Synthesis and Intramolecular Cyclization of a 2,3-seco-Oleanane Triterpenoid with an Ethylketone Fragment

1-Cyano-2,3-seco-18αH-oleanane 3-ethyl-3-ketone was synthesized and underwent base-catalyzed intramolecular oxo-nitrile C(1)–C(3) cyclization to produce the A-pentacyclic 1-cyano-3-ethyl-1(3)-alkene. Nitrile-anionic C(1)–C(31) cyclization of the Br-substituted 3-ethyl-3-ketone occurred with loss of the cyano group and formation of an α,β-unsaturated ketone in a six-membered ring A. The cytotoxic properties of the synthesized compounds against cultures of tumor cell lines HEp-2, HCT 116, MS, RD TE32, A549, MCF-7, and PC3 were studied.