Synthesis and Evaluation of Anticancer Activities of Novel C-28 Guanidine-Functionalized Triterpene Acid Derivatives.

Triterpene acids, namely, 20,29-dihydrobetulinic acid (BA), ursolic acid (UA) and oleanolic acid (OA) were converted into C-28-amino-functionalized triterpenoids 4⁻7, 8a, 15, 18 and 20. These compounds served as precursors for the synthesis of novel guanidine-functionalized triterpene acid derivatives 9b⁻12b, 15c, 18c and 20c. The influence of the guanidine group on the antitumor properties of triterpenoids was investigated. The cytotoxicity was tested on five human tumor cell lines (Jurkat, K562, U937, HEK, and Hela), and compared with the tests on normal human fibroblasts. The antitumor activities of the most tested guanidine derivatives was lower, than that of corresponding amines, but triterpenoids with the guanidine group were less toxic towards human fibroblasts. The introduction of the tris(hydroxymethyl)aminomethane moiety into the molecules of triterpene acids markedly enhanced the cytotoxic activity of the resulting conjugates 15, 15c, 18b,c and 20b,c irrespective of the triterpene skeleton type. The dihydrobetulinic acid amine 15, its guanidinium derivative 15c and guanidinium derivatives of ursolic and oleanolic acids 18c and 20c were selected for extended biological investigations in Jurkat cells, which demonstrated that the antitumor activity of these compounds is mediated by induction of cell cycle arrest at the S-phase and apoptosis.

Synthesis and antiviral activity of maleopimaric and quinopimaric acids' derivatives.

A series of maleopimaric and quinopimaric acids' derivatives modified in the E-ring, at the carbonyl- and carboxyl-groups were synthesized and evaluated for their activity in vitro against respiratory viruses (influenza; rhinovirus; adenovirus; and SARS), papilloma virus, and hepatitis B and C viruses. The antiviral screening of levopimaric acid diene adducts derivatives was carried out with minimal effect on SARS and influenza type B viruses. Excellent antiviral activity of the ozonolysis product of maleopimaric acid and dihydroquinopimaric methyl-(2-methoxycarbonyl)ethylene amide was found toward papilloma virus (HPV-11 strain) with the selectivity index of SI 30 and 20, respectively. Methyl (2-methoxycarbonyl)ethylene-, 1ß-hydroxy-5'-kaprolaktamo- and 4ß-hydroxy-4α,14α-epoxy-13(15)-ene-dihydroquinopimaric acid derivatives have also shown activity against replication of HCV nucleic acid and low toxicity.

Synthesis and activity of new triphenylphosphonium derivatives of betulin and betulinic acid against Schistosoma mansoni in vitro and in vivo.

We studied the antischistosomal activity of betulin, betulinic acid and its 9 triphenylphosphonium derivatives characterized by a covalently linkage of the hydrophobic fragment of triterpenoid at C(2)- or C(30)-position with the triphenylphosphonium moiety via a hydrocarbon bridge. The triphenylphosphonium salts showed in vitro antischistosomal activity against newly transformed schistosomula (NTS) and adult worms of Schistosoma mansoni at low micromolar concentrations. In contrast betulin and betulinic acid were inactive against NTS and adult S. mansoni. Of the 9 triphenylphosphonium derivatives tested, the allyl salts 10 (IC50 of 0.76 µg/mL) and 11 (IC50 of 0.64 µg/mL) demonstrated the highest antischistosomal activity against adult S. mansoni. Low worm burden reductions of 22% were observed in vivo for these two compounds. In conclusion, triphenylphosphonium derivatives were obtained from available natural betulin by simple transformations, rendering it practical and useful for large scale application. However, further structural modifications are necessary to translate the promising antischistosomal in vitro activities into in vivo.

Sonochemically assisted 2,3-dideoxygenation and skeletal rearrangement of ecdysteroid derivatives.

Sonochemical 2,3-dideoxygenation of ecdysteroids with the Δ 2(3)-bond generation and activation of the C-C bonds of the steroid core in the poststerone derivatives, that causes the skeletal rearrangement have been carried out for the first time. Thus, the ultrasonically assisted reaction of 2,3-dimesyloxy derivatives of ecdysteroids with the NaI-Zn-DMF system gives rise to their 2,3-dideoxy-Δ2(3)-analogues with yields 70-92%. In the case of 2,3-dimesyloxypoststerone as the initial ecdysteroid substrate the reaction is accompanied by the activation of the allyl moiety and semipinacol rearrangement, resulting in the C13-C14 bond migration with C/D rings contraction/expansion and providing novel short chain (8R)-13(14 → 8)-abeo-isomer.

Molecular rearrangements of poststerone derivative steroid core with formation of unique D-homostructures of pregnane and androstane series.

20R-Hydroxy short-chain ecdysteroids were synthesized by chemo- and stereoselective reduction of poststerone acetonide with L-Selectride or LiAlH4. The same reaction with the excess of L- Selectride followed by the treatment of the reaction mixture with hydrochloric acid is accompanied by (8R)-13(14 → 8)abeo- rearrangements, which resulted in the contraction/expansion of C/D pregnane rings. The reaction of 20R-hydroxy poststerone analogs with (diethylamino)sulfur trifluoride (DAST) proceeds through intramolecular rearrangements and provides D-homo- or 13,14-seco- androstane structures.

Mitochondria-targeted betulinic and ursolic acid derivatives: synthesis and anticancer activity.

A series of new betulinic and ursolic acid conjugates with a lipophilic triphenylphosphonium cation, meant to enhance the bioavailability and mitochondriotropic action of natural triterpenes, have been synthesized. The in vitro experiments on three human cancer cell lines (MCF-7, HCT-116 and TET21N) revealed that all the obtained triphenylphosphonium triterpene acid derivatives not only showed higher cytotoxicity as compared to betulinic acid but were also markedly superior in triggering mitochondria-dependent apoptosis, as assessed using a range of apoptosis markers such as cytochrome c release, stimulation of caspase-3 activity, and cleavage of poly(ADP-ribose) polymerase, which is one of the targets of caspase 3. The IC50 was much lower for all triphenylphosphonium derivatives when compared to betulinic acid. Out of the tested group of conjugates, the most potent toxicity was exhibited by the betulinic acid conjugate 9 (for 9, the IC50 values against MCF-7 and TET21N cells were 0.70 µM and 0.74 µM; for betulinic acid (BA), IC50 > 25 µM against MCF-7 cells).

Synthesis of 5,19-(2,6-Dimethylpyridin-4-yl)-trisnorlupane and Oleanane.

Acetylation of the 3,4-seco-derivatives of betulin, allobetulin and 28-oxyallobetulone gave the 5,19-(2,6-dimethylpyridin-4-yl)-4,23,24,20,29,30-hexanorlupane, and 5-(2,6-dimethylpyridin-4-yl)-4,23,24-trisnor-derivatives of oleanane and ursane.

Synthesis of a Novel 1,2,4-Oxadiazole Diterpene from the Oxime of the Methyl Ester of 1ß,13-Epoxydihydroquinopimaric Acid.

Oximation of the dihydroquinopimaric acid O-cyanoethylderivative (2) via the amidoxime 3, and cyclization with trifluoroacetic anhydride resulted in a new 1,2,4-oxadiazole diterpenoid (4).

Hyaluronic acid based hydroxamate and conjugates with biologically active amines: In vitro effect on matrix metalloproteinase-2.

In this study, water soluble hyaluronic acid (HA) based hydroxamate and conjugates with biologically active amines and hydrazides such as p- and o-aminophenols, anthranilic, 4- and 5-aminosalicylic acids, nicotinic, N-benzylnicotinic and isonicotinic hydrazides, p-aminobenzenesulfonamide (Streptocide), p-aminobenzoic acid diethylaminoethyl ester (Procaine), and 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one (4-aminoantipyrene) were examined as matrix metalloproteinase-2 inhibitors (MMPIs). In a dose of 0.27-270µM, the most efficient MMPIs were HA conjugates with o-aminophenol=4-aminoantipyrine>4-aminosalicylic acid>5-aminosalicylic acid. Conjugates with Streptocide, Procaine and HA hydroxamate showed 40-50% inhibitory effect at all used concentrations. Conjugates with anthranilic acid and isonicotinic hydrazide (Isoniazid) in a dose of 0.27µM inhibited enzyme activity by ∼70%, but with the concentration increase their inhibitory effect was decreased.

7α-alkylation and 7,7-bis-alkylation of 20-hydroxyecdysone with propargyl bromide in a lithium-ammonia solution and catalytic reductive spirocyclization of 7,7-bis(2-propyn-1-yl)-14-deoxy-Δ(8(14))-20-hydroxyecdysone.

7α-Alkylation and 7,7-bis-alkylation of 20-hydroxyecdysone with propargyl bromide in a lithium-ammonia solution resulted in the formation of 7α-(2-propyn-1-yl)- and 7,7-bis(2-propyn-1-yl)-14-deoxy-Δ(8(14))-20-hydroxyecdysone in 92% and 75% yield respectively. Upon catalytic hydrogenation (10% Pd-C) of 7,7-bis(2-propyn-1-yl) derivative spirocyclization occurs by geminal 2-propyn-1-yl groups.

Stoichiometric C6-oxidation of hyaluronic acid by oxoammonium salt TEMPO⁺Cl⁻ in an aqueous alkaline medium.

This paper reports the selective oxidation of hyaluronic acid (HA) by stoichiometric quantity of 2,2,6,6-tetramethylpiperidine-1-oxoammonium chloride (TEMPO(+)) in aqueous alkaline medium. High efficiency of the HA oxidation and quantitative yield of carboxy-HA per starting TEMPO(+), as well as unusual behavior of the oxidation system generating an oxygen upon alkali-induced oxoammonium chloride decomposition are demonstrated. The scheme for HA oxidation involving both TEMPO(+) and oxygen produced upon the TEMPO(+)Cl(-) decomposition and/or air oxygen is proposed. For comparison, the data on stoichiometric oxidation of such substrates as dermatan sulfate, water-soluble potato starch, methyl 2-acetamido-2-deoxy-ß-d-glucopyranoside and ethanol are presented.

Stereospecific 7α-alkylation of 20-hydroxyecdysone in a lithium-ammonia solution.

The reaction of 20-hydroxyecdysone with methyl or ethyl iodide or allyl bromide in a lithium-ammonia solution results in stereospecific 7α-alkylation to give 7α-methyl-, 7α-ethyl-, and 7α-allyl-14-deoxy-Δ(8(14))-20-hydroxyecdysones, respectively. By catalytic hydrogenation (Pd-C/MeOH), the 7α-allyl derivative was converted to 7α-n-propyl-14-deoxy-Δ(8(14))-20-hydroxyecdysone.

Hydroxylation and epimerization of ecdysteroids in alkaline media: stereoselective synthesis of 9α-hydroxy-5α-ecdysteroids.

Autoxidation of diacetonides of 20-hydroxyecdysone and ponasterone A under treatment with excess of NaOH in methanol leads to the formation of 9α-hydroxy-5α-ecdysteroids previously not described. Their structures have been determined by detailed NMR analysis. Catalytic hydrogenation (Pd-C, MeOH-MeONa) of hydroxylated ecdysteroids affords the 7,8α-dihydro-9α-hydroxy-5α-ecdysteroids.

Hydrogenation of ecdysteroids.

Catalytic hydrogenation is extensively used in steroid chemistry. The interest in transformations to the steroid skeleton of ecdysteroids has been increasing in the past years. Essential interest in the chemistry of ecdysteroids is caused by the selective reduction of Δ7 bond with the formation of 7,8-dihydro analogues, because this process allows one to obtain modified structures with new biological activity. Catalytic hydrogenation of isolated and conjugated double bonds and functional groups in ecdysteroids derivatives has been considered in review.

Synthesis of 7,8α-dihydro-14α-deoxyecdysteroids.

A Pd-C-catalyzed hydrogenation in methanol and in the presence of sodium methylate is a simple, convenient and high yielding reduction method to convert the 7,14-dien-6-one ecdysteroids to their corresponding 7,8α-dihydro-14α-deoxyecdysteroids.