series represents a continuation of efforts following on from previous studies of C-3 benzoic acid-substituted betulinic acid derivatives as HIV-1 maturation inhibitors (MIs) that were explored in the context of C-28 amide substituents. Compared to the C-28 amide series, the C-28 amine derivatives exhibited further improvements in HIV-1 inhibitory activity toward polymorphisms in the Gag polyprotein as well as improved activity in the presence of human serum. However, plasma exposure of basic amines following oral administration to rats was generally low, leading to a focus on moderating the basicity of the amine moiety distal from the triterpene core. The thiomorpholine dioxide (TMD) 20 emerged from this study as a compound with the optimal antiviral activity and an acceptable pharmacokinetic profile in the C-28 amine series. Compared to the C-28 amide 3, 20 offers a 2- to 4-fold improvement in potency towards the screening viruses, exhibits low shifts in the EC₅₀ values toward the V370A and ΔV370 viruses in the presence of human serum or human serum albumin, and demonstrates improved potency towards the polymorphic T371A and V362I virus variants.     

New analogue of arenastatin A, a potent cytotoxic spongean depsipeptide, with anti-tumor activity

Two analogues possessing steric hindered substituents on C-15 of arenastatin A (1), a potent cytotoxic spongean depsipeptide, were synthesized and shown to enhance stability in mouse serum. Notably, 15-tert-butylanalogue (6) with higher cytotoxicity exhibited in vivo anti-tumor activity through iv administration different from 1. Additionally, conformation analysis among the two analogues and arenastatin A (1) indicated that the torsion angle from C-14 to C-20 is a conclusive factor for the potent cytotoxicity of 1.     

A review of acacic acid-type saponins from Leguminosae-Mimosoideae as potent cytotoxic and apoptosis inducing agents

The aim of this review is to highlight updated results on the biologically active saponins from Leguminosae-Mimosoideae. Acacic acid-type saponins (AATS), is a class of very complex glycosides possessing a common aglycon unit of the oleanane-type (acacic acid = 3β, 16α, 21β trihydroxy-olean-12-en-28 oic acid), having various oligosaccharide moieties at C-3 and C-28 and an acyl group at C-21. About sixty molecules of this type have been actively explored in recent years from Leguminosae family, from a chemical point of view and some fifty were reported to possess cancer related activities. These include cytotoxic/antitumor, immunomodulatory, antimutagenic, and apoptosis inducing properties and appear to depend on the acylation and esterification by different moieties at C-21 and C-28 of the acacic acid-type aglycone. One can observe that the (6S) configuration of the outer monoterpenyl moiety (MT) seems more potent in mediating high cytotoxicity than its (6R) isomer. Furthermore, the trisaccharide moiety {β-d-Xylopyranosyl-(1→2)-β-d-Fucopyranosyl-(1→6)- N-Acetamido 2-β-d-Glucopyranosyl-} at C-3, the tetrasaccharide moiety {β-d-Glucopyranosyl-(1→3)-[α-L-Arabinofuranosyl-(1→4)]-α-l-Rhamnopyranosyl-(1→2)-β-d-Glucopyranosyl} at C-28 of the aglycone, and the inner MT hydroxylated at its C-9, having a (6S) configuration can be important substituent patterns for the induction of apoptosis of AATS. Because of their interesting cytotoxic/apoptosis inducing activity, some AATS can be useful in the search for new potential antitumor agents from Fabaceae. Furthermore, the sequence 28-O-{Glc-(1→3)-[Ara_f-(1→4)]-Rha-(1→2)-Glc-Acacic acid}, often encountered in the genera Acacia, Albizia, Archidendron, and Pithecellobium may represent a chemotaxonomic marker of the Mimosoideae subfamily.     

Synthesis and immunotropic activity of methyl esters of 2-alkylaminomethylene-3-oxolup-20(29)-en-28-ic acids

New lupane β-enaminoketones were synthesized by interaction of methyl 2-hydroxymethylene-3-oxolup-20(29)-en-28-oate with aliphatic amines. Immunotropic activity was found for some of these compounds.