Diesters based on isosteviol and dicarboxylic acids were synthesized and tested for antituberculous activity. Isosteviol and some of its derivatives exhibit appreciable tuberculostatic properties in vitro, the activity being dependent on the length of the polymethylene spacer connecting two ent-beyeran fragments.The mechanism of the antituberculous action of isosteviol derivatives are discussed. 473 0091-150X/06/4009-0473

Stevioside and steviolbioside, glycosides from Stevia rebaudiana Bertoni, in addition to hybrid compounds synthesized from steviolbioside and the antituberculosis drug isoniazid and its isomer nicotinic acid hydrazide exhibited moderate antituberculosis activity against M. tuberculosis strain H 37 R V in vitro (MIC = 7.5, 3.75,5, and 10 Pg/mL, respectively).

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Fluorine-substituted quinolonecarboxylic acids are known as synthetic antibacterial drugs with a broad spectrum of activity, which are successfully used for the therapy of various bacterial diseases, including tuberculosis [1 ]. Nevertheless, problems pertaining to the appearance of bacterial strains resistant to quinolones stimulate researchers to continue investigations aimed at a modification of the known fluroquinolones [2].We have attempted to modify a fluoroquinolone fragment responsible for penetration into bacterial ceils, with the pttrpose of increasing the transport function of the molecule, since it is known that fluoroquinolones (in particular, pefloxacin) penetrate into bacterial cells by a simple diffusion mechanism [3].In order to find reaction pathways to fluoroquinolones possessing increased penetrating ability with respect to the cell membranes, we have synthesized compounds containing podand residues that are known [4] to readily pass through the cellular barriers.Because of the low nucleophilicity of glycols, the oxygen-containing podands IV were obtained under rigid conditions from the ethyl ester of 1-ethyl-6,7-difluoro-4-oxo-l,4-dihydro-3-quinolinecarboxylic acid (Ib), in which the mobility of a fluorine atom in position 7 is somewhat higher than in the acid (Ia).Podands V and VI were obtained by direct interaction of acid Ia with polyethylene polyamines. Potassium carbonate was used as the acceptor of hydrogen chloride in the synthesis of compounds IV and VI, whereas triethylamine was used for the same purpose in the synthesis of compounds V known to form strong complexes with potassium cations.Podands-hydrazones VII were obtained by heating formylpodands III with 7-hydrazino-4-oxo-6-ftor-l-ethyl-l,4-dihydro-3-quinolinecarboxylic acid (II) in DMF.

Derivatives of the diterpenoid isosteviol (16-oxo-ent-beyeran-19-oic acid) with azine, hydrazone, and hydrazide moieties were synthesized. They exhibited high tuberculostatic activity in vitro against the strain Mycobacterium tuberculosis H 37 R V (minimum inhibiting concentration in the range 6.3-1.7 Pg/mL).Only streptomycin, capreomycin, and kanamycin of all drugs used today for tuberculosis chemotherapy are isolated from natural sources [1]. All other tuberculosis drugs [1] and agents undergoing preclinical and clinical trials [2, 3] are products from organic syntheses. Nevertheless, over 50 metabolites of various structures that inhibit the growth of Mycobacterium tuberculosis in the range of minimum inhibiting concentrations (MIC) 60-3 Pg/mL have currently been isolated from natural plant sources [4][5][6][7][8][9][10][11][12][13][14][15][16][17]. Diterpenoids [4,5,[8][9][10][11][12][13] and triterpenoids [4,5,11,[14][15][16][17] are most widely represented among them. The diterpenoid isosteviol (16-oxo-ent-beyeran-19-oic acid) (1) also exhibits moderate antituberculosis activity (MIC = 50 Pg/mL). Our group has investigated for several years chemical modification of 1 and its derivatives in which two isosteviol molecules are linked by a polymethylene spacer with C 16 atoms [18]. It was found that the length of the spacer affects considerably the activity. Increasing the number of methylenes in the spacer from one to eight decreases MIC from 25 to 12.5 Pg/mL [18]. These results were unusual because 1, its bis-derivatives [18], and the aforementioned di-and triterpenoids of different structures [4,5,[8][9][10][11][12][13][14][15][16][17] are not nitrogenous organic compounds yet they exhibit antituberculosis activity at the level of the N-containing antituberculosis drug pyrazinamide (MIC = 12.5 Pg/mL) [19,20]. This is probably evidence that they have a different mechanism of M. tuberculosis growth inhibition. It seemed interesting to determine how the introduction of pharmacophoric N-containing moieties (hydrazide and hydrazone) into 1 and its bis-derivatives [18] affects their antituberculosis activity.For this we reacted 1 and its acid chloride 4 with hydrazine hydrate and adipic acid hydrazide (Scheme 1) and studied the ability of the resulting products to inhibit the growth of M. tuberculosis.The reaction of 1 and an excess of hydrazine hydrate in MeOH gave not isosteviol hydrazone (3) but the azine 2, which was isolated as the salt (Scheme 1). The reason for this was probably that hydrazone 3 formed and reacted with both starting 1 and that formed via hydrolysis of 3. Compound 3 was obtained pure via reaction of 1 with a 10-fold excess of anhydrous hydrazine.The reaction of isosteviol acid chloride 4 with anhydrous hydrazine in CCl 4 produced 5. Its PMR spectrum showed characteristic resonances for protons of the ent-beyerane skeleton in addition to a broad singlet of the hydrazide amine at 3.83 ppm, a broad singlet of the hydrazone amine at 4.75, and a singlet of the hydrazide amide at 6.9. The reactio...