Synthesis and anticancer evaluation of new lupane triterpenoid derivatives containing various substituent at the 2 or 3 position.

Betulonic acid benzyl ester 1 has been subjected to a series of structural modifications for the purpose of new triterpenoid synthesis and evaluating for anticancer activity. The one-pot two step synthesis of 2α-(aminomethyl)betulinic acid benzyl ester derivatives 3a-f (yield 46-69 %) was achieved by the Mannich reaction of compound 1 with methyleneiminium salts, generated in situ from N,N-disubstituted bis(amino)methanes 2a-f by the action of acetyl chloride in dichloromethane, and subsequent reduction of aminomethylation products with sodium borohydride. Minor 2β-(aminomethyl) triterpenoids 4c,d,f were also isolated (yield 6-15 %). We found, that the stereoselective reaction of triterpenoid 1 with acetylides, generated at -78 °C from alkynes in the presence of n-BuLi, has been useful and noteworthy as the key step in providing of new alkyne substituted triterpenoids - benzyl 3-alkynyl-3-deoxy-2(3),20(29)-lupadiene-28-oates or 3-deoxy-2(3)-dehydro-28-oxoallobetulin derivative. The new compounds were examined for anticancer activity against the human cell lines (MTT assay). All tested derivatives were non-toxic on human fibroblasts. The 3-(phenylethynyl)lupa-2(3),20(29)-diene 9 showed selective cytotoxicity on cervical cancer cell lines. Tumor cells death trigged by the most active compound 4f resulted from apoptotic processes. These data make the series of synthesized 2 or 3 substituted lupane derivatives as promising compounds with anticancer potential.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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