Kyoko Nakagawa-Goto et al.
Bioorganic & medicinal chemistry letters, 19(13), 3378-3381 (2009-06-02)
C-3 esterifications of betulinic acid (BA, 1) and its A-ring homolog, ceanothic acid (CA, 2), were carried out to provide sixteen terpenoids, 4-19, including nine new compounds (4-12). All synthesized compounds were evaluated in an in vitro antitumor-promoting assay using