An efficient semi-synthesis and structure revision of a cytotoxic triterpenoid 25-acetoxy-3alpha-hydroxyolean-12-en-28-oic acid from Liquidamber styraciflua.

An efficient partial synthesis of 25-acetoxy-3alpha-hydroxyolean-12-en-28-oic acid (1), starting from oleanolic acid (2), has been developed in an efficient manner (13 steps, 21% yield), employing a photochemical reaction of nitrite 8 for the introduction of C-25 substituting group as the key step. Based on the comparison of its spectral data with those reported for compound 1 isolated from Liquidamber styraciflua, we found the structure in that paper was incorrectly assigned, and should be revised as 3alpha-acetoxy-25-hydroxyolean-12-en-28-oic acid (15).