Spiromyrrhenes A−D: Unprecedented Diterpene-Sesquiterpene Heterodimers as intermolecular [4+2] cycloaddition products from Resina Commiphora That Inhibit Tumor Stemness in Esophageal Cancer

The structures and stereochemistry of spiromyrrhenes A−D (1−4), isolated from Commiphora exudates, were elucidated using NMR and ECD methods. They are the first examples of hepta- and octa-cyclic heterodimers with C35 skeletons as intermolecular [4+2] cycloaddition products. A plausible route for biosynthesis of the spiromyrrhenes was proposed. Biological studies show that they suppress tumor stemness in esophageal cancer by inactivating the Hippo/Yap pathway.