Preparation of novel ring-A fused azole derivatives of betulin and evaluation of their cytotoxicity.

An efficient scheme to synthesize novel ring-A fused heterocyclic derivatives of betulin was developed. The starting reaction of this synthesis was one-pot selective bacterial oxidation of betulin to betulone used as the key compound to synthesize the substituted azoles such as C(2)-C(3)-fused 1,2,3-triazoles, oxazoles and 1,2,4-triazine, as well as C(1)-C(2)-fused isoxazoles. The semi-synthetic compounds were screened for their cytotoxic activity against human cancer cell lines A549, HCT 116, HEp-2, MS and RD TE32 with use of the photometric MTT assays. Among the tested compounds, N-acetyltriazole of betulin (10) displayed impressive cytotoxic activity with IC50 2.3-7.5 µM against HCT 116, HEp-2, MS and RD TE32 cell lines as well as 3-methyl-4-oxido-1,2,4-triazine-derivative of betulonic acid (12) that was active against HCT 116 and HEp-2 cell lines with IC50 1.4 and 1.5 µM, respectively. Comparative experiments showed triazole (10) to have a lower cytotoxicity to normal epithelial cells, in comparison with compound (12). In accord with the in vivo acute toxicity test, the LD50 of triazole (10) exceeded 600 mg/kg. The ability of the most potent active triazole (10) to trigger apoptotic cell death was explored in the Annexin V-FITC test and by analyzing of caspase activity and morphological alterations in mitochondria and nuclei of HCT 116 cells.

Functionalization, cyclization and antiviral activity of A-secotriterpenoids.

Triterpene derivatives with an α,ß-alkenenitrile moiety in the five-membered ring A have been synthesized by nitrile anion cyclizations of 1-cyano-2,3-secotriterpenoids. Oxime-containing precursors, 2,3-secointermediates and five-membered ring A products of cyclizations were screened for in vitro antiviral activity against enveloped viruses - influenza A virus and human immunodeficiency virus type I (HIV-1). Lupane ketoxime and the 2,3-secolupane C-3 aldoxime which possess antiviral activities against both influenza A virus (EC50 12.9-18.2 µM) and HIV-1 (EC50 0.06 µM) were the most promising compounds.

Synthesis, transformation and biological evaluation of 2,3-secotriterpene acetylhydrazones and their derivatives.

It has been previously shown that semi-synthetic A-secotriterpene acetylhydrazones of 1-cyano-28-methoxy-28-oxo-2,3-seco-2-norlup-20(29)-en-3-al and 1-cyano-2,3-seco-2-nor-19ß,28-epoxy-18αH-olean-3-al (1, 2) inhibit the vesicular stomatitis virus (VSV) replication. To improve the antiviral activity against VSV, structural modifications of compounds 1 and 2 were performed, and new A-secoderivatives containing the acetylhydrazone fragment were obtained from betulonic acid and its methyl ester, allobetulone, and 3-oxo-18ßH-glycyrrhetinic acid methyl ester. The inhibitory effects of these compounds on VSV replication in porcine embryo kidney (PEK) cells were determined after infection. It was shown that introduction of the 3'-acetyl-5'-methyl-1',3',4'-oxadiazoline fragment into lupane triterpene structures lead to an increase in the antiviral activity of A-secotriterpene derivatives. However, the presence of a heterocyclic moiety enhanced toxic activity and reduced the therapeutic indices of these agents. Investigation in the anti-proliferative activity of the heterocyclic derivatives has shown high sensitivity of A-549, MS and RD tumor cell lines to lupane (R)-oxadiazoline 11a. The pro-apoptotic effect of 11a was confirmed by the AnnexinV/PI analysis.