Cytotoxic principles and α-pyrone ring-opening derivatives of bufadienolides from Kalanchoe hybrida

Purification of the cytotoxic fractions of the methanol extracts of Kalanchoe hybrida leads to three new compounds with the basic skeleton of α-pyrone ring-opening products of bufadienolides, namely, kalanhybrin A-C (1-3). Moreover, four bufadienolides (4-7) and eight other compounds were also characterized from the title plant. The isolated compounds (1-7) were evaluated for their cytotoxicity toward MCF-7, NCI-H460, and SF-268 tumor cell lines. Among them, compounds 4 and 6 displayed significant cytotoxicity toward MCF-7 and NCI-H460 tumor cell lines at the tested concentration. In addition, the biosynthetic pathway of these α-pyrone ring-opening derivatives was also proposed.