Ozonolysis of 18 α -Oleanane triterpenoid with an alkenenitrile moiety in the five-membered ring A

Synthesis, Cyclization, and Cytotoxic Activity of 2,3-Secolupane Triterpenoids With an Ethylketone Fragment

3-Ethyl substituted triterpenoids with a fragmented and 5-membered A ring were synthesized from the lupane ketoxime via the Beckmann reaction and intramolecular oxonitrile cyclization, respectively. Transformations of the triterpenic isopropylidene fragment with the formation of C(30) and C(20) modified derivatives were performed by either allylic C(30) oxidation or ozonolytic cleavage of the C(20)-C(29) double bond. Antitumor activity of the synthesized compounds was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,3-diphenyl-tetrazolium bromide test against 7 human cancer cell lines. Methyl 1-cyano-3-ethyl-3-oxo-2,3-seco-2-norlup-20(29)-en-30-al-28-oate (4), methyl 3-[1-bromoethyl]-1-cyano-3-oxo-2,3-seco-2-norlup-20(29)-en-30-al-28-oate (6), and methyl 1-cyano-3-ethyl-2-norlup-1(3),20(29)-dien-30-al-28-oate (9) were selected as compounds with highest cytotoxicity (IC50 1.38-15.91 μM).

Diastereoselective Synthesis of Triterpenoid 1,2,4-Trioxolanes by Griesbaum Co-ozonolysis

Diastereoselective synthesis of triterpenoid 1,2,4-trioxolanes by Griesbaum co-ozonolysis was shown for the first time. Ozonolysis of 2-methoxyoximes (syn-anti-isomers mixture) of allobetulin or methyl oleanoate with CF₃-ketones resulted in asymmetrical spiro-1,2,4-trioxolanes as mixtures of diastereomers in yields up to 80-85%. The configuration of the spiro-C-2 center of individual ozonides was determined by 2D NMR spectra and X-ray crystallographic analysis. The products of ozonolysis of triterpenoid 3-methoxyoximes were mixtures of regioisomeric N-methoxylactams. Thus, the fundamental differences in the oxidation of homologous triterpenoid 2- or 3-methoxyoximes with ozone have been established. These results may afford a new stage in the development of the Griesbaum method as applied to natural compounds and biologically active peroxides.