Cytotoxic Triterpenoids from the Barks of Betula platyphylla var. japonica

Phytochemical investigation on the barks of Betula platyphylla var. japonica (Betulaceae) was carried out, resulting in the isolation and identification of three new triterpenoids, 27-O-cis-caffeoylcylicodiscic acid (1), 27-O-cis-feruloylcylicodiscic acid (2), and 27-O-cis-caffeoylmyricerol (3), along with six known triterpenoids, obtusilinin (4), winchic acid (5), 27-O-trans-caffeoylcylicodiscic acid (6), uncarinic acid E (7), myriceric acid B (8), and 3-O-trans-caffeoyloleanolic acid (9). The structures of the new compounds were elucidated by extensive spectroscopic methods, including 1D- and 2D-NMR, and HR-ESI-MS. All of the isolated compounds were evaluated for cytotoxicity against four human tumor cell lines (A549, SK-OV-3, SK-MEL-2, and Bt549). Compounds 2, 6, 8, and 9 exhibited potent cytotoxicity against all of the tumor cells tested (IC₅₀ < 10.0 μm), while compounds 3, 4, 5, and 7 showed moderate cytotoxicity against all of the tumor cells tested (IC₅₀ < 20.0 μm).