key: cord-0005280-ur15ywlr
authors: Kazakova, O. B.; Giniyatullina, G. V.; Tolstikov, G. A.
title: Synthesis of a-secomethylenamino- and substituted amidoximotriterpenoids
date: 2011-10-01
journal: Russ J Bioorgan Chem
DOI: 10.1134/s1068162011050086
sha: fc1a5c5433fc154bd35bac4431b802a5182af718
doc_id: 5280
cord_uid: ur15ywlr

Development of the functionalization of triterpenoids to A-secoamidoximes, A-secomethylenamines, and branched 3-(3-aminopropylamino)-3-(3-aminopropoxy)amidoximes is illustrated by the betulonic acid ketoxime. An effective way to get of the derivatives of 20,29-dihydrolupanes using diborane is suggested. The antiviral and antituberculosis activity data of some compounds are presented.

Triterpene oximes are important substances both for chemical transformations and in the pursuit of valuable biological properties. Thus, the dosage forms of drugs for the treatment and prevention of influenza can be developed on the basis of the betulonic acid ketoxime [1, 2] . Acylation of the oximes of betulonic acid, its methyl ester, 20 oxoallobetulone, and ursolic acid by acetic, succinic, and phthalic anhydrides weakens the antiviral activity of the parent compounds [3] [4] [5] [6] . Reduction of the oxime of ursolic acid to the 3 deoxy 3 amino derivative produces in the latter cytotoxicity against HL 60, Bel 7402, and Hela cells. It was also found that the 3β amino isomer is 20 times more active than the 3α isomer [7, 8] . The products of Beckmann rearrangements of betulonic acid oxime exhibit antibacterial activity against Streptococcus faecalis and Staphylococcus aureus at concentrations 25-50 mg/ml [9] . Derivatives of oleanolic acid can be used in cosmetology, because they transport biologi cally active compounds deep into tissue and make them more potent [10] . A seconitrile lupeol exhibits antimalarial activity against Plasmodium falciparum at MIC > 50 mg/ml [11] .

In this paper, the new conversion of the oxime methyl ester of betulonic acid (I) was implemented. One of the directions was to use cyanoethylation reac tions of triterpene oximes and amidoximes, examples of which are lacking in the literature. Cyanoethylation of oxime (I) by acrylonitrile led to a 2 cyanoethoxy imine (II) with 83% yield (scheme). NMR spectros copy established that the characteristic proton signals of С(2')Н 2 and С(1')Н 2 groups appeared in the form of triplets in the δ 2.64-2.72 and δ 4.14-4.25 ppm, respectively. Aminopropoxyaminoderivative (XIV) was formed in 72% yield in the reduction of the nitrile group of compound (II) by diborane in an inert atmosphere as described in [12] . The signals of methylene of С3'Н 2 and С1'Н 2 in the 1 H NMR spectrum were observed in the field δ 2.79-3.06 and 3.29-3.41 ppm, respectively. In the 13 C NMR spectrum of the compound (XIV), the signal of the C3 atom appears at δ 58.6 ppm unlike that at δ 63.2 ppm for compound (II).

Along with the reduction of the nitrile group, the hydrogenation of the isopropenyl fragment occurred, as is evidenced by the absence of signals of a double bond of C20(29) in the NMR spectra. We note that preparation of 20,29 dihydrolupanes described in the literature is based on two methods: gaseous hydrogen reduction catalyzed by Ni Raney [13] , Pd/C [14] , PtO 2 [15] , Pt [16] , and reduction by hydrogen pro duced in situ (application of amalgam of zinc in a mix ture of acetic and hydrochloric acids [17] ). Thus, we proposed an effective method of obtaining of 20,29 dihydrolupane derivatives using diborane.

Amidoxime (III), cyanoethylation of which by acrylonitrile led to 3 (2 cyanoethylamino) 3 (2 cya noethoxy) amidoximes (IV) with a yield of 74%, was synthesized by interaction of compound (II) with hydroxylamine in boiling ethanol. Its structure was confirmed by the signals of two CN groups at δ 113.3 and 114.3 ppm, as well as signals of C3, at δ 174.1 ppm in the spectrum of 13 C NMR. Because the amino group in amidoxime is electron deficient and therefore less reactive than the hydroxyl, cyanoethylation of only the hydroxyl group is most likely [18] , but in the case of compound (IV) reaction was at the hydroxyl and amino groups at the same time. 3 The available oxime of methyl betulonate deriva tive, having the structure of a nitrile group, is 2 cyano 3,4 secolupa 20(29) ene 28 oic acid methyl ester (VI). Previously, this was used for the synthesis of acid [19] , amide, and amine [11] , 4,20 diketone [20] . In this paper, we engaged the nitrile compound (VI) in the synthesis of amidoxime (VII) and 3 amino 3,4 secobetulin (VIII). Cyanoethylation of compound (VIII) by acrylonitrile proceeded to the hydroxyl and amino groups to formation of O,N di (2 cyanoethyl) derivative (IX). Judging from the spectral data, the substitution of one hydrogen atom occurred in the amino group. Displacement of the signal of the C28 atom in the spectrum of the 13 C NMR compound (IX) reaches ~2 ppm compared with the spectrum of deriv ative (VIII) (shown at δ 69.7 ppm). In the spectrum of 1 H NMR of compound (IX), the characteristic signals of protons H2', H4', H5', and H1' are observed as a multiplet at δ 2.54-2.67 and 3.42-3.84 ppm, respec tively.

Retro Michaelis dissociation on the C28 with the formation of 3 aminopropylamino 3,4 secobetulin (X) occurred in the reduction of compound (IX) with lithium aluminum hydride. Compound (VIII) is char acterized as a tert butoxycarbonate (XI) and N acy lates (XII), (XIII), containing fragments of 3 and 4 pyridinecarboxylic acids.

The investigation of the activity of several com pounds obtained was carried out in units of the National Institute of Allergy and Infectious Diseases (NIAID, United States, www.niaid aacf.org). According to the study of antiviral activity against res piratory infections, the selectivity index SI for com pounds (II), (VI), and (VII) had a range from 0 to > 3.1 (Table 1) . For compound (VII) the parameters of activity against hepatitis B virus (HBV) are CC 50 2 equal to 23 μmol/ml, ЕС 90 3 > 10 μmol/ml. With regard to the hepatitis C virus (HCV), the degree of suppression of replication of viral nucleic acid by com pound (VII) was 98.6%, and the cytotoxicity (percent age of cells remaining alive) was 8.9%, SI < 1. Thus, promising new antiviral agents among the studied group of betulin derivatives were not revealed.

A percentage growth inhibition of the virulent Micobacterium tuberculosis (strain H37Rv) by betulin and its derivatives (I), (II), (VI), (VII), and (ХI) in the studied concentration > 10 mcmol/ml amounted from -14.29 to 4.67%, indicating their low activity ( Table 2) . Oxime of betulonic acid and the compound (VI) inhibit the growth of the microbacteria by 77.55 and 60.06%; a sufficiently high activity may be associated with the aggregation of these substances with the bac teria. [7, 19] . Chlorides of nicotinic and isoni cotinic acid were obtained as described [21, 22] .

A mixture of 0.5 g (1 mmol) of com pound (I), 4 ml of acrylonitrile, 0.3 ml of 40% KOH in 15 ml of dioxane was stirred for 4 h at 20°С in an argon atmosphere, then the reaction mixture was poured onto 40 g of ice and 5 ml of HCl. The precipitate was filtered, washed with water and dried. The yield was 0.44 g (83%), R f 0.82, mp 165-167°С.

-0. 

A mixture of 1 mmol of compound (III), 12 ml of acrylonitrile, and 0.6 ml of 40% KOH in 15 ml of dioxane was stirred for 20 hours at room temperature under argon, and then the reaction mix ture was poured on 40 g of ice and 5 ml of HCl. The precipitate was filtered, washed with water, and dried. The residue was chromatographed on a column; the eluents were benzene and chloroform. 

Hydrogen was passed in an autoclave for 8 h at 100 atm through a solution of 0.67 g (1 mmol) of compound (IV) in 30 ml of methanol containing 0.14 g of the Ni Raney catalyst. The cata lyst was filtered, and the mixture was poured into 100 ml of water. The precipitate was washed with water and dried. The yield was 0.46 g (67%), R f 0. 22 

Berichte der Deutschen Chemis chen Gesllschaft LXI

The authors thank the National Institute of Allergy and Infectious Diseases (NIAID, United States, www.niaid aacf.org) for studying the antiviral and antituberculous activity of betulin, betulonic acid methyl ester, oxime of betulonic acid, and compounds (I), (II), (VI), (VII), and (XI).