A simple but unusual rearrangement of an oleanane to a taraxerane-28,14 β -olide
Niels Heise1, Bianka Siewert2, Dieter Ströhl1
1Martin-Luther-University Halle-Wittenberg, Organic Chemistry, Kurt-Mothes-Str. 2, D-06120 Halle (Saale), Germany.
Abstract:
Reaction of 3-O-acetyl-oleanolic acid (3) with formic acid/hydrogen peroxide at 100 °C for several hours provides an extraordinary but simple pathway to a taraxeran-28,14 β -olide type triterpenoid while the same reaction at 0 °C occurred without re-arrangement of the carbon skeleton, and an oleanane-28,13 β -olide was obtained instead. The products from these reactions were subjected to a cytotoxicity screening employing several human tumor cell lines showing the latter compound not cytotoxic while the former was cytotoxic especially for MCF-7 (breast adenocarcinoma), and FaDu (hypopharyngeal carcinoma) cells. The highest cytotoxicity, however, was observed for 3 β, 12α, 13 β -trihydroxy-oleanan-28-oic acid (6) holding with EC50 = 4.2 μM for MCF-7 tumor cells.
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