F. S. Zarudii

Synthesis of Betulinic Acid from Betulin Extract and Study of the Antiviral and Antiulcer Activity of Some Related Terpenoids

3 -Hydroxy-lup-20(29)-en-(28)-oic (betulinic) acid (I) was isolated at the beginning of the 20th century and originally called gratiolone [1]. In the past decade, some special biological properties of this triterpenoid has drawn the attention of researchers. In 1994, betulinic acid was found to exhibit anti-HIV-1 activity in H9 lymphocyte cell culture [2]. The most promising inhibitor of HIV-1 replication is 3-O-(3 ,3 -dimethylsuccinate) of betulinic acid [3]. In 1995, it was established that betulinic acid is capable of selectively inhibiting the growth of malignant human melanoma [4]. In addition, betulinic acid and its derivatives possess antibacterial, antimalarial, antiinflammatory, bile-expelling, and other properties [5 – 7]. Since the content of betulinic acid in plants is very low, isolation of this compound from raw plant material is poorly profitable. A more effective method of obtaining betulinic acid is synthesis from betulin (II) and betulonic acid (III). The first synthesis of betulinic acid was suggested by Ruzicka et al. [8]. This original procedure involved (i) protection of the hydroxy groups of II by acetylation, (ii) selective hydrolysis of the acetyl group at C-28, (iii) oxidation of the oxymethyl group to carboxy group, and (iv) removal of the protective acetyl group at C-3. The total yield of betulinic acid from this process did not exceed 30%. In the late 1990s, betulinic acid was synthesized (I) in two steps by oxidizing betulin (II) with Jones reagent or chromic anhydride in acetic acid, followed by selective oxidation of the resulting betulonic acid (III) with NaBH4 [9, 10], whereby the total yield of the target compound reached up to 60%. We used Jones reagent to oxidize the extract obtained by treating birch bark with aqueous isopropanol in an autoclave at 80°C. The initial extract contained up to 90% of betulin and about 5% of lupeol (IV). Betulonic acid (III) formed as a result of this oxidation process was isolated from the reaction mixture in the form of a potassium salt (V) with a yield of 82%, which allowed us to exclude the stage of intermediate product purification by column chromatography [10]. Upon acidification of an ethanol solution of the potassium salt V with a 5% hydrochloric acid solution, betulonic acid (III) of 95% purity was isolated with a yield of 85%. The physicochemical parameters of the product corresponded to the published data [2, 10, 11]. The total yield of betulonic acid (III) calculated for the initial betulin extract was 67%. Column chromatography of the organic fraction yielded 3-keto-lupeol (VI) with a yield of 1.7%.

Synthesis and Pharmacological Activity of Betulin, Betulinic Acid, and Allobetulin Esters

A series of new triterpene hemisuccinates, hemiphthalates and nicotinates have been obtained with 52 – 95% yields via reactions of monoacetates of betulin, betulinic acid, and allobetulin with succinic and phthalic anhydrides and with nicotinic acid chloroanhydride. 3-O-Acetylbetulin-28-O-hemiphthalate showed the most pronounced antiinflammatory activity comparable with the effect of ortophen (diclofenac). 3-O-Acetylbetulin-28-O-hemisuccinate exhibited the most pronounced antiulcer activity comparable with that of carbenoxolone.

Complex Compounds of Glycyrrhizic Acid with Antimicrobial Drugs

A promising direction in the development of new effective drugs is the synthesis of molecular complexes, for example, with cyclodextrins, which can protect parent substances from premature metabolic decay and provide for their transmembrane transport [1]. Previously, we suggested using 18 -glycyrrhizic acid (GA, I) as a complex-forming agent for the synthesis of new transport forms of the well-known drugs (nonsteroidal antiinflammatory agents, prostaglandins, uracils, etc.) and other biologically active substances [2 – 7]. In continuation of our work in the R&D of new GA-based preparations, we have synthesized a series of new molecular 1 : 1 complexes (II – XI) between antimicrobial drugs and GA (92 2 %) [8]

Synthesis and neuropharmacological activity of N -1-adamantylcytisine-12-carbamide and its 12-thiocarbonyl analog

The neuropharmacological activity of two (–)-cytisine derivatives with adamantyl fragments was studied. It was shown that N-1-adamantylcytisine-12-thiocarbamide exhibited in tests in vivo a pronounced mnestic effect, increased the lifespan of laboratory animals under hypoxic conditions, and also enhanced in vitro binding of transcription factors NFAT and NF-κB to the DNA sequences corresponding to them.

Synthesis and specific nootropic activity of (–)-cytisine derivatives with carbamide and thiocarbamide moieties in their structure

N-(methylcytisinyl)-N′-substituted ureas, N-substituted cytisine-12-carbamides, and cytisine-12-thiocarbamide were prepared by reaction of (–)-cytisine with urea and thiourea and of (–)-cytisine and its 12-N-methyl-3-amino derivative with isocyanates. Their specific nootropic activity was studied in vivo. The therapeutic index was determined for the lead compound. Promising candidates for further pharmacological testing were found.

SYNTHESIS AND PHARMACOLOGICAL ACTIVITY OF ACYLATED BETULONIC ACID OXIDES AND 28-OXO-ALLOBETULONE

In recent years, the chemical transformations and biological activity of triterpenoids of the lupane group have received much attention. It was found that betulin acylates possess antitumor properties [1], while lupeol esters with palmitic and linolic acids produce antiarrhythmic action [2]. The most promising inhibitors of HIV replication include 3-O-(3,3-dimethylsuccinate) of betulinic acid and 3-O(3,3-dimethylsuccinate)-28-O-(2,2-dimethylsuccinate) of betulin [3]. Recently, Kashiwada et al. [4] reported on the synthesis of derivatives of 3-alkylamino-3-deoxo-betulinic acid possessing anti-HIV-1 properties [4]. Another promising compound is betulin 3,28-di-O-nicotinate, which shows hepatoprotector, antiulcer, antiinflammatory, wound-healing, anti-HIV, and immunomodulant activity [5]. An analysis of published data suggests that the class of lupane triterpenoids and related compounds containing acyl groups is a promising source of new biologically active substances. Below we report on the first synthesis of acylated oximes based on betulonic acid (Ia), its methyl ester (IIa), and 28-oxo-allobetulone (IIIa). In the first step, boiling 3-oxo-triterpenoids (Ia, IIa, IIIa) with hydroxylamine hydrochloride in anhydrous pyridine led to a quantitative yield of the corresponding 3-oximes (Ib, IIb, IIIb). By acylating these compounds in anhydrous benzene with excess acetic, succinic, and phthalic anhydrides at room temperature in the presence of triethylamine, we obtained acylated oximes (Ic – Ie, IIc – IIe, IIIc – IIIe) with a yield of 64 – 78% after purification of the products by column chromatography (Table 1).

The synthesis and hepatoprotective activity of esters of the lupane group triterpenoids

Hemisuccinates, hemiphthalates, acetylsalicylates, cinnamates, andp-methoxycinnamates of lupeol, betulin, and 3-O-acetylbetulin were synthesized via interaction with corresponding acid anhydrides or acid chlorides. A number of betulin esters in position 3 and 28 were shown to exhibit a pronounced hepatoprotective effect similar to that of betulin and silibor. These experimental data were in a good agreement with the computer prediction of their biological activity. Betulin 3,28-bishemiphthalate was more effective than carsil in models of experimental hepatitis caused by carbon tetrachloride, tetracycline, and ethanol.

Synthesis and Antiinflammatory Activity of New Acylated Betulin Derivatives

The content of betulin, a triterpenoid of the lupane group, in the birch bark varies from 10 to 40% depending on the particular plant species, location, and growth conditions [1]. Betulin can be readily converted into allobetulin and betulinic acid. As is known, betulin (Ig), as well as allobetulin (IId), betulinic acid (IIId), and their derivatives, are low-toxicity substances possessing a wide spectrum of biological activity [2 – 5] and antioxidant properties [6]. These substances can be used as additives to improve existing products and create new products in pharmacy, cosmetics, and food industry. It was found that some derivatives of the lupane triterpenoids (in particular, those with ester and amide bonds) exhibit antiviral activity [7, 8]. Some drugs based on other triterpenoids contain the analogous residues of bioactive acids [9]. Recently [10, 11], we found highly active substances among betulin acylates: betulin dinicotinate, bis-hemisuccinate, bis-hemiphthalate, etc., were shown to possess hepatoprotector and anti-HIV-1 activity. Therefore, the synthesis and characterization of new biologically active substances in the series of acylates of these triterpenoids is of practical importance. Below we present data on a series of new esters of betulin, allobetulin, and betulinic acid. The interaction of initial triterpenoids Ig, IId, and IIId with chloroanhydrides of 2-(4-chlorophenyl)-3-methylbutyric, tetramethylcyclopropanecarboxylic, and permethric acids (representing semiproducts in the synthesis of pyrethroids) in a mixture of pyridine with tributylamine led to acylates Ia – If, IIa – IIc, and IIIa – IIIc (see scheme). 3-O-Acylates of allobetulin (IIa – IIc) and betulinic acid (IIIa – IIIc) were obtained with a yield of 55 – 87% at room temperature for a triterpenoid to chloroanhydride ratio of 1 : 1.5 (Table 1). Selective esterification performed under the same conditions led to 28-monosubstituted esters Ib, Id, If with a yield of 80 – 85%. In the presence of a threefold excess of chloroanhydrides over betulin, heating the reaction mixture up to 60 – 70°C led to the formation of 3,28-disubstituted betulin esters Ia, Ic, Ie with a yield of 75 – 80%. The structures of the synthesized acyl derivatives were established by NMR spectroscopy in comparison with the data published for analogous compounds [10, 12, 13]. The formation of ester bonds was confirmed by 2 – 4 ppm low-field shifts of the signals from C3 atoms (for compounds Ia, Ic, Ie, IIa – IIc, IIa – IIIc) and from C28 atoms (for compounds Ia – If) and by the appearance of signals from ester

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.

Synthesis and Antitumor Activity of Complex Compounds of β-Glycyrrhizic Acid with Antitumor Drugs

A promising way of creating new highly effective drugs is the synthesis of molecular complexes which can protect parent substances from premature metabolic decay and provide for their controlled release. A premise in our approach was that the complex-forming agent must contain both a hydrophilic component (binding the main parent substance) and a hydrophobic component (responsible for the drug transport). Previously, we demonstrated that the molecular complexes of -glycyrrhizic acid (I) with prostaglandins and nonsteroidal antiinflammatory drugs are characterized by reduced toxicity and increased therapeutic breadth as compared to those of the components [1 – 6]. The main disadvantage of the well-known antitumor drugs 5-fluorouracil (II), ftorafur (III), rubomycin (IV), and their analogs is high toxicity [7 – 9]. We have synthesized a series of complex compounds involving acid I and drugs II – V in 1 : 1 ratio. The molecular complexes of I with fluorouracil were obtained in a water – ethanol medium at ~50°C, and the complexes with anthracycline antibiotics, in ethanol at room temperature. All compounds were characterized by IR and UV spectra. The UV spectra of complexes I II and I III exhibit intense absorption maxima in the region of 250 – 260 nm, related to the total absorption of conjugated ketone and fluoropyrimidine chromophore groups. The UV spectra of complexes I IV and I V display intense maxima in the region characteristic of aromatic chromophores (234 – 235 nm) and new maxima related to anthracycline groups (470 – 530 nm). As can be seen from the data in Table 1, the complexes of I with compounds II – IV are less toxic than the initial antitumor drugs. According to the results of preliminary experiments, the molecular complex of acid I with drug III exhibits antitumor action with respect to Pliss lymphosarcoma, melanoma B-16, and Guerin’s carcinoma (Table 2).