Discovery of the Caged-Vibsane Norditerpenoids with Unprecedented Chemical Architectures and Exploration of Their Various Acid Tolerances

Cyclovibsanones A–D (1–4, respectively), featuring unprecedented caged tricyclo[5.4.1.05,9]dodecane and bicyclo[4.2.1]hexane cores, were isolated
from the leaves of Viburnum odoratissimum. Their
structures as well as that of one chemical derivative (5), which was transformed from 2, were determined by
spectroscopic data, theoretical calculations, and the ML-JDP4/MAEΔΔδ methods. In addition, compounds 1 and 2 were found to possess dissimilarities
in acid tolerance during nuclear magnetic resonance (NMR) experiments.
The potential mechanism was consequently postulated and further supported
through NMR analysis and mechanistic calculations. Biologically, chemical
derivative 5 exerted antiproliferative activity against
HepG2 cells.